- Details
- Parent Category: Products
- Category: Amplifier Measurements

Link: reviewed by Dan Kong on *SoundStage! Hi-Fi* on June 1, 2022

**General Information**

All measurements taken using an Audio Precision APx555 B Series analyzer.

The Atoll Electronique IN200 Signature integrated amplifier was conditioned for 1 hour at 1/8th full rated power (~15W into 8 ohms) before any measurements were taken. All measurements were taken with both channels driven, using a 120V/20A dedicated circuit, unless otherwise stated.

The IN200 Signature offers five unbalanced (RCA) line-level analog inputs, four unbalanced (RCA) line-level analog outputs (Tape Out, By-pass and two pre-outs), and one pair of speaker-level outputs. On the front of the unit is a 1/4″ TRS headphone output.

Most measurements were made with a standard 2Vrms line-level analog input. The signal-to-noise ratio (SNR) measurements were made with the same input signal values, but with the volume set to achieve 1% THD at the output (8 ohms). For comparison, an SNR measurement was also made with the volume at maximum, where only 0.42Vrms was required to achieve 104W into 8ohms.

Based on the accurate and non-repeatable results at various volume levels of the left/right channel matching (see table below), the IN200 Signature volume control is likely digitally controlled but still operating in the analog domain. The volume control offers a total range of 0 to 80 on the display, which measured from -38dB (position 1) to +37dB between the line-level analog input and the speaker outputs, in increments of 2dB from positions 1 through 15, 1dB from 16 to 47, and 0.5dB from 48 to 80.

**Volume-control accuracy (measured at speaker outputs): left-right channel tracking**

Volume position | Channel deviation |

1 | 0.55dB |

10 | 0.341dB |

20 | 0.253dB |

40 | 0.111dB |

60 | 0.017dB |

70 | 0.024dB |

80 | 0.43dB |

**Published specifications vs. our primary measurements**

The table below summarizes the measurements published by Atoll for the IN200 Signature compared directly against our own. The published specifications are sourced from Atoll’s website, either directly or from the manual available for download, or a combination thereof. With the exception of frequency response, where the Audio Precision bandwidth was extended from DC to 500kHz, assume, unless otherwise stated, 10W into 8ohms and a measurement input bandwidth of 10Hz to 90kHz, and the worst-case measured result between the left and right channel.

Parameter | Manufacturer | SoundStage! Lab |

Rated output power into 8 ohms (1% THD, 1kHz) | 120W | 105W |

Rated output power into 4 ohms (1% THD, 1kHz) | 200W | 170W |

SNR (A-weighted) | 100dB | 100dB |

Frequency response (line-level input) | 5Hz-100kHz | 5Hz-100kHz, -0.1/-12dB |

Input sensitivity | 100mVrms | 420mVrms |

Input impedance | 220k ohms | 39k ohms |

Our primary measurements revealed the following using the line-level analog input (unless specified, assume a 1kHz sinewave at 2Vrms, 10W output, 8-ohm loading, 10Hz to 90kHz bandwidth):

Parameter | Left channel | Right channel |

Maximum output power into 8 ohms (1% THD+N, unweighted) | 105W | 105W |

Maximum output power into 4 ohms (1% THD+N, unweighted) | 170W | 170W |

Maximum burst output power (IHF, 8 ohms) | 113.25W | 113.25W |

Maximum burst output power (IHF, 4 ohms) | 205.2W | 205.2W |

Continuous dynamic power test (5 minutes, both channels driven) | passed | passed |

Crosstalk, one channel driven (10kHz) | -74.6dB | -85.8dB |

Damping factor | 116 | 117 |

Clipping no-load output voltage | 32.9Vrms | 32.8Vrms |

DC offset | <-14mV | <-4mV |

Gain (pre-out) | 12.0dB | 12.0dB |

Gain (maximum volume) | 36.9dB | 36.8dB |

IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-42dB | <-36dB |

IMD ratio (SMPTE, 60Hz + 7kHz stimulus tones, 4:1 ) | <-28dB | <-28dB |

Input impedance (line input, RCA) | 39.4k ohms | 38.9k ohms |

Input sensitivity (for 1%THD power, maximum volume) | 420mVrms | 420mVrms |

Noise level (A-weighted) | <2.5mVrms | <2.4mVrms |

Noise level (unweighted) | <13mVrms | <13mVrms |

Output impedance (pre-out) | 389 ohms | 388 ohms |

Signal-to-noise ratio (104W, A-weighted, 2Vrms in) | 101dB | 100dB |

Signal-to-noise ratio (104W, unweighted, 2Vrms in) | 94dB | 93dB |

Signal-to-noise ratio (104W, A-weighted, max volume) | 99.4dB | 93.9dB |

THD ratio (unweighted) | <0.28% | <0.26% |

THD+N ratio (A-weighted) | <0.28% | <0.26% |

THD+N ratio (unweighted) | <0.37% | <0.33% |

Minimum observed line AC voltage | 123.2VAC | 123.2VAC |

For the continuous dynamic power test, the IN200 Signature was able to sustain 178W into 4 ohms (~4% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (17.8W) for 5 seconds, for 5 minutes without inducing any protection or shut down circuits. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the IN200 was quite warm to the touch.

Our primary measurements revealed the following using the analog input at the headphone output (unless specified, assume a 1kHz sine wave, 2Vrms output, 300 ohms loading, 10Hz to 90kHz bandwidth):

Parameter | Left channel | Right channel |

Maximum output power into 600 ohms (1% THD+N, unweighted) | 251mW | 251mW |

Maximum output power into 300 ohms (1% THD+N, unweighted) | 191mW | 191mW |

Maximum output power into 32 ohms (1% THD+N, unweighted) | 28mW | 28mW |

Gain | 36.9dB | 36.8dB |

Output impedance | 996 ohms | 997 ohms |

Noise level (A-weighted) | <52uVrms | <57uVrms |

Noise level (unweighted) | <139uVrms | <174uVrms |

Signal-to-noise (A-weighted, ref. max output voltage) | 101.5dB | 100.7dB |

Signal-to-noise (unweighted, ref. max output voltage) | 94.0dB | 91.8dB |

THD ratio (unweighted) | <0.051% | <0.055% |

THD+N ratio (A-weighted) | <0.059% | <0.063% |

THD+N ratio (unweighted) | <0.052% | <0.055% |

**Frequency response (8-ohm loading, line-level input)**

In our measured frequency-response chart above, the IN200 Signature is nearly flat within the audio band (20Hz to 20kHz). At the extremes the IN200 is at 0dB at 20Hz, and -0.4/0.3dB (left/right) at 20kHz. Atoll claims a frequency response of 5Hz to 100kHz, however, they do not specify deviations relative to 1kHz. At these extremes, the IN200 measured -0.1dB and -12/-11dB (left/right channels). In the graph above and most of the graphs below, only a single trace may be visible. This is because the left channel (blue or purple trace) is performing identically to the right channel (red or green trace), and so they perfectly overlap, indicating that the two channels are ideally matched.

**Phase response (8-ohm loading, line-level input)**

Above are the left- and right-channel phase-response plots from 20Hz to 20kHz for the line-level input, measured across the speaker outputs at 10W into 8 ohms. The IN200 Signature does not invert polarity and exhibits, at worst, about 30 degrees (at 20Hz) of phase shift within the audio band.

**RMS level vs. frequency vs. load impedance (1W, left channel only)**

The chart above shows RMS level (relative to 0dBrA, which is 1W into 8 ohms or 2.83Vrms) as a function of frequency, for the analog line-level input swept from 5Hz to 100kHz. The blue plot is into an 8-ohm load, the purple is into a 4-ohm load, the pink plot is an actual speaker (Focal Chora 806, measurements can be found here), and the cyan plot is no load connected. The chart below . . .

. . . is the same but zoomed in to highlight differences. Here we can see a maximum deviation within the audio band of about 0.15dB from 4 ohms to no load, which is an indication of a mid-level damping factor, or average output impedance. The maximum variation in RMS level when a real speaker was used is less, deviating by about 0.13dB within the flat portion of the curve (20Hz to 5kHz). Note that the dip in RMS level at higher frequencies is a result of the frequency response of the IN200 signature, and not a damping factor issue, as all four plots show the same dip, at roughly the same rate.

**THD ratio (unweighted) vs. frequency vs. output power**

The chart above shows THD ratios at the output into 8 ohms as a function of frequency for a sine-wave stimulus at the analog line-level input. The blue and red plots are for the left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at 95W. The power was varied using the volume control. The IN200 yields consistently high THD ratios across a wide range of power output levels. Above about 500Hz, THD is roughly the same at all power levels, ranging from about 0.2% up to 3-5%. Below 500Hz, the 1W data shows the lowest THD values, at 0.05% at 20Hz. The 10W data is just above at about 0.7% at 20Hz, while the 95W data is at 0.2% (30Hz).

**THD ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms**

The chart above shows THD ratios measured at the output of the IN200 Signature as a function of output power for the analog line-level input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). The 8-ohm THD ratios ranged from about 0.5% at 50mW down to about 0.2-0.3% from 30W to the “knee,” which is at roughly 80W. The 4-ohm data yielded THD ratios roughly 5dB higher, except for the right channel below 1W, which tracked the 8-ohm data very closely. The “knee” in the 4-ohm data occurs around 120W. The 1% THD values are reached at about 105W (8-ohm) and 170W (4-ohm). These measurements do not corroborate Atoll’s specified power ratings for the IN200 Signature of 120W and 200W into 8/4 ohms. It is possible that the European version, which would use 220VAC mains, does achieve this power rating. Note: our mains supply is a dedicated 120VAC/20A circuit, and it never dipped below 123VAC during these measurements.

**THD+N ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms**

The chart above shows THD+N ratios measured at the output of the IN200 Signature as a function of output power for the line level-input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). Since the IN200 produces high levels of THD, these dominate when measuring THD+N; therefore, the THD+N plots look very similar to the THD versus output power plots above.

**THD ratio (unweighted) vs. frequency at 8, 4, and 2 ohms (left channel only)**

The chart above shows THD ratios measured at the output of the IN200 Signature as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yields 10W at the output into 8 ohms (and roughly 20W into 4 ohms, and 40W into 2 ohms) for the analog line-level input. We find increasing THD values from 8 to 4 to 2 ohms; however, the differences are fairly small (2-3dB). Into 2 ohms, THD ratios range from 0.1% at 40Hz, up to almost 5% at 20kHz.

**THD ratio (unweighted) vs. frequency into 8 ohms and real speakers (left channel only)**

The chart above shows THD ratios measured at the output of the IN200 Signature as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). All three plots track relatively closely, ranging from 0.05% at low freqeuncies, up to 5% at 20kHz.

**IMD ratio (CCIF) vs. frequency into 8 ohms and real speakers (left channel only)**

The chart above shows intermodulation distortion (IMD) ratios measured at the output of the IN200 Signature as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here the CCIF IMD method is used, where the primary frequency is swept from 20kHz (F1) down to 2.5kHz, and the secondary frequency (F2) is always 1kHz lower than the primary, with a 1:1 ratio. The CCIF IMD analysis results are the sum of the second (F1-F2 or 1kHz) and third modulation products (F1+1kHz, F2-1kHz). The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a 3-way speaker (Paradigm Founder Series 100F, measurements can be found here). All three plots are similar. Just like the measured THD ratios, IMD ratios are high, ranging from about 0.3% up to almost 5% at 20kHz.

**IMD ratio (SMPTE) vs. frequency into 8 ohms and real speakers (left channel only)**

The chart above shows IMD ratios measured at the output of the IN200 Signature as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here, the SMPTE IMD method is used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). The 8-ohm dummy load and 2-way speaker tracked almost perfectly, with a constant 0.2% IMD. The three-way speaker yielded IMD results about 10dB higher, hovering around 1%.

**FFT spectrum – 1kHz (line-level input)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the output across an 8-ohm load at 10W for the analog line-level input. The signal harmonics are evident and very high in amplitude. The odd harmonics (3/5/7/9kHz, etc.) are higher than the even harmonics (2/4/6/8kHz, etc.) at -60dBrA and below, or 0.1%, compared to the even harmonics at -75dBrA and below, or 0.02%. The exception is the second harmonic (2kHz) at just below -60dBrA. On the left side of the main signal peak, we find noise peaks at the fundamental (60Hz) and all subsequent harmonics at -90dBrA, or 0.003%, and below. At the second harmonic (120Hz) noise peak and above, the left channel yielded higher peaks than the right, by roughly 10dB.

**FFT spectrum – 50Hz (line-level input)**

Shown above is the FFT for a 50Hz input sine-wave stimulus measured at the output across an 8-ohm load at 10W for the analog line-level input. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The second harmonic (100Hz) dominates at -60dBrA, or 0.1%, while even and odd signal and power-supply noise-related harmonics at lower levels (-90dBrA or 0.003% and below), as well as their resultant IMD products, can be seen throughout.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, line-level input)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sine-wave stimulus tone measured at the output across an 8-ohm load at 10W for the analog line-level input. The input RMS values are set at -6.02dBrA, so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -70dBrA (left/right), or 0.03%. The third-order modulation products, at 17kHz and 20kHz, are quite high at around -50dBrA, or 0.3%.

**Square-wave response (10kHz)**

Above is the 10kHz square-wave response using the analog line-level input, at roughly 10W into 8 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the IN200’s slew-rate performance. Rather, it should be seen as a qualitative representation of the IN200’s mid-level bandwidth. An ideal square wave can be represented as the sum of a sine wave and an infinite series of its odd-order harmonics (*e.g.*, 10kHz + 30kHz + 50kHz + 70kHz . . .). A limited bandwidth will show only the sum of the lower-order harmonics, which may result in noticeable undershoot and/or overshoot, as well as softening of the edges. Here we can see an average looking square-wave reproduction, with softened corners but little to no ringing.

**Damping factor vs. frequency (20Hz to 20kHz)**

The final graph above is the damping factor as a function of frequency. Both channels show a relatively constant damping factor from 20Hz to 500Hz, right around 116. Above 500Hz, the right channel outperforms the left, with a damping factor as high as 130 at 15kHz, compared to the left channel’s 92 at 20kHz.

*Diego Estan*

Electronics Measurement Specialist

- Details
- Parent Category: Products
- Category: Amplifier Measurements

Link: reviewed by Dennis Burger on *SoundStage! Access* on May 1, 2022

**General Information**

All measurements taken using an Audio Precision APx555 B Series analyzer.

The A12MKII was conditioned for 1 hour at 1/8th full rated power (~8W into 8 ohms) before any measurements were taken. All measurements were taken with both channels driven, using a 120V/20A dedicated circuit, unless otherwise stated.

The A12MKII offers three unbalanced line-level analog inputs (RCA), one unbalanced moving-magnet (MM) phono input (RCA), one S/PDIF coaxial input (RCA), one S/PDIF optical input (TosLink), one USB digital input, a Bluetooth receiver, one pair of line-level pre-outs (RCA), and two stets (A and B) of speaker level outputs. On the front panel is a 1/8” TRS headphone output. For the purposes of these measurements, the following inputs were evaluated: coaxial digital, plus the analog line-level and MM unbalanced inputs.

Most measurements were made with a standard 2Vrms line-level analog input, 5mVrms MM input, and 0dBFS digital input. For the analog inputs, the tone-control bypass function was enabled, except for the chart showing the effects of the tone controls. The signal-to-noise ratio (SNR) measurements were made with the same input signal values but with the volume set to achieve the rated output power of 60W (8 ohms). For comparison, on the line-level input, an SNR measurement was also made with the volume at maximum, where only 0.94Vrms was required to achieve 60W into 8 ohms.

Based on the high accuracy and non-repeatable results at various volume levels of the left/right channel matching (see table below), the A12MKII volume control is likely operating in the analog domain, but is digital controlled. The volume control offers a total range of 0 to 96 on the display, which measured from -53.3dB (position 1) to +27.4dB between the line-level analog input and the speaker outputs, in increments of 6 to 2dB below 6, 1dB from 6 to 80, then 0.5dB steps from 80 to 96. One oddity that was observed was that between volume steps 7 to 40, every second volume increment did not change the output voltage.

**Volume-control accuracy (measured at speaker outputs): left-right channel tracking**

Volume position | Channel deviation |

1 | 0.23dB |

10 | 0.071dB |

20 | 0.038dB |

40 | 0.078dB |

60 | 0.003dB |

80 | 0.029dB |

96 | 0.044dB |

**Published specifications vs. our primary measurements**

The table below summarizes the measurements published by Rotel for the A12MKII compared directly against our own. The published specifications are sourced from Rotel’s website, either directly or from the manual available for download, or a combination thereof. With the exception of frequency response, where the Audio Precision bandwidth was extended from DC to 500kHz, assume, unless otherwise stated, 10W into 8 ohms and a measurement input bandwidth of 10Hz to 90kHz, and the worst-case measured result between the left and right channels.

Parameter | Manufacturer | SoundStage! Lab |

Rated output power into 8 ohms (1% THD, 1kHz) | 60W | 91W |

Rated output power into 4 ohms (1% THD, 1kHz) | 120W | 142W |

THD (1kHz, 10W, 8 ohms) | <0.018% | <0.008% |

SNR (A-weighted, IHF 8 ohms, line-level input) | 100dB | 101.4dB |

SNR (A-weighted, IHF 8 ohms, digital input 24/96) | 103dB | 100.7dB |

SNR (A-weighted, IHF 8 ohms, phono input) | 90dB | 79.7dB |

Damping factor (ref. 8 ohms 1kHz) | 220 | 212 |

Frequency response (line-level input) | 10Hz-100kHz, 0±0.5dB | 10Hz-100kHz, -0.8,+0.1dB |

Frequency response (digital input, 24/192) | 10Hz-90kHz, 0±2dB | 10Hz-90kHz, -2,-1.5dB |

Frequency response (phono input) | 20Hz-20kHz, 0±0.5dB | 20Hz-20kHz, ±0.5dB |

Intermodulation distortion (60Hz:7kHz, 4:1, 10W into 8ohms) | <0.03% | <0.03% |

Input sensitivity (line-level) | 230mVrms | 940mVrms |

Input sensitivity (digital) | 0dBFS | -8.7dBFS |

Input sensitivity (phono) | 3.4mVrms | 3.03mVrms |

Input impedance (line-level) | 24k ohms | 25k ohms |

Input impedance (phono) | 47k ohms | 53.5k ohms |

Input overload (line-level) | 4Vrms | 4.08Vrms |

Input overload (phono, 1kHz) | 50mVrms | 63.7mVrms |

Tone controls | ±10dB at 100Hz/10kHz | ±8dB at 100Hz/10kHz |

Our primary measurements revealed the following using the line-level analog input and digital coaxial input (unless specified, assume a 1kHz sine wave at 2Vrms or 0dBFS, 10W output, 8-ohm loading, 10Hz to 90kHz bandwidth):

Parameter | Left channel | Right channel |

Maximum output power into 8 ohms (1% THD+N, unweighted) | 91W | 91W |

Maximum output power into 4 ohms (1% THD+N, unweighted) | 142W | 142W |

Maximum burst output power (IHF, 8 ohms) | 98.6W | 98.6W |

Maximum burst output power (IHF, 4 ohms) | 169.1W | 169.1W |

Continuous dynamic power test (5 minutes, both channels driven) | failed | failed |

Crosstalk, one channel driven (10kHz) | -62.5dB | -64.6dB |

Damping factor | 216 | 212 |

Clipping no-load output voltage | 31.7Vrms | 31.7Vrms |

DC offset | <4.3mV | <3.8mV |

Gain (pre-out) | 0.81dB | 0.76dB |

Gain (maximum volume) | 27.4dB | 27.4dB |

IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-81dB | <-85dB |

IMD ratio (SMPTE, 60Hz + 7kHz stimulus tones, 4:1 ) | <-70dB | <-78dB |

Input impedance (line input, RCA) | 24.8k ohms | 25.0k ohms |

Input sensitivity (for rated power, maximum volume) | 940mVrms | 940mVrms |

Noise level (A-weighted) | <230uVmrs | <250uVmrs |

Noise level (unweighted) | <640uVmrs | <660uVmrs |

Output impedance (pre-out) | 452.8 ohms | 453.6 ohms |

Signal-to-noise ratio (full rated power, A-weighted, 2Vrms in) | 99.2dB | 98.9dB |

Signal-to-noise ratio (full rated power, unweighted, 2Vrms in) | 90.7dB | 90.5dB |

Signal-to-noise ratio (full rated power, A-weighted, max volume) | 99.4dB | 99.2dB |

Dynamic Range (full rated power, A-weighted, digital 24/96) | 99.0dB | 99.0dB |

Dynamic Range (full rated power, A-weighted, digital 16/44.1) | 93.9dB | 93.9dB |

THD ratio (unweighted) | <0.0080% | <0.0035% |

THD ratio (unweighted, digital 24/96) | <0.0051% | <0.012% |

THD ratio (unweighted, digital 16/44.1) | <0.0049% | <0.011% |

THD+N ratio (A-weighted) | <0.0095% | <0.0047% |

THD+N ratio (A-weighted, digital 24/96) | <0.0065% | <0.014% |

THD+N ratio (A-weighted, digital 16/44.1) | <0.0081% | <0.014% |

THD+N ratio (unweighted) | <0.011% | <0.0082% |

Minimum observed line AC voltage | 125VAC | 125VAC |

For the continuous dynamic power test, the A12MKII was able to sustain 133W into 4 ohms (~1% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (13.3W) for 5 seconds, for about 4 minutes (out of a 5- minute test) before the protection circuit shut down the unit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the A12MKII was quite warm to the touch. It should be noted that this test was conducted after a few hours of testing with an average of 10W at the output.

Our primary measurements revealed the following using the phono-level input, MM configuration (unless specified, assume a 1kHz 5mVrms sine wave input, 10W output, 8-ohm loading, 10Hz to 90kHz bandwidth):

Parameter | Left channel | Right channel |

Crosstalk, one channel driven (10kHz) | -61.3dB | -66.5dB |

DC offset | <1.1mV | <-0.3mV |

Gain (default phono preamplifier) | 49.71dB | 49.78dB |

IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-85dB | <-76dB |

IMD ratio (CCIF, 3kHz + 4kHz stimulus tones, 1:1) | <-87dB | <-76dB |

Input impedance | 53.2k ohms | 53.5k ohms |

Input sensitivity (to max power with max volume) | 3.04mVrms | 3.03mVrms |

Noise level (A-weighted) | <0.9mVrms | <0.85mVrms |

Noise level (unweighted) | <8mVrms | <7.8mVrms |

Overload margin (relative 5mVrms input, 1kHz) | 22.1dB | 22.1dB |

Signal-to-noise ratio (full rated power, A-weighted) | 79.7dB | 79.6dB |

Signal-to-noise ratio (full rated power, unweighted) | 61.1dB | 61.3dB |

THD (unweighted) | <0.0015% | <0.01% |

THD+N (A-weighted) | <0.01% | <0.015% |

THD+N (unweighted) | <0.09% | <0.09% |

Our primary measurements revealed the following using the analog input at the headphone output (unless specified, assume a 1kHz sine wave, 2Vrms output, 300 ohms loading, 10Hz to 90kHz bandwidth):

Parameter | Left channel | Right channel |

Maximum output power into 600 ohms (1% THD+N, unweighted) | 17.8mW | 17.8mW |

Maximum output power into 300 ohms (1% THD+N, unweighted) | 48.8mW | 48.6mW |

Maximum output power into 32 ohms (1% THD+N, unweighted) | 203mW | 203mW |

Gain | 27.3dB | 27.2dB |

Output impedance | 320 ohms | 320 ohms |

Noise level (A-weighted) | <94uVmrs | <96uVmrs |

Noise level (unweighted) | <143uVmrs | <146uVmrs |

Signal-to-noise (A-weighted, ref. max output voltage) | 92.6dB | 92.4dB |

Signal-to-noise (unweighted, ref. max output voltage) | 89.6dB | 89.4dB |

THD ratio (unweighted) | <0.29% | <0.29% |

THD+N ratio (A-weighted) | <0.33% | <0.33% |

THD+N ratio (unweighted) | <0.29% | <0.29% |

**Frequency response (8-ohm loading, line-level input)**

In our measured frequency response chart above, the A12MKII is nearly flat within the audio band (20Hz to 20kHz). At the extremes the A12MKII is about 0.25dB down at 20Hz, and 0dB at 20kHz. The A12MKII appears to be AC coupled (i.e.*,* not flat down to DC), contradicting Rotel’s frequency response claim of 10Hz-100kHz, 0±0.5dB. At the high-frequency extremes, however, Rotel’s claim is verified as we are within 0.5dB of flat, even at 200kHz. In the graph above and most of the graphs below, only a single trace may be visible. This is because the left channel (blue or purple trace) is performing identically to the right channel (red or green trace), and so they perfectly overlap, indicating that the two channels are ideally matched.

**Frequency response (8-ohm loading, line-level input, bass and treble controls)**

Above are frequency response plots measured at the speaker-level outputs into 8 ohms, with the bass and treble controls set to maximum (blue/red plots) and minimum (purple/green plots). We see that for the bass and treble controls, roughly +/- 12dB and +/- 9dB, respectively, of gain/cut are available at 20Hz and 20kHz.

**Phase response (8-ohm loading, line-level input)**

Above are the phase response plots for the left and right channels from 20Hz to 20kHz for the line-level input, measured across the speaker outputs at 10W into 8 ohms. The A12MKII does not invert polarity and exhibits, at worst, less than 20 degrees (at 20Hz) of phase shift within the audio band.

**Frequency response vs. input type (8-ohm loading, left channel only)**

The chart above shows the A12MkII’s frequency response as a function of input type measured across the speaker outputs at 10W into 8 ohms. The green trace is the same analog input data from the previous graph. The blue trace is for a 16bit/44.1kHz dithered digital input signal from 5Hz to 22kHz using the coaxial digital input, and the purple trace is for a 24/96 dithered digital input signal from 5Hz to 48kHz, while the pink trace is for a 24/192 dithered digital input signal from 5Hz to 96kHz. The analog input shows slightly flatter response at low frequencies, with the digital input -2dB at 10Hz and -0.5dB at 20Hz. The 16/44.1 data exhibits brick-wall-type filtering, with a -3dB point at 21.0kHz. The 24/96 and 24/192 kHz data yielded -3dB points at 46.2kHz and 91.9kHz, respectively, reflecting the higher sampling frequencies and, therefore, increased bandwidth.

**Frequency response (8-ohm loading, MM phono input)**

The chart above shows the frequency response for the MM phono input. What is being displayed is the deviation from the RIAA curve, where the input signal sweep is EQ’d with an inverted RIAA curve supplied by Audio Precision analyzer (*i.e.*, zero deviation would yield a flat line at 0dB). We see a maximum deviation of about +0.5 at 40Hz and 20kHz, from 20Hz to 20kHz. The worst-case channel deviation is between about 10kHz to 20kHz, at about 0.2dB.

**Phase response (MM input)**

Above is the phase-response plot from 20Hz to 20kHz for the MM phono input, measured across the speaker outputs at 10W into 8 ohms. The A12MKII does not invert polarity. For the phono input, since the RIAA equalization curve must be implemented, which ranges from +19.9dB (20Hz) to -32.6dB (90kHz), phase shift at the output is inevitable. Here we find a worst case of about -60 degrees at 200Hz and 5kHz, and +20 degrees at 20Hz.

**Digital linearity (16/44.1 and 24/96 data)**

The chart above shows the results of a linearity test for the coaxial digital input for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the line-level pre-outs of the A12MKII for a 1Vrms (at 0dBFS) output signal. The digital input is swept with a dithered 1kHz input signal from -120dBFS to 0dBFS, and the output is analyzed by the APx555. The ideal response would be a straight flat line at 0dB. Both data were essentially perfect as of -100dBFS down to 0dBFS. At -120dBFS, the 16/44.1 data were about +3.5dB above reference, while the 24/96 data were within +1.5/2.5dB ((left/right) of reference. This is an acceptable linearity test result.

**Impulse response (24/44.1 data)**

The chart above shows the impulse response for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s) for one sample period then back to digital silence, measured at the line-level pre-outs of the A12MKII. We can see that the A12MKII utilizes a typical sinc function reconstruction filter.

**J-Test (coaxial)**

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level pre-outs of the A12MKII. J-Test was developed by Julian Dunn in the 1990s. It is a test signal, specifically a -3dBFS undithered 12kHz square wave sampled (in this case) at 48kHz (24 bits). Since even the first odd harmonic (*i.e.*, 36kHz) of the 12kHz square wave is removed by the bandwidth limitation of the sampling rate, we are left with a 12kHz sine wave (the main peak). In addition, an undithered 250Hz square wave at -144dBFS is mixed with the signal. This test file causes the 22 least significant bits to constantly toggle, which produces strong jitter spectral components at the 250Hz rate and its odd harmonics. The test file shows how susceptible the DAC and delivery interface are to jitter, which would manifest as peaks above the noise floor at 500Hz intervals (*e.g,*. 250Hz, 750Hz, 1250Hz, etc.). Note that the alternating peaks are in the test file itself, but at levels of -144dBrA and below. The test file can also be used in conjunction with artificially injected sine-wave jitter by the Audio Precision, to show how well the DAC rejects jitter.

The coaxial input exhibits significant peaks in the audio band, peaking near the 12kHz primary signal, at -95dBrA and below. This is a poor J-Test result, indicating that the A12MKII DAC likely has poor jitter immunity.

**J-Test (optical)**

The chart above shows the results of the J-Test test for the optical digital input measured at the line- level pre-outs of the A12MKII. The optical input exhibits significant peaks in the audio band, peaking near the 12kHz primary signal, at -85dBrA and below. This, as with the coaxial-input test above, is a poor J-Test result, indicating that the A12MKII DAC likely has poor jitter immunity.

**J-Test with 10ns of injected jitter (coaxial)**

Both the coaxial and optical inputs were also tested for jitter immunity by injecting artificial sine-wave jitter at 2kHz, which would manifest as sidebands at 10kHz and 14kHz without any jitter rejection. Jitter immunity proved poor, with visible sidebands at only 10ns of jitter level. Clear sidebands can be seen at nearly -70dBrA. The optical input jitter result was very similar to the coaxial input result shown above. This, again, is a poor J-Test result.

**Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (coaxial input)**

The plot above shows a fast Fourier transform (FFT) of the A12MKII’s line-level pre-outs with white noise at -4dBFS (blue/red), and a 19.1 kHz sine wave at 0dBFS (1Vrms) fed to the coaxial digital input, sampled at 16/44.1. The sharp roll-off above 20kHz in the white-noise spectrum shows the implementation of a brick-wall-type reconstruction filter. There are no aliased image peaks in the audio band above the -120dBrA noise floor. The main 25kHz alias peak is at -60dBrA. The second, third, and fourth distortion harmonics (38.2, 57.3, 76.4kHz) of the 19.1kHz tone are between -75dBrA and -105dBrA.

**RMS level vs. frequency vs. load impedance (1W, left channel only)**

The chart above shows RMS level (relative to 0dBrA, which is 1W into 8 ohms, or 2.83Vrms) as a function of frequency, for the analog line-level input swept from 5Hz to 100kHz. The blue plot is into an 8-ohm load, the purple is into a 4-ohm load, the pink plot is an actual speaker (Focal Chora 806, measurements can be found here), and the cyan plot is no load connected. The chart below . . .

. . . is the same, but zoomed in to highlight differences. Here we can see a maximum deviation within the audio band of about 0.08dB from 4 ohms to no load, which is an indication of a relatively high damping factor, or low output impedance. The maximum variation in RMS level when a real speaker was used is even less, deviating by about 0.06dB within the flat portion of the curve (100Hz to 20kHz). Note that the dip in RMS level at lower frequencies is a result of the frequency response of the A12MKII, and not a damping-factor issue, as all four plots show the same dip, at roughly the same rate.

**THD ratio (unweighted) vs. frequency vs. output power**

The chart above shows THD ratios at the output into 8 ohms as a function of frequency for a sine-wave stimulus at the analog line-level input. The blue and red plots are for the left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at the rated 60W. The power was varied using the volume control. The A12MKII manages to maintain consistent THD ratios across a wide range of power output levels, and easily makes the Rotel spec of <0.018% THD from 20Hz to about 10kHz, from 1W to 60W. The disparity in the plots is actually a channel disparity, with the right channel outperforming the left channel by as much as almost 10dB, with the right channel dipping as low as 0.003% from 50Hz to 2kHz across all power levels. We wanted to investigate whether the disparity was in the amp or preamp section, so . . .

. . . we plotted THD ratios with a 1Vrms input (instead of 2Vrms), increasing the volume by 6dB to achieve the same 10W output into 8 ohms. Above is a chart that shows these THD ratios as a function of frequency for a 1Vrms sine-wave stimulus at the analog line-level input. Here we find better tracking between the left and right channels, and interestingly, below 2kHz, the left channel outperforming the right channel by about 5dB—the opposite result compared to a 2Vrms input. We can conclude from this that at least part of the reason for the THD channel disparity with a 2Vrms input is due to distortion in the preamp section.

**THD ratio (unweighted) vs. frequency at 10W (MM input)**

The chart above shows THD ratios as a function of frequency plots for the MM phono input measured across an 8-ohm load at 10W. The input sweep is EQ’d with an inverted RIAA curve. The THD values for the MM configuration vary from around 0.1% (20/30Hz) down to 0.001% (1kHz) for the left channel, then up to 0.03% at 20kHz. The right channel showed more constant THD ratios of roughly 0.01% from 50Hz to 10kHz.

**THD ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms**

The chart above shows THD ratios measured at the output of the A12MKII as a function of output power for the analog line-level input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). Both 8- and 4-ohm data sets, for the left channel, track fairly closely, with THD ratios from about 0.01% down to 0.002% at 2-3W, then back up to 0.01% at the “knees”—roughly 70W for the 8-ohm load, and about 120W for the 4-ohm load. The right channel performed worse than the left channel by as much as 10-12dB, with the exception of a crossover point just over 20W into 8 ohms, where the right channel begins to outperform the left channel with a nearly 10dB advantage at the knee. As discussed above, this may be due to distortions in the preamp section, as at the knee, we are approaching 2Vrms at the input. The 1% THD values are reached at about 91W (8 ohms) and 142W (4 ohms).

**THD+N ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms**

The chart above shows THD+N ratios measured at the output of the A12MKII as a function of output power for the line-level input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). Overall, THD+N values for both loads were similar but slightly lower for the 8-ohm load, ranging from about 0.1%, down to 0.005%. The exception was the right channel into 4 ohms, which performed worse by almost 10dB from 10 to 50W.

**THD ratio (unweighted) vs. frequency at 8, 4, and 2 ohms (right channel only)**

The chart above shows THD ratios measured at the output of the A12MKII as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yields 5W at the output into 8 ohms (and roughly 10W into 4 ohms, and 20W into 2 ohms) for the analog line-level input. The right channel was chosen because with these conditions (2Vrms in, 5W into 8 ohms), the right channel clearly outperformed the left channel. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. We find increasing THD values from 8 to 4 to 2 ohms. Into 8 ohms, THD ratios are as low as 0.003% from 50Hz to 3kHz. The 4-ohm THD ratios are more than 10dB higher through most of the frequency range, while the 2-ohm data is about 6dB higher than the 4-ohm data. Basically, THD increases as impedance descreases.

**THD ratio (unweighted) vs. frequency into 8 ohms and real speakers (right channel only)**

The chart above shows THD ratios measured at the output of the A12MKII as a function of frequency into an 8-ohm load and two different speakers, for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). At high frequencies (5-20kHz), all three plots show similar THD ratios from 0.005% to about 0.015%. Through the upper bass and midband, however, THD ratios were higher with real speakers, hovering around 0.01%, more than 10dB higher than the 0.003% measured with a dummy load. At very low frequencies, THD ratios were the highest with the two-way speaker, measuring 0.05%, a full 20dB higher than the 0.005% measured in the dummy load.

**IMD ratio (CCIF) vs. frequency into 8 ohms and real speakers (right channel only)**

The chart above shows intermodulation distortion (IMD) ratios measured at the output of the A12MKII as a function of frequency into an 8-ohm load and two different speakers, for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here the CCIF IMD method was used, where the primary frequency is swept from 20kHz (F1) down to 2.5kHz, and the secondary frequency (F2) is always 1kHz lower than the primary, with a 1:1 ratio. The CCIF IMD analysis results are the sum of the second (F1-F2 or 1kHz) and third modulation products (F1+1kHz, F2-1kHz). The 8-ohm load is the blue trace, the purple plot is the same two-way speaker as above (Focal Chora 806, measurements can be found here), and the pink plot is the same three-way speaker as above (Paradigm Founder Series 100F, measurements can be found here). In the lower frequencies (4kHz and below), all three results are similar, with relatively constant IMD ratios from as low as 0.002% to 0.008% at 2.5kHz. At higher frequencies, IMD ratios were highest with a real speaker, as high as 0.01% at 20kHz for the three-way speaker, which is 5dB higher than with the dummy load, and 15dB higher than with two-way speaker, which yielded, in general, the lowest IMD values.

**IMD ratio (SMPTE) vs. frequency into 8 ohms and real speakers (right channel only)**

The chart above shows IMD ratios measured at the output of the A12MKII as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here, the SMPTE IMD method was used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is the same two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is the same three-way speaker (Paradigm Founder Series 100F, measurements can be found here). All three results are nearly identical, with flat IMD results just around 0.02%.

**FFT spectrum – 1kHz (line-level input)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the output across an 8-ohm load at 10W for the analog line-level input. We find the left channel dominating at the second harmonic (2kHz) at -80dBrA, or 0.01%, compared to the right channel at below -90dBrA, or 0.003%. At the fourth harmonic (4kHz), the right channel dominates at about -95dBrA, or 0.002%, compared to the left channel at -110dBrA, or 0.0003%. At the third (3kHz) and fifth harmonics (5kHz), both channels yielded peaks at roughly -105dBrA, or 0.0006%. On the left side of the main signal peak, we find a small peak at 60Hz due to power-supply noise at about -115dBrA, or 0.0002%, for the left channel, and more dominant higher-order peaks at 120Hz, and especially 240Hz (fourth harmonic) at -105dBrA, or 0.0006%. Power-supply and signal-related harmonic peaks can be seen right out to 100kHz.

**FFT spectrum – 1kHz (digital input, 16/44.1 data at 0dBFS)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 16/44.1. Here we find the right channel dominating at the second harmonic (2kHz) at -80dBrA, or 0.01%, compared to the left channel at below -100dBrA, or 0.001%. At the third (3kHz) harmonic, both channels yielded peaks at roughly -85dBrA, or 0.006%. The noise-related peaks on the left side of the signal peak are very similar to the line-level FFT above.

**FFT spectrum – 1kHz (digital input, 24/96 data at 0dBFS)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 24/96. The FFT spectrum is nearly identical within the audio band to the 16/44.1 FFT above.

**FFT spectrum – 1kHz (digital input, 16/44.1 data at -90dBFS)**

Shown above is the FFT for a 1kHz -90dBFS dithered 16/44.1 input sine-wave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, and signal harmonics are non-existent above the noise floor. The fourth (240Hz) and sixth (360Hz) power-supply related harmonics are visible at roughly -105dBrA, or 0.0006%.

**FFT spectrum – 1kHz (digital input, 24/96 data at -90dBFS)**

Shown above is the FFT for a 1kHz -90dBFS dithered 24/96 input sine-wave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. The FFT spectrum is nearly identical within the audio band to the 16/44.1 FFT above.

**FFT spectrum – 1kHz (MM phono input)**

Shown above is the FFT for a 1kHz input sine-wave stimulus, measured at the output across an 8-ohm load at 10W for the MM phono input. We see the right channel dominating the even-order harmonics (2, 4, 6kHz), as high as -80dBrA, or 0.01%, at 2kHz. We see the primary (60Hz) power-supply-related peak at just under -60dBrA, or 0.1%, and subsequent power-supply-related peaks (120, 180, 240Hz, etc.) extending beyond the 1kHz signal peak, at -80dBrA (at 180Hz), or 0.01%, and below.

**FFT spectrum – 50Hz (line-level input)**

Shown above is the FFT for a 50Hz input sine-wave stimulus measured at the output across an 8-ohm load at 10W for the analog line-level input. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The second harmonic (100Hz) dominates at -85/-95dBrA (left/right), or 0.006/0.002%, but even and odd signal harmonics at lower levels can be seen throughout. We also see the 60Hz power-supply-related peak at -120dBrA, or 0.0001%, with higher-order peaks at 180Hz and 240Hz, between -100 and -110dBrA, or 0.001 and 0.0003%.

**FFT spectrum – 50Hz (MM phono input)**

Shown above is the FFT for a 50Hz input sine-wave stimulus measured at the output across an 8-ohm load at 10W for the MM phono input. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most predominant (non-signal) peak is from the 60Hz power-supply fundamental at -60dBrA, or 0.1%. The second-order signal peak at 100Hz is dominated by the right channel at -80dBrA, or 0.01%, while the third-order noise peak (180Hz) is at the same level, but for both channels.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, line-level input)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sine-wave stimulus tone measured at the output across an 8-ohm load at 10W for the analog line-level input. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -90/-95dBrA (left/right), or 0.003/0.002%. The third-order modulation products, at 17kHz and 20kHz, are around -100dBrA, or 0.001%.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 16/44.1)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sine-wave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 16/44.1. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at 100/-85dBrA (left/right), or 0.001/0.006%. The third-order modulation products, at 17kHz and 20kHz, are around -85dBrA, or 0.006%. We also see the main aliased peaks at 25.1kHz and 26.1kHz around -70dBrA, due to the 44.1kHz sample rate (*e.g.*, 44.1kHz-19kHz = 25.1kHz).

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 24/96)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sine-wave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 24/96. The FFT spectrum is nearly identical within the audio band to the 16/44.1 FFT above.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, MM phono input)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sine-wave stimulus tone measured at the output across an 8-ohm load at 10W for the MM phono input. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at around -100/-80dBRa (left/right), or 0.001/0.01%, while the third-order modulation products, at 17kHz and 20kHz, are around -105dBrA, or 0.0006%.

**Square-wave response (10kHz)**

Above is the 10kHz square-wave response using the analog line-level input, at roughly 10W into 8 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the A12MKII’s slew-rate performance. Rather, it should be seen as a qualitative representation of the A12MKII’s extended bandwidth. An ideal square wave can be represented as the sum of a sine wave and an infinite series of its odd-order harmonics (*e.g.*, 10kHz + 30kHz + 50kHz + 70kHz . . .). A limited bandwidth will show only the sum of the lower-order harmonics, which may result in noticeable undershoot and/or overshoot, and softening of the edges. Here we can see an exceptionally clean square-wave reproduction, with sharp corners and little-to-no ringing, indicating a high bandwidth.

**Damping factor vs. frequency (20Hz to 20kHz)**

The final graph above is the damping factor as a function of frequency. Both channels show a relatively constant damping factor from 20Hz to 20kHz, right around 215. This is very close to Rotel’s claim of 220.

*Diego Estan*

Electronics Measurement Specialist

- Details
- Parent Category: Products
- Category: Amplifier Measurements

Link: reviewed by Jason Thorpe on *SoundStage! Hi-Fi* on April 15, 2023

**General information**

All measurements taken using an Audio Precision APx555 B Series analyzer.

The Hegel Music Systems H30A was conditioned for 1 hour at 1/8th full rated power (~60W into 8 ohms) before any measurements were taken. All measurements were taken with both channels driven, using a 120V/20A dedicated circuit, unless otherwise stated.

The Hegel H30A has both unbalanced (RCA) and balanced (XLR) inputs, and a pair of speaker level outputs. We found no appreciable differences in term of THD and noise between the RCA and XLR inputs. The H30A can be operated in stereo or mono mode, for which the latter uses a third unbalanced or balanced input. Hegel states that the H30A is designed as a mono power amplifier, but that it can also be used as a stereo amplifier. As such, essentially all measurements have been performed in both stereo (two-channel) and mono (single-channel) modes. Unless otherwise stated, the balanced inputs were used for all measurements.

**Published specifications vs. our primary measurements**

The table below summarizes the measurements published by Hegel for the H30A compared directly against our own. The published specifications are sourced from Hegel’s website, either directly or from the manual available for download, or a combination thereof. With the exception of frequency response, where the Audio Precision bandwidth was extended to 500kHz, assume, unless otherwise stated, 10W into 8 ohms and a measurement input bandwidth of 10Hz to 90kHz, and the worst-case measured result between the left and right channels.

Parameter | Manufacturer | SoundStage! Lab |

Rated output power into 8 ohms (1% THD, 1kHz, mono) | >1100W | 1060W |

Crosstalk (1kHz, 10W, 8 ohms) | <-100dB | -121dB |

THD (1kHz, 100W, 8 ohms) | <0.003% | 0.0025% |

SNR (A-weighted, 8 ohms, full rated power, mono) | >100dB | 117.2dB |

Intermodulation distortion (19kHz+20kHz, 1:1, 10W into 8 ohms) | <0.01% | <0.006% |

Damping factor (mono) | *>500 | *374 |

Input impedance (line-level, RCA) | 10k ohms | 10.7k ohms |

Input impedance (line-level, XLR) | 20k ohms | 11.3k ohms |

* Hegel measures damping factor directly at the output stage, whereas we measure at the amp’s output terminals.

Our primary measurements in stereo mode revealed the following using the line-level balanced analog input (unless specified, assume a 1kHz sinewave at 223mVrms, 10W output, 8-ohm loading, 10Hz to 90kHz bandwidth):

Parameter | Left channel | Right channel |

Maximum output power into 8 ohms (1% THD+N, unweighted) | 296W | 296W |

Maximum output power into 4 ohms (1% THD+N, unweighted) | 525W | 525W |

Maximum burst output power (IHF, 8 ohms) | 313.5W | 313.5W |

Maximum burst output power (IHF, 4 ohms) | 608.1W | 608.1W |

Continuous dynamic power test (5 minutes, both channels driven) | passed | passed |

Crosstalk, one channel driven (10kHz) | -97.0dB | -105.1dB |

Damping factor | 789 | 824 |

Clipping no-load output voltage | 52Vrms | 52Vrms |

DC offset | <-3.8mV | <1mV |

Gain | 32.09dB | 32.07dB |

IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-85dB | <-86dB |

IMD ratio (SMPTE, 60Hz + 7kHz stimulus tones, 4:1 ) | <-84dB | <-85dB |

Input impedance (line input, RCA) | 10.7k ohms | 10.7k ohms |

Input impedance (line input, XLR) | 11.3k ohms | 11.3k ohms |

Input sensitivity (for rated power, 1% THD) | 1.21Vrms | 1.21Vrms |

Noise level (A-weighted) | <98uVrms | <98uVrms |

Noise level (unweighted) | <268uVrms | <268uVrms |

Signal-to-noise ratio (full power, A-weighted) | 113.5dB | 113.5dB |

Signal-to-noise ratio (full power, unweighted) | 105.1dB | 105.1dB |

THD ratio (unweighted) | <0.0014% | <0.0014% |

THD+N ratio (A-weighted) | <0.0020% | <0.0020% |

THD+N ratio (unweighted) | <0.0033% | <0.0033% |

Minimum observed line AC voltage | 122 VAC | 122 VAC |

For the continuous dynamic power test, the H30A was able to sustain 553W into 4 ohms (~1.5% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (55.3W) for 5 seconds, for 5 continuous minutes without inducing a fault or the initiation of a protective circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the H30A was only warm to the touch, without causing any discomfort.

Our primary measurements in mono mode revealed the following using the line-level balanced analog input (unless specified, assume a 1kHz sinewave at 223mVrms, 10W output, 8-ohm loading, 10Hz to 90kHz bandwidth):

Parameter | Mono channel |

Maximum output power into 8 ohms (1% THD+N, unweighted) | 1060W |

Maximum burst output power (IHF, 8 ohms) | 1215.4W |

Damping factor | 374 |

Clipping no-load output voltage (instantaneous power into 8 ohms) | 105Vrms |

DC offset | <8.6mV |

Gain (maximum volume) | 32.07dB |

IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-85dB |

IMD ratio (SMPTE, 60Hz + 7kHz stimulus tones, 4:1 ) | <-85dB |

Input sensitivity (for full power) | 2.3Vrms |

Noise level (A-weighted) | <120uVrms |

Noise level (unweighted) | <325uVrms |

Signal-to-noise ratio (full power, A-weighted) | 117.2dB |

Signal-to-noise ratio (full power, unweighted) | 109.0dB |

THD ratio (unweighted) | <0.0014% |

THD+N ratio (A-weighted) | <0.0021% |

THD+N ratio (unweighted) | <0.0039% |

Minimum observed line AC voltage | 122VAC |

**Frequency response (8-ohm loading, stereo mode)**

In our frequency-response plots (relative to 1kHz) above, measured across the speaker outputs at 10W into 8 ohms, the H30A is near flat within the audioband (-0.2/0dB, 20Hz/20kHz). At the extremes, the H30A is at -1.5dB at 5Hz and +-1.2dB at 200kHz. In the graph above and most of the graphs below, only a single trace may be visible. This is because the left channel (blue or purple trace) is performing identically to the right channel (red or green trace), and so they perfectly overlap, indicating that the two channels are ideally matched.

**Phase response (8-ohm loading, line-level input, stereo mode)**

Above are the phase response plots from 20Hz to 20kHz for the line level input, measured across the speaker outputs at 10W into 8 ohms. The H30A does not invert polarity and exhibits, at worst, about 30 degrees (at 20kHz) of phase shift within the audioband.

**RMS level vs. frequency vs. load impedance (1W, left channel only, stereo mode)**

The chart above shows RMS level (relative to 0dBrA, which is 1W into 8 ohms or 2.83Vrms) as a function of frequency, for the analog line-level input swept from 5Hz to 100kHz, in stereo mode. The blue plot is into an 8-ohm load, the purple is into a 4-ohm load, the pink plot is an actual speaker (Focal Chora 806, measurements can be found here), and the cyan plot is no load connected. The chart below . . .

. . . is the same but zoomed in to highlight differences. Here we find that maximum deviation between no load and a 4-ohm load is very small, at around 0.02dB. This is an indication of a very high damping factor, or low output impedance. With a real speaker, maximum deviations in RMS level were roughly the same.

**RMS level vs. frequency vs. load impedance (1W, left channel only, mono mode)**

The chart above shows RMS level (relative to 0dBrA, which is 1W into 8 ohms or 2.83Vrms) as a function of frequency, for the analog line-level input swept from 5Hz to 100kHz, in mono mode. The blue plot is into an 8-ohm load, the purple is into a 4-ohm load, the pink plot is an actual speaker (Focal Chora 806, measurements can be found here), and the cyan plot is no load connected. The chart below . . .

. . . is the same but zoomed in to highlight differences. Here we find that maximum deviation between no load and a 4-ohm load is roughly double in mono mode compared to stereo, at around 0.04dB. This is normal for a bridged amplifier, as the output impedance roughly doubles because each speaker output terminal is wired to an amplifier output (but out of phase). In a conventional amplifier, only the positive speaker output terminal is connected to the amplifier output, while the negative speaker output terminal is connected to ground. Nonetheless, the output impedance is still very low in mono mode by any conventional standard. With a real speaker, maximum deviations in RMS level were roughly the same, at 0.04dB.

**THD ratio (unweighted) vs. frequency vs. output power (stereo mode)**

The chart above shows THD ratios at the output into 8 ohms as a function of frequency for a sinewave stimulus at the analog line-level input in stereo mode. The blue and red plots are for left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at 200W. We find fairly consistent THD ratios at 1W and 10W, from 0.001-0.003% at 20Hz, up to 0.005-0.008% at 20kHz. At 200W, THD ratios were higher, from 0.006% from 20Hz to 2kHz, up to nearly 0.02% at 20kHz.

**THD ratio (unweighted) vs. frequency vs. output power (mono mode)**

The chart above shows THD ratios at the output into 8 ohms as a function of frequency for a sinewave stimulus at the analog line-level input in mono mode. The blue plot is at 1W output into 8 ohms, purple at 10W, and pink at 600W. THD ratios at 1W were the lowest, from 0.002-0.001% between 20Hz and 5kHz, then up to 0.006% at 20kHz. At 10W, THD values were roughly 5dB higher. At 600W, THD ratios were still commendably low, at 0.003-0.004% from 20Hz to 2kHz, then up to 0.006% near 20kHz.

**THD ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms (stereo mode)**

The chart above shows THD ratios measured at the output of the H30A as a function of output power for the analog line-level input in stereo mode, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). The 8-ohm data ranged from about 0.003% at 50mW, down to 0.0015% from 0.5 to 50W, then up to the “knee” just shy of 300W. The 4-ohm data yielded THD ratios 5-10dB higher through the flat portion of the curve up to 200W, and hit the “knee” at nearly 500W. The 1% THD marks were hit at 296W (8 ohms) and 525W (4 ohms).

**THD+N ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms (stereo mode)**

The chart above shows THD+N ratios measured at the output of the H30A as a function of output power for the analog line-level input in stereo mode, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). THD+N values for the 8-ohm data ranged from 0.05% down to 0.002% at 50W. The 4-ohm data yielded THD+N values 3-4dB higher, except at the lowest point, where 0.002% was also reached, but at around 150W.

**THD ratio (unweighted) vs. output power at 1kHz into 8 ohms (mono mode)**

The chart above shows THD ratios measured at the output of the H30A as a function of output power for the analog line level-input in mono mode into 8 ohms. THD values were at 0.003% at 50mW, down to 0.001% at 1-3W then up to 0.002% up to 500W, then to the “knee” between 800 and 900W. The 1% THD mark was hit at 1060W (8-ohm).

**THD+N ratio (unweighted) vs. output power at 1kHz into 8 ohms (mono mode)**

The chart above shows THD+N ratios measured at the output of the H30A as a function of output power for the analog line level-input in mono mode into 8 ohms. THD+N values were at 0.05% at 50mW, down to as low as 0.002% between 100 and 500W.

**THD ratio (unweighted) vs. frequency at 8, 4, and 2 ohms (left channel only, stereo mode)**

The chart above shows THD ratios measured at the output of the HA30 as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yielded 100W at the output into 8 ohms (and roughly 200W into 4 ohms, and 400W into 2 ohms) for the analog line-level input in stereo mode. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. We see increasing levels (5dB) of THD from 8 to 4 to 2 ohms at 3kHz and above. Below 1kHz, are three THD data sets are fairly close, with THD ratios ranging from 0.002% to 0.005%.

**THD ratio (unweighted) vs. frequency at 8, 4, and 2 ohms (mono mode)**

The chart above shows THD ratios measured at the output of the H30A as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yielded 200W at the output into 8 ohms (and roughly 400W into 4 ohms, and 800W into 2 ohms) for the analog line-level input in mono mode. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. We see increasing levels (5-10dB) of THD from 8 to 4 to 2 ohms between about 300Hz and 3kHz, with the 8-ohm data as low as 0.001-0.002%. At the frequency extremes, THD ratios were quite similar: 0.002% at 20Hz, and 0.007% near 20kHz.

**THD ratio (unweighted) vs. frequency into 8 ohms and real speakers (left channel only, stereo mode)**

The chart above shows THD ratios measured at the output of the H30A as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the balanced analog line-level input in stereo mode. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). The 8-ohm plot is fairly flat and between 0.001% and 0.002% from 20Hz to 5kHz, but the two speaker plots vary considerably. The two-way speaker ranges from 0.02% at 20Hz, to as low as 0.0005% at 2kHz, then back up to 0.01% at 20kHz. The three-way speaker THD plot ranges from 0.003% at 100Hz, down to as low as 0.0007% at 4kHz, then up to 0.01% at 20kHz.

**THD ratio (unweighted) vs. frequency into 8 ohms and real speakers (mono mode)**

The chart above shows THD ratios measured at the output of the H30A as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the balanced analog line-level input in mono mode. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). The 8-ohm plot ranges from 0.002% at 20Hz down to 0.0008-0.0009% between 100Hz and 3kHz, then up to 0.006% at 20kHz. The two speaker plots vary considerably more. The two-way speaker ranges from 0.03% at 20Hz, to as low as 0.0006% at 2-3kHz, then back up to 0.002% at 10kHz. The three-way speaker THD plot ranges from 0.004% at 100Hz, down to as low as 0.0007% at 2kHz, then up to 0.015% at 20kHz.

**IMD ratio (CCIF) vs. frequency into 8 ohms and real speakers (left channel only, stereo mode)**

The chart above shows intermodulation distortion (IMD) ratios measured at the output of the H30A as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here the CCIF IMD method is used, where the primary frequency is swept from 20kHz (F1) down to 2.5kHz, and the secondary frequency (F2) is always 1kHz lower than the primary, with a 1:1 ratio. The CCIF IMD analysis results are the sum of the second (F1-F2 or 1kHz) and third modulation products (F1+1kHz, F2-1kHz). The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). The 8-ohm IMD data is fairly flat, between 0.002% and 0.003%. The two-way speaker data ranges from 0.001% at 2.5kHz up to 0.003% at 20kHz. The three-way speaker data ranges from 0.001% at 2.5kHz up to 0.007% at 20kHz.

**IMD ratio (CCIF) vs. frequency into 8 ohms and real speakers (mono mode)**

The chart above shows intermodulation distortion (IMD) ratios measured at the output of the H30A as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input in mono mode. Here the CCIF IMD method is used, where the primary frequency is swept from 20kHz (F1) down to 2.5kHz, and the secondary frequency (F2) is always 1kHz lower than the primary, with a 1:1 ratio. The CCIF IMD analysis results are the sum of the second (F1-F2 or 1kHz) and third modulation products (F1+1kHz, F2-1kHz). The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). The 8-ohm IMD data is fairly flat, between 0.002% and 0.003%. The two-way speaker data ranges from 0.001% at 2.5kHz up to 0.005% at 20kHz. The three-way speaker data ranges from 0.001% at 5.5kHz up to 0.01% at 20kHz.

**IMD ratio (SMPTE) vs. frequency into 8 ohms and real speakers (left channel only, stereo mode)**

The chart above shows IMD ratios measured at the output of the H30A as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input in stereo mode. Here, the SMPTE IMD method is used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). All three data sets are close enough to be judged as nearly identical, hovering around the 0.006-0.008% level.

**IMD ratio (SMPTE) vs. frequency into 8 ohms and real speakers (mono mode)**

The chart above shows IMD ratios measured at the output of the H30A as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input in mono mode. Here, the SMPTE IMD method is used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). All three data sets are close enough to be judged as nearly identical, hovering around the 0.006-0.008% level.

**FFT spectrum – 1kHz (line-level input, stereo mode)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the analog line-level input in stereo mode. We see that the signal’s second (2kHz) and third (3kHz) harmonic, are at roughly -100dBrA, or 0.001%. The subsequent harmonics (4/5/6/7/8kHz) are visible but at lower and descending levels below the -110dBrA, or 0.0003% mark. Power supply related noise peaks at the fundamental (60Hz) frequency are evident at -130/-115dBrA (left/right), or 0.00003/0.0002%, as well as both even and odd harmonics at a low -120dBrA, or 0.001%, and below.

**FFT spectrum – 1kHz (line-level input, mono mode)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the analog line-level input in mono mode. We see that the signal’s even harmonics are lower than is seen in stereo mode. For example, the 2kHz peak here is at -115dBrA, or 0.0002%, versus -100dBrA in stereo mode. Power-supply-related noise peaks are roughly the same as is seen in the stereo FFT above.

**FFT spectrum – 50Hz (line-level input, stereo mode)**

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the analog line-level input in stereo mode. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most dominant (non-signal) peaks are the second (100Hz) and third (150Hz) signal harmonic at roughly -100dBrA (right), or 0.001%. Power-supply-related harmonics are generally below the -120dBrA, or 0.0001% level.

**FFT spectrum – 50Hz (line-level input, mono mode)**

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the analog line-level input in mono mode. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. Here again we see that the signal’s even harmonics are lower than is seen in stereo mode. For example, the 200Hz (fourth harmonic) peak here is nearly at -120dBrA, or 0.0001%, versus -110dBrA (left channel) in stereo mode. Power-supply-related noise peaks are roughly the same as is seen in the stereo FFT above.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, line-level input, stereo mode)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the analog line-level input in stereo mode. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -100dBrA, or 0.001%, and the third-order modulation products, at 17kHz and 20kHz, are at the same level.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, line-level input, mono mode)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the analog line-level input in mono mode. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -110dBrA, or 0.0003%, which is lower than is seen in stereo mode, while the third-order modulation products, at 17kHz and 20kHz, are at -95dBrA, or 0.002%, which is higher than is seen in stereo mode.

**Squarewave response (10kHz, stereo mode)**

Above is the 10kHz squarewave response using the balanced analog line-level input, at roughly 10W into 8 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the H30A’s slew-rate performance. Rather, it should be seen as a qualitative representation of the H30A’s extended bandwidth. An ideal squarewave can be represented as the sum of a sinewave and an infinite series of its odd-order harmonics (*e.g.*, 10kHz + 30kHz + 50kHz + 70kHz . . .). A limited bandwidth will show only the sum of the lower-order harmonics, which may result in noticeable undershoot and/or overshoot, and softening of the edges. The H30A’s squarewave response is superb, showing no visible over/undershoot, or ringing near the sharp corners.

**Damping factor vs. frequency (20Hz to 20kHz, stereo mode)**

The graph above is the damping factor as a function of frequency in stereo mode. We see both channels tracking closely and a very high damping factor, ranging around the 800 mark between 40Hz and 1kHz, then down to 300 at 20kHz.

**Damping factor vs. frequency (20Hz to 20kHz, mono mode)**

The final graph above is the damping factor as a function of frequency in mono mode. We see roughly the same plot as above in stereo mode, but at half the values, due to each speaker output terminal being connected to an amplifier output (bridged mode), each with its own output impedance.

*Diego Estan*

Electronics Measurement Specialist

- Details
- Parent Category: Products
- Category: Amplifier Measurements

Link: reviewed by Dennis Burger on *SoundStage! Access* on April 1, 2022

**General Information**

All measurements taken using an Audio Precision APx555 B Series analyzer.

The C 399 was conditioned for 1 hour at 1/8th full rated power (~22W into 8 ohms) before any measurements were taken. All measurements were taken with both channels driven, using a 120V/20A dedicated circuit, unless otherwise stated.

The C 399 offers two unbalanced line-level analog inputs (RCA), one unbalanced moving-magnet (MM) phono input (RCA), two coaxial (RCA) and two optical S/PDIF digital inputs, one HDMI digital input, Bluetooth support, two line-level subwoofer outputs (RCA), two line-level pre-outs (RCA), two pairs of speaker level outputs, and, lastly, one ethernet input (RJ45) for streaming in the optional MDC module, which was included in this sample. On the front of the unit is a 1/4″ TRS headphone output. For the purposes of these measurements, the digital coaxial, analog line-level, and MM inputs were evaluated.

Most measurements were made with a 1Vrms line-level analog input, 5mVrms MM input, and 0dBFS digital input. For the analog inputs, the Analog Bypass function was enabled, so the signals would not be digitzied. For comparison, however, THD+N at 1kHz was measured with the Analog Bypass enabled (0.001%) and disabled (0.0023%). In addition, FFT and frequency response comparisons were made (see graphs below) between Analog Bypass settings.

The following volume settings yielded approximately 10W into 8 ohms: -14.5dB for analog line-level, -4.5dB for MM input, and -20.5dB for digital. The signal-to-noise ratio (SNR) measurements were made with the same input signal values, but with the volume set to achieve the rated output power of 180W (8 ohms). For comparison, on the line-level input, a SNR measurement was also made with the volume at maximum, where only 0.196Vrms was required to achieve 180W into 8 ohms.

Based on the accuracy and non-repeatable results (*i.e.*, they varied slighty over successive measurements) at various volume levels of the left/right channel matching (see table below), the C 399 volume control is likely digitally controlled in the analog domain. The volume control offers a total range from -80dB to +12dB on the C 399 display, which measured from -46dB to +46dB between the line-level analog input and the speaker outputs, in 0.5dB increments.

Because the C 399 is a digital amplifier technology that exhibits considerable noise above 20kHz (see FFTs below), our typical input bandwidth filter setting of 10Hz-90kHz was necessarily changed to 10Hz-22.4kHz for all speaker output measurements, except for frequency response and for FFTs. In addition, THD versus frequency sweeps were limited to 6kHz to adequately capture the second and third signal harmonics with the restricted bandwidth setting.

**Volume-control accuracy (measured at speaker outputs): left-right channel tracking**

Volume position | Channel deviation |

-80dB | 0.038dB |

-60dB | 0.025dB |

-50dB | 0.039dB |

-40dB | 0.023dB |

-20dB | 0.033dB |

0dB | 0.048dB |

12dB | 0.052dB |

**Published specifications vs. our primary measurements**

The table below summarizes the measurements published by NAD for the C 399 compared directly against our own. The published specifications are sourced from NAD’s website, either directly or from the manual available for download, or a combination thereof. With the exception of frequency response, where the Audio Precision bandwidth was extended from DC to 250kHz, assume, unless otherwise stated, 10W into 8 ohms and a measurement input bandwidth of 10Hz to 22.4kHz for the speaker outputs, and 10Hz to 90kHz for the line-level and headphone outputs, and the worst-case measured result between the left and right channels. All analog input measurements were taken with Analog Bypass engaged, as is specified by NAD.

Parameter | Manufacturer | SoundStage! Lab |

Rated output power into 8 ohms (0.02% THD, 1kHz) | 180W | 198W |

Rated output power into 4 ohms (0.02% THD, 1kHz) | 180W | 235W |

THD (20Hz-6.5kHz, 180W, 8 ohms) | <0.02% | <0.005% |

SNR (A-weighted, ref. 1W out in 8 ohms, 500mV input) | >95dB | 94.6dB |

Clipping power (1kHz, 8 ohms, 0.1%THD) | 210W | 204W |

IHF dynamic power (8 ohms) | 217W | 219W |

IHF dynamic power (4 ohms) | 400W | 399W |

Damping factor (ref. 8 ohms 20Hz and 6.5kHz) | >150 | 1442 |

Frequency response (20Hz-20kHz) | ±0.3dB | ±0.02dB |

Channel separation (1kHz, 1W) | >90dB | 93dB |

Channel separation (10kHz, 1W) | >75dB | 89dB |

Input sensitivity (analog) | 201mVrms | 196mVrms |

Input sensitivity (digital) | -10.25%FS | -20%FS |

Preamp out THD (20Hz-20kHz, 2V) | <0.002% | <0.003% |

Preamp out SNR (A-weighted, ref. 500mV out, unity gain) | >106dB | 109.7dB |

Preamp out channel separation (1kHz) | >100dB | 106dB |

Preamp out channel separation (10kHz) | >90dB | 94dB |

Input impedance | 56k ohms | 52.7k ohms |

Maximum input signal (0.1% THD) | >4.6Vrms | 5.27Vrms |

Preamp output impedance | 320 ohms | 330 ohms |

Maximum output signal (0.1% THD) | >5Vrms | 4.7Vrms |

Preamp out, phono in THD (20Hz-20kHz, 2V) | <0.01% | <0.01% |

Preamp out, phono in SNR (A-weighted, ref. 500mV out) | >84dB | 83dB |

Input impedance (phono) | 46k ohms | 45.7k ohms |

Preamp out, phono in frequency response (20Hz-20kHz) | ±0.3dB | ±0.13dB |

Maximum phono input signal (0.1% THD, 1kHz) | >80mVrms | 93mVrms |

Headphone out THD (20Hz-20kHz, 1V, 300 ohm load) | <0.005% | <0.007% (at 20kHz) |

Headphone out SNR (A-weighted, ref. 1V out, unity gain, 32 ohm load) | >107dB | 109dB |

Headphone out channel separation (1kHz, 1V out, 300 ohm load) | >62dB | 74dB |

Headphone output impedance | 2.2 ohms | 3.5 ohms |

Our primary measurements revealed the following using the line-level analog input and digital coaxial input (unless specified, assume a 1kHz sine wave at 1Vrms or 0dBFS, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

Parameter | Left channel | Right channel |

Maximum output power into 8 ohms (1% THD+N, unweighted) | 209W | 209W |

Maximum output power into 4 ohms (1% THD+N, unweighted) | 239W | 239W |

Continuous dynamic power test (5 minutes, both channels driven) | passed | passed |

Crosstalk, one channel driven (10kHz) | -91.9dB | -92.2dB |

Damping factor | 1624 | 1767 |

Clipping no-load output voltage (instantaneous power into 8 ohms) | 258W | 258W |

DC offset | -3mV | 4mV |

Gain (pre-out) | 17.8dB | 17.8dB |

Gain (maximum volume) | 45.7dB | 45.7dB |

IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-92dB | <-93dB |

IMD ratio (SMPTE, 60Hz + 7kHz stimulus tones, 4:1 ) | <-94dB | <-95dB |

Input impedance (line input, RCA) | 52.7k ohms | 52.7k ohms |

Input sensitivity (for rated power, maximum volume) | 196mVrms | 198mVrms |

Noise level (A-weighted) | <55uVrms | <55uVrms |

Noise level (unweighted) | <82uVrms | <79uVrms |

Output impedance (pre-out) | 330 ohms | 330 ohms |

Signal-to-noise ratio (full rated power, A-weighted, 1Vrms in) | 116.1dB | 116.1dB |

Signal-to-noise ratio (full rated power, unweighted, 1Vrms in) | 113.1dB | 113.2dB |

Signal-to-noise ratio (full rated power, A-weighted, max volume) | 102.6dB | 102.6dB |

Dynamic range (full rated power, A-weighted, digital 24/96) | 116.5dB | 116.7dB |

Dynamic range (full rated power, A-weighted, digital 16/44.1) | 96.0dB | 95.9dB |

THD ratio (unweighted) | <0.0005% | <0.0004% |

THD ratio (unweighted, digital 24/96) | <0.0011% | <0.0010% |

THD ratio (unweighted, digital 16/44.1) | <0.0012% | <0.0012% |

THD+N ratio (A-weighted) | <0.0008% | <0.0008% |

THD+N ratio (A-weighted, digital 24/96) | <0.0014% | <0.0014% |

THD+N ratio (A-weighted, digital 16/44.1) | <0.002% | <0.002% |

THD+N ratio (unweighted) | <0.001% | <0.001% |

Minimum observed line AC voltage | 124VAC | 124VAC |

For the continuous dynamic power test, the C 399 was able to sustain 230W into 4 ohms (~1% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (19.5W) for 5 seconds, for 5 continuous minutes without inducing a fault or the initiation of a protective circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the C 399 was only slightly warm to the touch.

Our primary measurements revealed the following using the phono-level input, MM configuration (unless specified, assume a 1kHz 5mVrms sine-wave input, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

Parameter | Left channel | Right channel |

Crosstalk, one channel driven (10kHz) | -89.9dB | -68.0dB |

DC offset | -4mV | 5mV |

Gain (default phono preamplifier) | 35.67dB | 35.66dB |

IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-86dB | <-86dB |

IMD ratio (CCIF, 3kHz + 4kHz stimulus tones, 1:1) | <-90dB | <-90dB |

Input impedance | 45.7k ohms | 46.2k ohms |

Input sensitivity (to max power with max volume) | 3.44mVrms | 3.46mVrms |

Noise level (A-weighted) | <0.6mVrms | <0.6mVrms |

Noise level (unweighted) | <3.5mVrms | <3.5mVrms |

Overload margin (relative 5mVrms input, 1kHz) | 25.7dB | 25.7dB |

Signal-to-noise ratio (full rated power, A-weighted) | 83.2dB | 82.7dB |

Signal-to-noise ratio (full rated power, unweighted) | 70.4dB | 68.3dB |

THD (unweighted) | <0.0013% | <0.0013% |

THD+N (A-weighted) | <0.007% | <0.007% |

THD+N (unweighted) | <0.04% | <0.04% |

Our primary measurements revealed the following using the analog input at the headphone output (unless specified, assume a 1kHz sine wave, 2Vrms output, 300 ohms loading, 10Hz to 90kHz bandwidth):

Parameter | Left channel | Right channel |

Maximum output power into 600 ohms (1% THD+N, unweighted) | 94.7mW | 94.1mW |

Maximum output power into 300 ohms (1% THD+N, unweighted) | 187.3mW | 186.0mW |

Maximum output power into 32 ohms (1% THD+N, unweighted) | 43mW | 43mW |

Gain | 21.8dB | 21.8dB |

Output impedance | 3.3 ohms | 3.5 ohms |

Noise level (A-weighted) | <3.5uVrms | <3.4uVrms |

Noise level (unweighted) | <12.5uVrms | <11.7uVrms |

Signal-to-noise (A-weighted, ref. max output voltage) | 122.4dB | 122.5dB |

Signal-to-noise (unweighted, ref. max output voltage) | 112.4dB | 112.6dB |

THD ratio (unweighted) | <0.00074% | <0.00073% |

THD+N ratio (A-weighted) | <0.00086% | <0.00084% |

THD+N ratio (unweighted) | <0.00096% | <0.00092% |

**Frequency response (8-ohm loading, line-level input)**

In our measured frequency response chart above, the C 399 is essentially perfectly flat within the audioband (20Hz to 20kHz), with both the Analog Bypass enabled (blue and red traces) and with Analog Bypass disabled (purple and green traces). At the extremes the C 399 is about 0.02dB down at 20Hz, and 0.02dB up at 20kHz. With Analog Bypass disabled, the incoming signal is digitized and sampled at 48kHz, which results in brick-wall-type filtering right around 24kHz. With Analog Bypass enabled, the incoming analog signal is not digitized, and we see a smooth high frequency rolloff, with a -3dB point around 90kHz. At low frequencies, there is also a small difference in rolloff between Analog Bypass enabled (-0.25dB at 5Hz) and Analog Bypass disabled (-0.5dB at 5Hz). In the chart above and most of the charts below, only a single trace may be visible. This is because the left channel (blue or purple trace) is performing identically to the right channel (red or green trace), and so they perfectly overlap, indicating that the two channels are ideally matched.

**Frequency response (8-ohm loading, line-level input, bass and treble controls)**

Above are frequency response plots measured at the speaker-level outputs into 8 ohms, with the bass and treble controls set to maximum (blue/red plots) and minimum (purple/green plots). We see that for the bass and treble controls, roughly +/- 7dB and +/- 6dB respectively of gain/cut are available at 20Hz and 20kHz. Note: the tone controls are available with Analog Bypass enabled, meaning they are operating in the analog domain.

**Phase response (8-ohm loading, line-level input)**

Above are the phase response plots from 20Hz to 20kHz for the line-level input, measured across the speaker outputs at 10W into 8 ohms, with Analog Bypass enabled. The C 399 does not invert polarity and exhibits, at worst, less than 20 degrees (at 20kHz) of phase shift within the audioband.

**Frequency response vs. input type (8-ohm loading, left channel only)**

The chart above shows the C 399’s frequency response as a function of input type measured across the speaker outputs at 10W into 8 ohms. The green trace is the same analog input data from the previous graph. The blue trace is for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz using the coaxial digital input, and the purple trace is for a 24/96 dithered digital input signal from 5Hz to 48kHz, while the pink trace (perfectly tracking the green trace) is for a 24/192 dithered digital input signal from 5Hz to 96kHz. The 16/44.1 data exhibits brick-wall-type filtering, with a -3dB at 21.0kHz. The 24/96 and 24/192 kHz data yielded -3dB points at 45.9kHz and 88.3kHz respectively. The analog data, with Analog Bypass enabled, looks nearly identical to the 24/192 digital data.

**Frequency response with subwoofer-crossover engaged (120Hz, 8-ohm loading)**

Above are two frequency response plots for the analog input, measured at 10W (8 ohms) at the speaker outputs, and at the line-level subwoofer output, with the crossover set at 120Hz. The C 399 DSP crossover uses 18dB/octave (third-order) slopes. Note: with Analog Bypass enabled, bass management is not operational, so the above plots were measured with Analog Bypass disabled, meaning that it is operating in the digital domain.

**Frequency response (8-ohm loading, MM phono input)**

The chart above shows the frequency response for the MM phono input. We see a maximum deviation of about -0.1/+0.15dB (20Hz/10kHz) from 20Hz to 20kHz. The worst-case channel deviation is between about 5kHz to 20kHz, at about 0.1dB. It’s important to know that what is shown is the deviation from the RIAA curve, where the input signal sweep is EQ’d with an inverted RIAA curve supplied by Audio Precision (*i.e.*, zero deviation would yield a flat line at 0dB). This is a very good phono frequency- response test result, since there’s close adherence to the RIAA curve.

**Phase response (MM input)**

Above is the phase response plot from 20Hz to 20kHz for the MM phono input, measured across the speaker outputs at 10W into 8 ohms. The C 399 does not invert polarity. For the phono input, since the RIAA equalization curve must be implemented, which ranges from +19.9dB (20Hz) to -32.6dB (90kHz), phase shift at the output is inevitable. Here we find a worst case of about -60 degrees at 200Hz and 5kHz, and +20 degrees at 20Hz.

**Digital linearity (16/44.1 and 24/96 data)**

The chart above shows the results of a linearity test for the coaxial digital input for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the line-level pre-outs of the C 399 for a 1Vrms (at 0dBFS) output signal. The digital input is swept with a dithered 1kHz input signal from -120dBFS to 0dBFS, and the output is analyzed by the APx555. The ideal response would be a straight flat line at 0dB. Both data were essentially perfect as of -110dBFS down to 0dBFS. At -120dBFS, the 16/44.1 data were about +2/4dB (left/right) above reference, while the 24/96 data were within +/-0.5dB of reference. This is a good linearity test result.

**Impulse response (24/44.1 data)**

The graph above shows the impulse response for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s) for one sample period then back to digital silence, measured at the line-level pre-outs of the C 399. We can see that the C 399 utilizes a typical sinc function reconstruction filter.

**J-Test (coaxial)**

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level pre-outs of the C 399. The J-Test test was developed by Julian Dunn in the 1990s. It is a test signal, specifically a -3dBFS undithered 12kHz square wave sampled (in this case) at 48kHz (24 bits). Since even the first odd harmonic (*i.e.*, 36kHz) of the 12kHz square wave is removed by the bandwidth limitation of the sampling rate, we are left with a 12kHz sine wave (the main peak). In addition, an undithered 250Hz square wave at -144dBFS is mixed with the signal. This test file causes the 22 least significant bits to constantly toggle, which produces strong jitter spectral components at the 250Hz rate and its odd harmonics. The test file shows how susceptible the DAC and delivery interface are to jitter, which would manifest as peaks above the noise floor at 500Hz intervals (*e.g.*, 250Hz, 750Hz, 1250Hz, etc.). Note that the alternating peaks are in the test file itself, but at levels of -144dBrA and below. The test file can also be used in conjunction with artificially injected sine-wave jitter by the Audio Precision, to show how well the DAC rejects jitter.

The coaxial input exhibits low-level peaks in the audioband, near the 12kHz primary signal peak, at -130dBrA and below. This is a reasonably good J-Test result, indicating that the C 399 DAC should yield good jitter immunity.

**J-Test (optical)**

The chart above shows the results of the J-Test test for the optical digital input measured at the line-level pre-outs of the C 399. The optical input exhibits low-level peaks in the audioband, near the 12kHz primary signal peak, at -130dBrA and below. This result is very similar to the coaxial input result above.

**J-Test with 100ns of injected jitter (coaxial)**

Both the coaxial and optical inputs were also tested for jitter immunity by injecting artificial sine-wave jitter at 2kHz, which would manifest as sidebands at 10kHz and 14kHz without any jitter rejection. Jitter immunity proved exceptional, with no visible sidebands at the 100ns jitter level. The C 399 DAC did lose sync with the signal when jitter was increased beyond 500ns or so. The optical input jitter result was very similar to the coaxial input result.

**Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (coaxial input)**

The plot above shows a fast Fourier transform (FFT) of the C 399’s line-level pre-outs with white noise at -4dBFS (blue/red), and a 19.1kHz sine wave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1. The sharp rolloff above 20kHz in the white-noise spectrum shows the implementation of a brick-wall-type reconstruction filter. There are no aliased image peaks in the audioband above the -135dBrA noise floor. The main 25kHz alias peak is near -75dBrA. The second, third, and fourth distortion harmonics (38.2, 57.3, 76.4kHz) of the 19.1kHz tone are between -75dBrA and -80dBrA.

**RMS level vs. frequency vs. load impedance (1W, left channel only)**

The chart above shows RMS level (relative to 0dBrA, which is 1W into 8 ohms, or 2.83Vrms) as a function of frequency, for the analog line-level input swept from 5Hz to 100kHz. The blue plot is into an 8-ohm load, the purple is into a 4-ohm load, the pink plot is an actual speaker (Focal Chora 806, measurements can be found here), and the cyan plot is no load connected. The chart below . . .

. . . is the same but zoomed in to highlight differences. Here we can see a maximum deviation within the audioband of a little more than 0.03dB from 4 ohms to no load, which is an indication of a very high damping factor, or very low output impedance. The maximum variation in RMS level when a real speaker was used is even less, deviating by just under 0.01dB within the flat portion of the curve (100Hz to 2kHz). Note that the rise in RMS level at higher frequencies is a result of the frequency response of the C 399, not a damping-factor issue, as all four plots show the same rise, at roughly the same rate.

**THD ratio (unweighted) vs. frequency vs. output power**

The chart above shows THD ratios at the output into 8 ohms as a function of frequency for a sine-wave stimulus at the analog line-level input. The blue and red plots are for left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at the rated 180W. The power was varied using the volume control. At 1W and 10W, THD ratios were relatively flat and very low at around 0.0005%, up to 1kHz. Above 1kHz, there is a rise in the 10W data, up to 0.002% at 6kHz. The 180W THD values are higher but still quite low, ranging from just over and under 0.002% at 20-3kHz, then up to 0.005% at 6kHz. The C 399 manages to maintain low THD across a wide range of power output levels, and easily makes the NAD spec of <0.02%THD at 180W, from 20Hz to 6kHz.

**THD ratio (unweighted) vs. frequency at 10W (MM input)**

The chart above shows THD ratio as a function of frequency plots for the MM phono input measured across an 8-ohm load at 10W. The input sweep is EQ’d with an inverted RIAA curve. The THD values for the MM configuration vary from around 0.02% (20Hz) down to 0.0006% (1.5-2kHz), then up to 0.0025% at 6kHz.

**THD ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms**

The chart above shows THD ratios measured at the output of the C 399 as a function of output power for the analog line-level input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). Both data sets track fairly closely, even the “knees” are close together. With an 8-ohm load, the “knee” occurs at about 180W, while the 4-ohm “knee” occurs at around 200W. From low to high power levels, THD ratios are very low and in the 0.005 to 0.0003% range. The 1% THD values are reached at about 209W (8 ohms) and 239W (4 ohms).

**THD+N ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms**

The chart above shows THD+N ratios measured at the output of the C 399 as a function of output power for the line-level input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). Overall, THD+N values for both loads were similar, ranging from 0.01%, down to 0.0005%, with the 8-ohm data outperforming the 4-ohm data by about 3-5dB.

**THD ratio (unweighted) vs. frequency at 8, 4, and 2 ohms (left channel only)**

The chart above shows THD ratios measured at the output of the C 399 as a function of frequency into three different loads (8/4/2 ohms), for a constant input voltage that yields 10W at the output into 8 ohms (and roughly 20W into 4 ohms, and 40W into 2 ohms), for the analog line-level input. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. We find roughly the same THD values of 0.0005% to 0.002% from 20Hz to 6Hz for the 8-ohm and 4-ohm data. For the 2-ohm data, THD ratios are also fairly constant from 20Hz to 6kHz, but are higher at around 0.001-0.003%. This is a good result, and shows the C 399 is stable, and yields low distortion, even into a 2-ohm load.

**THD ratio (unweighted) vs. frequency into 8 ohms and real speakers (left channel only)**

The chart above shows THD ratios measured at the output of the C 399 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). The dummy load and two-way Paradigm speaker yielded very similar and constant 0.0005 to 0.001% THD ratios from 20Hz to 6kHz. There were greater deviations with the two-way Focal at low frequencies, reaching 0.005% at 20Hz.

**IMD ratio (CCIF) vs. frequency into 8 ohms and real speakers (left channel only)**

The chart above shows intermodulation distortion (IMD) ratios measured at the output of the C 399 as a function of frequency into an 8-ohm load and two different speakers, for a constant output voltage of 2.83Vrms (1W into 8 ohms), for the analog line-level input. Here the CCIF IMD method is used, where the primary frequency is swept from 20kHz (F1) down to 2.5kHz, and the secondary frequency (F2) is always 1kHz lower than the primary, with a 1:1 ratio. The CCIF IMD analysis results are the sum of the second (F1-F2 or 1kHz) and third modulation products (F1+1kHz, F2-1kHz). The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). All three results are similar, with relatively constant IMD ratios from as low as 0.0005% to 0.001% at 20kHz.

**IMD ratio (SMPTE) vs. frequency into 8 ohms and real speakers (left channel only)**

The chart above shows IMD ratios measured at the output of the C 399 as a function of frequency into an 8-ohm load and two different speakers, for a constant output voltage of 2.83Vrms (1W into 8 ohms), for the analog line-level input. Here, the SMPTE IMD method is used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a two-way speaker (Paradigm Founder Series 100F, measurements can be found here). All three results are nearly identical, with flat IMD results just under 0.003%.

**FFT spectrum – 1kHz (line-level input, Analog Bypass enabled)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the output across an 8-ohm load at 10W for the analog line-level input. We see that the signal’s second and third harmonics, at 2 and 3kHz, are around -110dBrA, or 0.0003%. The subsequent signal harmonics are below -120dBrA, or 0.0001%. There are absolutely no noise related peaks on the left side of the main 1kHz peak, above the very low -130 to -140dBrA noise floor. There is also a rise in the noise above 20kHz, characteristic of digital amplifiers.

**FFT spectrum – 1kHz (line-level input, Analog Bypass disabled)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the output across an 8-ohm load at 10W for the analog line-level input, with the Analog Bypass function disabled (*i.e.*, the analog signal is being digitized after input). The main differences between this FFT and the one above with analog bypass enabled are a higher second harmonic (2kHz) level at just over -100dBrA, or 0.001%; a higher noise floor, at -120 to -130dBrA; and the evidence of 48kHz sampling, with IMD peaks at 47 and 49kHz (*i.e.*, 48kHz +/- the 1kHz signal).

**FFT spectrum – 1kHz (digital input, 16/44.1 data at 0dBFS)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 16/44.1. The second (2kHz) and third (3kHz) signal harmonics are between -100 and 110dBrA, or 0.001 and 0.0003%. There are no noise-related peaks above the -130dBrA noise floor.

**FFT spectrum – 1kHz (digital input, 24/96 data at 0dBFS)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 24/96. The second (2kHz) and third (3kHz) signal harmonics are between -100 and 110dBrA, or 0.001 and 0.0003%. There are no noise-related peaks above the characteristically lower (due to 24-bit depth) noise floor at -130 to -140dBrA.

**FFT spectrum – 1kHz (digital input, 16/44.1 data at -90dBFS)**

Shown above is the FFT for a 1kHz -90dBFS dithered 16/44.1 input sine-wave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, and signal harmonics at 2/3/4kHz for the right channel only, at -105 to -120dBrA, or 0.0006 to 0.0001%. The noise floor on the right channel is higher, at just above -140dBrA, than the left channel, at just above -150dBrA. But even the right channel’s noise-floor level is still very low.

**FFT spectrum – 1kHz (digital input, 24/96 data at -90dBFS)**

Shown above is the FFT for a 1kHz -90dBFS dithered 24/96 input sine-wave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, and the second (2kHz) signal harmonic at -125dBrA, or 0.00006%. The noise floor on the right channel is higher, at -140dBrA, than the left, at -150dBrA.

**FFT spectrum – 1kHz (MM phono input)**

Shown above is the FFT for a 1kHz input sine-wave stimulus, measured at the output across an 8-ohm load at 10W for the MM phono input. We see the second (2kHz), third (3kHz), fourth (4kHz), and fifth (5kHz) signal harmonics dominating ranging from -100 down to -120dBrA respectively, or 0.001% down to 0.0001%. We see the primary (60Hz) power-supply-related peak at just over -80dBrA, or 0.01%, and subsequent odd-order power-supply related peaks (180, 300, 420Hz, etc.) extending beyond the 1kHz signal peak, at -80 to -120dBrA, or 0.01 to 0.0001%.

**FFT spectrum – 50Hz (line-level input)**

Shown above is the FFT for a 50Hz input sine-wave stimulus measured at the output across an 8-ohm load at 10W for the analog line-level input. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The second (100Hz) and third (150Hz) signal harmonic are at -110dBrA, or 0.0003%. We also see the 60Hz power-supply-related peak, and subsequent harmonics, just above the noise floor at -135 to -140dBrA, or 0.00002 to 0.00001%.

**FFT spectrum – 50Hz (MM phono input)**

Shown above is the FFT for a 50Hz input sine-wave stimulus measured at the output across an 8-ohm load at 10W for the MM phono input. The X axis is zoomed in from 40 Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most predominant (non-signal) peaks are from the 60Hz power- supply fundamental and its third harmonic at -80dBrA, or 0.01%. Further odd-order power-supply-related peaks can be seen at lower amplitudes, while no signal harmonics are visible above the noise-floor.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, line-level input)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sine-wave stimulus tone measured at the output across an 8-ohm load at 10W for the analog line-level input. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -110/-115dBrA (left/right channels), or 0.0003/0.0002%. The third-order modulation products, at 17kHz and 20kHz, are around -105dBrA, or 0.0006%.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 16/44.1)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sine-wave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 16/44.1. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -110/-115dBrA (left/right), or 0.0003/0.0002%. The third-order modulation products, at 17kHz and 20kHz, are around -105dBrA, or 0.0006%. We also see the main aliased peaks at 25.1kHz and 26.1kHz around -80dBrA due to the 44.1kHz sample rate (*e.g.*, 44.1kHz-19kHz = 25.1kHz).

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 24/96)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sine-wave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 24/96. We find the same second- and third-order modulation products as seen in the 16/44.1 FFT above.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, MM phono input)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sine-wave stimulus tone measured at the output across an 8-ohm load at 10W for the MM phono input. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at around -105dBRa, or 0.0006%, while the third-order modulation products, at 17kHz and 20kHz, are around -100dBrA, or 0.001%.

**Square-wave response (10kHz)**

Above is the 10kHz square-wave response using the analog line-level input, at roughly 10W into 8 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the C 399’s slew-rate performance. Rather, it should be seen as a qualitative representation of the C 399’s restricted bandwidth. An ideal square wave can be represented as the sum of a sine wave and an infinite series of its odd-order harmonics (*e.g.*, 10kHz + 30kHz + 50kHz + 70kHz . . .). A limited bandwidth will show only the sum of the lower-order harmonics, which may result in noticeable undershoot and/or overshoot, and softening of the edges. Here we can see the 400kHz switching oscillator frequency used in the digital amplifier section visibly modulating the waveform.

**Square-wave response (10kHz, restricted 250kHz bandwidth)**

Above is the 10kHz square-wave response using the analog line-level input, at roughly 10W into 8 ohms, this time with a 250kHz input bandwidth on the analyzer to filter out the 400kHz switching frequency. We see more evidence here, in the overshoot/undershoot and soft corners of the square wave, of the C 399’s mid-level bandwidth with an analog input.

**FFT spectrum (1MHz bandwidth)**

The C 399’s class-D amplifier relies on a switching oscillator to convert the input signal to a pulse-width modulated (PWM) square wave (on/off) signal before sending the signal through a low-pass filter to generate an output signal. The C 399 oscillator switches at a rate of about 400kHz, and this graph plots a wide-bandwidth FFT spectrum of the amplifier’s output at 10W into 8 ohms as it’s fed a 1kHz sine wave. We can see that the 400kHz peak is quite evident, and at -35dBrA. There are also two peaks at 800kHz and 1.2MHz (the second and third harmonic of the 400kHz peak), at -60 and -110dBrA. Those peaks—the fundamental and its harmonics—are direct results of the switching oscillators in the C 399 amp modules. The noise around those very-high-frequency signals are in the signal, but all that noise is far above the audioband—and therefore inaudible—and so high in frequency that any loudspeaker the amplifier is driving should filter it all out anyway.

**Damping factor vs. frequency (20Hz to 20kHz)**

The final graph above is the damping factor as a function of frequency. Both channels show a relatively constant damping factor from 30Hz to 10kHz, ranging from 1731/1911 (left/right), down to 1361/1464 (left/right). The damping factor for the left and right channels is higher at the frequency extremes, reaching 2195 and 2351 for the right channel at 20Hz and 20kHz. The C 399 possesses an exceptionally high damping factor, meaning a very low output impedance.

*Diego Estan*

Electronics Measurement Specialist

- Details
- Parent Category: Products
- Category: Amplifier Measurements

Link: reviewed by James on *SoundStage! Xperience* on March 1, 2022

**General Information**

All measurements taken using an Audio Precision APx555 B Series analyzer.

The NAD Masters M10 V2 was conditioned for 1 hour at 1/8th full rated power (~12W into 8 ohms) before any measurements were taken. All measurements were taken with both channels driven, using a 120V/20A dedicated circuit, unless otherwise stated.

The M10 V2 offers two unbalanced analog inputs (RCA), one S/PDIDF coaxial (RCA) input, one optical S/PDIF digital input, one Ethernet (RJ45) digital input, Bluetooth support, two line-level subwoofer outputs (RCA), two line-level pre-outs (RCA), and a pair of speaker-level outputs. For the purposes of these measurements, the following inputs were evaluated unless indicated otherwise: digital coaxial and the analog line-level unbalanced input.

Based on the accuracy and repeatability at various volume levels of the left/right channel matching (see table below), the M10 V2 volume control is likely operating in the digital domain. Consequently, all analog signals are digitized at the M10’s inputs so the unit may apply volume adjustment, bass management, and tone controls. The volume control offers a total range from 0% (-64dB) to 100% (+36dB) in 1dB increments.

Most measurements were made with 1Vrms line-level analog or 0dBFS digital input signals. The following volume settings yielded approximately 10W into 8 ohms: 76% for analog line-level and 67% for digital. The signal-to-noise ratio (SNR) measurements were made with the same input signal values but with the volume set to achieve the rated output power of 100Wpc (8 ohms). For comparison, on the line-level input, a SNR measurement was also made with the volume at maximum, where only 0.450Vrms was required to achieve 100W into 8 ohms.

Because the M10 V2 uses a switching-amplifier technology that exhibits considerable noise above 20kHz (see FFTs below), our typical input bandwidth filter setting of 10Hz-90kHz was necessarily changed to 10Hz-22.4kHz for all measurements, except for frequency response and for FFTs. In addition, THD versus frequency sweeps were limited to 6kHz to adequately capture the second and third signal harmonics with the restricted bandwidth setting.

**Volume-control accuracy (measured at speaker outputs): left-right channel tracking**

Volume position | Channel deviation |

1 | 0.04dB |

10 | 0.04dB |

30 | 0.04dB |

50 | 0.04dB |

70 | 0.04dB |

90 | 0.04dB |

100 | 0.04dB |

**Published specifications vs. our primary measurements**

The table below summarizes the measurements published by NAD for the M10 V2 compared directly against our own. The published specifications are sourced from NAD’s website, either directly or from the manual available for download, or a combination thereof. With the exception of frequency response, where the Audio Precision bandwidth was extended from DC to 250kHz, assume, unless otherwise stated, 10W into 8 ohms and a measurement input bandwidth of 10Hz to 22.4kHz, and the worst-case measured result between the left and right channels.

Parameter | Manufacturer | SoundStage! Lab |

Rated output power into 8 ohms (0.03% THD, 1kHz) | 100W | 126W |

Rated output power into 4 ohms (0.03% THD, 1kHz) | 100W | 232W |

THD (20Hz-6.5kHz, 100W, 8 ohms) | <0.03% | <0.007% |

SNR (A-weighted, ref. 1W out in 8 ohms, 500mV input) | >85.1dB | 85.2dB |

Clipping power (1kHz, 8 ohms, 0.1%THD) | 130W | 128W |

Clipping power (1kHz, 4 ohms, 0.1%THD) | 230W | 246W |

IHF dynamic power (no-load clipping, 8 ohms) | 160W | 167W |

IHF dynamic power (no-load clipping, 4 ohms) | 300W | 333W |

Damping factor (ref. 8 ohms 20Hz and 6.5kHz) | >190 | 190 |

Frequency response (20Hz-20kHz) | ±0.6dB | -0.16dB/-0.54dB |

Channel separation (1kHz, 1W) | >83dB | 85dB |

Channel separation (10kHz, 1W) | >70.5dB | 66dB |

Input sensitivity (analog) | 456mVrms | 452mVrms |

Input sensitivity (digital) | -13.23%FS | -13.18%FS |

Our primary measurements revealed the following using the line-level analog input and digital coaxial input (unless specified, assume a 1kHz sinewave at 1Vrms or 0dBFS, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

Parameter | Left channel | Right channel |

Maximum output power into 8 ohms (1% THD+N, unweighted) | 151W | 152W |

Maximum output power into 4 ohms (1% THD+N, unweighted) | 285W | 288W |

Continuous dynamic power test (5 minutes, both channels driven) | passed | passed |

Crosstalk, one channel driven (10kHz) | -66dB | -72dB |

Damping factor | 198 | 190 |

Clipping no-load output voltage (instantaneous power into 8 ohms) | 36.5Vrms (167W) | 36.8Vrms (169W) |

DC offset | <13mV | <16mV |

Gain (pre-out) | 4.1dB | 4.1dB |

Gain (maximum volume) | 35.8dB | 35.9dB |

IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-91dB | <-93dB |

IMD ratio (SMPTE, 60Hz + 7kHz stimulus tones, 4:1 ) | <-80dB | <-80dB |

Input impedance (line input, RCA) | 16.5k ohms | 16.5k ohms |

Input sensitivity (for rated power, maximum volume) | 454mVrms | 452mVrms |

Noise level (A-weighted) | <190uVrms | <180uVrms |

Noise level (unweighted) | <310uVrms | <280uVrms |

Output Impedance (pre-out) | 93.5 ohms | 93.5 ohms |

Signal-to-noise ratio (full rated power, A-weighted, 1Vrms in) | 98.0dB | 97.8dB |

Signal-to-noise ratio (full rated power, unweighted, 1Vrms in) | 96.6dB | 96.4dB |

Signal-to-noise ratio (full rated power, A-weighted, max volume) | 93.4dB | 93.4dB |

Dynamic range (full rated power, A-weighted, digital 24/96) | 106.8dB | 108.0dB |

Dynamic range (full rated power, A-weighted, digital 16/44.1) | 98.6dB | 98.8dB |

THD ratio (unweighted) | <0.0022% | <0.0015% |

THD ratio (unweighted, digital 24/96) | <0.0012% | <0.0018% |

THD ratio (unweighted, digital 16/44.1) | <0.0012% | <0.0018% |

THD+N ratio (A-weighted) | <0.0034% | <0.0026% |

THD+N ratio (A-weighted, digital 24/96) | <0.0026% | <0.0028% |

THD+N ratio (A-weighted, digital 16/44.1) | <0.0026% | <0.0028% |

THD+N ratio (unweighted) | <0.0041% | <0.0036% |

Minimum observed line AC voltage | 122VAC | 122VAC |

For the continuous dynamic power test, the M10 V2 was able to sustain 195W into 4 ohms (~1% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (19.5W) for 5 seconds, for 5 continuous minutes without inducing a fault or the initiation of a protective circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the M10 V2 was warm to the touch, but did not cause discomfort to the touch.

**Frequency response (8-ohm loading, line-level input)**

In our measured frequency-response chart above, the M10 V2 is nearly flat within the audioband (20Hz to 20kHz). At the frequency extremes, the M10 V2 is down 0.16dB at 20Hz and down 0.54dB at 20kHz. The M10 V2 cannot be considered a high-bandwidth audio device as the -3dB point is just past 20kHz. In fact, the M10 V2 exhibits brick-wall-type filtering just past 20kHz for the analog input, because it is digitized using a 44.1kHz sample rate. In the graph above and most of the graphs below, only a single trace may be visible. This is because the left channel (blue or purple trace) is performing identically to the right channel (red or green trace), and so they perfectly overlap, indicating that the two channels are ideally matched.

**Frequency response vs. input type (8-ohm loading, left channel only)**

The chart above shows the M10 V2’s frequency response as a function of input type measured across the speaker outputs at 10W into 8 ohms. The green trace is the same analog input data from the previous graph. The blue trace (perfectly tracking the green trace) is for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz using the coaxial input, the purple trace is for a 24/96 dithered digital input signal from 5Hz to 48kHz, and the pink trace is for a 24/192 dithered digital input signal from 5Hz to 96kHz. The 16/44.1 data exhibits brick-wall-type filtering, with a -3dB at 20.9kHz. The 24/96 and 24/192 kHz data yielded -3dB points at 45.4kHz and 67.5kHz respectively. The analog data looks nearly identical to the 16/44.1 digital data, which is evidence for the M10 V2 sampling incoming analog signals at 44.1kHz.

**Frequency response (8-ohm loading, line-level input, bass and treble controls)**

Above are frequency-response plots measured at the speaker-level outputs into 8 ohms, with the bass and treble controls set to maximum (blue/red plots) and minimum (purple/green plots). We see that for the bass and treble controls, roughly +/-6dB of gain/cut is available.

**Frequency response (subwoofer output engaged, 120Hz crossover)**

Above are two frequency-response plots for the analog input, measured at 10W (8-ohm) at the speaker outputs, and at the line-level subwoofer output, with the crossover set to 120Hz. From the rolloff characteristics, we can see that the M10 V2 DSP crossover uses 18dB/octave slopes.

**Phase response (8-ohm loading, line-level input)**

Above are the left- and right-channel phase response plots from 20Hz to 20kHz for the line-level input, measured across the speaker outputs at 10W into 8 ohms. The M10 V2 does not invert polarity and exhibits, at worst, less than 20 degrees (at 20kHz) of phase shift within the audioband.

**Digital linearity (16/44.1 and 24/96 data)**

The chart above shows the results of a linearity test for the coaxial digital input for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the line-level output of the M10 V2. To produce this chart, the digital input is swept with a dithered 1kHz input signal from -120dBFS to 0dBFS, and the output is analyzed by the APx555. The ideal response would be a straight flat line at 0dB. Both data were essentially perfect as of -100dBFS down to 0dBFS. At -120dBFS, the 16/44.1 data were only about +2dB above reference, while the 24/96 data were within +/-1dB of reference. This is a good linearity test result.

**Impulse response (16/44.1 and 24/96 data)**

The chart above shows the impulse response for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s) for one sample period then back to digital silence, measured at the line-level pre-outs of the M10 V2. We can see that the M10 V2 utilizes a typical sinc function reconstruction filter.

**J-Test (coaxial input)**

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the M10 V2. The J-Test was developed by Julian Dunn in the 1990s. It is a test signal—specifically a -3dBFS undithered 12kHz square wave sampled (in this case) at 48kHz (24 bits). Since even the first odd harmonic (*i.e.*, 36kHz) of the 12kHz square wave is removed by the bandwidth limitation of the sampling rate, we are left with a 12kHz sine wave (the main peak). In addition, an undithered 250Hz square wave at -144dBFS is mixed with the signal. This test file causes the 22 least significant bits to constantly toggle, which produces strong jitter spectral components at the 250Hz rate and its odd harmonics. The test file shows how susceptible the DAC and delivery interface are to jitter, which would manifest as peaks above the noise floor at 500Hz intervals (*e.g.*, 250Hz, 750Hz, 1250Hz, etc.). Note that the alternating peaks are in the test file itself, but at levels of -144dBrA and below. The test file can also be used in conjunction with artificially injected sine-wave jitter by the Audio Precision, to show how well the DAC rejects jitter.

The coaxial input exhibits low-level peaks in the audioband, at -125dBrA and below. This is a good J-Test result, indicating that the M10 V2 DAC should yield good jitter immunity.

**J-Test (optical input)**

The chart above shows the results of the J-Test test for the optical digital input measured at the line- level output of the M10 V2. The optical input exhibits low-level peaks in the audioband, at -125dBrA and below. This result is very similar compared to the coaxial input, although with some visible higher amplitude peaks around the 12kHz fundamental.

**J-Test (coaxial input) 100ns of injected jitter**

Both the coaxial and optical inputs were also tested for jitter immunity by injecting artificial sine-wave jitter at 2kHz, which would manifest as sidebands at 10kHz and 14kHz without any jitter rejection. Jitter immunity proved exceptional through both inputs, with no visible sidebands at the 100ns jitter level (only the coaxial is shown above, since the optical performed similarly). The M10 V2 DAC did lose sync with the signal when jitter was increased beyond 200ns or so.

**Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (coaxial input)**

The plot above shows a fast Fourier transform (FFT) of the M10 V2’s line-level pre-outs with white noise at -4dBFS (blue/red), as well as a 19.1kHz sine wave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1. The sharp roll-off above 20kHz in the white-noise spectrum shows the implementation of a brick-wall-type reconstruction filter. There are effectively no aliased image peaks in the audioband above the -130dBrA noise floor. The main 25kHz alias peak is near -75dBrA. The second, third, and fourth distortion harmonics (38.2, 57.3, 76.4kHz) of the 19.1kHz tone are between -75dBrA and -105dBrA.

**RMS level vs. frequency vs. load impedance (1W, left channel only)**

The chart above shows RMS level (relative to 0dBrA, which is 1W into 8ohms or 2.83Vrms) as a function of frequency, for the analog line-level input swept from 10Hz to 100kHz. The blue plot is into an 8-ohm load, the purple is into a 4-ohm load, the pink plot is an actual speaker (Focal Chora 806, measurements can be found here), and the cyan plot is no load connected. The chart below . . .

. . . is the same but zoomed in to highlight differences. Here we can see a maximum deviation within the audioband of a little more than 0.1dB from 4 ohms to no load, which is an indication of a relatively high damping factor, or low output impedance. The maximum variation in RMS level when a real speaker was used is even less, deviating by just under 0.1dB within the flat portion of the curve (100Hz to 5kHz), with the lowest RMS level, which would correspond à to the lowest impedance point for the load, exhibited around 200Hz, and the highest RMS level, which would correspond to the highest impedance point for the load, at around 2kHz.

**THD ratio (unweighted) vs. frequency vs. output power**

The chart above shows THD ratios at the output into 8 ohms as a function of frequency for a sine-wave stimulus at the analog line-level input. The blue and red plots are for left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at 100W. The power was varied using the volume control. At 1W, THD ratios were relatively flat at around 0.003%. At 10W, THD values were slightly lower, hovering above and below 0.002%; however, the right channel outperformed the left by about 2-3dB. The 100W THD values are still quite low, ranging from just over 0.005% at 20-50Hz, down to 0.003% at 1 to 4kHz, then up to 0.007% at 6kHz. The M10 V2 manages to maintain low THD across a wide range of power-output levels.

**THD ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms**

The chart above shows THD ratios measured at the output of the M10 V2 as a function of output power for the analog line-level input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). Both data sets track fairly closely until the “knees,” which are at about 100W (8-ohm) and 200W (4-ohm). From low to high power levels, THD ratios are in the 0.005 to 0.001% range. The 1% THD values are reached at about 150W (8 ohms) and 285W (4 ohms).

**THD+N ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms**

The chart above shows THD+N ratios measured at the output of the M10 V2 as a function of output power for the line-level input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). Overall, THD+N values for both loads were similar up to 100W, ranging from 0.05%, down to 0.005%, with the 8-ohm data outperforming the 4-ohm data by about 3-5dB.

**THD ratio (unweighted) vs. frequency at 8, 4, and 2 ohms (left channel only)**

The chart above shows THD ratios measured at the output of the M10 V2 as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yields 10W at the output into 8 ohms (and roughly 20W into 4 ohms, and 40W into 2 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. We find roughly the same THD values of 0.002% to 0.003% from 20Hz to 6Hz for the 8- and 4-ohm data. For the 2-ohm data, THD ratios are also fairly constant from 20Hz to 6kHz, but are higher at around 0.003-0.005%.

**THD ratio (unweighted) vs. frequency into 8 ohms and real speakers (left channel only)**

The chart above shows THD ratios measured at the output of the M10 V2 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), while the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). The dummy load and three-way Paradigm speaker yielded very similar and constant 0.003 to 0.005% THD ratios from 20Hz to 6kHz. There were greater deviations with the two-way Focal, ranging from as low as 0.0015% at 200Hz, to as high as 0.06% at 20Hz. From 500Hz to 6kHz, all three plots are virtually identical and flat, at 0.003% THD.

**IMD ratio (CCIF) vs. frequency into 8 ohms and real speakers (left channel only)**

The chart above shows intermodulation distortion (IMD) ratios measured at the output of the M10 V2 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here the CCIF IMD method is used, where the primary frequency is swept from 20kHz (F1) down to 2.5kHz, and the secondary frequency (F2) is always 1kHz lower than the primary, with a 1:1 ratio. The CCIF IMD analysis results are the sum of the second (F1-F2, or 1kHz) and third modulation products (F1+1kHz, F2-1kHz). The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). All three results are similar, with relatively constant IMD ratios at around 0.003%. There is a peak in the IMD results around 13-14kHz, where both the dummy load and two-way Focal yielded a 0.005% IMD, while the two-way Paradigm yielded just over 0.01%.

**IMD ratio (SMPTE) vs. frequency into 8 ohms and real speakers (left channel only)**

The chart above shows IMD ratios measured at the output of the M10 V2 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here, the SMPTE IMD method was used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). All three results are nearly identical, with flat IMD results just over 0.01%.

**FFT spectrum – 1kHz (line-level input)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the output across an 8-ohm load at 10W for the analog line-level input. We see that the signal’s second harmonic, at 2kHz, is at around -95dBrA (left channel slightly higher than right), or 0.002%, while the odd harmonic at 3kHz is much lower at -110dBrA, or 0.0003%. There are various noise related peaks on the left side of the main 1kHz peak, including a 20Hz peak at -100dBrA, or 0.001%, and the 60Hz power-supply related peak at -110dBrA, or 0.0003%. There is also a rise in the noise above 20kHz, characteristic of digital amplifiers.

**FFT spectrum – 1kHz (digital input, 16/44.1 data at 0dBFS)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 16/44.1. Signal harmonics are very similar to the analog input FFT above, although the second harmonic (2kHz) here is slightly lower, and the third harmonic (3kHz) is slightly higher. The noise-related peaks are fewer here, with the dominant peak at 60Hz yielding a level of -110dBrA, or 0.0003%.

**FFT spectrum – 1kHz (digital input, 24/96 data at 0dBFS)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 24/96. Signal harmonics are very similar to the 16/44.1 FFT above. Noise related peaks are at or below -110dBrA, or 0.0003%.

**FFT spectrum – 1kHz (digital input, 16/44.1 data at -90dBFS)**

Shown above is the FFT for a 1kHz -90dBFS dithered 16/44.1 input sine-wave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, and other peaks, unrelated to signal harmonics, as high as -100dBrA (left channel), or 0.001%, at just shy of 4kHz.

**FFT spectrum – 1kHz (digital input, 24/96 data at -90dBFS)**

Shown above is the FFT for a 1kHz -90dBFS dithered 24/96 input sine-wave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, and other peaks, unrelated to signal harmonics, as high as -100dBrA (left channel), or 0.001%, at just shy of 4kHz. The noise floor on the left channel is slightly higher than the righ channel, by about 5dB.

**FFT spectrum – 50Hz (line-level input)**

Shown above is the FFT for a 50Hz input sine-wave stimulus measured at the output across an 8-ohm load at 10W for the analog line-level input. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The second signal harmonic (100Hz) is at -90dBrA, or 0.003%, while all other peaks are at or below -110dBrA, or 0.0003%, including the 60Hz power-supply-related peak.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, line-level input)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sine-wave stimulus tone measured at the output across an 8-ohm load at 10W for the analog line-level input. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -120dBrA, or 0.0001%, for the left channel, and -100dBRa, or 0.001%, for the right channel. The third-order modulation products, at 17kHz and 20kHz, are around -105dBrA, or 0.0006%. We also see the main aliased peaks at 25.1kHz and 26.1kHz around -85dBrA, indicating again that the M10 V2 ADC is digitizing the incoming analog signal at 44.1kHz (*i.e.*, 44.1kHz-19kHz = 25.1kHz).

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, digital 16/44.1)**

Shown above is an FFT of the intermodulation (IMD) products for an 18kHz + 19kHz summed sine-wave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 16/44.1. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -105dBrA, or 0.0006%, for the left channel, and -95dBRa, or 0.002%, for the right channel. The third-order modulation products, at 17kHz and 20kHz, are around -105dBrA to -110dBrA, or 0.0003% to 0.0006%.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, digital 24/96)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sine-wave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 24/96. We find the same second- and third-order modulation products as seen in the 16/44.1 FFT above.

**Square-wave response (10kHz)**

Above is the 10kHz square-wave response using the analog line-level input, at roughly 10W into 8 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the M10 V2’s slew-rate performance. Rather, it should be seen as a qualitative representation of the M10 V2’s low bandwidth. An ideal square wave can be represented as the sum of a sine wave and an infinite series of its odd-order harmonics (*e.g.*, 10kHz + 30kHz + 50kHz + 70kHz . . .). A limited bandwidth will show only the sum of the lower-order harmonics, which may result in noticeable undershoot and/or overshoot, and softening of the edges. Due to M10 V2’s very limited bandwidth, only the square wave’s fundamental (10kHz) sine wave is reproduced here. In addition, we can see the 400kHz switching-oscillator frequency used in the digital-amplifier section visibly modulating the waveform.

**Square-wave response (1kHz) — 250kHz bandwidth**

Above is the 1kHz square-wave response using the analog line-level input, at roughly 10W into 8 ohms, this time with a 250kHz input bandwidth on the analyzer to filter out the 400kHz switching frequency. We see more evidence here, in the overshoot and undershoot at the square-wave corners, of the M10 V2’s limited bandwidth with an analog input.

**FFT spectrum of 400kHz switching frequency relative to a 1kHz tone**

The M10 V2’s class-D amplifier relies on a switching oscillator to convert the input signal to a pulse-width modulated (PWM) square wave (on/off) signal before sending the signal through a low-pass filter to generate an output signal. The M10 V2 oscillator switches at a rate of about 400kHz, and this graph plots a wide-bandwidth FFT spectrum of the amplifier’s output at 10W into 8 ohms as it’s fed a 1kHz sine wave. We can see that the 400kHz peak is quite evident, and at -40dBrA. There is also a peak at 800kHz (the second harmonic of the 400kHz peak) at -65dBrA. Those two peaks—the fundamental and its second harmonic—are direct results of the switching oscillators in the M10 V2 amp modules. Also seen are the 43.1/44.1/45.1kHz peaks due to the ADC sampling the incoming signal at 44.1kHz. The noise around those very-high-frequency signals are in the signal, but all that noise is far above the audioband—and therefore inaudible—and so high in frequency that any loudspeaker the amplifier is driving should filter it all out anyway.

**Damping factor vs. frequency (20Hz to 20kHz)**

The final graph above is the damping factor as a function of frequency. Both channels show a relatively constant damping factor from 20Hz to 20kHz. The damping factor for the left and right channels are right around 200 from 20Hz to 6-7kHz, then rise up to about 240 at 20kHz.

*Diego Estan*

Electronics Measurement Specialist

- Details
- Parent Category: Products
- Category: Amplifier Measurements

Link: reviewed by Roger Kanno on *SoundStage! Hi-Fi* on March 1, 2023

**General information**

All measurements taken using an Audio Precision APx555 B Series analyzer.

The NAD Masters M23 was conditioned for 1 hour at 1/8th full rated power (~25W into 8 ohms) before any measurements were taken. All measurements were taken with both channels driven, using a 120V/20A dedicated circuit, unless otherwise stated.

The M23 has both unbalanced (RCA) and balanced inputs (XLR), and two pairs of speaker-level outputs. We found small differences in terms of THD between the RCA and XLR inputs (see published specifications vs. our primary measurements below).

The M23 can be operated in stereo or bridged (mono) modes. There is also a gain switch with Low, Mid, and High settings. As expected, there were small differences in THD and noise levels between the gain settings, with the Low gain setting yielding the lowest (*i.e.*, best) results and the High gain setting yielding the highest results (see primary measurements table below). Unless otherwise stated, the balanced inputs were used with the Mid gain setting for all measurements. With these settings, 580mVrms was required at the input to achieve the reference 10W into 8 ohms.

Because the M23 uses a digital amplifier technology that exhibits considerable noise above 20kHz (see FFTs below), our typical input bandwidth filter setting of 10Hz-90kHz was necessarily changed to 10Hz-22.4kHz for all measurements, except for frequency response and for FFTs. In addition, THD versus frequency sweeps were limited to 6kHz to adequately capture the second and third signal harmonics with the restricted bandwidth setting.

**Published specifications vs. our primary measurements**

The table below summarizes the measurements published by NAD for the Masters M23 compared directly against our own. The published specifications are sourced from NAD’s website, either directly or from the manual available for download, or a combination thereof. With the exception of frequency response, where the Audio Precision bandwidth was extended to 500kHz, assume, unless otherwise stated, 10W into 8 ohms and a measurement input bandwidth of 10Hz to 22.4kHz, and the worst-case measured result between the left and right channels.

Parameter | Manufacturer | SoundStage! Lab |

Rated output power into 8 ohms (0.1% THD) | >210W | 229W |

Rated output power into 8 ohms (bridged, 0.1% THD) | >770W | 862W |

Rated output power into 4 ohms (rated THD of 0.00069%) | >380W | 451W |

IHF dynamic power (8 ohms) | 260W | 285W |

IHF dynamic power (4 ohms) | 520W | 552W |

IHF dynamic power (bridged, 8 ohms) | 1017W | 1062W |

THD (20Hz-6.5kHz, 8 ohms, 200W, XLR) | <0.00069% | <0.0005% |

THD (20Hz-6.5kHz, 8 ohms, 200W, RCA) | <0.0013% | <0.0008% |

Damping factor (20Hz to 6.5kHz) | >800 | >2385 |

SNR (A-weighted, ref. 1W out in 8 ohms, balanced) | >101.7dB | 103.3dB |

SNR (A-weighted, ref. 200W out in 8 ohms, balanced) | >127dB | 126.3dB |

Channel separation (1kHz, low gain, XLR) | >115dB | 127.3dB |

Channel separation (10kHz, low gain, XLR) | >96dB | 99.4dB |

Frequency response (20Hz-20kHz) | ±0.06dB | -0.003,+0.08dB |

Stereo mode gain (Low/Mid/High) | 19/23.9/29.2dB | 19/23.9/29.1dB |

Bridge mode gain (Low/Mid/High) | 25.1/30/35.2dB | 25/29.9/35.1dB |

Input sensitivity (stereo for 200W in 8 ohms, low/mid/high gain) | 4.5/2.5/1.4Vrms | 4.5/2.6/1.4Vrms |

Input impedance (balanced) | 56k ohms | 118k ohms |

Input impedance (single-ended) | 56k ohms | 57.9k ohms |

Our primary measurements in stereo mode revealed the following using the line-level balanced analog input (unless specified, assume a 1kHz sinewave at 580mVrms, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

Parameter | Left channel | Right channel |

Maximum output power into 8 ohms (1% THD+N, unweighted) | 278W | 278W |

Maximum output power into 4 ohms (1% THD+N, unweighted) | 540W | 540W |

Maximum burst output power (IHF, 8 ohms) | 285W | 285W |

Maximum burst output power (IHF, 4 ohms) | 552W | 552W |

Continuous dynamic power test (5 minutes, both channels driven) | passed | passed |

Crosstalk, one channel driven (10kHz) | -99.2dB | -99.4dB |

Damping factor | 2477 | 3010 |

Clipping no-load output voltage | 46.7Vrms | 46.7Vrms |

DC offset | <2.72mV | <-3.16mV |

Gain (Low/Mid/High) | 19/23.9/29.1dB | 19/23.9/29.1dB |

IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-108dB | <-108dB |

IMD ratio (SMPTE, 60Hz + 7kHz stimulus tones, 4:1 ) | <-105dB | <-107dB |

Input impedance (line input, RCA) | 57.4k ohms | 57.9k ohms |

Input impedance (line input, XLR) | 117k ohms | 118k ohms |

Input sensitivity (for rated power, 200W) | 2.6Vrms | 2.6Vrms |

Noise level (A-weighted) | <19uVrms | <19uVrms |

Noise level (unweighted) | <27uVrms | <27uVrms |

Noise level (A-weighted, low gain) | <15uVrms | <15uVrms |

Noise level (A-weighted, high gain) | <29uVrms | <29uVrms |

Signal-to-noise ratio (full rated power 200W, A-weighted) | 126.4dB | 126.3dB |

Signal-to-noise ratio (full rated power 200W, unweighted) | 123.6dB | 123.6dB |

THD ratio (unweighted) | <0.000055% | <0.000055% |

THD ratio (unweighted, low gain) | <0.000050% | <0.000050% |

THD ratio (unweighted, high gain) | <0.000075% | <0.000075% |

THD+N ratio (A-weighted) | <0.00022% | <0.00022% |

THD+N ratio (unweighted) | <0.0003% | <0.0003% |

Minimum observed line AC voltage | 122 VAC | 122VAC |

For the continuous dynamic power test, the M23 was able to sustain 538W into 4 ohms (~1% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (53.8W) for 5 seconds, for 5 continuous minutes without inducing a fault or the initiation of a protective circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the M23 was only slightly warm to the touch.

Our primary measurements in mono mode revealed the following using the line-level balanced analog input (unless specified, assume a 1kHz sinewave at 290mVrms, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

Parameter | Mono channel |

Maximum output power into 8 ohms (1% THD+N, unweighted) | 1009W |

Maximum burst output power (IHF, 8 ohms) | 1062W |

Damping factor | 1917 |

Clipping no-load output voltage | 92.8Vrms |

DC offset | <5mV |

Gain (Low/Mid/High) | 25/29.9/35.1dB |

IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-104dB |

IMD ratio (SMPTE, 60Hz + 7kHz stimulus tones, 4:1 ) | <-103dB |

Input sensitivity (for full power 700W) | 2.4Vrms |

Noise level (A-weighted) | <33uVrms |

Noise level (unweighted) | <47uVrms |

Signal-to-noise ratio (full power 700W, A-weighted) | 126.8dB |

Signal-to-noise ratio (full power 700W, unweighted) | 123.9dB |

THD ratio (unweighted) | <0.0001% |

THD+N ratio (A-weighted) | <0.00038% |

THD+N ratio (unweighted) | <0.00053% |

Minimum observed line AC voltage | 122VAC |

**Frequency response (8-ohm loading, stereo mode)**

In our frequency- response plots above, measured across the speaker outputs at 10W into 8 ohms, the M23 is near flat within the audioband (0/+0.08dB, 20Hz/20kHz), which essentially corroborates NAD’s claim of 20Hz-20kHz at ±0.06dB. At the extremes, the M23 is at 0dB at 5Hz and -3dB at about 70kHz. In the chart above and most of the charts below, only a single trace may be visible. This is because the left channel (blue or purple trace) is performing identically to the right channel (red or green trace), and so they perfectly overlap, indicating that the two channels are ideally matched.

**Phase response (8-ohm loading, line-level input, stereo mode)**

Above are the phase-response plots from 20Hz to 20kHz for the line-level input, measured across the speaker outputs at 10W into 8 ohms. The M23 does not invert polarity and exhibits, at worst, about 15 degrees (at 20kHz) of phase shift within the audioband.

**RMS level vs. frequency vs. load impedance (1W, left channel only, stereo mode)**

The chart above shows RMS level (relative to 0dBrA, which is 1W into 8 ohms or 2.83Vrms) as a function of frequency, for the analog line-level input swept from 5Hz to 100kHz, in stereo mode. The blue plot is into an 8-ohm load, the purple is into a 4-ohm load, the pink plot is an actual speaker (Focal Chora 806, measurements can be found here), and the cyan plot is no load connected. The chart below . . .

. . . is the same but zoomed in to highlight differences. Here we find that maximum deviation between no-load and a 4-ohm load is very small, at around 0.02dB. This is an indication of a very high damping factor, or low output impedance. With a real speaker, there are essentially no deviations between 20Hz and 1kHz, then a rise up to 0.08dB at 20kHz, due to the M23’s frequency response.

**THD ratio (unweighted) vs. frequency vs. output power (stereo mode)**

The chart above shows THD ratios at the output into 8 ohms as a function of frequency for a sinewave stimulus at the analog line-level input in stereo mode. The blue and red plots are for the left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at 200W. The 10W data yielded the lowest THD figures, ranging from 0.0001% at 20Hz, down to nearly 0.00003% between 200Hz and 500Hz, then up to 0.0001% at 6kHz. These are extraordinarily low THD ratios, nearing the limits of the APx555 analyzer. At 1W, THD ratios ranged from 0.0001% from 20Hz to 1kHz, then down to 0.00005% at 6kHz. A 200W, THD ratios were higher, from 0.0003% at 20Hz, down to 0.0001% from 100Hz to 400Hz, then up to 0.0005% at 4kHz.

**THD ratio (unweighted) vs. frequency vs. output power (bridged mode)**

The chart above shows THD ratios at the output into 8 ohms as a function of frequency for a sinewave stimulus at the analog line-level input in bridged mode. The blue plot is at 1W output into 8 ohms, purple at 10W, and pink at 700W. The 10W data yielded the lowest THD figures, ranging from 0.0001% at 20Hz, down to just above 0.00005% between 200Hz and 500Hz, then up to 0.0001% at 2-3kHz. At 1W, THD ratios ranged from 0.0002% from 20Hz to 1kHz, then down to 0.00008% at 6kHz. A 700W, THD ratios were higher, from 0.01% from 20Hz to 1kHz, then up to 0.03% at 2-4kHz.

**THD ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms (stereo mode)**

The chart above shows THD ratios measured at the output of the M23 as a function of output power for the analog line-level input in stereo mode, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). The 8-ohm data ranged from about 0.002% at 50mW, down to 0.00005% from 5 to 100W, then up to the “knee” just past 200W. The 4-ohm data ranged from about 0.001% at 50mW, down to 0.00007% from 5 to 100W (for the left channel, the right channel showed 10dB higher THD ratios at 20W and 150W), then up to the “knee” around 350W. The 1% THD marks were hit at 278W (8 ohms) and 540W (4 ohms).

**THD+N ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms (stereo mode)**

The chart above shows THD+N ratios measured at the output of the M23 as a function of output power for the analog line level-input in stereo mode, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). THD+N values for the 8-ohm data ranged from 0.003% down to just below 0.0002% at 100W. The 4-ohm data yielded THD+N values 3-4dB higher.

**THD ratio (unweighted) vs. frequency at 8, 4, and 2 ohms (left channel only, stereo mode)**

The chart above shows THD ratios measured at the output of the M23 as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yields 20W at the output into 8 ohms (and roughly 40W into 4 ohms, and 80W into 2 ohms) for the balanced analog line-level input in stereo mode. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. The 8- and 4-ohm THD data are close, with the 4-ohm data yielding values about 5dB higher above 200Hz. The 8-ohm data ranged from 0.0001% at 20Hz, down to 0.00003% at 200-500Hz, then up to 0.0001% at 3-4kHz. The 2-ohm data ranged from 0.0001 to 0.0002% across the audioband.

**THD ratio (unweighted) vs. frequency at 8, 4, and 2 ohms (bridged mode)**

The chart above shows THD ratios measured at the output of the M23 as a function of frequency into two different loads (8/4ohms - the 2-ohm load tripped the M23’s protection circuit within about two to three seconds) for a constant input voltage that yields 100W at the output into 8 ohms (and roughly 200W into 4 ohms) for the analog line-level input in bridged mode. The 8-ohm load is the blue trace, and the 4-ohm load the purple trace. We see increasing levels (5-10dB) of THD from 8 to 4 ohms between about 50Hz and 6kHz, with the 8-ohm data ranging from 0.00006% to 0.0003%. When a stereo amplifier’s bridged mode applies the same signal (with one phase inverted) to each channel, and connects the speaker load across the outputs of both channels, the effective speaker impedance seen by the amplifier is halved. It is therefore not surprising that the M23 is not stable into 2-ohm loads when bridged.

**THD ratio (unweighted) vs. frequency into 8 ohms and real speakers (left channel only, stereo mode)**

The chart above shows THD ratios measured at the output of the M23 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the balanced analog line-level input in stereo mode. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). The 8-ohm plot is fairly flat and between 0.0001% and 0.00003% from 20Hz to 6kHz. Between 300Hz and 6kHz, the THD ratios when real speakers were used as loads are identical to the dummy load. The two-way speaker THD results were as high as 0.003% at 20Hz. Between 40Hz and 200Hz, the speaker THD results were roughly 5dB higher than that of the dummy load. This is an impressive result, showing that the M23 can maintain it’s ultra-low distrotion into real-world loads.

**IMD ratio (CCIF) vs. frequency into 8 ohms and real speakers (left channel only, stereo mode)**

The chart above shows intermodulation distortion (IMD) ratios measured at the output of the M23 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here the CCIF IMD method is used, where the primary frequency is swept from 20kHz (F1) down to 2.5kHz, and the secondary frequency (F2) is always 1kHz lower than the primary, with a 1:1 ratio. The CCIF IMD analysis results are the sum of the second (F1-F2 or 1kHz) and third modulation products (F1+1kHz, F2-1kHz). The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). All three IMD plots are within 5dB of one another, hovering between 0.0003% and 0.0001%.

**IMD ratio (SMPTE) vs. frequency into 8 ohms and real speakers (left channel only, stereo mode)**

The chart above shows IMD ratios measured at the output of the M23 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input in stereo mode. Here, the SMPTE IMD method is used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a two-way speaker (Paradigm Founder Series 100F, measurements can be found here). All three data sets are close enough to be judged as identical, hovering around the 0.001% level.

**FFT spectrum – 1kHz (line-level input, stereo mode)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the analog line-level input in stereo mode. We see that the signal’s second (2kHz) and third (3kHz) harmonic are slightly below -130dBrA, or 0.00003%. The power-supply-related noise peak at the fundamental (60Hz) frequency is evident at the -140dBrA, or 0.00001%, level. A rise in the noise floor can be seen above 20kHz, indicative of this type of digital amplifier technology. This is an exceptionally clean FFT result.

**FFT spectrum – 1kHz (line-level input, stereo mode)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the analog line-level input in bridged mode. We see that the signal’s second (2kHz) and third (3kHz) harmonic are slightly below and above -130dBrA, respectively, or 0.00003%. The power-supply-related noise peak at the fundamental (60Hz) frequency is evident at the -140dBrA, or 0.00001%, level. The M23 exhibits only slightly more THD in bridged mode compared to stereo mode.

**FFT spectrum – 50Hz (line-level input, stereo mode)**

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the analog line-level input in stereo mode. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most dominant (non-signal) peaks are the second (100Hz) and third (150Hz) signal harmonic at roughly -125dBrA, or 0.00006%, and -135/-150dBrA (left/right channels), or 0.00002/0.000003%. The power-supply-related noise peaks at the fundamental (60Hz) frequency is evident at the -135dBrA, or 0.00002%, level.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, line-level input, stereo mode)**

Shown above is an FFT of the intermodulation (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the analog line-level input in stereo mode. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -125dBrA, or 0.00006%, and the third-order modulation products, at 17kHz and 20kHz, are at roughly -115dBrA, or 0.0002%.

**Squarewave response (10kHz, stereo mode)**

Above is the 10kHz squarewave response using the balanced analog line-level input, at roughly 10W into 8 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the M23’s slew-rate performance. Rather, it should be seen as a qualitative representation of the M23’s mid-tier bandwidth. An ideal squarewave can be represented as the sum of a sinewave and an infinite series of its odd-order harmonics (*e.g.*, 10kHz + 30kHz + 50kHz + 70kHz . . .). A limited bandwidth will show only the sum of the lower-order harmonics, which may result in noticeable undershoot and/or overshoot, and softening of the edges. In the case of the M23, however, what dominates the plateaus of the squarewave in the top graph is a 500kHz sinewave, the frequency at which the switching oscillator in this class-D amp is operating (see FFT below).

**Squarewave response (10kHz, restricted 250kHz bandwidth, stereo mode)**

Above is the 10kHz squarewave response using the analog input, at roughly 10W into 8 ohms, with a 250kHz restricted bandwidth to remove the modulation from the 500kHz oscillator. Here we find a relatively clean squarewave, with some overshoot in the corners.

**FFT spectrum (1MHz bandwidth, stereo mode)**

The M23’s amplifier relies on a switching oscillator to convert the input signal to a pulse-width-modulated (PWM) squarewave (on/off) signal before sending the signal through a low-pass filter to generate an output signal. The M23 oscillator switches at a rate of about 500kHz, and this graph plots a wide bandwidth FFT spectrum of the amplifier’s output at 10W into 8 ohms as it’s fed a 1kHz sinewave. We can see that the 500kHz peak is quite evident, and at -40dBrA. There is also a peak at 1MHz (the second harmonic of the 500kHz peak), at -70dBrA. Those two peaks—the fundamental and its second harmonic—are direct results of the switching oscillators in the M23 amp modules. The noise around those very-high-frequency signals are in the signal, but all that noise is far above the audio band—and therefore inaudible—and so high in frequency that any loudspeaker the amplifier is driving should filter it all out anyway.

**Damping factor vs. frequency (20Hz to 20kHz, stereo mode)**

The graph above is the damping factor as a function of frequency in stereo mode. We see both channels with very high damping factors, ranging from around the 3500/5000 (left/right) mark at 20Hz, down to 2000/2200 (left/right) at 20kHz.

**Damping factor vs. frequency (20Hz to 20kHz, bridged mode)**

The final graph above is the damping factor as a function of frequency in bridged mode. We see a very high damping factor, ranging around the 4700 mark at 20Hz, down to 700 at 20kHz. The damping factor is less across the audioband than in stereo mode, but that is expected in bridged operation.

*Diego Estan*

Electronics Measurement Specialist

- Details
- Parent Category: Products
- Category: Amplifier Measurements

Link: reviewed by Roger Kanno on *SoundStage! Hi-Fi* on January 1, 2022

**General Information**

All measurements taken using an Audio Precision APx555 B Series analyzer.

The SU-R1000 was conditioned for 1 hour at 1/8th full rated power (~19W into 8 ohms) before any measurements were taken. All measurements were taken with both channels driven, using a 120V/20A dedicated circuit, unless otherwise stated.

The SU-R1000 offers two line-level analog inputs (RCA); one pair of line-level balanced inputs (XLR); one pair of phono RCA inputs, configurable for moving magnet (MM) or moving coil (MC); one pair of RCA pre-amp outputs; one pair of RCA main-in inputs; two digital coaxial (RCA) and two digital optical (TosLink) inputs; two USB digital inputs; two pair of speaker level outputs; and one headphone output (1/4” TRS). For the purposes of these measurements, the following inputs were evaluated: digital coaxial, analog (XLR) line-level, and phono (MM and MC). There were no differences observed between balanced and unbalanced line-level inputs in terms of gain and THD+N. The SU-R1000 is a sophisticated device that digitizes all incoming signals and can apply DSP for various functions. Unless otherwise stated, Direct In mode was used, with the Attenuation off, MQA off, LAPC off, and Cartridge Compensation off.

Most measurements were made with a 2Vrms line-level analog input, 5mVrms MM analog input, 0.5mVrms MC analog input, and 0dBFS digital input. The volume control is variable from -88dB to 0dB. The following volume settings yielded approximately 10W into 8 ohms: -33dB for analog line-level and digital, -21dB for MM and MC. The signal-to-noise ratio (SNR) measurements were made with the same input signal values but with the volume set to achieve the rated output power of 150W (8 ohms). For comparison, on the line-level input, a signal-to-noise ratio measurement was also made with the volume at maximum, where only 0.166Vrms was required to achieve 150W into 8ohms.

Based on the accuracy and repeatability of the left/right volume channel matching (see table below), the SU-R1000 volume control operates in the digital domain. The SU-R1000 offers 3dB volume steps ranging from -88dB to -79dB, 2dB steps from -77dB to -69dB, 1dB steps from -68dB to -22dB, and 0.5dB steps from -21.5dB to 0dB. Overall range is -41.7dB to +46.4dB (line-level input, speaker output).

Because the SU-R1000 is a digital amplifier technology that exhibits considerable noise above 20kHz (see FFTs below), our typical input bandwidth filter setting of 10Hz-90kHz was necessarily changed to 10Hz-22.4kHz for all measurements, except for frequency response and for FFTs. In addition, THD versus frequency sweeps were limited to 6kHz to adequately capture the second and third signal harmonics with the restricted bandwidth setting.

**Volume-control accuracy (measured at speaker outputs): left-right channel tracking**

Volume position | Channel deviation |

-88dB | 0.03dB |

-60dB | 0.011dB |

-50dB | 0.012dB |

-30dB | 0.013dB |

-20dB | 0.014dB |

-10dB | 0.013dB |

0dB | 0.014dB |

**Published specifications vs. our primary measurements**

The table below summarizes the measurements published by Technics for the SU-R1000 compared directly against our own. The published specifications are sourced from Technics’ website, either directly or from the manual available for download, or a combination thereof. With the exception of frequency response, where the Audio Precision bandwidth was extended to 250kHz, assume, unless otherwise stated, 10W into 8 ohms and a measurement input bandwidth of 10Hz to 22.4kHz, and the worst-case measured result between the left and right channels.

Parameter | Manufacturer | SoundStage! Lab |

Amplifier rated output power into 8 ohms (0.5% THD) | 150W | 189W |

Amplifier rated output power into 4 ohms (0.5% THD) | 300W | 310W |

THD (60W, 20Hz-20kHz, 8 ohms) | <0.02% | <0.05% |

Frequency response (analog line-level in, speaker out 8 ohms) | 5Hz-80kHz (-3dB) | 5Hz-80kHz (+1.5dB) |

Frequency response (digital in, speaker out 8-ohm) | 5Hz-80kHz (-3dB) | 5Hz-80kHz (+1dB) |

Frequency response (phono MM, speaker out 8-ohm) | RIAA 20Hz-20kHz (±1dB) | RIAA 20Hz-20kHz (±0.2dB) |

Input sensitivity (analog line-level in) | 200mVrms | 166mVrms |

Input impedance (analog line-level in) | 22k ohms | 47.5k ohms |

Input sensitivity (phono MM) | 2.5mVrms | 1.76mVrms |

Input impedance (phono MM) | 47k ohms | 45.3k ohms |

Input sensitivity (phono MC) | 0.3mVrms | 0.215mVrms |

Input impedance (phono MC) | 100 ohms | 129 ohms |

Our primary measurements revealed the following using the line-level analog and coaxial digital inputs (unless specified, assume a 1kHz sinewave at 2Vrms or 0dBFS, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

Parameter | Left channel | Right channel |

Maximum output power into 8 ohms (1% THD+N, unweighted) | 189W | 190W |

Maximum output power into 4 ohms (1% THD+N, unweighted) | 360W | 310W* |

Continuous dynamic power test (5 minutes, both channels driven) | passed | passed |

Crosstalk, one channel driven (10kHz) | -110dB | -111dB |

Damping factor | 334 | 343 |

Clipping no-load output voltage (instantaneous power into 8 ohms) | 39.7Vrms (197W) | 39.7Vrms (197W) |

DC offset | <3mV | <3mV |

Gain (pre-out) | 16.7dB | 16.7dB |

Gain (maximum volume) | 46.4dB | 46.4dB |

IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-65dB | <-64dB |

IMD ratio (SMPTE, 60Hz + 7kHz stimulus tones, 4:1 ) | <-65dB | <-64dB |

Input impedance (line input, XLR) | 99.7k ohms | 99.5k ohms |

Input impedance (line input, RCA) | 47.5k ohms | 47.4k ohms |

Input sensitivity (for rated power, maximum volume) | 166mVrms | 166mVrms |

Noise level (A-weighted) | <300uVrms | <300uVrms |

Noise level (unweighted) | <1200uVrms | <1200uVrms |

Output impedance (pre-out) | 722 ohms | 723 ohms |

Signal-to-noise ratio (full power, A-weighted, 2Vrms in) | 111.9dB | 111.0dB |

Signal-to-noise ratio (full power, unweighted, 2Vrms in) | 107.1dB | 106.3dB |

Signal-to-noise ratio (full power, A-weighted, max volume) | 96.0dB | 95.9dB |

Dynamic range (full power, A-weighted, digital 24/96) | 113.0dB | 112.0dB |

Dynamic range (full power, A-weighted, digital 16/44.1) | 96.2dB | 96.2dB |

THD ratio (unweighted) | <0.011% | <0.012% |

THD ratio (unweighted, digital 24/96) | <0.011% | <0.012% |

THD ratio (unweighted, digital 16/44.1) | <0.011% | <0.012% |

THD+N ratio (A-weighted) | <0.013% | <0.014% |

THD+N ratio (A-weighted, digital 24/96) | <0.013% | <0.014% |

THD+N ratio (A-weighted, digital 16/44.1) | <0.013% | <0.014% |

THD+N ratio (unweighted) | <0.017% | <0.017% |

Minimum observed line AC voltage | 123 VAC | 123 VAC |

*The right channel clamped down and reduced power just above 310W (4 ohms) even though 1% THD had not yet been reached.

For the continuous dynamic power test, the SU-R1000 was able to sustain 343W into 4 ohms (~1% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (34.3W) for 5 seconds, for 5 continuous minutes without inducing a fault or the initiation of a protective circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the SU-R1000 was warm to the touch, but did not cause discomfort to the touch.

Our primary measurements revealed the following using the phono-level input, MM configuration (unless specified, assume a 1kHz 5mVrms sinewave input, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

Parameter | Left channel | Right channel |

Crosstalk, one channel driven (10kHz) | -84.8dB | -76.8dB |

DC offset | <3mV | <3mV |

Gain (default phono preamplifier) | 39.4dB | 39.4dB |

IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-64dB | <-63dB |

IMD ratio (CCIF, 3kHz + 4kHz stimulus tones, 1:1) | <-73dB | <-72dB |

Input impedance | 45.3k ohms | 46.2k ohms |

Input sensitivity (to max power with max volume) | 1.76mVrms | 1.76mVrms |

Noise level (A-weighted) | <500uVrms | <600uVrms |

Noise level (unweighted) | <1500uVrms | <2600uVrms |

Overload margin (relative 5mVrms input, 1kHz) | 15.5dB | 15.5dB |

Signal-to-noise ratio (full rated power, A-weighted) | 82.7dB | 84.0dB |

Signal-to-noise ratio (full rated power, unweighted) | 70.2dB | 72.7dB |

THD (unweighted) | <0.012% | <0.013% |

THD+N (A-weighted) | <0.013% | <0.014% |

THD+N (unweighted) | <0.021% | <0.031% |

Our primary measurements revealed the following using the phono-level input, MC configuration (unless specified, assume a 1kHz 0.5mVrms sinewave input, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

Parameter | Left channel | Right channel |

Crosstalk, one channel driven (10kHz) | -65.9dB | -56.0dB |

DC offset | <3mV | <3mV |

Gain (default phono preamplifier) | 57.7dB | 57.7dB |

IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-65dB | <-63dB |

IMD ratio (CCIF, 3kHz + 4kHz stimulus tones, 1:1) | <-71dB | <-70dB |

Input impedance | 129 ohms | 129 ohms |

Input sensitivity (to max power with max volume) | 217uVrms | 215uVrms |

Noise level (A-weighted) | <3200uVrms | <5000uVrms |

Noise level (unweighted) | <9000uVrms | <24000uVrms |

Overload margin (relative 0.5mVrms input, 1kHz) | 17.4dB | 17.4dB |

Signal-to-noise ratio (full rated power, A-weighted) | 67.9dB | 64.5dB |

Signal-to-noise ratio (full rated power, unweighted) | 59.3dB | 52.4dB |

THD (unweighted) | <0.014% | <0.017% |

THD+N (A-weighted) | <0.038% | <0.060% |

THD+N (unweighted) | <0.11% | <0.26% |

Our primary measurements revealed the following using the analog input at the headphone output (unless specified, assume a 1kHz sinewave, 2Vrms output, 300 ohms loading, 10Hz to 22.4kHz bandwidth):

Parameter | Left channel | Right channel |

Maximum output power into 600 ohms (1% THD+N, unweighted) | 43mW | 43mW |

Maximum output power into 300 ohms (1% THD+N, unweighted) | 66mW | 66mW |

Maximum output power into 32 ohms (1% THD+N, unweighted) | 57mW | 58mW |

Gain | 33.1dB | 33.1dB |

Output impedance | 102.7 ohms | 102.9 ohms |

Noise level (A-weighted) | <65uVrms | <65uVrms |

Noise level (unweighted) | <250uVrms | <250uVrms |

Signal-to-noise ratio (A-weighted, ref. max output voltage) | 112.6dB | 112.7dB |

Signal-to-noise ratio (unweighted, ref. max output voltage) | 109.8dB | 109.8dB |

THD ratio (unweighted) | <0.0006% | <0.0005% |

THD+N ratio (A-weighted) | <0.003% | <0.003% |

THD+N ratio (unweighted) | <0.012% | <0.012% |

**Frequency response (8-ohm loading, line-level input)**

In our frequency-response plots above, measured across the speaker outputs at 10W into 8 ohms, the SU-R1000 is nearly flat within the audioband (20Hz to 20kHz). At the extremes the SU-R1000 is 0dB at 20Hz and -0.3dB down at 20kHz. These data essentially corroborate Technics’ claim of 5Hz to 80kHz (-3dB). There’s a rise in the frequency response above 20kHz, where we see +2dB at 70kHz, which is a result of the digital amplifier and its high output impedance at high frequencies. Into a 4-ohm load (see “RMS level vs. frequency vs load impedance” chart below), instead of a rise there is a significant dip at and above 20kHz. The -3dB point was also explored and found to be at 92kHz, exactly where it was measured for a 24-bit/192kHz digital input signal (see “Frequency response vs. input type” chart below). In the chart above and most of the charts below, only a single trace may be visible. This is because the left channel (blue or purple trace) is performing identically to the right channel (red or green trace), and so they perfectly overlap, indicating that the two channels are ideally matched.

**Frequency response (8-ohm loading, line-level input, bass and treble controls)**

Above is a frequency-response plot measured at the speaker-level outputs into 8 ohms, with the bass and treble controls set to maximum (blue/red plots) and minimum (purple/green plots). We see that for the bass and treble controls, roughly +/- 8dB of gain/cut is available.

**Frequency response (8-ohm loading, line-level input, midrange control)**

Above is a frequency response plot measured at the speaker-level outputs into 8 ohms, with the midrange control set to maximum (blue/red plots) and minimum (purple/green plots). We see that there is roughly +/- 8dB of gain/cut available centered around 1kHz.

**Frequency response (8-ohm loading, line-level input, bass and treble and midrange controls)**

Above is a frequency response plot measured at the speaker-level outputs into 8 ohms, with the bass, treble, and midrange controls set to maximum (blue/red plots) and minimum (purple/green plots). The levels are relative to 3kHz. We see that with all controls set to either minimum or maximum, there is a maximum deviation of no more than 4dB. When all the tone controls are at their maximum, there are two dips in the frequency response at roughly 400Hz and 3kHz. When the tone controls are at their minimum, we see troughs at 400Hz and 3kHz.

**Phase response (8-ohm loading, line-level input)**

Above are the phase-response plots from 20Hz to 20kHz for the line-level input, measured across the speaker outputs at 10W into 8 ohms. The SU-R1000 does not invert polarity and exhibits, at worst, 20 degrees (at 20kHz) of phase shift within the audioband.

**Frequency response vs. input type (8-ohm loading, left channel only)**

The chart above shows the SU-R1000’s frequency response as a function of input type measured across the speaker outputs at 10W into 8 ohms. The green trace is the same analog input data from the previous graph. The blue trace is for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz using the coaxial input, and the purple trace is for a 24/96 dithered digital input signal from 5Hz to 48kHz, while the pink trace is for a 24/192 dithered digital input signal from 5Hz to 96kHz. The 16/44.1 signal exhibits brick-wall type filtering, with a -3dB at 20.9kHz. The 24/96 and 24/192 kHz signals yielded -3dB points at 46.3kHz and 91.9kHz, respectively. The analog data looks nearly identical to the 24/192 digital data, which is evidence for the SU-R1000 sampling incoming analog signals at 192kHz.

**Frequency response (8-ohm loading, MM phono input)**

The chart above shows the frequency response for the phono input (MM configuration) without (blue/red) and with (purple/green) the subsonic filter enabled. We see a maximum deviation of about +0.1/-0.2dB (20Hz/10kHz) from 20Hz to 20kHz. With the subsonic filter engaged, we find the -3dB point at 20Hz. What is shown is the deviation from the RIAA curve, where the input signal sweep is EQ’d with an inverted RIAA curve supplied by Audio Precision (*i.e.,* zero deviation would yield a flat line at 0dB).

**Frequency-response correction curve (8-ohm loading, MM phono input, reviewer Roger Kanno’s custom calibration)**

The chart above shows the frequency response for the phono input (MM configuration), but with the Cartridge Optimizer engaged, as per Roger Kanno’s calibration for the review of the SU-R1000. This is a correction curve for each channel. We can clearly see that, using digital signal processing (DSP), the SU-R1000 is applying changes to the frequencies from 10Hz to 10kHz, and applying different gain to the left and right channels at various frequencies, to achieve a flat frequency response from each channel with the cartridge used (Pro-Ject Audio Systems Pick it S2 MM).

**Frequency response (line-level pre-out, MM phono input, various EQ curves)**

The chart above shows the frequency response for the phono input (MM configuration), left channel only, as measured at the pre-outs without any EQ applied to the frequency sweep. The SU-R1000 allows the user to select between 7 phono EQ curves. What is shown are the RIAA (blue), RCA (green), NAB (red), AES (brown) . . .

. . . Decca/FFRR (pink), Columbia (cyan) and IEC (grey) response curves, from 20Hz to 20kHz, which are there to accomodate different recording types.

**Frequency response (8-ohm loading, MC phono input)**

The chart above shows the frequency response for the phono input (MC configuration) without (blue/red) and with (purple/green) the subsonic filter enabled. We see a maximum deviation of about -0.5/-0.3dB (20Hz/20kHz) from 20Hz to 20kHz. With the subsonic filter engaged, we find the -3dB point at 21Hz. What is shown is the deviation from the RIAA curve, where the input signal sweep is EQ’d with an inverted RIAA curve supplied by Audio Precision (*i.e.,* zero deviation would yield a flat line at 0dB).

**Phase response (MM input)**

Above is the phase response plot from 20Hz to 20kHz for the phono input (MM configuration), measured across the speaker outputs at 10W into 8 ohms. The SU-R1000 does not invert polarity. For the phono input, since the RIAA equalization curve must be implemented, which ranges from +19.9dB (20Hz) to -32.6dB (90kHz), phase shift at the output is inevitable. Here we find a worst case of about -60 degrees at 200Hz and 5kHz.

**Phase response (MC input)**

Above is the phase response plot from 20Hz to 20kHz for the phono input (MC configuration), measured across the speaker outputs at 10W into 8 ohms. The SU-R1000 does not invert polarity. Here we find a worst case of about -60 degrees at 200Hz and 5kHz.

**Digital linearity (16/44.1 and 24/96 data)**

The chart above shows the results of a linearity test for the coaxial digital input for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the line-level output of the SU-R1000. The digital input is swept with a dithered 1kHz input signal from -120dBFS to 0dBFS, and the output is analyzed by the APx555. The ideal response would be a straight flat line at 0dB. Both data were essentially perfect from -100dBFS down to 0dBFS. At -120dBFS, the 16/44.1 data were only +2dB (left) and +4dB (right) above reference, while the 24/96 data were at -1/-2dBFS.

**Impulse response (24/44.1 data)**

The graph above shows the impulse response for the SU-R1000 with MQA turned off, fed to the coaxial digital input, measured at the line-level output, for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s), for one sample period, then back to digital silence. We find a reconstruction filter that favors no pre-ringing.

**Impulse response (24/44.1 data, MQA on)**

The graph above shows the impulse response for the SU-R1000 with MQA turned on, fed to the coaxial digital input, measured at the line-level output, for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s), for one sample period, then back to digital silence. We find a reconstruction filter that favors no pre-ringing, and less post-ringing compared to when MQA is turned off.

**J-Test (coaxial)**

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the SU-R1000. The J-Test was developed by Julian Dunn the 1990s. It is a test signal, specifically a -3dBFS undithered 12kHz squarewave sampled (in this case) at 48kHz (24 bits). Since even the first odd harmonic (*i.e.*, 36kHz) of the 12kHz squarewave is removed by the bandwidth limitation of the sampling rate, we are left with a 12kHz sinewave (the main peak). In addition, an undithered 250Hz squarewave at -144dBFS is mixed with the signal. This test file causes the 22 least significant bits to constantly toggle, which produces strong jitter spectral components at the 250Hz rate and its odd harmonics. The test file shows how susceptible the DAC and delivery interface are to jitter, which would manifest as peaks above the noise floor at 500Hz intervals (*e.g,*. 250Hz, 750Hz, 1250Hz, etc.). Note that the alternating peaks are in the test file itself, but at levels of -144dBrA and below. The test file can also be used in conjunction with artificially injected sinewave jitter by the Audio Precision, to show how well the DAC rejects jitter.

The coaxial input exhibits low-level peaks in the audioband, at -115dBrA and below. This is a good J-Test result, indicating that the SU-R1000 DAC should yield good jitter immunity.

**J-Test (optical)**

The chart above shows the results of the J-Test test for the optical digital input measured at the line- level output of the SU-R1000. The optical input exhibits low-level peaks in the audioband, at -115dBrA and below. This result is very similar compared to the coaxial input.

**J-Test (coaxial, MQA on)**

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the SU-R1000 with MQA turned on. We see peaks at 9kHz and 15kHz at -130dBrA that were not present when MQA was turned off, as well as a distinct rise in the noise floor at lower frequencies. This indicates less jitter immunity. The optical input yielded effectively the same result.

**J-Test with 100ns of injected jitter (coaxial)**

Both the coaxial and optical inputs were also tested for jitter immunity by injecting artificial sinewave jitter at 2kHz, which would manifest as sidebands at 10kHz and 14kHz without any jitter rejection. MQA *was not* turned on. Jitter immunity proved exceptional, with no visible sidebands at the 100ns jitter level.

**J-Test with 900ns of injected jitter (coaxial)**

Both the coaxial and optical inputs were also tested for jitter immunity by injecting artificial jitter sinewave jitter at 2kHz, which would manifest as sidebands at 10kHz and 14kHz without any jitter rejection. Once again, MQA was not turned on. Jitter immunity proved exceptional again, with sidebands down at a very low -125dBrA even with a very high 900ns of injected jitter. Above this level of jitter, the SU-R1000 DAC lost sync with the signal.

**Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (coaxial input)**

The chart above shows a fast Fourier transform (FFT) of the SU-R1000’s line-level output with white noise at -4dBFS (blue/red), and a 19.1kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1. The steep roll-off around 20kHz in the white-noise spectrum shows the behavior of the SU-R1000’s reconstruction filter. There are no aliased image peaks within the audioband. The primary aliasing signal at 25kHz is at -95dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are at -105 and -120dBrA.

**Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (coaxial input, MQA on)**

The chart above shows a fast Fourier transform (FFT) of the SU-R1000’s line-level output with white noise at -4dBFS (blue/red), and a 19.1kHz sinewave at -1dBFS fed to the coaxial digital input, sampled at 16/44.1, with MQA turned on. We find a much gentler slope above 20kHz for the noise spectrum compared to when MQA was turned off. We find one small aliased image peak within the audioband, at around -120dBrA, at around 6kHz. The primary aliasing signal at 25kHz is significant at -20dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are at -110 and -120dBrA.

**RMS level vs. frequency vs. load impedance (1W, left channel only)**

The chart above shows RMS level (relative to 0dBrA, which is 1W into 8ohms or 2.83Vrms) as a function of frequency, for the balanced analog line-level input swept from 5Hz to 100kHz. The blue plot is into an 8-ohm load, the purple plot is into a 4-ohm load, the pink plot is an actual speaker (Focal Chora 806, measurements can be found here), and the cyan plot is no load connected. The chart below . . .

. . . is the same but zoomed in to highlight differences. Here we find that at low frequencies, the deviations between no load and 4 ohms are small, at about 0.05dB; but at high frequencies, the differences are significant, at about 1.4dB at 20kHz. This is a result of the digital amplifier technology used, which exhibits a high damping factor at low frequencies, but a low damping factor at high frequencies (see “Damping factor vs frequency graph below”). When a real speaker is used, the major deviations appear once again at high frequencies, with a 0.6dB deviation between 5kHz and 20kHz.

**RMS level vs. frequency (1W, left channel only, real speaker, LPAC on and off)**

The chart above shows RMS level (relative to 0dBrA, which is 1W into 8 ohms, or 2.83Vrms) as a function of frequency, for the balanced analog line-level input swept from 20Hz to 20kHz. Both plots are for the Focal Chora 806 speaker, with (blue) and without (purple) LAPC enbaled. LPAC stands for Load Adaptive Phase Calibration, a feature in the SU-R1000 that measures the outputs of the amplifier while the speakers are connected using test tones to establish a correction curve to deal with the amplifier’s inherently high output impedance at high frequencies. The theoretical goal is to achieve a flat frequency response for the user’s speakers across the audioband when LAPC is enabled. We can see here that the blue trace is still not flat, even though LAPC is enabled, but it is closer to the ideal flat response compared to when LAPC is not enabled. When LAPC is disabled, we are at -0.5dB at 20kHz, compared to the roughly -0.15dB at 20kHz with LAPC enabled.

**THD ratio (unweighted) vs. frequency vs. output power**

The chart above shows THD ratios at the output into 8 ohms as a function of frequency for a sinewave stimulus at the balanced analog line-level input. The blue and red plots are for the left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at 140W. The power was varied using the volume control. At 1W, the left channel outperformed the right by almost 5dB from 300Hz to 6kHz, and ranged from around 0.01% at 20Hz, down to 0.0007% at 200Hz, then up to 0.005% at 6kHz. At 10W, the same THD values were seen from 20Hz to about 150Hz as the 1W data, then we see a rise from 0.002% up to 0.02% at 20kHz. The 140W THD values were higher, starting at the same 0.01% at 20Hz, and then rising steadily up to 0.3% at 4kHz.

**THD ratio (unweighted) vs. frequency at 10W (MM and MC phono inputs)**

The chart above shows THD ratios as a function of frequency plots for the phono input measured across an 8-ohm load at 10W. The MM configuration is shown in blue/red (left/right channels), and MC in purple/green (left/right channels). The input sweep is EQ’d with an inverted RIAA curve. The THD values for the MM configuration vary from around 0.03% (20Hz) down to 0.003% (200Hz), then up to 0.03% (3kHz to 6kHz). The THD values for the MC configuration vary from around 0.3% (20Hz) down to 0.01-0.02% (200Hz to 1kHz), then up to 0.03% (3kHz to 6kHz).

**THD ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms**

The chart above shows THD ratios measured at the output of the SU-R1000 as a function of output power for the balanced analog line-level input, for an 8-ohm load (purple/green for left/right channels) and a 4-ohm load (blue/red for left/right channels). Both data sets track closely, except for maximum power. There is a dip in THD, from 0.02% down to 0.002% in both data sets that occurs when the output voltage is at 2Vrms (0.5W into 8 ohms, 1W into 4 ohms). With this digital amplifier technology, there is no distinct “knee” in the curve. We find that the 8-ohm data reaches the 1% THD mark at about 190W. We were unable to collect reliable data with an input sweep for the 4-ohm data above about 300W at the output. We found that the right channel would clamp the output and reduce power, then the left channel would follow at a higher power output. When feeding constant and continuous input stimuli with a 4-ohm load, we were able to measure 310W for the right channel before the clamping occurred (at about 0.3% THD), while the left channel yielded up to 360W (at 1% THD). Overall, THD values for both loads were similar up to 100W, ranging from 0.05%, down to 0.002%, then up to 0.05%.

**THD+N ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms**

The chart above shows THD+N ratios measured at the output of the SU-R1000 as a function of output power for the balanced line-level input, for an 8-ohm load (purple/green for left/right channel) and a 4-ohm load (blue/red for left/right channels). Overall, THD+N values for both loads were similar up to 100W, ranging from 0.5%, down to 0.01%, then up to 0.05%.

**THD ratio (unweighted) vs. frequency at 8, 4, and 2 ohms (left channel only)**

The chart above shows THD ratios measured at the output of the SU-R1000 as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yields 10W at the output into 8 ohms (and roughly 20W into 4 ohms, and 40W into 2 ohms) for the balanced analog line-level input. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. We find roughly the same THD values of 0.01% to 0.005% from 20Hz to 50Hz for all three loads. From 50Hz to 1kHz the 8- and 4-ohm data track closely, down to 0.002% then up to 0.01%. For the 2-ohm data, from 50Hz to 6kHz, there’s a steady rise in THD from 0.005% to 0.08%. At 20kHz, the 8-ohm data is at 0.03%, while the 4-ohm data fared slightly better at 0.01%.

**THD ratio (unweighted) vs. frequency into 8 ohms and real speakers (left channel only)**

The chart above shows THD ratios measured at the output of the SU-R1000 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the balanced analog line-level input. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). In general, the measured THD ratios for the real speakers were close to the 8-ohm resistive load. The worst-case diffrence was in the order of 10dB at 200Hz (between the Focal and dummy load). The two-way Focal yielded the highest THD values (0.04% at 20Hz) at very low frequencies, while the three-way Paradigm yielded the highest THD values at high frequencies (0.01% at 6kHz). Between 200Hz and 2kHz, while the 8-ohm dummy load yielded results between 0.001 to 0.003%, with real speakers the THD values ranged from 0.0015% to 0.005%.

**IMD ratio (CCIF) vs. frequency into 8 ohms and real speakers (left channel only)**

The chart above shows intermodulation distortion (IMD) ratios measured at the output of the SU-R1000 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the balanced analog line-level input. Here the CCIF IMD method is used, where the primary frequency is swept from 20kHz (F1) down to 2.5kHz, and the secondary frequency (F2) is always 1kHz lower than the primary, with a 1:1 ratio. The CCIF IMD analysis results are the sum of the second (F1-F2 or 1kHz) and third modulation products (F1+1kHz, F2-1kHz). The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). At high frequencies, there is a significant 12dB difference between the dummy load (-84dB) and real speaker (-72dB) IMD values. Between 2.5 and 7kHz, the Focal IMD values were close to that of the dummy load values (-85 to -95dB), whereas the Paradigm IMD values were significantly higher, reaching -80dB at 4-5kHz, about 10dB worse than both the dummy load and Focal speaker.

**IMD ratio (SMPTE) vs. frequency into 8 ohms and real speakers (left channel only)**

The chart above shows IMD ratios measured at the output of the SU-R1000 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the balanced analog line-level input. Here, the SMPTE IMD method is used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a two-way speaker (Paradigm Founder Series 100F, measurements can be found here). Between 40Hz and 60Hz, all results are essentially identical, around -81dB. Above 60Hz, the highest IMD ratios are associate with the Paradigm speakers, rising up to -74dB from 100Hz to 250Hz. When the Focal was used as a load, there is a small rise in IMD ratios starting at 100Hz, rising up to -76dB. When the load was purely resistive, IMD ratios were consistently flat at around -81dB.

**FFT spectrum – 1kHz (line-level input)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the balanced analog line-level input. We see that the signal’s second harmonic, at 2kHz, is at -110dBrA, or 0.0003%, while the odd harmonics at 3 and 5kHz dominate at -80 and -90dBrA, or 0.01% and 0.003%. There are no power-supply related noise peaks to speak of; however, there is a distinct rise in the noise floor from -120dBrA at 1kHz up to -100dBrA from 200Hz to 10Hz. There is also a rise in the noise above 20kHz, a typical characteristic of switching amplifiers.

**FFT spectrum – 1kHz (digital input, 16/44.1 data at 0dBFS)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 16/44.1. Signal harmonics are very similar to the analog input FFT above. Here again, there are no power-supply related noise peaks to speak of; however, there is a distinct rise in the noise floor from -130dBrA at 1kHz up to -120dBrA from 200Hz to 10Hz.

**FFT spectrum – 1kHz (digital input, 24/96 data at 0dBFS)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 24/96. Signal harmonics are very similar to the analog input FFT above. Here again, there are no power-supply related noise peaks to speak of; however, there is again a rise in the noise floor from -140dBrA at 1kHz up to -110dBrA from 200Hz to 10Hz.

**FFT spectrum – 1kHz (digital input, 16/44.1 data at -90dBFS)**

Shown above is the FFT for a 1kHz -90dBFS dithered 16/44.1 input sinewave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, and no other peaks above the noise floor at -110dBrA.

**FFT spectrum – 1kHz (digital input, 24/96 data at -90dBFS)**

Shown above is the FFT for a 1kHz -90dBFS dithered 24/96 input sinewave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, and no other peaks above the noise floor at -110dBrA.

**FFT spectrum – 1kHz (MM phono input)**

Shown above is the FFT for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the phono input, configured for MM. We see the second (2kHz), third (3kHz), and fifth (5kHz) signal harmonics dominating at around -100, -80, and -90dBrA, respectively, or 0.001%, 0.01%, and 0.003%. The most significant power-supply-related noise peaks can be seen at 60Hz at -85/-75dBrA (left/right channels), or 0.006/0.02%. Higher-order power-supply related peaks can also be seen at lower amplitudes.

**FFT spectrum – 1kHz (MC phono input)**

Shown above is the FFT for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the phono input, configured for MC. We see the second (2kHz), third (3kHz), and fifth (5kHz) signal harmonics dominating at around -80dBrA (2/3kHz) and below -90dBrA (5kHz), or 0.01% and 0.003%. The most significant power-supply-related noise peaks can be seen at 60Hz at -70/55dBrA (left/right channels), or 0.03/0.2%. Higher-order power-supply related peaks can also be seen at lower amplitudes.

**FFT spectrum – 50Hz (line-level input)**

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the analog line-level input. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. There are no harmonic peaks of any kind to be observed above the noise floor.

**FFT spectrum – 50Hz (MM phono input)**

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the phono input (MM configuration). The X axis is zoomed in from 40 Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most predominant (non-signal) peak is from the 60Hz power supply fundamental at -85/-75dBrA (left/right channels), or 0.006/0.02%. The most predominant signal related harmonic is at 100Hz at -85dBrA, or 0.006%. Higher-order signal-related and power-supply-related peaks can also be seen at lower amplitudes.

**FFT spectrum – 50Hz (MC phono input)**

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the phono input (MC configuration). The X axis is zoomed in from 40 Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most predominant (non-signal) peak is from the 60Hz at -70/55dBrA (left/right channels), or 0.03/0.2%. The most predominant signal-related harmonic is at 100Hz at -70dBrA, or 0.03%. Higher-order signal-related and power-supply-related peaks can also be seen at lower amplitudes.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, line-level input)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the balanced analog line-level input. The input RMS values are set at -6.02dBrA, so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -110dBrA, or 0.0003%, while the third-order modulation products, at 17kHz and 20kHz, are around -80dBrA, or 0.01%.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 16/44.1)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 16/44.1. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -120dBrA, or 0.0001%, while the third-order modulation products, at 17kHz and 20kHz, are around -80dBrA, or 0.01%.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 16/44.1, MQA on)**

Shown above is an FFT of the intermodulation (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 16/44.1, with MQA turned on. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -110dBrA, or 0.0003%, while the third-order modulation products, at 17kHz and 20kHz, are around -80dBrA, or 0.01%. What we also see clear aliasing products above 20kHz reaching above -30dBrA, and a multitude of subsequent low-level (-90 to -110dBrA) IMD products within the audioband. This result may be an argument for keeping MQA turned off with non-MQA 16/44.1 program material.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 24/96)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 24/96. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -120dBrA, or 0.0001%, while the third-order modulation products, at 17kHz and 20kHz, are around -80dBrA, or 0.01%.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, MM phono input)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the phono input configured for MM. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -80dBrA, or 0.01%, while the third-order modulation products, at 17kHz and 20kHz, are also around -80dBrA, or 0.01%.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, MC phono input)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the phono input configured for MC. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -90/80dBrA (left/right), or 0.003/0.01%, while the third-order modulation products, at 17kHz and 20kHz, are also around -80dBrA, or 0.01%.

**Square-wave response (10kHz)**

Above is the 10kHz squarewave response using the balanced analog line-level input, at roughly 10W into 8 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the SU-R1000’s slew-rate performance. Rather, it should be seen as a qualitative representation of the SU-R1000’s mid-tier bandwidth. An ideal squarewave can be represented as the sum of a sinewave and an infinite series of its odd-order harmonics (*e.g.*, 10kHz + 30kHz + 50kHz + 70kHz . . .). A limited bandwidth will show only the sum of the lower-order harmonics, which may result in noticeable undershoot and/or overshoot, and softening of the edges. In this case, because of the switching nature of the amplifier, we see a 768kHz switching frequency (see 1MHz FFT below) riding on top of the squarewave.

**Square-wave response (10kHz, restricted 500kHz bandwidth)**

Above is the same 10kHz squarewave response using the balanced analog line-level input, at roughly 10W into 8 ohms, this time with a 500kHz input bandwidth on the Audio Precision analyzer to filter out the 768kHz switching frequency. We can see significant overshoot and undershoot in the corners of the squarewave, a consequence of the SU-R1000’s mid-tier bandwidth.

**FFT spectrum (1MHz bandwidth)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the balanced analog line-level input, with an extended 1MHz input bandwidth. This enables us to see the high-frequency noise above 20kHz reaching almost -70dBrA at 300kHz. We also see a clear peak at 768kHz, reaching just past -30dBrA. The peak, as well as the noise, are a result of the switching amplifier technology used in the SU-R1000; however, they are far above the audioband—and therefore inaudible—and so high in frequency that any loudspeaker the amplifier is driving should filter it all out anyway.

**Damping factor vs. frequency (20Hz to 20kHz)**

The final chart above is the damping factor as a function of frequency. We can see here the clear trend of a high damping factor at low frequencies—around 400 from 20Hz to 200Hz—and then the steep decline down to 15 at 20kHz. This is a limitation of the switching amplifier technology used in the SU-R1000, and the reason Technics has incorporated their clever Load Adaptive Phase Calibration (LAPC) feature, to compensate for losses into low impedances at high frequencies.

*Diego Estan*

Electronics Measurement Specialist

- Details
- Parent Category: Products
- Category: Amplifier Measurements

Link: reviewed by Dennis Burger *SoundStage! Access* on December 1, 2021

**General Information**

All measurements taken using an Audio Precision APx555 B Series analyzer.

The TA1 was conditioned for 1 hour at 1/8th full rated power (~7.5W into 8 ohms) before any measurements were taken. All measurements were taken with both channels driven, using a 120V/20A dedicated circuit, unless otherwise stated.

The TA1 offers two line-level analog inputs (RCA); one pair of phono RCA inputs, configurable for moving magnet (MM) or moving coil (MC); one pair of RCA pre-amp outputs (full-range or high-pass at 90Hz); RCA 2.1 preamp outputs with subwoofer channel (90Hz crossover); one coaxial (RCA) and one optical (TosLink) digital input; one USB digital input; Bluetooth connectivity; two pairs of speaker-level outputs (left and right channels); and one headphone output using a 1/8″ TRS connector. For the purposes of these measurements, the following inputs were evaluated: coaxial, analog line-level, and phono (RCA, MM and MC).

Most measurements were made with a 2Vrms line-level analog input, 5mVrms MM input, 0.5mVrms MC input, and 0dBFS digital input. The volume control is variable from 0 to 80. The following volume settings yielded 10W into 8 ohms: 52 for analog line-level and digital, 67.5 for MM, and 66.5 for MC. The signal-to-noise ratio (SNR) measurements were made with the same input signal values but with the volume set to achieve the rated output power of 60W. For comparison, on the line-level input, a SNR measurement was also made with the volume at maximum, where only 0.192Vrms was required to achieve 60W into 8 ohms.

Based on the high accuracy of the left/right volume channel matching (see table below), the TA1 volume control is likely digitally controlled in the analog domain. The TA1 offers 0.5dB volume steps ranging from 0 to 80. Overall range is -38.4dB to +41.2dB (line-level input, speaker output).

**Volume-control accuracy (measured at speaker outputs): left-right channel tracking**

Volume position | Channel deviation |

0.5 | 0.035dB |

10 | 0.04dB |

30 | 0.049dB |

50 | 0.024dB |

60 | 0.026dB |

70 | 0.037dB |

80 | 0.01dB |

**Published specifications vs. our primary measurements**

The table below summarizes the measurements published by Emotiva for the TA1 compared directly against our own. The published specifications are sourced from Emotiva’s website, either directly or from the manual available for download, or a combination thereof. With the exception of frequency response, where the Audio Precision bandwidth is set at its maximum (DC to 1MHz), assume, unless otherwise stated, 10W into 8ohms and a measurement input bandwidth of 10Hz to 90kHz, and the worst-case measured result between the left and right channels.

Parameter | Manufacturer | SoundStage! Lab |

Amplifier rated output power into 8 ohms (0.5% THD) | 60W | 62.5W |

Amplifier rated output power into 4 ohms (0.5% THD) | 100W | 89W |

THD (60W, 20Hz-20kHz, 8 ohms) | <0.02% | <0.02% (40Hz - 7kHz) |

Frequency response (analog line-level in, speaker out) | 20Hz-20kHz (±0.15dB) | 20Hz-20kHz (-0.09,-0.3dB) |

Frequency response (analog line-level, speaker out) | 5Hz-80kHz (0, -1.8dB) | 5Hz-80kHz (-0.8,-1.6dB) |

Signal-to-noise ratio (speaker out, 60W, A-weighted) | 116dB | 107.6dB |

Maximum output level (pre-out) | 4Vrms | 4.5Vrms |

Frequency response (analog line-level in, pre-out) | 5Hz-50kHz (±0.04dB) | 5Hz-50kHz (-0.06,+0.001dB) |

THD+N (analaog line-level in, pre-out @ 1kHz, 1Vrms, A-weighted) | <0.001% | <0.0017% |

IMD (analog line-level in, pre-out, SMPTE) | <0.004% | <0.0048% |

Signal-to-noise ratio (analog line-level in, pre-out 4V, A-weighted) | >120dB | 119.3dB |

Crosstalk (analog line-level in, pre-out 1V, 10kHz) | <90dB | 97.1dB |

THD+N (MM in, pre-out @ 1kHz, 1Vrms, A-weighted) | <0.015% | <0.03% |

THD+N (MC in, pre-out @ 1kHz, 1Vrms, A-weighted) | <0.06% | <0.07% |

Gain (MM, pre-out max vol) | 44dB | 36.1dB |

Gain (MC, pre-out max vol) | 55dB | 57.2dB |

Signal-to-noise ratio (MM ref 5 mV in, 60W, A-weighted) | >78dB | 82.6dB |

Signal-to-noise ratio (MC ref 0.5 mV in, 60W, A-weighted) | >58dB | 62.0dB |

Frequency response (digital in, pre-out, 16/44.1) | 5Hz-20kHz (±0.15dB) | 5Hz-20kHz (-0.06,-0.3dB) |

Frequency response (digital in, pre-out, 24/192) | 5Hz-80kHz (±0.25dB) | 5Hz-80kHz (-0.06,-3.6dB) |

THD+N (digital in, pre-out @ 1kHz, 1Vrms, A-weighted) | <0.003% | <0.005% |

IMD (digital in, pre-out, SMPTE) | <0.007% | <0.009% |

Signal-to-noise ratio (digital in 24/96, pre-out 4V, A-weighted) | >110dB | 112.9dB |

Our primary measurements revealed the following using the line-level analog input and digital coaxial input (unless specified, assume a 1kHz sinewave at 2Vrms or 0dBFS, 10W output, 8-ohm loading, 10Hz to 90kHz bandwidth):

Parameter | Left channel | Right channel |

Maximum output power into 8 ohms (1% THD+N, unweighted) | 62.5W | 62.5W |

Maximum output power into 4 ohms (1% THD+N, unweighted) | 89W | 89W |

Continuous dynamic power test (5 minutes, both channels driven) | passed | passed |

Crosstalk, one channel driven (10kHz) | -56.5dB | -60.8dB |

Damping factor | 190 | 209 |

Clipping no-load output voltage (instantaneous power into 8 ohms) | 28Vrms (98W) | 28Vrms (98W) |

DC offset | <-18mV | <-21mV |

Gain (pre-out) | 11.9dB | 11.9dB |

Gain (maximum volume) | 41.2dB | 41.2dB |

IMD ratio (18kHz + 19kHz stimulus tones) | <-72dB | <-73dB |

Input impedance (line input, RCA) | 14.2k ohms | 14.2k ohms |

Input sensitivity (for rated power, maximum volume) | 192mVrms | 192mVrms |

Noise level (A-weighted) | <84uVrms | <81uVrms |

Noise level (unweighted) | <263uVrms | <302uVrms |

Output Impedance (pre-out) | 1.5 ohms | 1.7 ohms |

Signal-to-noise ratio (full power, A-weighted, 2Vrms in) | 107.6dB | 107.6dB |

Signal-to-noise ratio (full power, unweighted, 2Vrms in) | 98.2dB | 96.8dB |

Signal-to-noise ratio (full power, A-weighted, max volume) | 99.1dB | 98.9dB |

Dynamic range (full power, A-weighted, digital 24/96) | 107.5dB | 107.5dB |

Dynamic range (full power, A-weighted, digital 16/44.1) | 95.7dB | 95.7dB |

THD ratio (unweighted) | <0.0055% | <0.0024% |

THD ratio (unweighted, digital 24/96) | <0.007% | <0.004% |

THD ratio (unweighted, digital 16/44.1) | <0.006% | <0.002% |

THD+N ratio (A-weighted) | <0.0062% | <0.0028% |

THD+N ratio (A-weighted, digital 24/96) | <0.0066% | <0.0028% |

THD+N ratio (A-weighted, digital 16/44.1) | <0.0068% | <0.0031% |

THD+N ratio (unweighted) | <0.0062% | <0.0042% |

Minimum observed line AC voltage | 123.5 VAC | 123.5 VAC |

For the continuous dynamic power test, the TA1 was able to sustain 88W into 4 ohms (1% THD) using an 80Hz tone for 500ms, alternating with a signal at -10 dBof the peak (8.8W) for 5 seconds, for 5 continuous minutes without inducing a fault or the initiation of a protective circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the TA1 was warm to the touch, but did not cause discomfort to the touch.

Our primary measurements revealed the following using the phono-level input, MM configuration (unless specified, assume a 1kHz 5mVrms sinewave input, 10W output, 8-ohm loading, 10Hz to 90kHz bandwidth):

Parameter | Left channel | Right channel |

Crosstalk, one channel driven (10kHz) | -56.6dB | -59.2dB |

DC offset | <-20mV | <-20mV |

Gain (default phono preamplifier) | 36.2dB | 36.1dB |

IMD ratio (18kHz and 19 kHz stimulus tones) | <-50dB | <-50dB |

IMD ratio (3kHz and 4kHz stimulus tones) | <-52dB | <-52dB |

Input impedance | 32.4k ohms | 32.3k ohms |

Input sensitivity (to max power with max volume) | 2.95Vrms | 2.95Vrms |

Noise level (A-weighted) | <0.9mVrms | <0.9mVrms |

Noise level (unweighted) | <3.7mVrms | <3.7mVrms |

Overload margin (relative 5mVrms input, 1kHz) | 23.9dB | 23.9dB |

Signal-to-noise ratio (full rated power, A-weighted) | 82.6dB | 82.6dB |

Signal-to-noise ratio (full rated power, unweighted) | 76.6dB | 76.6dB |

THD (unweighted) | <0.028% | <0.027% |

THD+N (A-weighted) | <0.038% | <0.037% |

THD+N (unweighted) | <0.055% | <0.053% |

Our primary measurements revealed the following using the phono-level input, MC configuration (unless specified, assume a 1kHz 0.5mVrms sinewave input, 10W output, 8-ohm loading, 10Hz to 90kHz bandwidth):

Parameter | Left channel | Right channel |

Crosstalk, one channel driven (10kHz) | -56.4dB | -49.8dB |

DC offset | <-20mV | <-20mV |

Gain (default phono preamplifier) | 57.2dB | 57.2dB |

IMD ratio (18kHz and 19 kHz stimulus tones) | <-50dB | <-50dB |

IMD ratio (3kHz and 4kHz stimulus tones) | <-52dB | <-52dB |

Input impedance | 124.5 ohms | 124.4 ohms |

Input sensitivity (to max power with max volume) | 262uVrms | 262uVrms |

Noise level (A-weighted) | <10mVrms | <9mVrms |

Noise level (unweighted) | <35mVrms | <35mVrms |

Overload margin (relative 0.5mVrms input, 1kHz) | 22.8dB | 22.8dB |

Signal-to-noise ratio (full rated power, A-weighted) | 62.0dB | 62.2dB |

Signal-to-noise ratio (full rated power, unweighted) | 56.8dB | 57.2dB |

THD (unweighted) | <0.032% | <0.032% |

THD+N (A-weighted) | <0.11% | <0.11% |

THD+N (unweighted) | <0.4% | <0.4% |

Our primary measurements revealed the following using the analog input at the headphone output (unless specified, assume a 1kHz sinewave, 2Vrms output, 300 ohms loading, 10Hz to 90kHz bandwidth):

Parameter | Left channel | Right channel |

Maximum output power into 600 ohms (1% THD+N, unweighted) | 72mW | 72mW |

Maximum output power into 300 ohms (1% THD+N, unweighted) | 107mW | 107mW |

Maximum output power into 32 ohms (1% THD+N, unweighted) | 83mW | 85mW |

Gain | 21.5dB | 21.5dB |

Output impedance | 95.6 ohms | 95.9 ohms |

Noise level (A-weighted) | <7.4uVrms | <12.1uVrms |

Noise level (unweighted) | <67uVrms | <219uVrms |

Signal-to-noise ratio (A-weighted, ref. max output voltage) | 117.5dB | 113.3dB |

Signal-to-noise ratio (unweighted, ref. max output voltage) | 98.5dB | 88.2dB |

THD ratio (unweighted) | <0.0014% | <0.0015% |

THD+N ratio (A-weighted) | <0.0017% | <0.0019% |

THD+N ratio (unweighted) | <0.0044% | <0.0138% |

**Frequency response (8-ohm loading, line-level input)**

In our frequency response plots above, measured across the speaker outputs at 10W into 8 ohms, the blue and red (left/right channels) traces are for the full-range output, while purple and green represents output with the 90Hz high-pass filter enabled. Full-range, the TA1 is nearly flat within the audioband (20Hz to 20kHz). At the frequency extremes, the TA1 is -0.09dB down at 20Hz and -0.3dB down at 20Hz. These data do not quite corroborate Emotiva’s claim of 20Hz to 20kHz (+/-0.15dB). Emotiva’s claim of -1.8dB at 80kHz, was not corroborated, as we measured –3.3dB at 80kHz. With the high-pass filter engaged, the -3dB point is at 90Hz, and the slope of the filter is 12dB/octave. There are two curious observations to be made with the high-pass filter. The first is a 1dB bump at around 170Hz, and the second is a reduced high-frequency extension compared to the full-range output, with a -3dB point around 45kHz, compared to roughly 80kHz without the high-pass filter enabled.

**Frequency response (8-ohm loading, line-level input, bass and treble controls)**

Above is a frequency response plot measured at the speaker-level outputs into 8 ohms, with the bass and treble controls set to maximum (blue/red plots) and minimum (purple/green plots). We see that for the bass control, the +/-10dB controls of the TA1 yielded measured results of nearly +/-11dB at 20Hz. The treble controls yielded about +9dB, and just shy of -10dB at 20kHz.

**Frequency response (2.1-channel preamplifier outputs)**

Above is a frequency response plot measured at the line-level 2.1 pre-outs, where the high-pass output is relative to 1kHz, and the subwoofer low-pass output is relative to 20Hz. We see that the -3dB point is at 90kHz, as advertised. While the high-pass filtered output exhibits a slope of 12dB/octave, the subwoofer low-pass filtered output exhibits a slope of 6dB/octave. The same 1dB bump at 170Hz is seen here for the high-pass filtered pre-output, as is seen above at the speaker-level outputs with the high-pass filter enabled. High-frequency extension on the pre-outs is not limited, and is essentially flat out to 80kHz.

**Phase response (8-ohm loading, line-level input)**

Above is the phase response plot from 20Hz to 20kHz for the line-level input, measured across the speaker outputs at 10W into 8 ohms. The tone controls were not engaged. The TA1 does not invert polarity and exhibits, at worst, 20 degrees (at 20kHz) of phase shift within the audioband.

**Frequency response vs. input type (8-ohm loading, left channel only)**

The chart above shows the TA1’s frequency response as a function of input type measured across the speaker outputs at 10W into 8 ohms. The green trace is the same analog input data from the previous graph. The blue trace is for a 16bit/44.1kHz dithered digital input signal from 5Hz to 22kHz using the coaxial input, and the purple trace is for a 24/96 dithered digital input signal from 5Hz to 48kHz, while the pink trace is for a 24/192 dithered digital input signal from 5Hz to 96kHz. The 16/44.1 data exhibits brick-wall-type filtering, with a -3dB at 21kHz. The 24/96 and 24/192 kHz data yielded -3dB points at 44.3kHz and 48.7kHz respectively. These data do not corroborate Emotiva’s claim of 5Hz-80kHz (±0.25dB) for a 24/192 digital input.

**Frequency response (8-ohm loading, MM phono input)**

The chart above shows the frequency response for the phono input (MM configuration) with maximum deviations of about -0.4/+0.5dB (20Hz/20kHz) from 20Hz to 20kHz. What is shown is the deviation from the RIAA curve, where the input signal sweep is EQ’d with an inverted RIAA curve supplied by Audio Precision (*i.e.*, zero deviation would yield a flat line at 0dB).

**Frequency response (8-ohm loading, MC phono input)**

The chart above shows the frequency response for the phono input (MC configuration), with maximum deviations of about -4.0/+0.4dB (20Hz/200Hz) from 20Hz to 20kHz.

**Phase response (MM input)**

Above is the phase response plot from 20Hz to 20kHz for the phono input (MM configuration), measured across the speaker outputs at 10W into 8 ohms. The TA1 does not invert polarity. For the phono input, since the RIAA equalization curve must be implemented, which ranges from +19.9dB (20Hz) to -32.6dB (90kHz), phase shift at the output is inevitable. Here we find a worst case of about -60 degrees at 200Hz and 5kHz.

**Phase response (MC input)**

Above is the phase response plot from 20Hz to 20kHz for the phono input (MC configuration), measured across the speaker outputs at 10W into 8 ohms. The TA1 does not invert polarity. Here we find a worst case of about +40 degrees at 20Hz and -60 degrees at 200Hz and 5kHz.

**Digital linearity (24/44.1 data, filters 1-7)**

The chart above shows the results of a linearity test for the coaxial digital input for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the line-level output of the TA1. The digital input is swept with a dithered 1kHz input signal from -120dBFS to 0dBFS, and the output is analyzed by the APx555. The ideal response would be a straight flat line at 0dB. The 24/96 input data yielded near perfect results all the way down to -120dBFS, while the 16/44.1 input data were perfect from -110dBFS to 0dBFS. At -120dBFS, the 16/44.1 data were only +2.5dB (left) and +4dB (right) above reference.

**Impulse response (16/44.1 data)**

The graph above shows the impulse response for the TA1, fed to the coaxial digital input, measured at the line-level output. Emotiva’s filter implementation appears to minimize pre-ringing.

**J-Test (coaxial)**

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line level output of the SA30. The J-Test test was developed by Julian Dunn the 1990s. It is a test signal—specifically, a -3dBFS, undithered 12kHz squarewave sampled (in this case) at 48kHz (24 bits). Since even the first odd harmonic (*i.e.*, 36kHz) of the 12kHz squarewave is removed by the bandwidth limitation of the sampling rate, we are left with a 12kHz sinewave (the main peak). In addition, an undithered 250Hz squarewave at -144dBFS is mixed with the signal. This test file causes the 22 least significant bits to constantly toggle, which produces strong jitter spectral components at the 250Hz rate and its odd harmonics. The test file shows how susceptible the DAC and delivery interface are to jitter, which would manifest as peaks above the noise floor at 500Hz intervals (*e.g.*, 250Hz, 750Hz, 1250Hz, etc.). Note that the alternating peaks are in the test file itself, but at levels of -144dBrA and below. The test file can also be used in conjunction with artificially injected sinewave jitter by the Audio Precision, to show how well the DAC rejects jitter.

The coaxial input exhibits low-level peaks in the audioband, at -115dBrA and below. This is a good J-Test result, indicating that TA1 DAC should yield good jitter immunity.

**J-Test (optical)**

The chart above shows the results of the J-Test test for the optical digital input measured at the line level output of the SA30. The optical input exhibits low-level peaks in the audioband, at -110dBrA and below. This result is not quite as good as the was seen with the coaxial input.

**J-Test with 10ns of injected jitter (coaxial)**

Both the coaxial and optical inputs were also tested for jitter immunity by injecting artificial jitter sinewave jitter at 2kHz, which would manifest as sidebands at 10kHz and 14kHz without any jitter rejection. Despite the TA1’s good J-test results, jitter immunity proved quite poor in this test, showing clear sidebands at -70dBrA with only 10ns of injected jitter. Shown is the coaxial input result, but the optical input yielded the same result.

**Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (coaxial input)**

The chart above shows a fast Fourier transform (FFT) of the TA1’s line-level output with white noise at -4 dBFS (blue/red), and a 19.1kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1. The steep roll-off around 20kHz in the white-noise spectrum shows the behavior of the TA1’s reconstruction filter. Only one small aliased image within the audioband, at about -110dBrA, at around 4kHz can be seen. The primary aliasing signal at 25kHz is just below -90dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are at -80 and -70dBrA.

**RMS level vs. frequency vs. load impedance (1W, left channel only)**

The chart above shows RMS level (relative to 0dBrA, which is 1W into 8ohms or 2.83Vrms) as a function of frequency, for the analog line-level input swept from 5Hz to 100kHz. The blue plot is into an 8-ohm load, the purple is into a 4-ohm load, the pink plot is an actual speaker (Focal Chora 806, measurements can be found here), and the cyan plot is no load connected. The chart below . . .

. . . is the same but zoomed in to highlight differences. Here we find that there’s a total deviation of about 0.1 dB from no-load to 4-ohms, which is an indication of a high damping factor, or low output impedance. The maximum variation in RMS level when a real speaker was used as a load is less, deviating by just over 0.08dB within the flat portion of the curve (20Hz to 10kHz), with the lowest RMS level, which would correspond to the lowest impedance point for the load, exhibited around 200Hz, and the highest RMS level, which would correspond to the highest impedance point for the load, at around 2kHz.

**THD ratio (unweighted) vs. frequency vs. output power**

The chart above shows THD ratios at the output into 8 ohms as a function of frequency for a sinewave stimulus at the analog line-level input. The blue and red plots are for left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at 60W. The power was varied using the volume control. At 1W, the left channel outperformed the right channel by about 5dB, whereas at 10W, the opposite was observed, with the right channel outperforming the left channel by nearly 10dB from 20Hz to 1kHz. At the lower power levels, THD values were low, between 0.002% and 0.02% at 20kHz. At the rated 60W, THD values were as high as 0.3% at 20Hz, then down to 0.01% between 40Hz and 2kHz, then up to 0.03% at 20kHz. These data do not quite corroborate Emotiva’s claim of less than 0.02% at 60W from 20Hz to 20kHz.

**THD ratio (unweighted) vs. frequency at 10W (MM and MC phono inputs)**

The chart above shows THD ratios as a function of frequency plot for the phono input measured across an 8 ohms load at 10W. The MM configuration is shown in blue/red (left/right channels), and MC in purple/green (left/right channels). The input sweep is EQ’d with an inverted RIAA curve. The THD values for the MM configuration vary from around 0.1% (20Hz) down to 0.05% (1kHz), then up to 0.07% (3kHz to 20kHz). The MC THD values essentially tracked the MM values at 100Hz and above. Below 100Hz, MC THD values were higher, reaching 0.4% at 20Hz.

**THD ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms**

The chart above shows THD ratios measured at the output of the TA1 as a function of output power for the analog line-level input, for an 8-ohm load (blue/red for left/right channels) and a 4 ohms load (purple/green for left/right channels). The 8-ohm data generally outperformed the 4-ohm data by 5dB for the left channel, with the 8-ohm data showing a relatively flat response at 0.006-0.007% up to 20W, then up to 0.01% at the “knee” just past 50W, then hitting the 1% THD mark just past 60W. The right channel clearly outperformed the left channel into 8-ohms, by as much as 12dB or so at 5W. The right channel into 4 ohms outperformed the left by about 5dB on average, yielding around 0.005-0.007% through most of the power range, but displayed some up and down trending between 3 and 80W. The “knee” for the 4-ohm data is at around 80W, hitting the 1% THD mark around 90W.

**THD+N ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms**

The chart above shows THD+N ratios measured at the output of the TA1 as a function of output power for the analog line level-input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). Overall, THD+N values for the 8-ohm load before the “knee” ranged from around 0.05% (50mW) down to about 0.005%. The 4-ohm data was similar, but 2-5 dB worse.

**THD ratio (unweighted) vs. frequency at 8, 4, and 2 ohms (left channel only)**

The chart above shows THD ratios measured at the output of the TA1 as a function of load (8/4/2 ohms) for a constant input voltage that yields 5W at the output into 8 ohms (and roughly 10W into 4 ohms, and 20W into 2 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. We find increasing levels of THD from 8 to 4 to 2 ohms, with about a 5dB increase each time the load is halved, except at 20kHz, where the 8- and 4-ohm data merge. Overall, even with a 2-ohm load at roughly 20W, THD values were low and constant at roughly 0.02% across the audioband. Given that the TA1 is not specified to drive 2-ohm loads, these results are admirable.

**FFT spectrum – 1kHz (line-level input)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the analog line-level input. We see that the signal’s second harmonic, at 2kHz, is at -85/-100dBrA (left/right), or 0.006/0.001%, and around -95dBrA (left/right), or 0.002%, at the third harmonic (3kHz). Several higher order signal harmonics can be seen beyond 3kHz in decreasing amplitude. The right channel outperformed the left channel at the even-order signal harmonics (2, 4, 6kHz, etc.). Below 1kHz, we see the power-supply fundamental (60Hz) at around -110/-120dBRa (left/right), or 0.0003/0.0001%, the second harmonic (120Hz) at nearly -100dBrA, or 0.001%, and several higher-order noise harmonics at lower amplitudes.

**FFT spectrum – 1kHz (digital input, 16/44.1 data at 0dBFS)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 16/44.1. Signal and power-supply noise harmonics are very similar to the analog input FFT above, but for a slightly higher noise floor due to the 16-bit dynamic range limitation.

**FFT spectrum – 1kHz (digital input, 24/96 data at 0dBFS)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 24/96. Signal and power-supply noise harmonics are very similar to the analog input FFT above, expect for a higher third signal harmonic (3kHz) amplitude compared to both the 16/44.1 and analog input, at around -90dBrA, or 0.003%.

**FFT spectrum – 1kHz (digital input, 16/44.1 data at -90dBFS)**

Shown above is the FFT for a 1kHz -90dBFS dithered 16/44.1 input sinewave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, and minor power-supply related noise peaks below -110dBrA, or 0.0003%.

**FFT spectrum – 1kHz (digital input, 24/96 data at -90dBFS)**

Shown above is the FFT for a 1kHz -90dBFS dithered 24/96 input sinewave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, and minor power-supply related noise peaks below -110dBrA, or 0.0003%.

**FFT spectrum – 1kHz (MM phono input)**

Shown above is the FFT for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the phono input, configured for MM. We see the second (2kHz) and third (3kHz) signal harmonics dominating at around -85/-100dBrA (left/right), or 0.006/0.001%, and at -80dBrA, or 0.01%. The most significant power-supply related noise peaks can be seen at 60Hz and 180Hz at -70dBrA, or 0.03%.

**FFT spectrum – 1kHz (MC phono input)**

Shown above is the FFT for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the phono input, configured for MC. We see the third (3kHz) signal harmonic dominating at around -75dBrA, or 0.02%, followed by the fifth harmonic (5kHz) at just below -80dBrA, or 0.01%. The most significant power-supply related noise peaks can be seen at 60Hz and 180Hz at -50dBrA, or 0.3%.

**FFT spectrum – 50Hz (line-level input)**

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the analog line-level input. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most predominant (non-signal) peaks are that of the signal’s second (100Hz), third (150Hz), and fourth (200Hz) harmonic, at between -90dBrA, or 0.003%, and -100dBrA, or 0.001%. Even-order signal harmonics are worse for the left channel, showing clear peaks at 200, 300, 400, 500, 600Hz, etc. The most significant power-supply related peak is at the second harmonic at 120Hz, at -105dBrA, or 0.0006%.

**FFT spectrum – 50Hz (MM phono input)**

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the phono input (MM configuration). The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most predominant (non-signal) peak is from the signal’s third harmonic (150Hz) at -70dBrA, or 0.03%, while the power-supply fundamental (60Hz) and third harmonic (180Hz) reach almost the same level.

**FFT spectrum – 50Hz (MC phono input)**

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the phono input (MC configuration). The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most predominant (non-signal) peak is from power-supply noise, both from the fundamental (60Hz) and third harmonic (180Hz), at just below -50dBrA, or 0.3%. The third signal harmonic (150Hz) is at -65dBrA, or 0.06%.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, line-level input)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the analog line-level input. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -90/100dBRA (left/right), or 0.003/0.001%, while the third-order modulation products, at 17kHz and 20kHz, are around -85dBrA, or 0.006%.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 16/44.1)**

Shown above is an FFT of the intermodulation (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 16/44.1. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -90/100dBRA (left/right), or 0.003/0.001%, while the third-order modulation products, at 17kHz and 20kHz, are higher than for the analog input at -70dBrA, or 0.03%.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 24/96)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 24/96. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -90/100dBRA (left/right), or 0.003/0.001%, while the third-order modulation products, at 17kHz and 20kHz, are higher than for the analog input at -70dBrA, or 0.03%.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, MM phono input)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the phono input configured for MM. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -90/100dBRA (left/right), or 0.003/0.001%, while the third-order modulation products, at 17kHz and 20kHz, are higher than for the line-level analog input at roughly -65dBrA, or 0.06%.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, MC phono input)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the phono input configured for MC. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at around -90dBrA, or 0.003%, while the third-order modulation products, at 17kHz and 20kHz, are the same as the MM configuration at roughly -65dBrA, or 0.06%.

**Square-wave response (10kHz)**

Above is the 10kHz square-wave response using the analog line-level input, at roughly 10W into 8 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the TA1’s slew-rate performance. Rather, it should be seen as a qualitative representation its relatively extended bandwidth. An ideal square wave can be represented as the sum of a sinewave and an infinite series of its odd-order harmonics (*e.g.*, 10kHz + 30kHz + 50kHz + 70kHz . . .). A limited bandwidth will show only the sum of the lower-order harmonics, which may result in noticeable undershoot and/or overshoot, and softening of the edges. The TA1’s reproduction of the 10kHz square wave is clean, with some softening of the edges.

**Damping factor vs. frequency (20Hz to 20kHz)**

The final graph above is the damping factor as a function of frequency. Both channels show a trend of higher damping factor at lower frequencies, with the right channel slightly outperforming the left channel. The left channel measured from around 230 down to 130 at 20kHz, while the right measured around 260 down to 150 at 20kHz. For such an affordable receiver, the damping factor figures are quite good.

*Diego Estan*

Electronics Measurement Specialist

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