Pro-Ject Audio Systems MaiA DS3 Integrated Amplifier-DAC Measurements

Link: reviewed by Dennis Burger on SoundStage! Access on May 1, 2023

General Information

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

The Pro-Ject Audio Systems MaiA DS3 was conditioned for 1 hour at 1/8th full rated power (~10W 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 MaiA DS3 offers three unbalanced line-level analog inputs (RCA); one unbalanced phono input (RCA) for moving-magnet (MM) or moving-coil (MC) cartridges (selectable with a switch on the rear panel); one coaxial S/PDIF (RCA), two optical S/PDIF (TosLink), and one USB digital input; a Bluetooth input; one line-level subwoofer output (RCA); two line-level pre-outs (RCA, fixed and variable); and a pair of speaker-level outputs. On the front of the unit are a 1/4″ TRS headphone output and a +6dB gain switch for the preamp section. For the purposes of these measurements, the following inputs were evaluated: digital coaxial and the analog line-level and MM/MC unbalanced inputs, with the +6dB gain switch engaged.

Most measurements were made with a 2Vrms line-level analog input, 5mVrms MM input, 0.5mVrms MC input, and 0dBFS digital input. 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 80W (8 ohms). For comparison, on the line-level input, a SNR measurement was also made with the volume at maximum, but with a lower input voltage to achieve the same 80W output.

Based on the inaccuracy and non-repeatable results at various volume levels of the left/right channel matching (see table below), the MaiA DS3 volume control is likely a potentiometer operating in the analog domain. The volume control offers a total range from -66dB to +35.2dB between the line-level analog input and the speaker outputs, with the +6dB switch engaged.

The analyzer’s input bandwidth filter was set to 10Hz–22.4kHz for all measurements, except for frequency-response and FFT charts. Because the MaiA DS3 is a digital amplifier technology that exhibits considerable noise above 20kHz (see FFTs below), the 22.4kHz bandwidth setting was maintained for THD versus frequency sweeps as well. For these sweeps, the highest frequency was 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

Published specifications vs. our primary measurements

The table below summarizes the measurements published by Pro-Ject for the MaiA DS3 compared directly against our own. The published specifications are sourced from Pro-Ject’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 8ohms and 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 line-level analog input and digital coaxial input (unless specified, assume a 1kHz sinewave at 2Vrms or 0dBFS, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

For the continuous dynamic power test, the MaiA DS3 was able to sustain 141W into 4 ohms (~2% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (14.1W) for 5s, 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 MaiA DS3 was only slightly warm to the touch.

Our primary measurements revealed the following using the phono-level input, MM configuration (unless specified, assume a 1kHz 5mVrms 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 output, 300 ohms loading, 10Hz to 22.4kHz bandwidth, and the +6dB gain switch disengaged):

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

In our measured frequency response (relative to 1kHz) chart above, the MaiA DS3 is essentially flat within the audioband (-0.09dB at 20Hz, +0.28dB at 20kHz). The rise in relative response at high frequencies is due to the class-D amplifier’s poor damping factor (i.e., high output impedance) at high frequencies. When the frequency response into 4 ohms is plotted (see RMS level v frequency v load graphs below), we find a dip in response at high frequencies. 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. Because the MaiA DS3 exhibited poor channel tracking, we’ve also plotted . . .

. . . RMS level vs frequency, to show the channel-to-channel deviations. In the chart above, we can see that the right channel is roughly 0.8dB lower in output than the left channel. This is due to the deviations inherent to the potentiometer used to control the volume.

Phase response (line-level input)

Above is the phase response plot from 20Hz to 20kHz for the line-level input, measured across the speaker outputs at 10W into 8 ohms. The MaiA DS3 does not invert polarity. Here we find a worst case of about +30 degrees at 20Hz and 20kHz.

Frequency response (line-level analog input, subwoofer line-level output)

In our measured frequency response of the line-level subwoofer output shown above, the MaiA DS3 is at 0dB at 20Hz and -0.5dB at 20kHz. As a result, it is clear that the sub-out does not offer any built-in low-pass filtering.

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

The chart above shows the MaiA DS3’s frequency response (relative to 1kHz) as a function of input type measured across the speaker outputs at 10W into 8 ohms. The blue trace is for a 16-bit/44.1kHz dithered digital input signal from 10Hz to 22kHz using the coaxial digital input, and the purple trace is for a 24/96 dithered digital input signal from 10Hz to 48kHz, while the pink trace is for a 24/192 dithered digital input signal from 10Hz to 96kHz. The green trace is the same analog input frequency response seen above. The 16/44.1 data exhibits brickwall-type filtering, with a -3dB at 21.2kHz. The 24/96 and 24/192 kHz data were nearly identical, yielding -3dB points at 45.3kHz and 46.5kHz respectively. The analog input data yields a -3dB point at 58kHz.

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

The chart above shows the frequency response (relative to 1kHz) for the MM phono input. We see maximum deviations within about ±0.25dB from 20Hz to 20kHz for the left channel, and about ±0.5dB for the right channel. 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 MM phono input, measured across the speaker outputs at 10W into 8 ohms. The MaiA DS3 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.

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

The chart above shows the frequency response (relative to 1kHz) for the MC phono input. 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 maximum deviations within about ±0.5dB from 20Hz to 20kHz for both channels, although the left channel is much flatter than the right channel between 100Hz and 10kHz.

Phase response (MC input)

Above is the phase response plot from 20Hz to 20kHz for the MC phono input, measured across the speaker outputs at 10W into 8 ohms. The MaiA DS3 does not invert polarity. The response is essentially identical to the phase response for the MM input above.

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 fixed line-level pre-outs of the MaiA DS3 for a 1.36Vrms (at 0dBFS) output signal. The digital input is swept with a dithered 1kHz input signal from -120dBFS to 0dBFS, and the output is analyzed by the APx555. The ideal response would be a straight flat line at 0dB. Both data were essentially perfect as of -100dBFS down to 0dBFS. At -120dBFS, the 16/44.1 data were about +2dB (left/right channels) above reference, while the 24/96 data were still at the reference 0dB level. This is a good linearity test result.  

Impulse response (24/44.1 data)

The graph above shows the impulse response for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s) for one sample period then back to digital silence, measured at the fixed line-level pre-outs of MaiA DS3. We can see that the MaiA DS3 utilizes a typical symmetrical sinc function reconstruction filter.

J-Test (coaxial)

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line level pre-outs of the MaiA DS3. J-Test was developed by Julian Dunn in 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, as high as -130dBrA. This is an average J-Test result, indicating that the MaiA DS3 DAC may be susceptible to jitter.

J-Test (optical)

The chart above shows the results of the J-Test test for the optical digital input measured at the fixed line-level pre-outs of the MaiA DS3. It is essentially the same result as with the coax input shown above.

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

Both the coaxial and optical inputs were also tested for jitter immunity by injecting 100ns of artificial sinewave jitter at 2kHz, which would manifest as sidebands at 10kHz and 14kHz without any jitter rejection. Jitter immunity proved poor at the 100ns level, with visible sidebands at -100dBrA. The optical input jitter result was very similar to the coaxial input result.

J-Test with 500ns of injected jitter (coaxial)

Both the coaxial and optical inputs were also tested for jitter immunity by injecting 500ns of artificial sinewave jitter at 2kHz, which would manifest as sidebands at 10kHz and 14kHz without any jitter rejection. Jitter immunity proved poor, with visible sidebands at -85dBrA. The MaiA DS3DAC did lose sync with the signal when jitter was increased beyond 500ns. The optical input jitter result was very similar to the coaxial input result.

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

The plot above shows a fast Fourier transform (FFT) of the MaiA DS3’s fixed line-level pre-outs with white noise at -4 dBFS (blue/red) and a 19.1 kHz sinewave (purple/green) 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 no aliased image peaks in the audioband above the noise floor at -135dBrA. The main 25kHz alias peak is highly suppressed at -105dBrA. The second, third, and fourth distortion harmonics (38.2, 57.3, 76.4kHz) of the 19.1kHz tone are between -90dBrA and -100dBrA.

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

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

. . . is the same but zoomed in to highlight differences. Here we can see a significant maximum deviation at 20kHz of about 2.3dB from 4 ohms to no load, which is an indication of a very low damping factor at high frequencies, or high output impedance. The deviation in RMS level below 2kHz from no load to 4 ohms is much less, at about 0.2dB. The variation in RMS level when a real speaker was used is also significant, deviating by about 0.3-0.4dB, with the lowest response at 200Hz, and the highest at 5kHz.

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

The chart above shows THD ratios at the output into 8 ohms as a function of frequency for a sinewave stimulus at the analog line-level input. The blue and red plots are for left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at 55W. The power was varied using the volume control. At 1W, THD ratios ranged from 0.007% at 20Hz, down to 0.002% at 6kHz. At 10W, THD ratios ranged from 0.02% at 20Hz, down to 0.005% at 2-3kHz. The 55W THD values are higher and range from 0.05% at 20Hz, down to 0.015% at 2kHz, then up to 0.03% at 6kHz. These data corroborate Pro-Ject’s claim of less than 0.01% THD at 10W at 1kHz.

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

The chart above shows THD ratios as a function of frequency plots for the MM and MC phono input configurations measured across an 8-ohm load at 10W. The input sweep is EQ’d with an inverted RIAA curve. The THD values for the MM configuration vary from around 0.02% (20Hz) down to just beow 0.01% at 1-2kHz, the back up to 0.02% at 6kHz. The THD values for the MC configuration vary from around 0.08% (20Hz) down to as low as 0.003% (left channel) at 3kHz, then up to 0.01% at 6kHz.

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

The chart above shows THD ratios measured at the output of the MaiA DS3 as a function of output power for the analog line-level input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). Both data sets track fairly closely, with the 8-ohm data outperforming the 4-ohm data by about 5dB. The 8-ohm data ranges from around 0.002% at 1W and below, up to 0.015% at the “knee” around 70W, then up to the 1% THD mark at the rated 80W. With a 4-ohm load, the “knee” occurs at about 120W, and the 1% THD value was reached at 144W.

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 MaiA DS3 as a function of output power for the analog line-level input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). Overall, THD+N values for both loads were similar, ranging from 0.02%, down to just below 0.01%, with the 8-ohm data outperforming the 4-ohm data by about 2-5dB.

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

The chart above shows THD ratios measured at the output of the MaiA DS3 as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yielded 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 the 8-ohm trace ranging from 0.01% at 20Hz down to 0.003% at 2kHz, and outperforming the 4-ohm trace by about 5dB (except at 6kHz, where both data sets yielded THD ratios of 0.01%).  THD values with a 2-ohm load were much higher, ranging from 0.05% at 20Hz, down to 0.03% at 400Hz, then up to 0.1% at 6kHz. Nonetheless, these data show that the MaiA DS3 is stable into 2-ohm loads.

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 MaiA DS3 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). At lower frequencies, the two-way speaker yielded the highest THD ratios, as high as 0.15% at 20Hz, but as low as 0.001% at 3-4kHz. The three-way speaker ranged from a high of 0.015% at 20Hz, down to 0.0025% at 2kHz, and up to 0.015% at 6kHz. Generally, THD ratios were higher with real speakers compared to the 8-ohm dummy resistive load.

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 MaiA DS3 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). The results for the dummy load were fairly consistent, hovering between 0.003% and 0.005% from 2.5kHz to 20kHz. We find that the two-way speaker yielded IMD ratios 15dB higher than the dummy load above 10kHz, reaching 0.04% at 20kHz, compared to 0.005% for the dummy load. The three-way speaker yielded IMD ratios roughly 15dB higher than the dummy load across the swepted frequencies.

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 MaiA DS3 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 similar, with the two-way speaker and dummy load consistently yielding 0.01% IMD, and the three-way speaker reaching 0.02% from 100Hz to 250Hz.

FFT spectrum – 1kHz (line-level input)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the analog line-level input. We see that the signal’s second harmonic (2kHz) dominates at around -85dBrA, or 0.006%. The subsequent signal harmonics are around or below -100dBrA, or 0.001%. There are clearly visible power-supply-related noise peaks at even harmonics (120Hz, 240Hz, 360Hz, etc.) on the left side of the main 1kHz peak, at -95dBrA, or 0.002%, down to -120dBrA, or 0.0001%. There is also a rise in the noise above 20kHz, characteristic of digital amplifiers.

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

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 16/44.1. The signal and noise-related harmonics are very similar to the FFT above for the analog input.

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. The signal- and noise-related harmonics are very similar to the FFT above for the analog input.

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 signal harmonics from the right channel at -90dBrA, or 0.003%, and below. The noise floor is also elevated, as high as -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 signal harmonics from the right channel at -90dBrA, or 0.003%, and below. The noise floor is also elevated, as high as -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 MM phono input. We see that the signal’s second harmonic (2kHz) dominates at around -85dBrA, or 0.006%. The subsequent signal harmonics are around or below -100dBrA, or 0.001%. There are clearly visible power-supply-related noise peaks at even and odd harmonics (60Hz, 120Hz, 180Hz, 240Hz, etc.) on the left side of the main 1kHz peak, at -90dBrA, or 0.003%, down to -110dBrA, or 0.0003%.

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 MC phono input. We see that the signal’s second harmonic (2kHz) dominates at around -90/85dBrA (left/right channels), or 0.003/0.006%. Most of the subsequent signal harmonics are buried beneath the noise-floor, which ranges from -100dBrA to -120dBrA from 2kHz to 20kHz. There are three clearly visible power-supply related noise peaks at 60Hz, 120Hz and 180Hz, on the left side of the main 1kHz peak, at -70dBrA, or 0.03%, and -85dBrA, or 0.006%.

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. We see that the signal’s second harmonic (100Hz) dominates at around -75dBrA, or 0.02%. The subsequent signal harmonics are around or below -100dBrA, or 0.001%. There are clearly visible power-supply-related noise peaks at even harmonics (120Hz, 240Hz, 360Hz, etc.) at -95dBrA, or 0.002%, down to -120dBrA, or 0.0001%.

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 MM phono input. The X axis is zoomed in from 40 Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. We see that the signal’s second harmonic (100Hz) dominates at around -75dBrA, or 0.02%. The subsequent signal harmonics are around or below -100dBrA, or 0.001%. There are clearly visible power-supply-related noise peaks at even and odd harmonics (60Hz, 120Hz, 180Hz, 240Hz, etc.) at -90dBrA, or 0.003%, down to -110dBrA, or 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 MC phono input. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. We see that the signal’s second harmonic (100Hz) dominates at around -80dBrA, or 0.01%. Most of the subsequent signal harmonics are buried beneath the noise-floor, which ranges from -90dBrA to -110dBrA from 50Hz to 1kHz. There are three clearly visible power-supply-related noise peaks at 60Hz, 120Hz, and 180Hz at -70dBrA, or 0.03%, and -85dBrA, or 0.006%.

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

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

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 -90dBrA, or 0.003%. The third-order modulation products, at 17kHz and 20kHz, are at around the same level.

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 MM phono input. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -70dBrA, or 0.03%. The third-order modulation products, at 17kHz and 20kHz, are at around the same level.

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 MC phono input. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -90dBrA, or 0.003%. The third-order modulation products, at 17kHz and 20kHz, are at around the same level.

Square-wave response (10kHz)

Above is the 10kHz squarewave 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 MaiA DS3’s slew-rate performance. Rather, it should be seen as a qualitative representation of the MaiA DS3’s average 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 can see the 600kHz switching oscillator frequency used in the digital amplifier section visibly modulating the waveform.

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

Above is the 10kHz squarewave 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 600kHz switching frequency. We see more evidence here, in the overshoot and soft corners of the squarewave, of the MaiA DS3’s average bandwidth.

FFT spectrum (1MHz bandwidth)

The MaiA DS3’s class-D amplifier relies on a switching oscillator to convert the input signal to a pulse-width-modulated (PWM) squarewave (on/off) signal before sending the signal through a low-pass filter to generate an output signal. The MaiA DS3 oscillator switches at a rate of about 600kHz, and this graph plots a wide bandwidth FFT spectrum of the amplifier’s output at 10W into 8 ohms as it’s fed a 1kHz sinewave. We can see that the 600kHz peak is quite evident, and at -40dBrA. There is also a peak at 1.2MHz (the second harmonic of the 600kHz peak), at -80dBrA. Those peaks—the fundamental and its harmonic—are direct results of the switching oscillators in the MaiA DS3’s amp modules. The noise around those very-high-frequency signals are in the signal, but all that noise is far above the audioband—and therefore inaudible—and so high in frequency that any loudspeaker the amplifier is driving should filter it all out anyway.

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

The final graph above is the damping factor as a function of frequency. Both channels show a relatively constant damping factor from 20Hz to 2kHz, at around 86/80 (left/right). Above 2kHz, we see a steep decline in damping factor, as low as 10 at 20kHz, which is typical of this type of digital-amplifier technology.

Diego Estan
Electronics Measurement Specialist