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

**General Information**

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

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

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

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

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

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

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

Volume position | Channel deviation |

-88dB | 0.03dB |

-60dB | 0.011dB |

-50dB | 0.012dB |

-30dB | 0.013dB |

-20dB | 0.014dB |

-10dB | 0.013dB |

0dB | 0.014dB |

**Published specifications vs. our primary measurements**

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

Parameter | Manufacturer | SoundStage! Lab |

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

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

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

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

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

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

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

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

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

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

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

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

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

Parameter | Left channel | Right channel |

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

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

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

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

Damping factor | 334 | 343 |

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

DC offset | <3mV | <3mV |

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Parameter | Left channel | Right channel |

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

DC offset | <3mV | <3mV |

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

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

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

Input impedance | 45.3k ohms | 46.2k ohms |

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

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

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

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

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

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

THD (unweighted) | <0.012% | <0.013% |

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

THD+N (unweighted) | <0.021% | <0.031% |

Our primary measurements revealed the following using the phono-level input, MC configuration (unless specified, assume a 1kHz 0.5mVrms sinewave input, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

Parameter | Left channel | Right channel |

Crosstalk, one channel driven (10kHz) | -65.9dB | -56.0dB |

DC offset | <3mV | <3mV |

Gain (default phono preamplifier) | 57.7dB | 57.7dB |

IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-65dB | <-63dB |

IMD ratio (CCIF, 3kHz + 4kHz stimulus tones, 1:1) | <-71dB | <-70dB |

Input impedance | 129 ohms | 129 ohms |

Input sensitivity (to max power with max volume) | 217uVrms | 215uVrms |

Noise level (A-weighted) | <3200uVrms | <5000uVrms |

Noise level (unweighted) | <9000uVrms | <24000uVrms |

Overload margin (relative 0.5mVrms input, 1kHz) | 17.4dB | 17.4dB |

Signal-to-noise ratio (full rated power, A-weighted) | 67.9dB | 64.5dB |

Signal-to-noise ratio (full rated power, unweighted) | 59.3dB | 52.4dB |

THD (unweighted) | <0.014% | <0.017% |

THD+N (A-weighted) | <0.038% | <0.060% |

THD+N (unweighted) | <0.11% | <0.26% |

Our primary measurements revealed the following using the analog input at the headphone output (unless specified, assume a 1kHz sinewave, 2Vrms output, 300 ohms loading, 10Hz to 22.4kHz bandwidth):

Parameter | Left channel | Right channel |

Maximum output power into 600 ohms (1% THD+N, unweighted) | 43mW | 43mW |

Maximum output power into 300 ohms (1% THD+N, unweighted) | 66mW | 66mW |

Maximum output power into 32 ohms (1% THD+N, unweighted) | 57mW | 58mW |

Gain | 33.1dB | 33.1dB |

Output impedance | 102.7 ohms | 102.9 ohms |

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

Noise level (unweighted) | <250uVrms | <250uVrms |

Signal-to-noise ratio (A-weighted, ref. max output voltage) | 112.6dB | 112.7dB |

Signal-to-noise ratio (unweighted, ref. max output voltage) | 109.8dB | 109.8dB |

THD ratio (unweighted) | <0.0006% | <0.0005% |

THD+N ratio (A-weighted) | <0.003% | <0.003% |

THD+N ratio (unweighted) | <0.012% | <0.012% |

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

In our frequency-response plots above, measured across the speaker outputs at 10W into 8 ohms, the SU-R1000 is nearly flat within the audioband (20Hz to 20kHz). At the extremes the SU-R1000 is 0dB at 20Hz and -0.3dB down at 20kHz. These data essentially corroborate Technics’ claim of 5Hz to 80kHz (-3dB). There’s a rise in the frequency response above 20kHz, where we see +2dB at 70kHz, which is a result of the digital amplifier and its high output impedance at high frequencies. Into a 4-ohm load (see “RMS level vs. frequency vs load impedance” chart below), instead of a rise there is a significant dip at and above 20kHz. The -3dB point was also explored and found to be at 92kHz, exactly where it was measured for a 24-bit/192kHz digital input signal (see “Frequency response vs. input type” chart below). In the chart above and most of the charts below, only a single trace may be visible. This is because the left channel (blue or purple trace) is performing identically to the right channel (red or green trace), and so they perfectly overlap, indicating that the two channels are ideally matched.

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

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

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

Above is a frequency response plot measured at the speaker-level outputs into 8 ohms, with the midrange control set to maximum (blue/red plots) and minimum (purple/green plots). We see that there is roughly +/- 8dB of gain/cut available centered around 1kHz.

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

Above is a frequency response plot measured at the speaker-level outputs into 8 ohms, with the bass, treble, and midrange controls set to maximum (blue/red plots) and minimum (purple/green plots). The levels are relative to 3kHz. We see that with all controls set to either minimum or maximum, there is a maximum deviation of no more than 4dB. When all the tone controls are at their maximum, there are two dips in the frequency response at roughly 400Hz and 3kHz. When the tone controls are at their minimum, we see troughs at 400Hz and 3kHz.

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

Above are the phase-response plots from 20Hz to 20kHz for the line-level input, measured across the speaker outputs at 10W into 8 ohms. The SU-R1000 does not invert polarity and exhibits, at worst, 20 degrees (at 20kHz) of phase shift within the audioband.

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

The chart above shows the SU-R1000’s frequency response as a function of input type measured across the speaker outputs at 10W into 8 ohms. The green trace is the same analog input data from the previous graph. The blue trace is for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz using the coaxial input, and the purple trace is for a 24/96 dithered digital input signal from 5Hz to 48kHz, while the pink trace is for a 24/192 dithered digital input signal from 5Hz to 96kHz. The 16/44.1 signal exhibits brick-wall type filtering, with a -3dB at 20.9kHz. The 24/96 and 24/192 kHz signals yielded -3dB points at 46.3kHz and 91.9kHz, respectively. The analog data looks nearly identical to the 24/192 digital data, which is evidence for the SU-R1000 sampling incoming analog signals at 192kHz.

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

The chart above shows the frequency response for the phono input (MM configuration) without (blue/red) and with (purple/green) the subsonic filter enabled. We see a maximum deviation of about +0.1/-0.2dB (20Hz/10kHz) from 20Hz to 20kHz. With the subsonic filter engaged, we find the -3dB point at 20Hz. What is shown is the deviation from the RIAA curve, where the input signal sweep is EQ’d with an inverted RIAA curve supplied by Audio Precision (*i.e.,* zero deviation would yield a flat line at 0dB).

**Frequency-response correction curve (8-ohm loading, MM phono input, reviewer Roger Kanno’s custom calibration)**

The chart above shows the frequency response for the phono input (MM configuration), but with the Cartridge Optimizer engaged, as per Roger Kanno’s calibration for the review of the SU-R1000. This is a correction curve for each channel. We can clearly see that, using digital signal processing (DSP), the SU-R1000 is applying changes to the frequencies from 10Hz to 10kHz, and applying different gain to the left and right channels at various frequencies, to achieve a flat frequency response from each channel with the cartridge used (Pro-Ject Audio Systems Pick it S2 MM).

**Frequency response (line-level pre-out, MM phono input, various EQ curves)**

The chart above shows the frequency response for the phono input (MM configuration), left channel only, as measured at the pre-outs without any EQ applied to the frequency sweep. The SU-R1000 allows the user to select between 7 phono EQ curves. What is shown are the RIAA (blue), RCA (green), NAB (red), AES (brown) . . .

. . . Decca/FFRR (pink), Columbia (cyan) and IEC (grey) response curves, from 20Hz to 20kHz, which are there to accomodate different recording types.

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

The chart above shows the frequency response for the phono input (MC configuration) without (blue/red) and with (purple/green) the subsonic filter enabled. We see a maximum deviation of about -0.5/-0.3dB (20Hz/20kHz) from 20Hz to 20kHz. With the subsonic filter engaged, we find the -3dB point at 21Hz. What is shown is the deviation from the RIAA curve, where the input signal sweep is EQ’d with an inverted RIAA curve supplied by Audio Precision (*i.e.,* zero deviation would yield a flat line at 0dB).

**Phase response (MM input)**

Above is the phase response plot from 20Hz to 20kHz for the phono input (MM configuration), measured across the speaker outputs at 10W into 8 ohms. The SU-R1000 does not invert polarity. For the phono input, since the RIAA equalization curve must be implemented, which ranges from +19.9dB (20Hz) to -32.6dB (90kHz), phase shift at the output is inevitable. Here we find a worst case of about -60 degrees at 200Hz and 5kHz.

**Phase response (MC input)**

Above is the phase response plot from 20Hz to 20kHz for the phono input (MC configuration), measured across the speaker outputs at 10W into 8 ohms. The SU-R1000 does not invert polarity. Here we find a worst case of about -60 degrees at 200Hz and 5kHz.

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

The chart above shows the results of a linearity test for the coaxial digital input for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the line-level output of the SU-R1000. The digital input is swept with a dithered 1kHz input signal from -120dBFS to 0dBFS, and the output is analyzed by the APx555. The ideal response would be a straight flat line at 0dB. Both data were essentially perfect from -100dBFS down to 0dBFS. At -120dBFS, the 16/44.1 data were only +2dB (left) and +4dB (right) above reference, while the 24/96 data were at -1/-2dBFS.

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

The graph above shows the impulse response for the SU-R1000 with MQA turned off, fed to the coaxial digital input, measured at the line-level output, for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s), for one sample period, then back to digital silence. We find a reconstruction filter that favors no pre-ringing.

**Impulse response (24/44.1 data, MQA on)**

The graph above shows the impulse response for the SU-R1000 with MQA turned on, fed to the coaxial digital input, measured at the line-level output, for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s), for one sample period, then back to digital silence. We find a reconstruction filter that favors no pre-ringing, and less post-ringing compared to when MQA is turned off.

**J-Test (coaxial)**

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the SU-R1000. The J-Test was developed by Julian Dunn the 1990s. It is a test signal, specifically a -3dBFS undithered 12kHz squarewave sampled (in this case) at 48kHz (24 bits). Since even the first odd harmonic (*i.e.*, 36kHz) of the 12kHz squarewave is removed by the bandwidth limitation of the sampling rate, we are left with a 12kHz sinewave (the main peak). In addition, an undithered 250Hz squarewave at -144dBFS is mixed with the signal. This test file causes the 22 least significant bits to constantly toggle, which produces strong jitter spectral components at the 250Hz rate and its odd harmonics. The test file shows how susceptible the DAC and delivery interface are to jitter, which would manifest as peaks above the noise floor at 500Hz intervals (*e.g,*. 250Hz, 750Hz, 1250Hz, etc.). Note that the alternating peaks are in the test file itself, but at levels of -144dBrA and below. The test file can also be used in conjunction with artificially injected sinewave jitter by the Audio Precision, to show how well the DAC rejects jitter.

The coaxial input exhibits low-level peaks in the audioband, at -115dBrA and below. This is a good J-Test result, indicating that the SU-R1000 DAC should yield good jitter immunity.

**J-Test (optical)**

The chart above shows the results of the J-Test test for the optical digital input measured at the line- level output of the SU-R1000. The optical input exhibits low-level peaks in the audioband, at -115dBrA and below. This result is very similar compared to the coaxial input.

**J-Test (coaxial, MQA on)**

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the SU-R1000 with MQA turned on. We see peaks at 9kHz and 15kHz at -130dBrA that were not present when MQA was turned off, as well as a distinct rise in the noise floor at lower frequencies. This indicates less jitter immunity. The optical input yielded effectively the same result.

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

Both the coaxial and optical inputs were also tested for jitter immunity by injecting artificial sinewave jitter at 2kHz, which would manifest as sidebands at 10kHz and 14kHz without any jitter rejection. MQA *was not* turned on. Jitter immunity proved exceptional, with no visible sidebands at the 100ns jitter level.

**J-Test with 900ns of injected jitter (coaxial)**

Both the coaxial and optical inputs were also tested for jitter immunity by injecting artificial jitter sinewave jitter at 2kHz, which would manifest as sidebands at 10kHz and 14kHz without any jitter rejection. Once again, MQA was not turned on. Jitter immunity proved exceptional again, with sidebands down at a very low -125dBrA even with a very high 900ns of injected jitter. Above this level of jitter, the SU-R1000 DAC lost sync with the signal.

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

The chart above shows a fast Fourier transform (FFT) of the SU-R1000’s line-level output with white noise at -4dBFS (blue/red), and a 19.1kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1. The steep roll-off around 20kHz in the white-noise spectrum shows the behavior of the SU-R1000’s reconstruction filter. There are no aliased image peaks within the audioband. The primary aliasing signal at 25kHz is at -95dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are at -105 and -120dBrA.

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

The chart above shows a fast Fourier transform (FFT) of the SU-R1000’s line-level output with white noise at -4dBFS (blue/red), and a 19.1kHz sinewave at -1dBFS fed to the coaxial digital input, sampled at 16/44.1, with MQA turned on. We find a much gentler slope above 20kHz for the noise spectrum compared to when MQA was turned off. We find one small aliased image peak within the audioband, at around -120dBrA, at around 6kHz. The primary aliasing signal at 25kHz is significant at -20dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are at -110 and -120dBrA.

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

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

. . . is the same but zoomed in to highlight differences. Here we find that at low frequencies, the deviations between no load and 4 ohms are small, at about 0.05dB; but at high frequencies, the differences are significant, at about 1.4dB at 20kHz. This is a result of the digital amplifier technology used, which exhibits a high damping factor at low frequencies, but a low damping factor at high frequencies (see “Damping factor vs frequency graph below”). When a real speaker is used, the major deviations appear once again at high frequencies, with a 0.6dB deviation between 5kHz and 20kHz.

**RMS level vs. frequency (1W, left channel only, real speaker, LPAC on and off)**

The chart above shows RMS level (relative to 0dBrA, which is 1W into 8 ohms, or 2.83Vrms) as a function of frequency, for the balanced analog line-level input swept from 20Hz to 20kHz. Both plots are for the Focal Chora 806 speaker, with (blue) and without (purple) LAPC enbaled. LPAC stands for Load Adaptive Phase Calibration, a feature in the SU-R1000 that measures the outputs of the amplifier while the speakers are connected using test tones to establish a correction curve to deal with the amplifier’s inherently high output impedance at high frequencies. The theoretical goal is to achieve a flat frequency response for the user’s speakers across the audioband when LAPC is enabled. We can see here that the blue trace is still not flat, even though LAPC is enabled, but it is closer to the ideal flat response compared to when LAPC is not enabled. When LAPC is disabled, we are at -0.5dB at 20kHz, compared to the roughly -0.15dB at 20kHz with LAPC enabled.

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

The chart above shows THD ratios at the output into 8 ohms as a function of frequency for a sinewave stimulus at the balanced analog line-level input. The blue and red plots are for the left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at 140W. The power was varied using the volume control. At 1W, the left channel outperformed the right by almost 5dB from 300Hz to 6kHz, and ranged from around 0.01% at 20Hz, down to 0.0007% at 200Hz, then up to 0.005% at 6kHz. At 10W, the same THD values were seen from 20Hz to about 150Hz as the 1W data, then we see a rise from 0.002% up to 0.02% at 20kHz. The 140W THD values were higher, starting at the same 0.01% at 20Hz, and then rising steadily up to 0.3% at 4kHz.

**THD ratio (unweighted) vs. frequency at 10W (MM and MC phono inputs)**

The chart above shows THD ratios as a function of frequency plots for the phono input measured across an 8-ohm load at 10W. The MM configuration is shown in blue/red (left/right channels), and MC in purple/green (left/right channels). The input sweep is EQ’d with an inverted RIAA curve. The THD values for the MM configuration vary from around 0.03% (20Hz) down to 0.003% (200Hz), then up to 0.03% (3kHz to 6kHz). The THD values for the MC configuration vary from around 0.3% (20Hz) down to 0.01-0.02% (200Hz to 1kHz), then up to 0.03% (3kHz to 6kHz).

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

The chart above shows THD ratios measured at the output of the SU-R1000 as a function of output power for the balanced analog line-level input, for an 8-ohm load (purple/green for left/right channels) and a 4-ohm load (blue/red for left/right channels). Both data sets track closely, except for maximum power. There is a dip in THD, from 0.02% down to 0.002% in both data sets that occurs when the output voltage is at 2Vrms (0.5W into 8 ohms, 1W into 4 ohms). With this digital amplifier technology, there is no distinct “knee” in the curve. We find that the 8-ohm data reaches the 1% THD mark at about 190W. We were unable to collect reliable data with an input sweep for the 4-ohm data above about 300W at the output. We found that the right channel would clamp the output and reduce power, then the left channel would follow at a higher power output. When feeding constant and continuous input stimuli with a 4-ohm load, we were able to measure 310W for the right channel before the clamping occurred (at about 0.3% THD), while the left channel yielded up to 360W (at 1% THD). Overall, THD values for both loads were similar up to 100W, ranging from 0.05%, down to 0.002%, then up to 0.05%.

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

The chart above shows THD+N ratios measured at the output of the SU-R1000 as a function of output power for the balanced line-level input, for an 8-ohm load (purple/green for left/right channel) and a 4-ohm load (blue/red for left/right channels). Overall, THD+N values for both loads were similar up to 100W, ranging from 0.5%, down to 0.01%, then up to 0.05%.

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

The chart above shows THD ratios measured at the output of the SU-R1000 as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yields 10W at the output into 8 ohms (and roughly 20W into 4 ohms, and 40W into 2 ohms) for the balanced analog line-level input. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. We find roughly the same THD values of 0.01% to 0.005% from 20Hz to 50Hz for all three loads. From 50Hz to 1kHz the 8- and 4-ohm data track closely, down to 0.002% then up to 0.01%. For the 2-ohm data, from 50Hz to 6kHz, there’s a steady rise in THD from 0.005% to 0.08%. At 20kHz, the 8-ohm data is at 0.03%, while the 4-ohm data fared slightly better at 0.01%.

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

The chart above shows THD ratios measured at the output of the SU-R1000 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the balanced analog line-level input. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). In general, the measured THD ratios for the real speakers were close to the 8-ohm resistive load. The worst-case diffrence was in the order of 10dB at 200Hz (between the Focal and dummy load). The two-way Focal yielded the highest THD values (0.04% at 20Hz) at very low frequencies, while the three-way Paradigm yielded the highest THD values at high frequencies (0.01% at 6kHz). Between 200Hz and 2kHz, while the 8-ohm dummy load yielded results between 0.001 to 0.003%, with real speakers the THD values ranged from 0.0015% to 0.005%.

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

The chart above shows intermodulation distortion (IMD) ratios measured at the output of the SU-R1000 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the balanced analog line-level input. Here the CCIF IMD method is used, where the primary frequency is swept from 20kHz (F1) down to 2.5kHz, and the secondary frequency (F2) is always 1kHz lower than the primary, with a 1:1 ratio. The CCIF IMD analysis results are the sum of the second (F1-F2 or 1kHz) and third modulation products (F1+1kHz, F2-1kHz). The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). At high frequencies, there is a significant 12dB difference between the dummy load (-84dB) and real speaker (-72dB) IMD values. Between 2.5 and 7kHz, the Focal IMD values were close to that of the dummy load values (-85 to -95dB), whereas the Paradigm IMD values were significantly higher, reaching -80dB at 4-5kHz, about 10dB worse than both the dummy load and Focal speaker.

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

The chart above shows IMD ratios measured at the output of the SU-R1000 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the balanced analog line-level input. Here, the SMPTE IMD method is used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a two-way speaker (Paradigm Founder Series 100F, measurements can be found here). Between 40Hz and 60Hz, all results are essentially identical, around -81dB. Above 60Hz, the highest IMD ratios are associate with the Paradigm speakers, rising up to -74dB from 100Hz to 250Hz. When the Focal was used as a load, there is a small rise in IMD ratios starting at 100Hz, rising up to -76dB. When the load was purely resistive, IMD ratios were consistently flat at around -81dB.

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

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the balanced analog line-level input. We see that the signal’s second harmonic, at 2kHz, is at -110dBrA, or 0.0003%, while the odd harmonics at 3 and 5kHz dominate at -80 and -90dBrA, or 0.01% and 0.003%. There are no power-supply related noise peaks to speak of; however, there is a distinct rise in the noise floor from -120dBrA at 1kHz up to -100dBrA from 200Hz to 10Hz. There is also a rise in the noise above 20kHz, a typical characteristic of switching amplifiers.

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

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 16/44.1. Signal harmonics are very similar to the analog input FFT above. Here again, there are no power-supply related noise peaks to speak of; however, there is a distinct rise in the noise floor from -130dBrA at 1kHz up to -120dBrA from 200Hz to 10Hz.

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

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 24/96. Signal harmonics are very similar to the analog input FFT above. Here again, there are no power-supply related noise peaks to speak of; however, there is again a rise in the noise floor from -140dBrA at 1kHz up to -110dBrA from 200Hz to 10Hz.

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

Shown above is the FFT for a 1kHz -90dBFS dithered 16/44.1 input sinewave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, and no other peaks above the noise floor at -110dBrA.

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

Shown above is the FFT for a 1kHz -90dBFS dithered 24/96 input sinewave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, and no other peaks above the noise floor at -110dBrA.

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

Shown above is the FFT for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the phono input, configured for MM. We see the second (2kHz), third (3kHz), and fifth (5kHz) signal harmonics dominating at around -100, -80, and -90dBrA, respectively, or 0.001%, 0.01%, and 0.003%. The most significant power-supply-related noise peaks can be seen at 60Hz at -85/-75dBrA (left/right channels), or 0.006/0.02%. Higher-order power-supply related peaks can also be seen at lower amplitudes.

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

Shown above is the FFT for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the phono input, configured for MC. We see the second (2kHz), third (3kHz), and fifth (5kHz) signal harmonics dominating at around -80dBrA (2/3kHz) and below -90dBrA (5kHz), or 0.01% and 0.003%. The most significant power-supply-related noise peaks can be seen at 60Hz at -70/55dBrA (left/right channels), or 0.03/0.2%. Higher-order power-supply related peaks can also be seen at lower amplitudes.

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

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the analog line-level input. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. There are no harmonic peaks of any kind to be observed above the noise floor.

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

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the phono input (MM configuration). The X axis is zoomed in from 40 Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most predominant (non-signal) peak is from the 60Hz power supply fundamental at -85/-75dBrA (left/right channels), or 0.006/0.02%. The most predominant signal related harmonic is at 100Hz at -85dBrA, or 0.006%. Higher-order signal-related and power-supply-related peaks can also be seen at lower amplitudes.

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

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the phono input (MC configuration). The X axis is zoomed in from 40 Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most predominant (non-signal) peak is from the 60Hz at -70/55dBrA (left/right channels), or 0.03/0.2%. The most predominant signal-related harmonic is at 100Hz at -70dBrA, or 0.03%. Higher-order signal-related and power-supply-related peaks can also be seen at lower amplitudes.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the balanced analog line-level input. The input RMS values are set at -6.02dBrA, so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -110dBrA, or 0.0003%, while the third-order modulation products, at 17kHz and 20kHz, are around -80dBrA, or 0.01%.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 16/44.1. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -120dBrA, or 0.0001%, while the third-order modulation products, at 17kHz and 20kHz, are around -80dBrA, or 0.01%.

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

Shown above is an FFT of the intermodulation (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 16/44.1, with MQA turned on. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -110dBrA, or 0.0003%, while the third-order modulation products, at 17kHz and 20kHz, are around -80dBrA, or 0.01%. What we also see clear aliasing products above 20kHz reaching above -30dBrA, and a multitude of subsequent low-level (-90 to -110dBrA) IMD products within the audioband. This result may be an argument for keeping MQA turned off with non-MQA 16/44.1 program material.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 24/96. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -120dBrA, or 0.0001%, while the third-order modulation products, at 17kHz and 20kHz, are around -80dBrA, or 0.01%.

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

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

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the phono input configured for MC. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at -90/80dBrA (left/right), or 0.003/0.01%, while the third-order modulation products, at 17kHz and 20kHz, are also around -80dBrA, or 0.01%.

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

Above is the 10kHz squarewave response using the balanced analog line-level input, at roughly 10W into 8 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the SU-R1000’s slew-rate performance. Rather, it should be seen as a qualitative representation of the SU-R1000’s mid-tier bandwidth. An ideal squarewave can be represented as the sum of a sinewave and an infinite series of its odd-order harmonics (*e.g.*, 10kHz + 30kHz + 50kHz + 70kHz . . .). A limited bandwidth will show only the sum of the lower-order harmonics, which may result in noticeable undershoot and/or overshoot, and softening of the edges. In this case, because of the switching nature of the amplifier, we see a 768kHz switching frequency (see 1MHz FFT below) riding on top of the squarewave.

**Square-wave response (10kHz, restricted 500kHz bandwidth)**

Above is the same 10kHz squarewave response using the balanced analog line-level input, at roughly 10W into 8 ohms, this time with a 500kHz input bandwidth on the Audio Precision analyzer to filter out the 768kHz switching frequency. We can see significant overshoot and undershoot in the corners of the squarewave, a consequence of the SU-R1000’s mid-tier bandwidth.

**FFT spectrum (1MHz bandwidth)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the balanced analog line-level input, with an extended 1MHz input bandwidth. This enables us to see the high-frequency noise above 20kHz reaching almost -70dBrA at 300kHz. We also see a clear peak at 768kHz, reaching just past -30dBrA. The peak, as well as the noise, are a result of the switching amplifier technology used in the SU-R1000; however, they are far above the audioband—and therefore inaudible—and so high in frequency that any loudspeaker the amplifier is driving should filter it all out anyway.

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

The final chart above is the damping factor as a function of frequency. We can see here the clear trend of a high damping factor at low frequencies—around 400 from 20Hz to 200Hz—and then the steep decline down to 15 at 20kHz. This is a limitation of the switching amplifier technology used in the SU-R1000, and the reason Technics has incorporated their clever Load Adaptive Phase Calibration (LAPC) feature, to compensate for losses into low impedances at high frequencies.

*Diego Estan*

Electronics Measurement Specialist