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- Category: Amplifier Measurements

Link: reviewed by Roger Kanno *SoundStage! Access* on March 15, 2021

**General information**

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

The NAD Masters M28 offers seven channels of amplification, each with an unbalanced (RCA) and balanced (XLR) input connector. However, since our measurement setup is optimized for stereo amplifiers, we were only able to test two channels at a time; therefore, we were not able to test the M28 with all seven channels being driven simultaneously.

The M28 was conditioned for one hour at 1/8th power (27W, 8 ohms) before any measurements were taken. All measurements were performed with two channels driven, unless otherwise stated, with the M28 connected to a dedicated 120V/20A circuit.

Unless otherwise specified, balanced input connections were used for all measurements, using channels 2 (as the right channel) and 3 (as the left channel). No important differences were seen between unbalanced and balanced input connections in terms of THD+N. There were small signal-to-noise ratio (SNR) differences highlighted in the table below. We found no differences in maximum output power (1% THD+N) between all seven channels when measured separately; however, significant differences in THD were observed between about 210W and 240W output (8 ohms)—channels 1-3 outperformed channels 5-7 in terms of THD by 20-30dB. Below 200W, and at the 1% THD power level (about 268W, 8 ohms), all channels performed similarly.

**Published specifications vs. our primary measurements**

The table below summarizes the measurements published by NAD for the M28 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 set at its maximum (DC to 1MHz), assume, unless otherwise stated, a measurement input bandwidth of 10Hz to 90kHz, and the worst-case measured result between one of the two channels driven.

Parameter | Manufacturer | SoundStage! Lab |

Rated output power into 8 ohms | 220W | 268W (1% THD) |

Rated output power into 4 ohms | 400W | 509W (1% THD) |

*THD (20Hz-6.5kHz, 220W, 8 ohms, 20Hz - 20kHz BW) | <0.003% | 0.001% to 0.3% |

*THD (20Hz-6.5kHz, 110W, 8 ohms, 20Hz - 20kHz BW) | <0.0005% | 0.0002% to 0.0007% |

IMD (CCIF, 5 + 6kHz, 220W, 8 ohms) | <0.003% | <0.0023% |

IMD (CCIF, 5 + 6kHz, 110W, 8 ohms) | <0.0005% | <0.0016% |

SNR (A-weighted, ref. 1W out in 8 ohms, balanced) | >102dB | 97.5dB |

SNR (A-weighted, ref. 1W out in 8 ohms, single-ended) | >97dB | 95.5dB |

SNR (A-weighted, ref. 220W out in 8 ohms, balanced) | >124dB | 120.8dB |

SNR (A-weighted, ref. 220W out in 8 ohms, single-ended) | >120dB | 118.8dB |

Damping factor (ref. 8 ohms 50Hz and 1kHz) | >750 | 1249/1114 |

Frequency response (20Hz-20kHz) | ±0.1dB | ±0.05dB |

Frequency response (3Hz-60kHz) | -3dB | +0.6/-2.3dB |

Voltage Gain | 29.5dB +/-0.3dB | 29.47dB |

Input Sensitivity (stereo for 220W in 8 ohms) | 1.3Vrms | 1.41Vrms |

Input Impedance (balanced) | 47k ohms | **78.4k ohms |

Input Impedance (single-ended) | 23k ohms | 23.3k ohms |

*The NAD THD specification on their website is published as “20Hz-20kHz”; however, after discussions with NAD, it was discovered that the company measures THD from 20Hz to 6.5kHz, with a 20Hz to 20kHz input bandwidth filter.

**The discrepancy in balanced input impedance may be due to NAD specifying this value for the inverting and noninverting pins separately. Our measurement considers both inputs on the balanced connector together. Treated separately, our measurement would be halved, or 39.2k ohms.

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

Parameter | Channel 3 | Channel 2 |

Maximum output power into 8 ohms (1% THD+N, unweighted) | 267W | 269W |

Maximum output power into 4 ohms (1% THD+N, unweighted) | 509W | 509W |

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

Crosstalk, one channel driven (10kHz) | -91.1dB | -87.7dB |

DC offset | 15mV | -6mV |

Damping factor | 1140 | 1114 |

Clipping headroom (8 ohms) | 0.84dB | 0.87dB |

Gain (fixed) | 29.47dB | 29.50dB |

IMD ratio (18kHz + 19kHz stimulus tones) | <-97dB | <-97dB |

Input impedance (line input) | 78.2k ohms | 78.4k ohms |

Input sensitivity | 1.41Vrms | 1.41Vrms |

Noise level (A-weighted) | <50uVrms | <50uVrms |

Noise level (unweighted) | <440uVrms | <440uVrms |

Signal-to-noise ratio (full power, A-weighted) | 120.8dB | 120.9dB |

Signal-to-noise ratio (full rated power, 20Hz to 20kHz) | 119.6dB | 119.6dB |

THD ratio (unweighted) | <0.0002% | <0.0002% |

THD+N ratio (A-weighted) | <0.0006% | <0.0007% |

THD+N ratio (unweighted) | <0.005% | <0.005% |

Minimum observed line AC voltage | 121VAC | 121VAC |

For the continuous dynamic power test, the M28 was able to sustain 500W (1dB over rated output and roughly 1%THD) into 4 ohms using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (50W) for five seconds for five 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 M28 was just slightly warm to the touch.

**Frequency response (8-ohm loading)**

In our measured frequency response plot above, the M28 is essentially perfectly flat within the audio band (20Hz to 20kHz), with the exception of an insignificant 0.05dB rise at 20Hz and 20kHz. NAD’s claim of ±0.1dB from 20Hz to 20kHz is corroborated by our measurement, as is the -3dB point at 60kHz (we measured -2.3dB). The M28 cannot be considered a high-bandwidth audio device , due to the steep rolloff that begins at around 30kHz. In the graph above and most of the graphs below, only a single trace may be visible. This is because channel 3 (blue or purple trace) is performing identically to channel 2 (red or green trace), and so they perfectly overlap, indicating that the two channels are ideally matched.

**RMS level vs. frequency vs. load impedance (1W, channel 3 only)**

The charts above and below show RMS level (relative to 0dBrA, which is 1W into 8 ohms or 2.83Vrms) as a function of frequency, for the balanced line-level inputs swept from 5Hz to 100kHz. The blue plot is into an 8-ohm load, the purple is into a 4-ohm load, the pink is an actual speaker (Focal Chora 806, measurements can found here), and the cyan is no load connected. The top graph shows that all four plots are indistinguishable from one another. This is an indication of a high damping factor, or low output impedance. The graph below. . .

. . . shows the same data, but with the vertical and horizontal axis expanded to show differences more clearly. Here we find that there’s a total deviation of only about 0.03dB in the flat portion of the curve between 4 ohms and no load. At 20kHz, the spread is a little larger, perhaps 0.04dB. The maximum variation in RMS level when a real speaker was used as a load is extremely small, deviating by about 0.01dB within the flat portion of the curve. There is a rise at low and high frequencies; however, this is due to the M28’s inherent frequency response, and not the output impedance of the M28 interacting with a load that varies with frequency.

**Phase response**

Above is the phase response plot for the M28 from 20Hz to 20kHz. The M28 does not invert polarity, and there is virtually no phase shift throughout the audioband, with a worst case of just over +10 degrees at 20Hz.

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

The chart above shows THD ratios at the M28’s output into 8 ohms as a function of frequency (20Hz to 20kHz) for a sine-wave stimulus at the balanced line-level inputs. The blue and red plots are for channels 3 and 2 at 1W output, purple/green at 10W, and pink/orange at the rated 220W, all into 8 ohms. There is about a 5dB improvement in THD ratios at 10W versus 1W throughout most of the audioband. At 10W, the THD values are as low as 0.00007% at 40Hz, and as high as 0.01% at 20kHz. Due to these extremely low values, it’s important to note that we are approaching the limits of the APx555 analyzer, which inherently measures at approximately 0.00001-0.00002% THD when fed its own signal at this level. The THD levels at 220W are significantly higher than at 1W and 10W, ranging from 0.3% at 20Hz down to about 0.002% around 2-3kHz, then back up to 0.04% at 20kHz. These differences are more of an indicator that NAD may not have been conservative in specifying output power for the M28, and that 200W into 8 ohms, or just below, would have been a more appropriate value for the M28 (also see chart detailing THD vs. output power below).

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

The chart above shows THD ratios measured at the output of the M28 as a function of output power for the balanced line level input, for an 8-ohm load (blue/red for channels 3 and 2) and a 4-ohm load (purple/green for channels 3 and 2). At 50mW, THD values are near 0.001% for both 8- and 4-ohm data. At 10W, the 8-ohm THD value is just below 0.0002%, and about 0.0004% at 4 ohms. At the “knees,” the 8-ohm THD value is at around 0.0005%, nearing 200W, while the 4 ohms THD value is at around 0.002% at around 350W. Here is another indication that 200W may be a more appropriate rated output power into 8 ohms for the M28.

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

The plot above shows THD+N ratios measured at the output of the M28 as a function of output power for the balanced line-level inputs, for an 8-ohm load (blue/red for channels 3 and 2) and a 4-ohm load (purple/green for channels 3 and 2). At 50mW, THD+N values are near 0.03% for both 8- and 4-ohm data, dipping down to near 0.002% between 50 and 150W (8 ohms), and roughly 0.003% between 50 and 300W (4 ohms).

**THD+N ratio (A-weighted) vs. output power at 1kHz into 4/8 ohms**

The chart above shows THD+N ratios (A-weighted) measured at the output of the M28 as a function of output power for the balanced line-level input, for an 8-ohm load (blue/red for channels 3 and 2) and a 4-ohm load (purple/green for channels 3 and 2). At 50mW, THD+N values are just below (8 ohms) and above (4 ohms) 0.005%, dipping down to near 0.0003% between 30 and 50W (8 ohms), and roughly 0.0004% between 10 and 30W (4 ohms).

**THD ratio (unweighted) vs. frequency at 8/4/2 ohms (channel 3 only)**

The chart above shows THD ratios measured at the output of the M28 as a function of load (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 channel 3 balanced 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 10db difference between 8, 4, and 2 ohms respectively, from 50Hz to 3kHz. There’s a convergence of THD values between all loads at higher frequencies. Overall, even with a 2-ohm load at roughly 80W, THD values ranged from 0.001% at 20Hz to just above 0.01% at 20kHz.

**FFT spectrum – 1kHz**

Shown above is a fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the output across an 8-ohm load at 10W. We see that the second harmonic, at 2kHz, is at a very low -130dBrA (relative to the reference 0dB signal), or 0.00003%. The third harmonic, at 3kHz, is just above -120dBrA, or 0.0001%. The fifth harmonic is approaching -140dBrA, or 0.00001%. Below 1kHz, we see no noise artifacts, either at 60Hz or 120Hz due to power-supply noise.

**FFT spectrum – 50Hz**

Shown above is the FFT for a 50Hz input sine-wave stimulus measured at the output across an 8-ohm load at 10W. 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 of the 50Hz signal (100Hz) can be seen at around -130dBrA, or 0.00003%. The third harmonic at 150Hz is at -125 dBrA, or 0.00006%. Here again, no noise artifacts due to power-supply noise can be seen.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus)**

Shown above is the FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sine-wave stimulus tone at the balanced 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 about -125dBrA, or 0.00006%, while the third-order modulation products, at 17kHz and 20kHz are just above -110dBrA, or 0.0003%.

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

Above and below are the 10kHz square-wave responses of the M28 into an 8-ohm load. The top chart is using the Audio Precision’s highest input bandwidth setting of 1MHz, while the chart below . . .

. . . is bandwidth limited to 250kHz. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, these charts should not be used to infer or extrapolate the M28’s slew-rate performance. Rather, they should be seen as a qualitative representation of the M28’s limited bandwidth (*e.g.*, slow rise time and mild overshoot in the corners), but also as a representation of the noise artifacts present due to the class-D amp topology that the M28 relies on. 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 M28, however, what dominates the plateaus of the square wave in the top graph is a 500kHz (approximate) sine wave, the frequency at which the switching oscillator in the class-D amp is operating (see FFT below). With the bandwidth limited to 250kHz (bottom graph), the 500kHz switching signal is no longer visible.

**FFT spectrum of 500kHz switching frequency relative to a 1kHz tone**

The M28’s topology relies on a roughly 500kHz modulation frequency in the feedback network of the amplifier. The graph above plots an FFT spectrum of the amplifier’s output at 10W into 8 ohms as it’s fed a 1kHz sine wave, but with a wide 1MHz bandwidth. We can see that the peak at about 500kHz is quite evident, at -40dBrA or 1% relative to the 1kHz signal. There is also a peak at 1MHz, (the second harmonic of the 500kHz peak), which is -70dBrA relative to the 1kHz signal. Those two peaks—the fundamental and its second harmonic—are direct results of the design of the C 298 amp modules. The noise around those very-high-frequency signals is always present within the amplifier, but far above the audioband, and therefore inaudible. The noise is also so high in frequency that any loudspeaker the amplifier is driving should filter it all out anyway, since the output of most tweeters begins to fall off not far above 20kHz.

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

The chart above represents the damping factor (DF for an 8-ohm load) of the M28 as a function of frequency. Damping factor is calculated by measuring the voltages across an 8-ohm load (V_{L}) and across no load (V_{NL}), which, in our tests, is the 200k ohms input impedance of the analyzer, and then applying the formula DF = V_{L} / (V_{NL} – V_{L}). Both channels show a general trend of a higher damping factor at lower frequencies, and lower damping factor at higher frequencies, varying by almost a factor of 2 between 20Hz and 20kHz. The left channel just barely outperformed the right (although they are very closely matched) with a peak value around 1270 at 30Hz, down to about 800 at 20kHz.

*Diego Estan*

Electronics Measurement Specialist

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

Link: reviewed by James Hale on *SoundStage! Xperience* on February 1, 2021

**General information**

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

The Music hall a15.3 was conditioned for 1 hour at 1/8th full rated power (~6W 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 a15.3 offers five sets of line-level unbalanced (RCA) inputs, one moving-magnet (MM) phono input, a set of variable line-level RCA pre-outputs, and one pair of speaker outputs. Also available is a headphone output via a 3.5mm TRS jack on the front panel. Based on the high accuracy of the left/right channel matching (see table below), the a15.3’s volume knob is not a potentiometer in the signal path, which is typically less accurate, but rather provides digital control over a proprietary or integrated analog-domain volume circuit. The a15.3’s volume control offers between 1 and 2dB step increments throughout most of the volume range. At the lowest end of the range, the first 3 steps offer 4dB increments, and the next 3 steps 3dB.

All measurements, with the exception of signal-to-noise ratio (SNR) or otherwise stated, were made with the volume set to unity gain for the preamplifier (about 3 o’clock) as measured at the pre-outputs. SNR measurements were made with the volume control set to maximum. At the unity-gain volume position, to achieve 10W into 8 ohms, 275mVrms was required at the line-level input and 2.65mVrms at the phono input.

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

Volume position | Channel deviation |

Just above minimum | 0.08dB |

9 o'clock | 0.03dB |

12 o'clock | 0.06dB |

3 o'clock | 0.04dB |

Maximum | 0.02dB |

**Published specifications vs. our primary measurements**

The tables below summarize our primary measurements performed on the a15.3. Here we can compare our results against Music Hall’s own published specifications for the a15.3, which are stated as follows:

- Rated output power: 50W into 8 ohms, 75W into 4 ohms
- Input sensitivity: 330mV (RCA), 1mV (phono)
- SNR: >90dB
- THD+N: <0.02% (20Hz-20kHz)
- Frequency response: RCA: -0.5dB (20Hz-20kHz), PHONO: RIAA compliant

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

Parameter | Left channel | Right channel |

Maximum output power into 8 ohms (1% THD+N, unweighted) | 63W | 63W |

Maximum output power into 4 ohms (1% THD+N, unweighted) | 86W | 86W |

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

Crosstalk, one channel driven (10kHz) | -69.3dB | -67.3dB |

DC offset | <-7mV | <-1mV |

Damping factor | 159 | 186 |

Clipping headroom (8 ohms) | 1dB | 1dB |

Gain (maximum - total) | 36.2dB | 36.3dB |

Gain (maximum - amplifier) | 30.2dB | 30.3dB |

Gain (maximum - preamplifier) | 6.0dB | 6.0dB |

IMD ratio (18kHz + 19kHz stimulus tones) | <-84dB | <-85dB |

Input impedance (line input) | 24.6k ohms | 24.7k ohms |

Input sensitivity (maximum volume) | 309mVrms | 308mVrms |

Noise level (A-weighted) | <240uVrms | <240uVrms |

Noise level (unweighted) | <600uVrms | <600uVrms |

Output impedance (pre out) | 101 ohms | 102 ohms |

Signal-to-noise ratio (full rated power, A-weighted) | 98.5dB | 98.5dB |

Signal-to-noise ratio (full rated power, 20Hz to 20kHz) | 96.2dB | 96.1dB |

THD ratio (unweighted) | <0.0037% | <0.0031% |

THD+N ratio (A-weighted) | <0.0047% | <0.0043% |

THD+N ratio (unweighted) | <0.0076% | <0.0073% |

Our primary measurements revealed the following using the phono-level inputs (unless specified, assume a 1kHz sinewave, 10W output, 8-ohm loading, 10Hz to 90kHz bandwidth):

Parameter | Left channel | Right channel |

Crosstalk, one channel driven (10kHz) | -64dB | -63dB |

DC offset | <7mV | <0.8mV |

Gain (default phono preamplifier) | 40.2dB | 40.3dB |

IMD ratio (18kHz and 19 kHz stimulus tones) | <-81dB | <-82dB |

IMD ratio (3kHz and 4kHz stimulus tones) | <-79dB | <-80dB |

Input impedance | 47.1k ohms | 47.1k ohms |

Input sensitivity | 3.02mVrms | 2.98Vrms |

Noise level (A-weighted) | <1200uVrms | <1200uVrms |

Noise level (unweighted) | <4000uVrms | <4000uVrms |

Overload margin (relative 5mVrms input, 1kHz) | 15.8dB | 15.6dB |

Overload margin (relative 5mVrms input, 20Hz) | -2.45dB | -2.41dB |

Overload margin (relative 5mVrms input, 20kHz) | 35.1dB | 35.0dB |

Signal-to-noise ratio (full rated power, A-weighted) | 76.9dB | 76.8dB |

Signal-to-noise ratio (full rated power, 20Hz to 20kHz) | 56.5dB | 56.8dB |

THD (unweighted) | <0.0053% | <0.0039% |

THD+N (A-weighted) | <0.017% | <0.017% |

THD+N (unweighted) | <0.18% | <0.18% |

Music Hall’s power output claims of 50 and 75WPc into 8- and 4-ohm loads were corroborated with our maximum (1% THD+N) measurements of 63Wpc and 86Wpc into 8 and 4 ohms, during which time our line AC voltage never dipped below 121VAC.

Our clipping headroom result was 1dB for the a15.3, defined as the ratio of max power over rated power into 8 ohms. The Music Hall a15.3 was also able to sustain 86Wpc (1dB over rated output) into 4 ohms using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (8.6Wpc) 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 a15.3 was very warm to the touch, causing some discomfort on the skin after 10 seconds of direct contact.

Music Hall’s input sensitivity claims (volume at maximum) were verified, where we measured 308mVrms and 3mVrms respectively for the single-end RCA and phono inputs, which are close to the 330mVrms and 1mVrms specs.

Music Hall’s 90dB SNR claim was corroborated by our own measurements, where we measured 98.5dB (A-weighted) and 96.2dB (20Hz-20kHz) for the left and right channels.

Music Hall’s THD+N claim of <0.02% (20Hz to 20kHz) was corroborated at 1KHz in our primary table; however, as our THD versus frequency graph below shows, THD ratios were above 0.02% from 6kHz to 20kHz at 10W into 8ohms.

Our primary measurements revealed the following using the line-level inputs at the headphone output (unless specified, assume a 1kHz sinewave, 2Vrms output, 300 ohms loading, 10Hz to 90kHz bandwidth):

Parameter | Left and right channels |

Maximum gain | 36.2dB |

Maximum output power into 600 ohms (1% THD+N, unweighted) | 562mW |

Maximum output power into 300 ohms (1% THD+N, unweighted) | 610mW |

Maximum output power into 32 ohms (1% THD+N, unweighted) | 175mW |

Output impedance | 330 ohms |

Noise level (A-weighted) | <58uVrms |

Noise level (unweighted) | <156uVrms |

Signal-to-noise ratio (A-weighted) | 82.4dB |

Signal-to-noise ratio (20Hz to 20 kHz) | 84.6dB |

THD ratio (unweighted) | <0.001% |

THD+N ratio (A-weighted) | <0.006% |

THD+N ratio (unweighted) | <0.013% |

Music Hall does not supply any headphone-output specifications, so there there was nothing for us to compare to.

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

In our measured frequency response plot above, the a15.3 is nearly flat within the audio band (20Hz to 20kHz) for the line-level input. These data corroborate Music Hall’s claim of 20Hz to 20kHz (-0.5dB) as the worst-case deviation is at 20kHz, where the response is about -0.2dB. At 20Hz, the response is at 0dB, and -0.5dB at 5Hz. The a15.3 can be considered a high-bandwidth audio device since the response at 100kHz is approximately +0.1dB. 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, phono input)**

The plot above shows frequency response for the phono input, and shows a maximum deviation of -1dB (20Hz, right channel) from flat within the audioband. 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, horizontal line at 0dB). Between 100Hz and 500Hz, there is a 0.2dB deviation between channels, as well as at 30Hz and below, indicating small channel-to-channel differences in the RIAA curve implementaion.

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

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

This chart is the same test as above, but the chart has been zoomed in to highlight differences. Here we find that there’s a total deviation of about 0.1 dB throughout the audioband, 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 (in this case, a Focal Chora 806, with measurements available through this link) as a load is very small, deviating by a little over 0.05dB within the flat portion of the curve (20Hz to 1kHz), 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 1kHz.

**Phase response (line-level input)**

Above is the phase response plot from 20Hz to 20kHz for the line-level input. The a15.3 does not invert polarity on the line-level input, and the plot shows very little phase shift, with a worst case of just under +30 degrees at 20kHz.

**Phase response (phono input)**

Above is the phase response plot from 20Hz to 20kHz for the phono input from 20Hz to 20kHz. 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 -60 degrees at 200Hz and 5kHz.

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

The plot above shows THD ratios at the output into 8 ohms as a function of frequency (20Hz to 20kHz) for a sinewave stimulus at the line-level input. The blue and red plots are for left and right at 1W output into 8 ohms, purple/green at 10W, and pink/orange at the full rated power of 50W. The power was varied using the volume control. All three THD plots exhibit a rise in THD above a “knee” at roughly 1.5kHz. At 1W, the THD values in the flat portion (20Hz to 1kHz) are hovering between 0.005-0.006%, then rise up to about 0.07% at 20kHz. At 10W, the flat portion shows THD ratios around 0.003%, then up to 0.06% at 20Hz. The 50W data shows the flat portion around 0.004%, rising up to just above 0.1% at 20kHz. At 50W, the right channel outperforms the left throughout the sweep by about 2dB.

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

The chart above shows the THD ratio as a function of frequency plot for the phono input measured across an 8-ohm load at 10W output. The input sweep is EQ’d with an inverted RIAA curve. The THD values vary from about 0.2% at 20Hz and 30Hz, down to about 0.003/0.005% (left/right channels) at 1kHz, then up to about 0.07/0.06% (left/right channels) at 20kHz.

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

The above chart shows THD ratios measured at the output of the a15.3 as a function of output power for the line level-input, for an 8-ohm load (blue/red lines for left/right chanels) and a 4-ohm load (purple/green for left/right). The 4-ohm data shows consistently slightly higher THD values compared to the 8-ohm data (about a 5dB difference), and the right channel outperforms the left in both plots by about 2dB. At the 50mW level, THD values measured around 0.01% (8 ohms) and 0.02% (4 ohms), dipping down to around 0.004/0.003% at 10W to 30W for the 8-ohm data, and 0.005% for the 4-ohm data from 10W to 50W. The “knee” in the 8-ohm data occurs near 50W, hitting the 1% THD mark at 63W. For the 4-ohm data, the “knee” occurs near 70W, hitting the 1% THD mark at 86W.

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

This chart shows THD+N ratios measured at the output of the a15.3 as a function of output power for the line level-input, for an 8-ohm load (blue/red lines for left/right channels) and a 4-ohm load (purple/green for left/right). The 4-ohm data shows consistently slightly higher THD+N values compared to the 8-ohm data (about a 5dB difference). At the 50mW level, THD+N values measured around 0.1% (8 ohms) and 0.15% (4 ohms), dipping down to around 0.005% at 20W to 40W for the 8-ohm data, and 0.006% for the 4-ohm data from 30 to 50W.

**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 a15.3 as a function of load (8, 4, and 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 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 difference from 20Hz to 1kHz, with a smaller degradation in THD performance (1-2dB) between 4 and 2 ohms from 1kHz to 20kHz. Overall, even with a 2-ohm load at roughly 40W, THD values ranged from 0.005% at 20Hz to just below 0.2% at 20 kHz.

**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 line-level input. As seen in the plots above, we see that the right channel (red) outperforms the left channel (blue) with slightly lower peaks. We see that the signal’s second and third harmonic, at 2kHz and 3kHz, are both at around -95dBrA, while the remaining harmonics are below -100dBRA. Below 1kHz, we see noise artifacts, with the 60Hz peak due to power-supply noise just above -110dBrA, and the 120Hz peak at -105/110dBrA (left/right channels).

**FFT spectrum – 1kHz (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. The second signal harmonic at 2kHz is at -90/-100dBRA (left/right channels), with subsequent harmonics below this level. The highest peak from power supply noise is at the fundamental (60Hz), reaching almost -55dBrA, and the third noise harmonic (180Hz) is near -75dBrA.

**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 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 peak is that of the signal’s third harmonic (150Hz) at about -95dBrA. The signal second harmonic (100Hz) is at around -100dBRA, while the noise second harmonic (120Hz) is at around -105/-110dBrA (left/right channels).

**FFT spectrum – 50Hz (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 . The most predominant peak is the noise signal’s fundamental (60Hz) at near -55dBRA. The most predominant signal harmonic peak is the third harmonic (150Hz) at -90dBrA.

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

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 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 near -105/-110dBRA (left/right channels), while the third-order modulation products, at 17kHz and 20kHz, are higher, at around -100dBrA.

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

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 phono input. Here we find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -95/-100dBrA (left/right channels), and smaller in magnitude than some of the harmonic peaks from the noise signal surrounding it. The third-order modulation products, at 17kHz and 20kHz, are at around -100dBrA.

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

Above is the 10kHz squarewave response using the 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 Music Hall’s slew-rate performance. Rather, it should be seen as a qualitative representation of it’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 a15.3’s reproduction of the 10kHz squarewave can be considered clean, with sharp edges and very mild overshoot.

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

The final plot above is the damping factor as a function of frequency. Both channels show a general trend of a higher damping factor at lower frequencies, and lower damping factor at higher frequencies (about 20% lower at 20kHz compared to 20Hz). The right channel outperformed the left with a peak value around 190 from 20Hz to 400Hz, while the left channel achieved a damping factor of around 160 within the same frequency range.

*Diego Estan*

Electronics Measurement Specialist

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

Link: reviewed by Roger Kanno on *SoundStage! Hi-Fi* on January 1, 2021

**General information**

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

The A-S3200 was conditioned for 30 minutes at 10W (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 A-S3200 offers four sets of line-level unbalanced (RCA) inputs, two sets of balanced (XLR) line-level inputs, one phono input with selectable moving-magnet (MM) and moving-coil (MC) options, a set of fixed line-level RCA outputs, a set of variable RCA pre-outs, and two pairs of speaker outputs (A and B). Based on the accuracy of the left/right channel matching (see table below) and 0.5dB volume-step resolution, I determined that the A-S3200’s volume knob is not a potentiometer in the signal path, but rather provides digital control over a proprietary or integrated analog-domain volume circuit. The balance and tone-control knobs were left in the center positions, and the speaker selection switch was left on “A.” There are also two small toggle switches behind the unit for the balanced inputs, one to invert polarity (it was left on Normal), and one to provide 6dB of attenuation (it was left on Bypass).

I attempted to optimize the volume position to achieve the best signal-to-noise (SNR) and THD+N measurements at the speaker-level outputs (8 ohms). I found very little differences with the volume at various positions (for the same output voltage). Most measurements were made with the volume set to unity gain for the preamplifier (about 12 o’clock), as measured at the pre-outputs. At this volume position, to achieve 10W into 8 ohms, 242mVrms was required at the balanced line-level input and 4/0.25mVrms at the phono input (MM/MC settings). I also found no appreciable differences in THD+N values between the balanced and single ended line-level inputs, and both yielded the same gain.

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

Volume position | Channel deviation |

Just above minimum | 0.027dB |

9 o'clock | 0.028dB |

12 o'clock | 0.021dB |

3 o'clock | 0.029dB |

Maximum | 0.033dB |

**Published specifications vs. our primary measurements**

The tables below summarize our primary measurements performed on the A-S3200. Here we can compare directly against Yamaha’s own published specifications for the A-S3200, which are stated as follows:

- Rated output power (20Hz to 20kHz, 0.07% THD): 100W into 8 ohms, 150W into 4 ohms
- Dynamic power: 120W into 8 ohms, 200W into 4ohms, 300W into 2 ohms
- Maximum effective output power (1kHz, 10% THD): 130W into 8ohms, 210W into 4 ohms
- Damping factor: >250 (8 ohms)
- Input sensitivity (1kHz, 100W/8-ohm): MC: 150uVrms, MM: 3.5mVrms, CD/BAL: 200mVrms
- Input impedance: MC: 60 ohms, MM: 47k ohms, CD: 47k ohms, BAL: 100k ohms
- Overload margin: MM: 20dB, MC: 12dB
- Headphone jack rated output power (1kHz, 32 ohms, 0.2% THD): 50mW (measured: 47mW)
- Frequency response: 5Hz to 100kHz (+0/-3dB), 20Hz to 20kHz (+0/-0.3dB)
- Deviation from RIAA: MM/MC +/-0.5dB
- THD+N (phono): MC to Line Out (ref 1.2Vrms): 0.02%, MM to Line Out (ref 1.2Vrms): 0.005% (measured: MC: <0.015%, MM: <0.001%)
- THD+N: CD/BAL to speaker out (50W/8-ohm): 0.035%
- Signal-to-noise ratio (A-weighted): MC: 90dB, MM: 96dB, CD: 110dB, BAL: 114dB
- Residual noise (A-weighted): 33uVrms
- Channel separation (1/10kHz): MC: 66/77dB, MM: 90/77dB, CD/BAL: 74/54dB

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

Parameter | Left channel | Right channel |

Maximum output power into 8 ohms (1% THD+N, unweighted) | 102W | 102W |

Maximum output power into 4 ohms (1% THD+N, unweighted) | 169W | 169W |

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

Crosstalk, one channel driven (10kHz) | -93dB | -110dB |

DC offset | 15mV | 11mV |

Damping factor | 289 | 291 |

Clipping headroom (8 ohms) | 0.086dB | 0.086dB |

Gain (maximum - total) | 43.6dB | 43.6dB |

Gain (maximum - amplifier) | 29.3dB | 29.3dB |

Gain (maximum - preamplifier) | 13.5dB | 13.5dB |

IMD ratio (18kHz + 19kHz stimulus tones) | <-71dB | <-71dB |

Input impedance (line input) | 83.6k ohms | 83.3k ohms |

Input sensitivity | 190mVrms | 190mVrms |

Noise level (A-weighted) | <85uVrms | <65uVrms |

Noise level (unweighted) | <218uVrms | <206uVrms |

Output impedance (pre out) | 1480 ohms | 1482 ohms |

Signal-to-noise ratio (full rated power, A-weighted) | 111.9dB | 112.8dB |

Signal-to-noise ratio (full rated power, 20Hz to 20kHz) | 110.3dB | 107.3dB |

THD ratio (unweighted) | <0.0085% | <0.0082% |

THD+N ratio (A-weighted) | <0.0099% | <0.0096% |

THD+N ratio (unweighted) | <0.0088% | <0.0086% |

Our primary measurements revealed the following using the phono-level inputs (MM, unless specified, assume a 1kHz sinewave, 10W output, 8-ohm loading, 10Hz to 90kHz bandwidth):

Parameter | Left channel | Right channel |

Crosstalk, one channel driven (10kHz) | -77dB | -75dB |

DC offset | -11mV | -10mV |

Gain (default phono preamplifier) | 35.9dB | 35.9dB |

IMD ratio (18kHz and 19kHz stimulus tones) | <-71dB | <-71dB |

IMD ratio (3kHz and 4kHz stimulus tones) | <-74dB | <-74dB |

Input impedance | 45.7k ohms | 45.8k ohms |

Input sensitivity | 3mVrms | 3mVrms |

Noise level (A-weighted) | <380uVrms | <850uVrms |

Noise level (unweighted) | <1200uVrms | <2800uVrms |

Overload margin (relative 5mVrms input, 1kHz) | 20.3dB | 20.3dB |

Overload margin (relative 5mVrms input, 20Hz) | 1.14dB | 1.14dB |

Overload margin (relative 5mVrms input, 20kHz) | 39.5dB | 39.4dB |

Signal-to-noise ratio (full rated power, A-weighted) | 98.1dB | 95.2dB |

Signal-to-noise ratio (full rated power, 20Hz to 20kHz) | 93.0dB | 87.2dB |

THD (unweighted) | <0.0083% | <0.0081% |

THD+N (A-weighted) | <0.0098% | <0.0128% |

THD+N (unweighted) | <0.016% | <0.032% |

Our primary measurements revealed the following using the phono-level inputs (MC, unless specified; assume a 1kHz sinewave, 10W output, 8-ohm loading, 10Hz to 90kHz bandwidth):

Parameter | Left channel | Right channel |

Crosstalk, one channel driven (10kHz) | -55.1dB | -57.7dB |

DC offset | -13mV | -12mV |

Gain (default phono preamplifier) | 60.4dB | 60.4dB |

IMD ratio (18kHz and 19kHz stimulus tones) | <-59dB | -59dB |

IMD ratio (3kHz and 4kHz stimulus tones) | <-68dB | -68dB |

Input impedance | 70 ohms | 70 ohms |

Input sensitivity | 0.18mVrms | 0.18mVrms |

Noise level (A-weighted) | <10200uVrms | <9100uVrms |

Noise level (unweighted) | <34000uVrms | <28000uVrms |

Overload margin (relative 0.5mVrms input, 1kHz) | 16.0dB | 16.0dB |

Overload margin (relative 0.5mVrms input, 20Hz) | -2.85dB | -2.90dB |

Overload margin (relative 0.5mVrms input, 20kHz) | 35.4dB | 35.3dB |

Signal-to-noise ratio (A-weighted) | 75.2dB | 76.2dB |

Signal-to-noise ratio (unweighted, 20Hz to 20kHz) | 66.7dB | 68.4dB |

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

THD+N (A-weighted) | <0.12% | <0.10% |

THD+N (unweighted) | <0.38% | <0.31% |

Yamaha’s power output claims of 100/150W into 8/4 ohms were corroborated with our maximum (1% THD+N) measurements of 102/169W into 8/4 ohms, during which time our line AC voltage never dipped below 123VAC. Yamaha’s claim of 120W of dynamic power into 8 ohms is difficult to corroborate, as they have not defined the term or the level of THD. However, their claim of effective maximum power of 130/210W into 8/4 ohms at 10% THD can be verified. Under these conditions, we measured 121/202W into 8/4 ohms, again with our line AC voltage dipping to a low of 123VAC.

The clipping headroom result of 0.086dB, defined as the ratio of max power over rated power into 8 ohms, is low. Nonetheless, the Yamaha was able to sustain 170W into 4 ohms using an 80 Hz tone for 500ms, alternating with a signal at -10dB of the peak (17.0W) for 5 seconds, for five 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 A-S3200 was warm to the touch, but not hot enough to cause discomfort.

Yamaha’s claim of a damping factor of 250 was corroborated with our measurements of 289/291 (L/R) at 1kHz (see graphs below for damping factor versus frequency).

Yamaha’s input sensitivity claims (volume at maximum) were verified, where we measured 190/3/0.18mVrms (BAL/MM/MC), which are very close to Yamaha’s 200/3.5/0.15Vrms specs. Our input impedance measurements were also very close to Yamaha’s specs of 60/47k/100k ohms for MC/MM/BAL, with our measured values of 70/46k/83k ohms. Our measured output impedance for the pre-outs was on the high side, with 1480 ohms, but Yamaha did not provide this spec.

Yamaha’s maximum input signals for the phono input of 2/50mVrms (MC/MM), which we converted to overload margins at 12/20dB (MC/MM), were corroborated and bettered with our 16/20dB measurements.

Yamaha’s THD+N (A-weighted) claims for the phono input of 0.02/0.005% (MC/MM), referenced to 1.2Vrms at the line outputs, were also corroborated, where we measured 0.015/0.001%. The THD+N values found in our tables above for the phono input are measured at 10W across an 8-ohm load at the speaker outputs, and therefore show higher THD+N values. The claim of 0.035% THD+N (A-weighted) measured with the line-level inputs at 50W (8-ohms) at the speaker outputs was corroborated, where we found 0.0099% (10W), and also measured roughly the same THD+N values at 50W.

We found one (MC) of Yamaha’s SNR claims (A-weighted) to be on the high side compared to our own measurements, although it’s not clear if for the phono inputs, the SNR values are referenced to the line-out like with the THD+N values, or the speaker outputs at the rated power of 100W. Our SNR values are referenced to 100W at 8 ohms. Yamaha has claimed 90/96/114dB (MC/MM/BAL), where we measured 76/98/113dB.

Yamaha’s residual noise value of 33uVrms (A-weighted) could not be corroborated, as we measured a still very low 85/65uVrms (L/R) at the speaker outputs for the balanced line-level input. The channel separation (or crosstalk) claims (1/10kHz) of 66/77dB, 90/77dB, 74/54dB (MC/MM/BAL) were either conservatively low, or a bit high as compared to our own worst-case measurements of 56/55dB, 78/75dB, 110/93dB.

Our primary measurements revealed the following using the balanced line-level inputs at the headphone output (unless specified, assume a 1kHz sinewave, 2Vrms output, 300 ohms loading, 10Hz to 90kHz bandwidth, gain set to “0”):

Parameter | Left and right channel |

Gain (default) | 17.8dB |

Gain (-6) | 11.8dB |

Gain (+6) | 23.8dB |

Gain (+12) | 29.9dB |

Maximum output power into 600 ohms (1% THD+N, unweighted) | 390mW |

Maximum output power into 300 ohms (1% THD+N, unweighted) | 520mW |

Maximum output power into 32 ohms (1% THD+N, unweighted) | 65mW |

Output impedance | 4.7 ohms |

Noise level (A-weighted) | <15uVrms |

Noise level (unweighted) | <42uVrms |

Signal-to-noise ratio (A-weighted) | 102dB |

Signal-to-noise ratio (20Hz to 20kHz) | 98dB |

THD ratio (unweighted) | <0.00017% |

THD+N ratio (A-weighted) | <0.00075% |

THD+N ratio (unweighted) | <0.002% |

Here, Yamaha only provided one spec of 50nW into 32 ohms at 0.2% THD. This value was validated by our measured 47mW under the same conditions.

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

In our measured frequency response plot above, the A-S3200 is perfectly flat within the audioband (20Hz to 20kHz) for the line-level input. These data corroborate Yamaha’s claims of 5Hz to 100kHz (+0/-3dB) and 20Hz to 20kHz (+0/-0.3dB) for the line-level input. The A-S3200 is at about -0.1dB at 5Hz, and -3dB at about 150kHz. The A-S3200 can be considered a high-bandwidth audio device. 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 perfectly overlap, indicating that the two channels are ideally matched.

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

The plot above shows left- and right-channel frequency response for the phono input (MM and MC behaved the same), and shows a maximum deviation of +0.5dB from flat within the audio band. What is shown is the deviation from the RIAA curve, where the input signal sweep is EQd with an inverted RIAA curve supplied by Audio Precision (*i.e.*, no deviation would yield a flat line at 0dB). This corroborates Yamaha’s claim of a worst-case RIAA deviation of +/-0.5dB.

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

Above are two frequency response plots for the balanced line-level input, measured at 10W (8-ohm) at the speaker outputs, with the treble/balance controls set at both minimum and maximum. They show that the A-S3200 will provide a maximum gain/cut of approximately 9dB at 20Hz, and a maximum gain/cut of approximately 8dB at 20kHz.

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

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

This plot is the same test but the chart has been zoomed in on the y-axis to highlight differences. Here we find that there’s a total deviation of less than 0.1dB in the flat portion of the curve, which is an indication of a high damping factor, or low output impedance. At the frequency extremes (20Hz and 20kHz), the spread is close to the same. The maximum variation in RMS level when a real speaker was used as a load is very small, deviating by about 0.05dB 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 2-3kHz.

**Phase response (line-level input)**

Above is the phase response plot from 20Hz to 20kHz for the balanced line-level input. The A-S3200 does not invert polarity on the line-level input, and the plot shows very little phase shift, with a worst case of just under +20 degrees at 20kHz.

**Phase response (phono input)**

Above is the phase response plot from 20Hz to 20kHz for the phono input (blue/red traces for the MM setting, purple/green traces for the MC setting) from 20Hz to 20kHz. With the MC setting, polarity appears to be reversed, as there is an almost 180 degree difference between the MM and MC phase plots. 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 -50 degrees at 200Hz and 5kHz for the MM setting, with the MC setting following roughly the same trend, but with an extra 180 degrees of phase shift (*i.e.*, just above -250 degrees at 200Hz and 5kHz.

**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 (20Hz to 20kHz) for a sinewave stimulus at the balanced 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 full rated power of 100W. The power was varied using the volume control. At 1W and 10W, the THD values are quite close, with the 1W figures slightly outperforming the 10W figures by about 2-3dB. The general trend of the lower THD figures from 20Hz to 1kHz (between 0.005% and 0.007%), with higher figures at frequencies above 1kHz (0.02% to 0.025% at 20kHz), was consistent for both the 1W and 10W data. The 100W data shows considerably higher THD values, and a 5dB disparity between channels. In general, the THD values hovered between 0.2% to 0.5% at 100W, and decreased down to between 0.1% to 0.2% at 20kHz.

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

This is a THD ratio as a function of frequency plot for the phono input measured across an 8-ohm load at 10W. The blue/red traces represent the MM setting, the purple and green the MC setting. The input sweep is EQ’d with an inverted RIAA curve. The THD values vary from about 0.05% at 20Hz, down to about 0.007% from 200Hz to 1kHz for the MM setting, then up to about 0.03% at 20kHz. The MC setting performed considerable worse at lower frequencies (20Hz to 1kHz), with large fluctiations; between about 0.6% and 0.01%. Above 1kHz, both MM and MC settings yielded very close THD values.

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

The plot above shows THD ratios measured at the output of the A-S3200 as a function of output power for the balanced line level-input, for an 8-ohm load (blue/red for left/right) and a 4-ohm load (purple/green for left/right). The 4-ohm data shows consistently higher THD values compared to the 8-ohm data (about a 5dB difference). At the 50mW level, THD values measured around 0.002% (8 ohms) and 0.004% (4 ohms), rising up to around 0.006% at 10W to 90W for the 8-ohm data, and 0.01% for the 4-ohm data. The “knee” in the 8-ohm data occurs at around 90W, hitting the 1% THD mark just above the rated output of 100W (102W). For the 4-ohm data, the “knee” occurs near 150W, hitting the 1% THD mark at 169W.

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

The plot above shows THD+N ratios measured at the output of the A-S3200 as a function of output power for the balanced line level-input, for an 8 ohm load (blue/red for left/right) and a 4-ohm load (purple/green for left/right). The 4-ohm data shows consistently slightly higher THD+N values compared to the 8-ohm data (about a 5dB difference). At the 50mW level, THD+N values measured around 0.03% (8 ohms) and 0.04% (4 ohms), dipping down to around 0.007% at 30 to 90W for the 8-ohm data, and 0.01% for the 4-ohm data from 50 to about 150W.

**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 A-S3200 as a function of load (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 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 ohms, with about a 5dB difference, and almost no degradation in THD performance between 4 and 2 ohms. Overall, even with a 2 ohms load at roughly 40W, THD values ranged from 0.015% at 20Hz to just above 0.04% at 20kHz.

**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 line-level input. We see that the signal’s second harmonic, at 2kHz, is at -100/-110dBrA (L/R), while the third harmonic, at 3kHz, is higher, at -85dBrA. The fifth harmonic is at -100dBrA, and the other harmonics measured lower. Below 1kHz, we see noise artifacts, with the 60Hz peak due to power-supply noise just above (R) and below (L) -110dBrA, and the 120Hz peak at -100dBrA. The third order harmonic at 180Hz is still quite predominant, at just below -100dBrA.

**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 with MM selected. The odd signal harmonics dominate, with the 3kHz peak sitting at -85dBrA, and the 5kHz peak just above -100dBrA. The highest peak from power-supply noise for the MM setting is at the third harmonic (180Hz), reaching almost -70dBrA for the right channel, and -85dBrA for the left channel. Again, the odd-harmonic (*i.e.*, 180, 300, 420Hz, . . .) noise peaks are the ones that dominate the FFT, and can be found both below and above 1kHz.

**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 with MC selected. The odd harmonics from the 60Hz peak (*i.e.*, 180, 300, 420Hz, . . .) dominate the entire FFT spectrum, with the left channel yielding slightly higher results. At 180Hz, the peak is nearing -50dBrA. Even the 2kHz peak (second harmonic of 1kHz signal), at around -85dBrA, is drowned out by the 33rd 60Hz harmonic (1980Hz) peak at around -80dBrA.

**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 balanced line-level 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 harmonic peak is that of the signal’s third harmonic (150Hz) at about -85dBrA. The signal second harmonic (100Hz), the noise second (120Hz) and third harmonic (180Hz), are all around -100dBrA.

**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 with MM selected. The most predominant harmonic peak is noise signal’s third harmonic (180Hz) at about -85/-75dBrA (L/R). The most predominant signal harmonic peak is the third harmonic (150Hz) at -85dBrA.

**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 with MC selected. The most predominant harmonic peak is the noise signal’s third harmonic (180Hz) at about -50dBrA. The most predominant signal harmonic peak is the third harmonic (150Hz) at -85dBrA, barely peaking above the noise floor.

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

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 balanced 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 -100/-115dBrA (L/R), while the third-order modulation products, at 17kHz and 20kHz are much higher, at around -85dBrA.

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

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 phono input with MM selected. Here we find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -100/-105dBrA (L/R), and smaller in magnitude than the harmonic peaks from the noise signal surrounding it. The third-order modulation products, at 17kHz and 20kHz dominate, at around -85dBrA.

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

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 phono input with MC selected. Here we find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is just above -70dBrA (L/R), and very close in magnitude to the odd harmonic peaks from the noise signal surrounding it. The third-order modulation products, at 17kHz and 20kHz dominate, at around -85dBrA.

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

Above is the 10kHz squarewave response using the balanced 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 Yamaha’s slew-rate performance. Rather, it should be seen as a qualitative representation of its 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 A-S3200’s reproduction of the 10kHz squarewave can be considered clean, with sharp edges devoid of undershoot and overshoot.

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

The final plot above is the damping factor as a function of frequency. Both channels show a general trend of a higher damping factor at lower frequencies, and lower damping factor at higher frequencies, with roughly a factor of 2x difference at 30Hz compared to 20kHz. Both channels’ damping factors tracked very closely, with a peak value just over 300 at around 30Hz, and a low value around 150 at 20kHz.

*Diego Estan*

Electronics Measurement Specialist

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

Link: reviewed by Roger Kanno on *SoundStage! Hi-Fi* on December 15, 2020

**General information**

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

The EX-M1+ was conditioned for 30 minutes at 10W (8 ohms) before any measurements were taken. All measurements were taken with both channels driven, at 10W into 8 ohms, unless otherwise stated. Maximum power, continuous rated power, and THD+N versus output power measurements were taken with the EX-M1+ connected to a dedicated 120V/20A circuit.

The EX-M1+ uses a digitally controlled, analog-domain volume control, implemented with an integrated circuit (IC) from Muses. The volume can be adjusted from 0 to 100 in 1dB increments, though maximum volume is reached at position 90 – varying the volume from 90 to 100 does not further increase signal amplitude.

We attempted to optimize the volume position to achieve the best signal-to-noise ratio (SNR) and THD+N measurements at the speaker-level outputs (8-ohm loading). Typically, volume set to unity gain is a good starting point. In the case of the EM-X1+, we found better THD+N values with the volume set to 69 as opposed to 86. Most primary measurements and graph data are collected with 10W output into an 8-ohm load. For these measurements, unless otherwise specified, the volume control was set to 69. At this position, 2.1Vrms was required at the balanced input to achieve 10W into 8 ohms.

The EX-M1+ offers one set of balanced (XLR) and three sets of unbalanced (RCA) inputs. Unless otherwise specified, balanced input connections were used for all measurements. With the exception of gain, no significant differences were seen between unbalanced and balanced inputs. There are two toggle switches on the back panel of the EX-M1+, one to lift the signal ground from chassis ground (left on “link” position), the other to engage DC filtering (left on). Neither switch had any effect on THD+N results.

There is a 6dB difference in gain at the output between the balanced and unbalanced inputs. We found volume setting 86 yielded unity gain (+0.29dB) at the unbalanced preamplifier outputs. With the balanced inputs, maximum volume yielded -1.2dB of gain at the preamplifier outputs. The volume control provides a total range of gain (as measured at the preamplifier outputs) from -84dB (volume position 1) to +4.8dB using the unbalanced inputs, and from -90dB to -1.2dB for the balanced inputs.

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

Volume position | Channel deviation |

1 | 0.06dB |

10 | 0.08dB |

30 | 0.015dB |

50 | 0.035dB |

70 | 0.001dB |

80 | 0.013dB |

100 | 0.001dB |

**Published specifications vs. our primary measurements**

The table below summarizes our primary measurements performed on the EX-M1+. Here we can compare directly against Kinki Studio’s own published specifications for the EX-M1+, which are stated as follows:

- Frequency response: 10-150kHz (±3dB)
- THDN: 0.0232%; 0.006% (A-Weighted)
- S/N ratio: >103dB
- Output power: 215W (8Ω and 4Ω)*, both channels driven
- Damping factor: 2000
- Gain: Normal Gain 26dB
- Max output voltage: 55VAC
- Input sensitivity: 2.25Vrms - 3.6Vrms
- Input impedance: 50k ohms

* Kinki Studio originally specified the EX-M1+ at 215W (8Ω) and 400W (4Ω). They have recently amended the specification to 215W (8Ω and 4Ω)

Our primary measurements revealed the following using the balanced input (unless specified, assume a 1kHz sinewave, 10W output, 8-ohm loading, and 10Hz to 90kHz bandwidth):

Parameter | Left channel | Right channel |

Maximum output power into 8 ohms (1% THD+N, unweighted) | 208W | 208W |

Maximum output power into 4 ohms (1% THD+N, unweighted) | 290W | 290W |

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

Crosstalk, one channel driven (10kHz) | -92.3dB | -90.0dB |

DC offset | -7.5mV | -17mV |

Damping factor | 378 | 411 |

Clipping headroom | -0.14dB | -0.14dB |

Gain (maximum, unbalanced input – total) | 39.8dB | 39.8dB |

Gain (maximum, balanced input – total) | 33.8dB | 33.8dB |

Gain (amplifier, HT bypass input) | 32.9dB | 32.9dB |

Gain (maximum, unbalanced input – preamplifier) | +4.8dB | +4.8dB |

Gain (maximum, balanced input – preamplifier) | -1.2dB | -1.2dB |

IMD ratio (18kHz + 19kHz stimulus tones) | <-72dB | <-72dB |

Input impedance | 193k ohms | 190k ohms |

Input sensitivity (HT bypass input to reach 182W) | 870mVrms | 870mVrms |

Noise level (A-weighted) | <183uVrms | < 200uVrms |

Noise level (unweighted) | <720uVrms | < 640uVrms |

Output impedance (preamplifier outputs) | 76 ohms | 76 ohms |

Signal-to-noise ratio (full rated power, A-weighted) | 103.2dB | 102.1dB |

Signal-to-noise ratio (full rated power, 20Hz to 20kHz) | 91.6dB | 98.1dB |

THD ratio (unweighted) | <0.015% | <0.013% |

THD+N ratio (A-weighted) | <0.017% | <0.016% |

THD+N ratio (unweighted) | <0.017% | <0.015% |

Our unweighted THD+N measurement of <0.017% corroborates Kinki Studio’s value of 0.0232%; however, the 0.006% A-weighted value provided by the manufacturer was not substantiated by our measurement of 0.017%. When A-weighted THD+N values are very similar to those measured at full bandwidth (in our case 10Hz to 90kHz), it is an indication that the noise component is low, and the THD component dominates. This is illustrated in our THD measurements, which are just below our THD+N measurements.

Kinki Studio’s signal-to-noise ratio (SNR) claim of >103dB was corroborated by our 103.2dB/102.1dB (L/R) A-weighted SNR measurements. In terms of maximum power output, we measured 208W (1% THD+N unweighted) into 8 ohms (both channels driven) and 290W into 4 ohms, which is slightly below the company’s 8-ohm specification (215Wpc) and well above their 4-ohm specification of equal value. For this test, the line AC voltage never dipped below 123VAC. When we performed this same test on another day, we did manage to squeeze out 216W into 8 ohms (both channels driven) from the EX-M1+; however, during the test, the AC line voltage never dipped below 126VAC, which was 3V higher than the first time.

The 208W (8 ohms) measurement yields a clipping headroom result of -0.14dB (8 ohms). Nonetheless, the EX-M1+ was able to sustain 208W using an 80Hz tone into 8 ohms for 500ms, alternating with the same signal at -20dB of the peak (2.08W) for five seconds, for five 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.

Kinki Studio’s damping factor claim of 2000 is also quite a bit higher than our measured values of 378 (left channel) and 411 (right channel). Nevertheless, our measured values are high and translate to a very low output impedance of about 0.02 ohms. A full damping factor versus frequency plot can be found below.

Kinki Studio’s maximum output voltage claim of 55VAC is difficult to decipher. It is likely a measure of the output voltage, measured with no load, when 1% THD+N is reached. Under these conditions, we measured close to the claimed value at 51Vrms (VAC and Vrms are synonyms).

For the gain and input impedance/sensitivity specs, our measurements were all quite different than what the manufacturer provided; however, our measured results are not problematic. We measured 32.9dB of gain in the amplifier (HT bypass input) compared to the claimed 26dB, with an input sensitivity of 870mVrms compared to the claimed 2.25 to 3.6Vrms. Our input impedance measurement (balanced input) came in at 190k ohms, well above Kinki Studio’s 50k ohms.

**Frequency response (8-ohm loading)**

In our measured frequency response plot above, the EX-M1+ is essentially perfectly flat within the audio band (20Hz to 20kHz). Therefore, Kinki Studio’s claim of +/-3dB from 10Hz to 150kHz is corroborated by our measurement. The EX-M1+ is at about -0.1dB at 10Hz and no worse than +0.3dB at 150kHz. As a result, the EX-M1+ can be considered a high-bandwidth audio device. In the graph above and most of the graphs below, only a single trace may be visible, which 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.

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

The chart above shows RMS level (relative to 0 dBrA, which is 1W into 8 ohms or 2.83Vrms) as a function of frequency, for the balanced input swept from 5Hz to 100kHz. The blue line is into an 8-ohm load, the purple line is into a 4-ohm load, the pink line is an actual speaker (Focal Chora 806, measurements can found here), and the cyan line is no load connected to the EX-M1+. The top graph shows that all four plots are tightly bunched together, only deviating above 30kHz. This is an indication of a high damping factor, with a correspondingly low output impedance.

The chart above shows the same data, but with the vertical axis expanded to show differences. Here we find that there’s a total deviation of only 0.05dB in the flat portion of the curve between 4 ohms and no load. At the frequency extremes (20Hz and 20kHz), the spread is essentially the same at 20Hz compared to the flat portion of the curve, and about 0.09dB at 20kHz. The maximum variation in RMS level when a real speaker was used as a load is very small, deviating by less than 0.04 dB within almost the entire audio band (-0.06dB at 20kHz relative to 2kHz). The lowest RMS level, which would correspond to the lowest impedance point for the load, was exhibited at around 50Hz and 200Hz, and the highest RMS level, which would correspond to the highest impedance point for the load, was seen between 2 and 4kHz.

**Phase response**

Above is the phase response plot for the EX-M1+, from 20Hz to 20kHz. The EX-M1+ does not invert polarity, and there is virtually no phase shift throughout the audio band, with a worst case of under +5 degrees at 20Hz.

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

The chart above shows THD ratios with 8-ohm loading as a function of frequency (20Hz to 20kHz) for a sinewave stimulus at the line level input. The blue and red lines are for left and right channels at 1W output, purple/green at 10W, and pink/orange at 143W (all into 8 ohms). The power was varied using the EX-M1+’s volume control. At 1W and 10W, the THD values are quite close, with the 1W figures slightly outperforming the 10W figures by a few dB at 1kHz and below, and by as much as 10dB at 20kHz. The general trend of the lowest THD figures appearing at lower frequencies (between 0.01% and 0.02%), with higher figures at high frequencies (0.05% to 0.1% at 20kHz), was consistent for both the 1W and 10W data. The 143W data showed higher THD values, with the same general trend as the lower-output power data, but ranging in values from 0.02% (20Hz to 300Hz) to 0.4% at 20kHz.

**THD ratio (unweighted) vs. output power at 1kHz into 4/8 ohms (volume at 86, 10mV to 4V input)**

The chart above shows THD ratios measured at the output of the EX-M1+ as a function of output power for the balanced input, as well as for 8-ohm (blue/red for left/right channels) and 4-ohm (purple/green for left/right) loading. The 4-ohm data shows consistently slightly higher THD values compared to the 8-ohm data (about a 5dB difference). At the 50mW level, THD values measured around 0.01% (8 ohms) and 0.02% (4 ohms), then a slow and steady increase to 0.02% at 8 ohms and 0.03% at 4 ohms. The “knee” in the 8-ohm data occurs around 160W, hitting the 1% THD around 210W. For the 4-ohm data, the “knee” occurs at around 220W, hitting 1% THD around 300W.

**THD+N ratio (unweighted) vs. output power at 1kHz into 4/8 ohms (volume at 86, 10mV to 4V input)**

The chart above shows THD+N ratios measured at the output of the EX-M1+ as a function of output power for the line-level input, for 8-ohm (blue/red for left/right channels) and 4-ohm (purple/green for left/right) loading. The 4-ohm data shows consistently slightly higher THD+N values compared to the 8-ohm data (about a 2-5dB difference). At the 50mW level, THD+N values measured around 0.5% (8 and 4 ohms), then a steady derease to 0.02% at 8 ohms (10-50W) and 0.03% at 4 ohms (10-100W).

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

The chart above shows THD ratios measured at the output of the EX-M1+ as a function of load (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 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 difference between each. Each trace shows a distinct rise in THD from 1kHz to 20kHz, at best rising from 0.015% to 0.1% for the 8-ohm load, and at worst, rising from 0.05% to 0.3% for the 2-ohm load.

**FFT spectrum – 1kHz**

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. We see that the second harmonic, at 2kHz, is just above -80dBrA (relative to the reference 0dB signal), while the third harmonic, at 3kHz, is at about -95dBrA. The even-order harmonics are higher in amplitude than the odd order, with the fourth harmonic at 4kHz sitting just below -90 dBRa, but higher than the 3kHz distortion product. Below 1kHz, we see noise artifacts, with the 60Hz peak due to power supply noise at around -90dBrA, and the 120Hz peak just exceeding the 60Hz peak at -85dBrA. The third- and fourth-order harmonics from the power-supply noise at 180 and 240Hz are both at around -95dBrA.

**FFT spectrum – 50Hz**

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W. 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 of the 50Hz signal (100Hz) dominates at -80dBrA with the second-highest distortion artifact resulting from the 60Hz power-supply noise second harmonic at 120Hz at around -85dBrA. The 180Hz peak (third harmonic due to noise), 200Hz peak (fourth harmonic from signal), and 240Hz peak (fourth harmonic from noise) are all residing around -95dBrA.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus)**

Shown above is the FFT of the intermodulation (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone at the balanced 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 approaching -80dBrA, while the third-order modulation products, at 17kHz and 20kHz are almost as high, at around -85dBrA.

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

Above is the 10kHz squarewave response of the EX-M1+ using the balanced input, at 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 EX-M1+’s slew-rate performance. Rather, it should be seen as a qualitative representation of the EX-M1+’s 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 wave’s edges. The Kinki Studio’s reproduction of the 10kHz squarewave is very clean, with sharp edges, with minimal overshoot in the corners.

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

The final plot above is the damping factor of the EX-M1+ as a function of frequency. Both channels show a general trend of a higher damping factor at lower frequencies, and lower damping factor at higher frequencies, varying by almost a factor of 2 between 20Hz and 20kHz. The right channel outperformed the left channel, with a peak value around 425 around 30Hz, while the left channel peaked around 391 at the same frequency.

*Diego Estan*

Electronics Measurement Specialist

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

Link: reviewed by Doug Schneider on *SoundStage! Hi-Fi* on August 1, 2020

**General Information**

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

The H95 was conditioned for 30 minutes at 10W (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 H95 offers two sets of line-level unbalanced (RCA) inputs, one set of unbalanced variable line outputs, and six digital inputs (three optical, one coaxial, one USB, one Ethernet). For the purposes of these measurements, the following inputs were evaluated: digital coaxial, analog (RCA) line-level.

We attempted to optimize the volume position to achieve the best signal-to-noise ratio (SNR) and THD+N measurements at the speaker outputs (8 ohms) for both analog and digital inputs. For all analog input primary measurements (unless otherwise specified), the best measurements were achieved with the volume was set to 99. At a volume setting of 99, 240mVrms was required at the input for 10W (8 ohms) at the output. For the digital input, we found a volume setting of 59 yielded 10W (8 ohms) at the output for a 0dBFS input. We found essentially no differences between the optical and coaxial S/PDIF inputs, as well as the USB input, in terms of THD+N.

Based on the accuracy of the left/right volume channel matching (see table below), the H95 volume control is likely digitally controlled in the analog domain. The volume range is 0 to 99, in increments of 1-3dB from 0 to 9, and of 1dB from 9 to 99. Beyond volume level 58, every second volume increment has no effect. When the volume is set to 99 (maximum), at the variable RCA outputs, there is a gain of -0.57dB (almost unity) for the analog inputs. For the digital inputs, 2.35Vrms was measured at the variable RCA outputs (volume at maximum) for a 0dBFS input, with a 16-bit and 24-bit input bit depth dynamic range (AES17 method, A-weighted) of 96dB and 110dB, respectively.

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

Volume position | Channel deviation |

1 | 2.045dB |

5 | 0.165dB |

10 | 0.134dB |

30 | 0.140dB |

50 | 0.125dB |

70 | 0.088dB |

80 | 0.030dB |

99 | 0.000dB |

**Published specifications vs. our primary measurements**

The table below summarizes the measurements published by Hegel for the H95 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 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 channel.

Parameter | Manufacturer | SoundStage! Lab |

Amplifier rated output power into 8 ohms (1% THD) | 60W | 69W |

Frequency response | 5Hz-100kHz | 5Hz-100kHz (-1/-2dB) |

Signal-to-noise ratio (A-weighted) | >100dB | 111dB |

Crosstalk (1kHz) | <-100dB | -84dB |

THD (25W/8ohm/1kHz) | <0.01% | <0.006% |

Intermodulation distortion (19kHz+20kHz) | 0.01% | 0.018% |

Damping factor | >2000 | 403 |

Our primary measurements revealed the following using the analog line-level input, and the coaxial digital input (unless specified, assume a 1kHz input sinewave at 240mVrms 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) | 69W | 69W |

Maximum output power into 4 ohms (1% THD+N, unweighted) | 97W | 97W |

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

Crosstalk, one channel driven (10kHz) | -83.0dB | -86.3dB |

DC offset | -26mV | -45mV |

Damping factor | 522 | 403 |

Clipping no-load output voltage (instantaneous power into 8 ohms) | 30.5Vrms (117W) | 30.5Vrms (117W) |

Gain (maximum - total) | 31.5dB | 31.4dB |

Gain (maximum - preamplifier) | -0.57dB | -0.57dB |

IMD ratio (analog in, 18kHz + 19kHz stimulus tones) | <-75dB | <-75dB |

Input impedance (line input) | 55.6k ohms | 55.6 kohms |

Input sensitivity (for rated power, maximum volume) | 590mVrms | 590mVrms |

Noise level (analog in, A-weighted) | <77uVrms | <77uVrms |

Noise level (analog in, unweighted) | <350uVrms | <370uVrms |

Output impedance (line out) | 828 ohms | 825 ohms |

Signal-to-noise ratio (analog in, full power, A-weighted) | 110.7dB | 110.9dB |

Signal-to-noise ratio (analog in, full rated power, 20Hz to 20kHz) | 102.9dB | 106.9dB |

Dynamic Range (full power, A-weighted, digital 24/96) | 106.0dB | 105.4dB |

Dynamic Range (full power, A-weighted, digital 16/44.1) | 95.6dB | 95.6dB |

THD ratio (analog in, unweighted) | <0.0047% | <0.0057% |

THD ratio (unweighted, digital 24/96) | <0.0080% | <0.0082% |

THD ratio (unweighted, digital 16/44.1) | <0.0078% | <0.0080% |

THD+N ratio (analog in, A-weighted) | <0.0053% | <0.0064% |

THD+N ratio (digital in 24/96, A-weighted) | <0.0084% | <0.0099% |

THD+N ratio (digital in 16/44.1, A-weighted) | <0.0084% | <0.0096% |

THD+N ratio (anaolog in, unweighted) | <0.0058% | <0.0069% |

Minimum observed line AC voltage | 122.9VAC | 122.9VAC |

For the continuous dynamic power test, the H95 was able to sustain 96W (1% THD) into 4 ohms using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (9.6W) 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 H95 was quite warm to the touch, but not hot enough to induce pain.

Our primary headphone measurements revealed the following using the analog line-level input (unless specified, assume volume at 99, 1kHz sinewave, 2Vrms output, 300-ohm loading, 10Hz to 90kHz bandwidth):

Parameter | Left and right channels |

Maximum gain | 17.7dB |

Maximum output power into 600 ohms (1% THD+N, unweighted) | 59mW |

Maximum output power into 300 ohms (1% THD+N, unweighted) | 97mW |

Maximum output power into 32 ohms (1% THD+N, unweighted) | 112mW |

Output impedance | 77 ohms |

Noise level (A-weighted) | <28uVrms |

Noise level (unweighted) | <80uVrms |

Signal-to-noise ratio (A-weighted) | 96dB |

Signal-to-noise ratio (20Hz to 20 kHz) | 96dB |

THD ratio (unweighted) | <0.0027% |

THD+N ratio (A-weighted) | <0.0033% |

THD+N ratio (unweighted) | <0.0045% |

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

In our measured frequency response plots above, the H95 is just under -1dB at 5Hz (better than -0.2dB at 20Hz), and just under -2dB at 100kHz (better than -0.2dB at 20kHz). While Hegel does not include “-dB” points in their specifications, this measurement clearly demonstrates that the H95 is a wide-bandwidth (in audio terms) product, corroborating the manufacturer’s claim of a frequency response of 5Hz to 100kHz. 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)**

Shown above is the phase response of the H95 from 20Hz to 20kHz, using the analog input measured across the speaker outputs at 10W into 8 ohms. The H95 does not invert polarity. The plot is clean, with only +20 degrees of phase shift at 20kHz, and less than +10 degrees at 20Hz.

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

The chart above shows the H95’s frequency response as a function of input type. The blue trace is the same analog input data from the previous chart. The red trace is for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz, the purple trace is for a 24/96 dithered digital input signal from 5Hz to 48kHz, and finally green is 24/192 from 5Hz to 96kHz. The behavior at low frequencies is the same across input types—better than -0.2dB at 20Hz. The 16/44.1 digital input exhibits a sharp brick-wall-type attenuation near the limit of its theoretical frequency range (22.05kHz), with the “knee” at roughly 18kHz (-1.5dB at 20kHz). The 24/96 digital input also exhibits a sharp brick-wall-type attenuation near the limit of its frequency range (48kHz), with the “knee” at roughly 35kHz. The 24/192 digital input frequency response is nearly identical to the 24/96 plot, despite the extended theoretical range up to 96kHz, which indicates that the H95 may be downsampling 24/192 data to 24/96.

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

The chart above shows the results of a linearity test for the coaxial digital input (the optical input performed identically) for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the line level output. 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 digital input types performed similarly, approaching the ideal 0dB relative level at -100 dBFS, then yielding perfect results from -96dBFS to 0dBFS. At -120dBFS, both channels at 16/44.1 overshot the ideal output signal amplitude by about 4dB, while the left/right channels at 24/96 undershot by 3 and 1dB respectively.

**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 outputs of the H95. We can see that the H95 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 outputs of the H95. 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. 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 -144dBFS 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.

We see a few peaks in the audioband just below -110dbFS, the rest are below -130dBFS. This is a good J-Test result, and an indication that the H95 DAC has good jitter immunity. When sinewave jitter was injected at 2kHz, which would manifest as sidebands at 10kHz and 14kHz without any jitter rejection, no further peaks, or worsening of existing peaks, were observed up to a significant 600ns of jitter level, beyond which the H95 DAC lost sync with the signal.

**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 outputs of the H95. We see very small peaks in the audioband at -120to 130dBFS. This result and the results of the jitter-rejection test are essentially identical to the coaxial input.

**Wideband FFT spectrum of white noise and 19.1kHz sinewave tone (coaxial input)**

The chart above shows a fast Fourier transform (FFT) of the H95’s line-level outputs with white noise at -4dBFS (blue/red), plus a 19.1kHz sinewave 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. The aliased image at 24kHz and the reciprocal alias at 15kHz are down below -110 dBrA, or 0.0003%. The second, third, and fourth distortion harmonics (38.2, 57.3, 76.4kHz) of the 19.1kHz tone are much higher in amplitude, lying between -70 and -80dBrA, or 0.003% and 0.001%, respectively.

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

The plots above show RMS level (relative to 0dBrA, which is 1W into 8ohms or 2.83Vrms) as a function of frequency, for the analog 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 is an actual speaker (Focal Chora 806, measurements can found here), and the cyan is no load connected. The chart below . . .

. . . is the same but zoomed in to highlight differences. Zoomed in, within the flat portion of the plot, at 1kHz, the deviation from a 4-ohm load to no load is about 0.03dB. At the frequency extremes (20Hz and 20kHz), the spread is larger, between 0.06 to 0.08dB. This 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 also very small, deviating by just under 0.04dB within the flat portion of the curve (100Hz to 5kHz), with the lowest RMS level, which would correspond to the lowest impedance point for the load, exhibited at 100Hz, and the RMS highest level, which would correspond to the highest impedance point for the load, at around 4kHz.

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

The chart above shows THD at the H95’s output as a function of frequency (20Hz to 20kHz) for a sinewave stimulus at the analog 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 full rated power of 60W. The power was varied using the H95’s volume control. At 1W and 10W, the THD values are quite close, with the 10W figures slightly outperforming the 1W figures, especially at the lowest frequencies (0.01% vs 0.02% for the left channel). The general trend of the lowest THD figures appearing between about 300Hz to 1kHz (around 0.005%), with higher figures at both low and high frequencies (0.025% at 20kHz at worst) was consistent for both the 1W and 10W data. The 60W data showed much higher THD values, with a general trend of lower figures at 20Hz (0.3%), then rising with frequency and peaking at just below 2% near 20kHz.

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

The chart above shows THD ratios measured at the output as a function of output power, for an 8-ohm load (blue/red for left/right) and a 4-ohm load (purple/green for left/right). The 4-ohm data shows consistently higher THD values compared to the 8-ohm data (about a 5 dB difference). THD ratio values are fairly steady from 10mW to the “knee” for both 8-ohm and 4-ohm data. The 8-ohm values hover between 0.01% and 0.005%, trending towards lower values with increased output power, while the 4-ohm values are largely between 0.02% and 0.01%. The “knee” in the 8-ohm data occurs around 40W, hitting the 1% THD mark at 69W, just above the rated output of 60W. For the 4-ohm data, the “knee” occurs just above 60W, hitting the 1% THD at 97W.

**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 as a function of output power, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right). The 4-ohm data shows consistently higher THD values compared to the 8-ohm data (about a 4-5 dB difference). THD+N ratio values start at 0.1/0.15% (8/4 ohms) at 10mW, then down to 0.006/0.008% (8/4 ohms) at 30/40W (8/4ohms).

**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 H95 as a function of load (8/4/2 ohms), for a constant input voltage that yielded 5W at the output into 8 ohms (and roughly 10W into 4 ohms, and 20W into 2 ohms). 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 difference between 8 and 4 ohms above 1kHz (and very close tracking below 1kHz), and a 40-15dB difference between 4 and 2 ohms from 20Hz to 20kHz, with the largest differences in THD exhibited at lower frequencies, where at 2 ohms and roughly 20W, the H95 exhibits 2% THD at 20Hz.

**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 H95 as a function of load (8/4/2 ohms), for a constant input voltage that yielded 5W at the output into 8 ohms (and roughly 10W into 4 ohms, and 20W into 2 ohms). 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 difference between 8 and 4 ohms above 1kHz (and very close tracking below 1kHz), and a 40-15dB difference between 4 and 2 ohms from 20Hz to 20kHz, with the largest differences in THD exhibited at lower frequencies, where at 2 ohms and roughly 20W, the H95 exhibits 2% THD at 20Hz.

**THD+N (unweighted) vs. output level at 1kHz for line outputs (analog and digital)**

The chart above shows THD+N versus output voltage measured at the variable line-level outputs of the H95, with the volume set to 99 (-0.5dB of gain at the line outputs). The blue/red traces (left/right channels) are for the analog input, swept from 0.2mVrms to 2.4Vrms, while the purple/green traces (left/right) are for a dithered 24/96 digital signal fed to the coaxial input swept from -90dBFS to 0dBFS. We find that the analog input outperformed the DAC section by about 8dB up until about 650mVrms at the output. Above this point, THD+N values jump up from 0.002% to 0.06% (left channel) for the analog input, and from 0.005% to the same 0.06% (left channel) for the DAC input. The right channel faired better at about 0.03% at 2Vrms out. This behaviour of more than a 20dB increase in THD+N between 0.6 and 2Vrms is curious; however, in most home-use cases, analog levels from the variable line outputs of the H95 driving most power amplifiers would not exceed 0.6Vrms.

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

Shown above are FFTs for a 1kHz 0dBFS dithered 16/44 input sinewave stimulus at the coaxial digital input, measured at the output across an 8-ohm load at 10W. We see that the second through fifth harmonics, at 2,3,4, and 5kHz, are between -80dBrA, or 0.01%, and -100dBrA, or 0.001%. The highest peak is for the odd third harmonic, just below -80dBrA. The other harmonics within the audio band measured lower, below -100dBrA, down to about -125dBRa, or 0.00006% at 20kHz. Below 1kHz, we see noise artifacts, with the 60Hz peak reaching -85dBrA (left), or 0.006%, and -120dBrA (right), or 0.0001%. The second noise harmonic (120Hz) is at -105dBrA (left), or 0.0006%, and -95dBrA (right), or 0.002%. The higher harmonics of these two peaks can also be seen at lower levels.

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

Shown above are FFTs for a 1kHz 0dBFS dithered 24/96 input sinewave stimulus at the coaxial digital input, measured at the output across an 8-ohm load at 10W. We see effectively the same result as with the 16/44.1 FFT above.

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

Shown above is an 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 at 10W. We see the peaks from noise artifacts on the left side of the main signal dominating (with respect to amplitude) the peaks due to the harmonics of the signal on the right side. The 60Hz peak due to power-supply noise is nearing -80dBrA, or 0.01%, above the signal peak at -90dBrA.

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

Shown above is an 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 at 10W. We see effectively the same result as with the 16/44.1 FFT above.

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

Shown above is an FFT for a 50Hz input sinewave stimulus at the analog input, measured at the output across an 8-ohm load at 10W. 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 peak is from the third signal harmonic at 150Hz, reaching -85dBrA, or 0.006%. The second largest peak is from power-supply noise at 120Hz, reaching almost -90dBrA, or 0.003%, followed by the second signal harmonic at 100Hz on the left channel, reaching -95dBrA, or 0.002%.

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

Above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone at the analog 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. Here we find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is just above -100dBrA, or 0.001%, while the third-order modulation products, at 17kHz and 20kHz, are are both just above -90dBrA, or 0.003%.

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

Above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone at the digital input, where the top plot is for a dithered 16/44.1 digital input. The input digital values are set at -6.02dBFS so that, if summed for a mean frequency of 18.5kHz, would yield 0dBFS at the input and 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%, so slightly better than the analog input, while the third-order modulation products, at 17kHz and 20kHz, are both at -85dBrA, or 0.008%, so slightly worse than the analog input.

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

Above is an FFT of the intermodulation (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone at the digital input, where the top plot is for a dithered 24/96 digital input. There is very little difference between the 16/44.1 and 24/96 IMD FFTs, other than a lower noise floor on the 24-bit spectrum below 22kHz.

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

Above is the 10kHz squarewave response of the H95 using the analog 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 H95’s slew-rate performance. Rather, it should be seen as a qualitative representation of the H95’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. The H95’s reproduction of the 10kHz squarewave is reasonably clean, and although the edges are slightly rounded, they are nonetheless devoid of undershoot and overshoot.

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

The final chart above is the damping factor of the H95 as a function of frequency. Both channels show a general trend of a higher damping factor in the midrange frequencies, and lower damping factors at both the lowest and highest frequencies. The left channel generally outperformed the right channel, with a peak value around 520 between 300Hz and 2kHz, while the right channel peaked around 400 between 200 and 300Hz. At 20Hz, the damping factor for the left channel measured 220, while for the right channel it was around 300. At 20kHz, the damping factor for the left channel measured 340, for the right channel it was around 190.

*Diego Estan*

Electronics Measurement Specialist

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

All amplifier measurements are performed independently by BHK Labs. All measurement data and graphical information displayed below are the property of the SoundStage! Network and Schneider Publishing Inc. Reproduction in any format is not permitted.

Measurements were taken at both channels’ Coaxial S/PDIF, Line 2, and Phono inputs, at 120V AC line voltage, both channels driven.

All unless otherwise noted: the volume control was set for 5W output into 8 ohms, for an input level into Line 2 of 500mV; the results discussed below are for the left channel only; and an Audio Precision AUX-0025 external low-pass filter was used for the speaker-output measurements.

- Power output at 1% THD+N: 64.1W @ 8 ohms, 76.7W @ 4 ohms
- Power output at 10% THD+N: 75.0W @ 8 ohms, 82.5W @ 4 ohms

- Input/output polarity (analog and digital): noninverting
- AC-line current draw
- Idle: <0.5W
- Operating: 14.1W, 0.22A, 0.54PF

- Gain: output voltage divided by input voltage, 8-ohm load, volume at +10dB

- Speaker output, Line 2 input: 60.2X, 35.6dB
- Speaker output, Phono input: 3810.0X, 71.6dB
- Pre/Sub output, Line 2 input: 6.16X, 15.8dB
- Pre/Sub putput, Phono input: 390.6X, 51.8dB

- Input sensitivity for 1W output into 8 ohms

- Line 2 input: 47.0mV
- Phono input: 0.74mV

- Output impedance @ 50Hz
- Speaker output: 0.016 ohm
- Pre/Sub output: 440 ohms

- Input impedance @ 1kHz
- Line 2 input: 18.0k ohms
- Phono: 44.0k ohms

- Output noise, speaker output, 8-ohm load, input terminated with 1k ohm, Lch/Rch

- Without AUX-0025 measurement filter (high-frequency switching)
- Wideband: 165.2mV / 158.6mV, -24.7dBW / -25.0dBW

- With AUX-0025 filter, volume at -3.5dB (ref 5W output for 500mV input)

- Wideband: 486.1uV / 382.1uV, -75.3dBW / -77.4dBW
- A weighted: 58.4uV / 53.0uV, -93.7dBW / -94.6dBW

- With AUX-0025 filter, volume at -90dB

- Wideband: 197.8uV / 175.9uV, -83.1dBW / -84.1dBW
- A weighted: 32.1uV / 32.2uV, -98.9dBW / -98.9dBW

- With AUX-0025 filter, volume at +10dB

- Wideband: 1970.0uV / 1390.0uV, -63.1dBW / -66.2dBW
- A weighted: 196.5uV / 149.7uV, -83.2dBW / -85.5dBW

- Without AUX-0025 measurement filter (high-frequency switching)

The NAD D 3045 is a feature-laden little integrated amplifier offering digital inputs as well as analog line and phono inputs.

Chart 1 shows the D 3045’s frequency response with varying loads, with and without the Audio Precision AUX-0025 external low-pass filter. The output LC filtering must have been included in the overall feedback loop to produce a response so invariant with load. Most impressive!

Chart 2 illustrates how the D 3045’s total harmonic distortion plus noise (THD+N) vs. power varies for 1kHz and SMPTE intermodulation test signals and amplifier output load for 8- and 4-ohm loads.

The D 3045’s THD+N as a function of frequency at several different power levels is plotted in Chart 3. The amount of increase of distortion with frequency is admirably low, if not absent -- in my career of measuring many amplifiers, this is *very* rare.

The damping factor vs. frequency of the D 3045 is shown in Chart 4. Like the unchanging THD+N vs. frequency, the damping factor remains high at a much higher frequency than most power amplifiers.

Chart 5 plots the spectrum of the D 3045’s harmonic distortion and noise residue of a 10W, 1kHz test signal. The AC-line harmonics are low and simple, with some 120Hz visible. The signal harmonics are dominated by third-order harmonics, with second- and higher-order harmonics of much lower magnitude.

Chart 6 is a measure of the phono section’s RIAA equalization error. It shows extremely good accuracy.

Chart 7 is the frequency response of the D 3045’s digital input for sample rates of 44.1, 96, and 192kHz. Of interest is the gentle rolloff of the high frequencies for the two higher rates, which implies less ringing of the leading edges of transient signals.

Chart 8 shows the D 3045’s input/output linearity. This is usually done with a bandpass filter, to exclude noise and see only the signal amplitude. It is also instructive to take the same measurement within an audioband bandwidth, as that shows the ultimate noise level when the signal level descends into the noise.

I also looked briefly at the performance of the D 3045’s headphone amplifier. With a 32-ohm load, hard clipping began at about 1.5W, and low distortion below about 1.3W. With a 600-ohm load, clipping began at about 115mW.

Red line = with AUX-0025 measuring filter

Magenta line = without AUX-0025 measuring filter

(Note: these responses are representative of 4-, 8-, and open-load curves)

(Line up at 20W to determine lines)

Top line = 8-ohm SMPTE IM distortion

Second line = 4-ohm SMPTE IM distortion

Third line = 8-ohm THD+N

Bottom line = 4-ohm THD+N

(8-ohm loading)

Cyan line = 1W

Magenta line = 10W

Blue line = 30W

Red line = 60W

Damping factor = output impedance divided into 8

1kHz signal at 10W into an 8-ohm load

Red line = 44.1kHz sample rate

Magenta line = 96.0kHz sample rate

Blue line - 192.kHz sample rate

Magenta line = with usual bandpass filter

Red line = 10Hz - 20kHz

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

All amplifier measurements are performed independently by BHK Labs. All measurement data and graphical information displayed below are the property of the SoundStage! Network and Schneider Publishing Inc. Reproduction in any format is not permitted.

Measurements were made at a line voltage of 120V AC, both channels driven, and were taken on both channels using the Hegel H590’s AES, Analog 1, and BNC digital inputs. Unless otherwise noted, the data reported below are for the left channel.

- Power output at 1% THD+N: 322.7W @ 8 ohms, 524.9W @ 4 ohms
- Power output at 10% THD+N: 400.0W @ 8 ohms, 648.6W @ 4 ohms

- Input/output polarity (analog and digital): noninverting
- AC-line current draw at idle: 98.0W, 1.3A, 0.64PF
- Gain: output voltage divided by input voltage, 8-ohm load, Lch/Rch

- Balanced inputs: 42.7X, 32.6dB / 42.6X, 32.6dB
- Unbalanced inputs: 42.9X, 32.7dB / 42.7X, 32.6dB

- Input sensitivity for 1W output into 8 ohms, Lch/Rch

- Balanced inputs: 66.2mV / 66.4mV
- Unbalanced inputs: 65.9mV / 66.2mV

- Output impedance @ 50Hz: 0.013 ohm
- Input impedance @ 1kHz
- Balanced inputs: 9.3k ohms
- Unbalanced inputs: 7.0k ohms

- Output noise, 8-ohm load, balanced inputs terminated with 600 ohms, Lch/Rch

- At reference volume setting
- Wideband: 0.646mV / 0.629mV, -72.8dBW / -73.1dBW
- A weighted: 0.084mV / 0.080mV, -90.6dBW / -91.0dBW

- At maximum volume

- Wideband: 0.659mV / 0.643mV, -72.6dBW / -72.9dBW
- A weighted: 0.122mV / 0.120mV, -87.3dBW / -87.5dBW

- At minimum volume

- Wideband: 1.13mV / 1.07mV, -68.0dBW / -68.4dBW
- A weighted: 0.107mV / 0.105mV, -88.4dBW / -88.6dBW

- At reference volume setting
- Output noise, 8-ohm load, unbalanced inputs terminated with 1k ohms, Lch/Rch

- At reference volume setting
- Wideband: 0.633mV / 0.618mV, -73.0dBW / -73.2dBW
- A weighted: 0.077mV / 0.076mV, -91.3dBW / -91.4dBW

- At maximum volume

- Wideband: 0.465mV / 0.468mV, -75.7dBW / -75.6dBW
- A weighted: 0.072mV / 0.075mV, -91.9dBW / -91.5dBW

- At minimum volume

- Wideband: 1.15mV / 1.06mV, -67.8dBW / -68.5dBW
- A weighted: 0.106mV / 0.104mV, -88.5dBW / -88.7dBW

- At reference volume setting

The H590 is Hegel Music Systems’ newest, most powerful integrated amplifier-DAC.

Chart 1 shows the H590’s frequency response with varying loads. The output impedance is low enough that there was negligible variation with the NHT dummy speaker load.

Chart 2 illustrates how the H590’s total harmonic distortion plus noise (THD+N) vs. power varied for 1kHz and SMPTE IM test signals and amplifier output for loads of 8 and 4 ohms. The level of distortion is quite low.

The Hegel’s THD+N as a function of frequency at a number of increasing power levels is plotted in Chart 3. The increase in distortion with frequency is moderate.

Chart 4 plots the H590’s damping factor vs. frequency. The shape of the low-frequency rolloff curve is unusual, and the high-frequency rolloff begins at a lower frequency than the norm.

The Hegel’s spectrum of harmonic distortion and noise residue of a 10W, 1kHz test signal is shown in Chart 5. The AC line harmonics are quite low but relatively complex. The signal harmonics are dominated by the second and third harmonics, with the higher harmonics decreasing quickly.

Some key measurements of the Hegel H590’s digital section were taken. Its BNC input was fed with a full-scale, 0dBFS digital signal level, and, using the volume control, the main amplifier outputs were set as close as possible to 5W/8 ohms. The frequency response is shown in Chart 6.

Chart 7 shows the results of a revealing measurement that I always do on a DAC: a test of its input/output linearity. This measures the amplitude of a decreasing 1kHz signal for both channels with a 1kHz bandpass filter, in order to track the signal down into the noise. The results for sample rates of 44.1, 96, and 192kHz were about the same; for clarity, I’ve shown here only the result for the 44.1kHz sample rate. I additionally changed the measurement bandwidth to 22kHz; the resulting curve shows the residual noise level in the audioband, which in this case is at about CD resolution.

Red line = open circuit

Magenta line = 8-ohm load

Blue line = 4-ohm load

(Line up at 200W to determine lines)

Top line = 8-ohm SMPTE IM distortion

Second line = 4-ohm SMPTE IM distortion

Third line = 8-ohm THD+N

Bottom line = 4-ohm THD+N

(8-ohm loading)

Red line = 1W

Magenta line = 10W

Blue line = 70W

Cyan line = 200W

Green line = 270W

Yellow line = 290W

Damping factor = output impedance divided into 8

1kHz signal at 10W into an 8-ohm load

Red line = 44.1kHz

Magenta line = 96kHz

Blue line = 192kHz

24-bit/44.1kHz resolution with 1kHz bandwidth filter

Red line = left channel

Magenta line = right channel

24-bit/44.1kHz resolution with 22kHz bandwidth filter

Cyan line = left channel

Blue line = right channel

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

All amplifier measurements are performed independently by BHK Labs. All measurement data and graphical information displayed below are the property of the SoundStage! Network and Schneider Publishing Inc. Reproduction in any format is not permitted.

These measurements were taken at 120V AC line voltage, both channels driven. Measurements were taken on both channels, using inputs 1 and 2. Unless otherwise noted, the data reported below are for the left channel.

- Power output at 1% THD+N: 133.3W @ 8 ohms, 241.3W @ 4 ohms
- Power output at 10% THD+N: 179.2W @ 8 ohms, 318.0W @ 4 ohms

- Input/output polarity (analog and digital): noninverting
- AC-line current draw at idle: 95.0W, 1.06A, 0.65PF
- Gain: output voltage divided by input voltage, 8-ohm load, Lch/Rch

- Balanced inputs: 69.9X, 36.9dB / 69.7X, 36.9dB
- Unbalanced inputs: 71.4X, 37.1dB / 71.1X, 37.0dB

- Input sensitivity for 1W output into 8 ohms, Lch/Rch

- Balanced inputs: 40.4mV / 40.6mV
- Unbalanced inputs: 39.6mV / 36.7mV

- Output impedance @ 50Hz: 0.2 ohm
- Input impedance @ 1kHz
- Balanced inputs: 37.5k ohms
- Unbalanced inputs: 260.0k ohms

- Output noise, 8-ohm load, balanced inputs terminated with 600 ohms, Lch/Rch

- At reference volume setting
- Wideband: 1.69mV / 0.815mV, -64.5dBW / -70.8dBW
- A weighted: 0.161mV / 0.0764mV, -84.9dBW / -91.3dBW

- At maximum volume

- Wideband: 2.28mV / 2.09mV, -61.9dBW / -62.6dBW
- A weighted: 0.407mV / 0.389mV, -76.6dBW / -77.2dBW

- At minimum volume

- Wideband: 4.23mV / 1.01mV, -56.5dBW / -68.9dBW
- A weighted: 0.423mV / 0.106mV, -76.5dBW / -88.5dBW

- At reference volume setting
- Output noise, 8-ohm load, unbalanced inputs terminated with 1k ohms, Lch/Rch

- At reference volume setting
- Wideband: 1.67mV / 0.773mV, -64.6dBW / -71.3dBW
- A weighted: 0.161mV / 0.0774mV, -84.9dBW / -91.3dBW

- At maximum volume

- Wideband: 1.40mV / 1.03mV, -66.1dBW / -68.8dBW
- A weighted: 0.145mV / 0.0999mV, -85.0dBW / -91.0dBW

- At minimum volume

- Wideband: 4.24mV / 1.02mV, -56.5dBW / -68.9dBW
- A weighted: 0.393mV / 0.106mV, -77.1dBW / -88.5dBW

- At reference volume setting

Gryphon Audio Designs’ Diablo 120 integrated amplifier builds on the ten-year-long success of Gryphon’s Diablo 300 model.

Chart 1 shows the frequency response of the Diablo 120 with varying loads. The output impedance is low enough that there was negligible variation with the NHT dummy speaker load.

Chart 2 illustrates how the Diablo 120’s total harmonic distortion plus noise (THD+N) vs. power varied for 1kHz and SMPTE IM test signals and amplifier output for 8- and 4-ohm loads. Note that Gryphon claims to use zero overall feedback in the Diablo 120; the levels of distortion, though higher than in most feedback designs, are still reasonable.

The Diablo 120’s THD+N as a function of frequency at a number of increasing power levels is plotted in Chart 3. The levels of increase are moderate.

The Gryphon’s damping factor vs. frequency, plotted in Chart 4, is unusual in its relative flatness. This is a natural consequence of the absence of any overall negative feedback being used, and of not having a series inductor in an output-stabilizing network.

Chart 5 plots the Diablo 120’s spectrum of THD+N residue of a 10W, 1kHz test signal. The AC line harmonics are very low but relatively complex. The signal harmonics are dominated by the second and third harmonics, with higher harmonics of decreasing magnitude.

Some key measurements of the Diablo 120’s digital section were taken. Its AES input was fed with a full-scale 0dBFS digital signal level, and the main amplifier outputs were set as close to 5W/8 ohm as possible with the volume control. Chart 6 shows the frequency response with both of the filter settings, Slow and Fast.

Chart 7 plots the results of a revealing test that I always do on DACs: measure the output amplitude of a 1kHz signal with a 1kHz bandpass filter at full-scale digital level with decreasing input signal level, down to where the output level meets the noise floor. This reveals that the Diablo 120’s noise floor in this test was about -110dBFS, which is pretty good for 24-bit input data.

Red line = open circuit

Magenta line = 8-ohm load

Blue line = 4-ohm load

Cyan line = NHT dummy-speaker load

(Line up at 30W to determine lines)

Top line = 4-ohm SMPTE IM distortion

Second line = 8-ohm SMPTE IM distortion

Third line = 4-ohm THD+N

Bottom line = 8-ohm THD+N

(8-ohm loading)

Red line = 1W

Magenta line = 10W

Blue line = 30W

Cyan line = 70W

Green line = 120W

Damping factor = output impedance divided into 8

1kHz signal at 10W into an 8-ohm load

Slow filters

Red line = 44.1kHz

Magenta line = 96kHz

Yellow line = 192kHz

Fast filters

Cyan line = 44.1kHz

Green line = 96kHz

Blue line = 192kHz

24-bit/44.1kHz resolution with 1kHz bandwidth filter

Red line = left channel

Magenta line = right channel

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