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

General Information

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

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

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

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

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

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

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

Volume position Channel deviation
1 0.04dB
10 0.04dB
30 0.04dB
50 0.04dB
70 0.04dB
90 0.04dB
100 0.04dB

Published specifications vs. our primary measurements

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

Parameter Manufacturer SoundStage! Lab
Rated output power into 8 ohms (0.03% THD, 1kHz) 100W 126W
Rated output power into 4 ohms (0.03% THD, 1kHz) 100W 232W
THD (20Hz-6.5kHz, 100W, 8 ohms) <0.03% <0.007%
SNR (A-weighted, ref. 1W out in 8 ohms, 500mV input) >85.1dB 85.2dB
Clipping power (1kHz, 8 ohms, 0.1%THD) 130W 128W
Clipping power (1kHz, 4 ohms, 0.1%THD) 230W 246W
IHF dynamic power (no-load clipping, 8 ohms) 160W 167W
IHF dynamic power (no-load clipping, 4 ohms) 300W 333W
Damping factor (ref. 8 ohms 20Hz and 6.5kHz) >190 190
Frequency response (20Hz-20kHz) ±0.6dB -0.16dB/-0.54dB
Channel separation (1kHz, 1W) >83dB 85dB
Channel separation (10kHz, 1W) >70.5dB 66dB
Input sensitivity (analog) 456mVrms 452mVrms
Input sensitivity (digital) -13.23%FS -13.18%FS

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

Parameter Left channel Right channel
Maximum output power into 8 ohms (1% THD+N, unweighted) 151W 152W
Maximum output power into 4 ohms (1% THD+N, unweighted) 285W 288W
Continuous dynamic power test (5 minutes, both channels driven) passed passed
Crosstalk, one channel driven (10kHz) -66dB -72dB
Damping factor 198 190
Clipping no-load output voltage (instantaneous power into 8 ohms) 36.5Vrms (167W) 36.8Vrms (169W)
DC offset <13mV <16mV
Gain (pre-out) 4.1dB 4.1dB
Gain (maximum volume) 35.8dB 35.9dB
IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) <-91dB <-93dB
IMD ratio (SMPTE, 60Hz + 7kHz stimulus tones, 4:1 ) <-80dB <-80dB
Input impedance (line input, RCA) 16.5k ohms 16.5k ohms
Input sensitivity (for rated power, maximum volume) 454mVrms 452mVrms
Noise level (A-weighted) <190uVrms <180uVrms
Noise level (unweighted) <310uVrms <280uVrms
Output Impedance (pre-out) 93.5 ohms 93.5 ohms
Signal-to-noise ratio (full rated power, A-weighted, 1Vrms in) 98.0dB 97.8dB
Signal-to-noise ratio (full rated power, unweighted, 1Vrms in) 96.6dB 96.4dB
Signal-to-noise ratio (full rated power, A-weighted, max volume) 93.4dB 93.4dB
Dynamic range (full rated power, A-weighted, digital 24/96) 106.8dB 108.0dB
Dynamic range (full rated power, A-weighted, digital 16/44.1) 98.6dB 98.8dB
THD ratio (unweighted) <0.0022% <0.0015%
THD ratio (unweighted, digital 24/96) <0.0012% <0.0018%
THD ratio (unweighted, digital 16/44.1) <0.0012% <0.0018%
THD+N ratio (A-weighted) <0.0034% <0.0026%
THD+N ratio (A-weighted, digital 24/96) <0.0026% <0.0028%
THD+N ratio (A-weighted, digital 16/44.1) <0.0026% <0.0028%
THD+N ratio (unweighted) <0.0041% <0.0036%
Minimum observed line AC voltage 122VAC  122VAC

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

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

frequency response

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

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

frequency response vs input type

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

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

frequency response tone controls

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

Frequency response (subwoofer output engaged, 120Hz crossover)

frequency response sub on

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

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

phase response

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

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

digital linearity 1644 1 2496

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

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

impulse response 2444 1

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

J-Test (coaxial input)

jtest coax 2448

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

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

J-Test (optical input)

jtest optical 2448

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

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

jtest coax 2448

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

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

wideband fft noise plus 19 1khz 1644 1kHz

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

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

rms level vs frequency vs load impedance

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

rms level vs frequency vs load impedance

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

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

thd ratio unweighted vs frequency vs output power

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

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

thd ratio unweighted vs output power at 4 8 ohms

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

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

thd n ratio unweighted vs output power at 4 8 ohms

The chart above shows THD+N ratios measured at the output of the M10 V2 as a function of output power for the line-level input, for an 8-ohm load (purple/green for left/right channels) 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 0.05%, down to 0.005%, with the 8-ohm data outperforming the 4-ohm data by about 3-5dB.

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

thd vs frequency load

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

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

thd vs frequency vs speakers

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

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

IMD CCIF vs frequency vs speakers

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

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

IMD SMPTE vs frequency vs speakers

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

FFT spectrum – 1kHz (line-level input)

FFT spectrum 1khz

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

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

fft spectrum 1khz 1644 1 0dbfs

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

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

fft spectrum 1khz 2496 0dbfs

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

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

fft spectrum 1khz 2444 1 90dbfs

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

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

fft spectrum 1khz 2496 90dbfs

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

FFT spectrum – 50Hz (line-level input)

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 for the analog line-level input. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The second signal harmonic (100Hz) is at -90dBrA, or 0.003%, while all other peaks are at or below -110dBrA, or 0.0003%, including the 60Hz power-supply-related peak.

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

intermodulation distortion fft 18khz 19khz summed stimulus

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

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

intermodulation distortion fft 18khz 19khz summed stimulus

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

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

intermodulation distortion fft 18khz 19khz summed stimulus

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

Square-wave response (10kHz)

square wave response 10kHz

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

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

square wave response 1kHz 250kHz BW

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

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

 fft spectrum 1khz 1MHz BW

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

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

damping factor vs frequency

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

Diego Estan
Electronics Measurement Specialist

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