Simaudio Moon 371 Streaming Integrated Amplifier Measurements

Link: reviewed by Doug Schneider on SoundStage! Hi-Fi on April 1, 2026

General Information

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

The Simaudio Moon 371 was conditioned for 1 hour at 1/8th full rated power (~15W into 8 ohms) before any measurements were taken. All measurements were taken with both channels driven, using a 120V/20A dedicated circuit, unless otherwise stated.

The 371 offers two analog line-level inputs (RCA and XLR), four digital inputs (two coaxial, one optical, one HDMI), a phono input (RCA) configurable for both moving-magnet (MM) or moving-coil (MC), an ethernet connection for streaming, line-level pre-outs (RCA), and a pair of speaker-level outputs. Also on offer is a headphone output over 1/4″ TRS connector. For the purposes of these measurements, the following inputs were evaluated: coaxial digital (RCA), and the analog line-level (XLR) and phono (RCA) inputs. Comparisons were made between the balanced and unbalanced inputs, and no appreciable differences were seen (FFTs for both are included in this report).

Most measurements were made with a 2Vrms line-level analog input, 0dBFS digital input, and 5/0.5mVrms phono inputs (MM/MC). The signal-to-noise (SNR) measurements were made with the same input signal values but with the volume set to achieve the rated output power of 100W. For comparison, on the analog input, an SNR measurement was also made with the volume at maximum, but the input voltage reduced to achieve the same 100W output. The 371 offers a range of gain settings, though the default 6dB was maintained for these measurements.

Based on the accuracy and repeatability at various volume levels of the left/right channel matching (see table below), the 371 volume control is likely digitally controlled but operating in the analog domain. The volume range is from -41dB to +37.5dB (line-level inputs, speaker level outputs). Below volume level 20, steps are 1dB each; above 20, volume step size is 0.5dB.

Our typical input bandwidth filter setting of 10Hz-22.4kHz was applied for all measurements, except for frequency response (DC to 1MHz) and for FFTs and frequency sweeps (10Hz to 90kHz).

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

Published specifications vs. our primary measurements

The table below summarizes the measurements published by Simaudio for the Moon 371 compared directly against our own. The published specifications are sourced from Simaudio’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 22.4kHz, and the worst-case measured result between the left and right channels.

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

For the continuous dynamic power test, the Moon 371 was able to sustain 263W (1% THD) into 4 ohms using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (10W) 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 371 was very hot 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):

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):

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

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

In our measured frequency-response chart above, the 371 is essentially perfectly flat within the audioband (20Hz to 20kHz). At the extremes the 371 is 0dB at 5Hz and -1.8dB at 200kHz. The 371 appears to be DC-coupled, as we see no attenuation even at 5Hz.  In the graph above and most of the graphs below, only a single trace may be visible. This is because the left channel (blue or purple trace) is performing identically to the right channel (red or green trace), and so they perfectly overlap, indicating that the two channels are ideally matched.

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

Above is the phase response plot from 20Hz to 20kHz for the analog input. The 371 does not invert polarity and exhibits about -15 degrees of phase shift at 20kHz.

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

The chart above shows the frequency response for the phono input configured for MM. 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). We see an exceptionally flat response from 20Hz to 20kHz, with essentially zero channel-to-channel deviations. At the extremes, the 371 is -1dB at 5Hz and -0.5dB at 90kHz. This is an exceptional example of RIAA EQ implementation, especially when we consider it’s implemented in the analog domain.

Phase response (8-ohm loading, MM phono input)

Above is the phase response plot from 20Hz to 20kHz for the phono input configured for MM, measured across the speaker outputs at 10W into 8 ohms. The 371 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 +40 degrees at 20Hz and -10 degrees at 200Hz, and +60 degrees at 20kHz.

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

The chart above shows the frequency response for the phono input configured for MC. We see essentially the same result as with the MM configuration.

Phase response (8-ohm loading, MC phono input)

Above is the phase response plot from 20Hz to 20kHz for the phono input configured for MC, measured across the speaker outputs at 10W into 8 ohms. The 371 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 -100 degrees at 20kHz.

Frequency response vs. input type (8-ohm loading)

The chart above shows the 371’s frequency response as a function of input type. The green traces are the same analog input data from the previous graph (limited to 80kHz). The blue/red traces are for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz, the purple/green traces are for a 24/96 dithered digital input signal from 5Hz to 48kHz, and finally orange/pink is 24/192 from 5Hz to 96kHz. The behavior at low frequencies is the same across all input types: 0dB at 5Hz. The behavior at high frequencies for all digital input types is typical, sharp filtering around half the sample rate. The -3dB points are at roughly 22kHz, 46kHz, and 91kHz.

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

The chart above shows the results of a linearity test for the coaxial digital input for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the line-level pre-outs of the 371. For this test, 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 are essentially perfect from -110 dBFS down to 0dBFS. At -120dBFS, the 16/44.1 input data overshot the ideal output signal amplitude by 2dB (right channel only), while the 24/96 data remained perfect. The sweep was extended down to -140dBFS to . . .

. . . verify the performance of the 24/96 data. The traces show only a +2/3dB overshoot at -140dBFS. A superb result.

Impulse response (24/44.1 data)

The graph above shows the impulse response for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s) for one sample period then back to digital silence, measured at the line-level pre-outs of the 371. We can see that the 371 utilizes a reconstruction filter with no pre-ringing but obvious post-ringing.

J-Test (coaxial)

The plot above shows the results of the J-Test test for the coaxial digital input measured at the line-level pre-outs of the 371. 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 (24bit). 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 only very small peaks in the audioband at -140dBFS and below. This is a very good J-Test result and an indication that the 371 DAC has good jitter immunity.

J-Test (optical)

The plot above shows the results of the J-Test test for the optical digital input measured at the line-level pre-outs of the 371. We see essentially the same result as with the coaxial input above.

J-Test (coaxial, 10ns jitter)

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the 371, with an additional 10ns of 2kHz sinewave jitter injected by the APx555. The telltale peaks at 10kHz and 12kHz cannot be seen. The optical input yielded the same result.

J-Test (coaxial, 100ns jitter)

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the 371, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The telltale peaks at 10kHz and 12kHz cannot be seen above the -160dBFS noise floor. Further evidence of the 371 DAC’s superb jitter rejection. The optical input produced a similar result.

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

The plot above shows a fast Fourier transform (FFT) of the 371’s line-level pre-outs with white noise at -4 dBFS (blue/red) and a 19.1 kHz 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 brickwall-type reconstruction filter. There are no aliased image peaks in the audioband above the -135dBrA noise floor. The main 25kHz alias peak is at -100dBrA. The second, third, and fourth distortion harmonics (38.2, 57.3, 76.4kHz) of the 19.1kHz tone are at roughly the same level.

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

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

. . . is the same but zoomed in to highlight differences. Zoomed in, we can see a maximum deviation within the audioband of roughly 0.04dB from 4 ohms to no load, which is an indication of a very high damping factor, or very low output impedance. The maximum variation in RMS level into a real speaker was about the same.

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 6kHz) 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 roughly 100W. The power was varied using the volume control. The 1W data exhibited the highest THD values, with values varying around 0.0007% at 20Hz, down to 0.0005% from 60Hz to 600Hz, then up to 0.01% at 20kHz. The 10W data varied from 0.0004% at 20Hz, down to 0.0003% from 30Hz to 600Hz, then up to 0.004% at 20kHz. At 100W, THD values varied from 0.0006% at 20Hz, down to 0.0002% from 200Hz to 500Hz, then up to 0.02% at 20kHz.

THD ratio (unweighted) vs. frequency at 10W (phono input, MM and MC)

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 blue/red traces are for the MM configuration, purple/green for MC. For this test, the input sweep is EQ’d with an inverted RIAA curve. The THD values for the MM configuration vary from around 0.04% at 20Hz, down to 0.0006-0.001% from 300Hz to 3kHz (right channel), then up to 0.005% at 20kHz. The left channel for the MM configuration yielded THD ratios roughly 10dB higher than the right channel between 300Hz and 3kHz. The THD values for the MC configuration vary from around 0.2% at 20Hz, down to 0.005-0.01% from 300Hz to 8kHz (right channel), then up to 0.05% at 20kHz. The left channel for the MC configuration yielded THD ratios roughly 10dB higher than the right channel between 300Hz and 6kHz, but 15dB lower at 20kHz.

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 371 as a function of output power for the analog line level-input, for an 8-ohm load (blue/red for left/right) and a 4-ohm load (purple/green for left/right), with the volume set to maximum. The 8-ohm data ranges from 0.003% at 50mW, down to 0.0003% from 20W to the “knee,” at about 130W.  The 4-ohm data ranges from 0.005% at 50mW, down to 0.0006-0.0008% from 5W to the “knee,” at about 230W. The 1% THD marks were hit at 145W and 264W for the 8-ohm and 4-ohm loads respectively.

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 371 as a function of output power for the analog line level-input, for an 8-ohm load (blue/red for left/right) and a 4-ohm load (purple/green for left/right), with the volume set to maximum. The 8-ohm data ranges from 0.03% at 50mW, down to 0.0007% at the “knee.”  The 4-ohm data ranges from 0.05% at 50mW, down to 0.001% at the “knee.”

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 371 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 analog line-level input. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. We find increasing levels of THD from 8 to 4 to 2 ohms, with about a 5-8dB increase when halving the load beyond 1kHz. Overall, even with a 2-ohm load at roughly 80W, THD values were fairly low, between 0.0002-0.0003% from 20Hz to 50Hz, then up to 0.02% at 20kHz.

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

The chart above shows THD ratios measured at the output of the 371 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). Generally, THD ratios into the real speakers were higher than those measured across the resistive dummy load. The differences ranged from 0.03% at 20Hz for the two-way speaker versus 0.0007% for the resistive load, and 0.015% at 20kHz into the three-way speaker versus 0.01% for the resistive load. Between the important frequencies of 300Hz to 6kHz, all three THD traces were very close, between 0.0005% and 0.003% mark, with the speaker THD ratios outperforming the resistive load by a few dB.

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 371 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here the CCIF IMD method was used, where the primary frequency is swept from 20kHz (F1) down to 2.5kHz, and the secondary frequency (F2) is always 1kHz lower than the primary, with a 1:1 ratio. The CCIF IMD analysis results are the sum of the second (F1-F2 or 1kHz) and third modulation products (F1+1kHz, F2-1kHz). The 8-ohm load is the blue trace, the purple plot is 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). We find that all three IMD traces are close to one another, with the three-way speaker yielding 5dB higher results in the 10-20kHz range. Most of the IMD results are hovering between the 0.001% and 0.01% level.

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 371 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here, the SMPTE IMD method was used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). We find very similar IMD ratios into all three loads, between 0.004 and 0.005% across the sweep.

FFT spectrum – 1kHz (line-level input, XLR)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the analog balanced line-level input. We see that the signal’s second (2kHz) and third (3kHz) harmonics dominate at a low -110dBrA, or 0.0003%. The remaining signal harmonics are at and below -120dBrA, or 0.0001%. On the left side of the main signal peak, we see only minor power-supply noise-related peaks from the left channel only at -120dBrA to -130dBrA, or 0.0001% to 0.00003%, at 60/300/420 Hz.

FFT spectrum – 1kHz (line-level input, RCA)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the analog unbalanced line-level input. We see that the signal’s second (2kHz) and third (3kHz) harmonics dominate and are higher than the balanced input FFT above at -100dBrA, or 0.001%. The remaining harmonic and noise peaks are very similar to the balanced input FFT above, other than spurious high-frequency peaks at 16-17kHz at -120dBrA, or 0.0001%.

FFT spectrum – 1kHz (MM phono 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 phono input configured for MM. We see that the signal’s second (2kHz) and fourth (4kHz) harmonics dominate at -90dBrA and -105dBrA respectively, or 0.003% and 0.0006%. These peaks are for the left channel, the right channel peaks are up to 20dB lower in amplitude. On the left side of the main signal peak, we see power-supply noise-related peaks at 60Hz  at -80dBrA, or 0.001%, followed by smaller peaks (right channel only) at 120/180/240Hz at -90dBrA to -100dBrA, or 0.003% to 0.001%.

FFT spectrum – 1kHz (MC phono 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 phono input configured for MC. We see that the signal’s second (2kHz) and fourth (4kHz) harmonics dominate at -70dBrA and -85dBrA respectively, or 0.03% and 0.006%. These peaks are for the left channel, the right channel peaks are up to 30dB lower in amplitude. On the left side of the main signal peak, we see power-supply noise-related peaks at 60Hz at -60dBrA, or 0.01%, followed by smaller peaks (right channel only) at 120/180/240/360Hz at -70dBrA to -85dBrA, or 0.03% to 0.006%.

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. We see that the signal’s second (2kHz) and third (3kHz) harmonics dominate at -110dBrA and -100dBrA, respectively, or 0.0003% and 0.001%. The remaining signal harmonics are below -110dBrA, or 0.0003%. On the left side of the main signal peak, we see only minor power-supply noise-related peaks from the left channel only at -120dBrA to -130dBrA, or 0.0001% to 0.00003%, at 60/300/420 Hz.

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. We see effectively the same FFT as the 16/44.1 result above, but with a lower noise floor due to the increased bit depth.

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, no signal harmonics above the noise floor, and power-supply noise-related peaks from the left channel only at -125dBrA to -130dBrA, or 0.00006% to 0.00003%, at 60/180/300Hz.

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, no signal harmonics above the noise floor, and power-supply noise-related peaks from the left channel only at -125dBrA to -130dBrA, or 0.00006% to 0.00003%, at 60/180/300Hz.

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 input. The X axis is zoomed in from 40 Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most predominant (non-signal) peaks are the signal third (150Hz) harmonic just below -110dBrA, or 0.0003%, and power-supply-related noise peaks from the left channel at -120dBrA to -130dBrA, or 0.0001% to 0.00003%.

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 configured for MM. 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 the main power-supply-related noise peak at 60Hz at 80dBrA, or 0.001%. Signal harmonic peaks and subsequent power-supply-related noise peaks can be seen between -90dBrA and -110dBrA, or 0.003% and 0.0003%.

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 configured for MC. 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 the main power-supply-related noise peak at 60Hz at 60dBrA, or 0.01%. Signal harmonic peaks and subsequent power-supply-related noise peaks can be seen (mostly from the right channel) between -70dBrA and -90dBrA, or 0.03% and 0.003%.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the analog input. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -120dBrA, or 0.0001%, while the third-order modulation products, at 17kHz and 20kHz, are at -105dBrA, or 0.0006%.

Intermodulation distortion FFT (line-level input, APx 32 tone)

Shown above is the FFT of the speaker-level output of the 371 with the APx 32-tone signal applied to the analog input. The combined amplitude of the 32 tones is the 0dBrA reference, and corresponds to 10W into 8 ohms. The intermodulation products—i.e., the “grass” between the test tones—are distortion products from the amplifier and are at and below the very low -125dBrA, or 0.00006%, level.

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 at -100dBrA, or 0.001%.

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 at -100dBrA, or 0.001%.

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. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -100dBrA, or 0.001%, while the third-order modulation products, at 17kHz and 20kHz, are at roughly the same level.

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 configured for MC. 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 -80dBrA (left channel only), or 0.01%, while the third-order modulation products, at 17kHz and 20kHz, are at -105dBrA, or 0.0006%.

Squarewave response (10kHz)

Above is the 10kHz squarewave response 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 371’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. Here we see a very clean result, with only very mild softening in the corners.

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

The final plot above is the damping factor as a function of frequency. Both channels show a relatively constant damping factor from 20Hz to 3kHz at roughly 425. The damping factor then dips to roughly 200 at 20kHz.

Diego Estan
Electronics Measurement Specialist