Details

Parent Category: Products

Category: Amplifier Measurements

Created: 15 July 2024

Link: reviewed by George de Sa on SoundStage! Hi-Fi on July 15, 2024

General information

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

The Chord Electronics Ultima integrated amplifier was conditioned for one 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 Ultima offers four line-level analog inputs (three unbalanced over RCA, one balanced over XLR), one balanced (XLR) line-level set of pre-outs, and a pair of speaker level outputs. For the purposes of these measurements, the following input was evaluated: analog (XLR) line level.

Most measurements were made with a 2Vrms line-level analog input. The signal-to-noise ratio (SNR) measurements were made with the default input signal values but with the volume set to achieve the rated output power of 125W (8 ohms). For comparison, SNR measurements were also made with the volume at maximum. There was no significant difference in terms of THD and noise between the RCA and XLR inputs (FFTs are provided as a point of comparison in this report), though there is an extra 6dB gain while using the unbalanced inputs.

Based on the inaccuracy and non-repeatability of the left/right volume channel matching (see table below), the Ultima volume control is a potentiometer operating in the analog domain. The Ultima overall volume range is from -56.5dB to +30.6dB (XLR line-level input, speaker output). One curiosity with this integrated amplifier is that the balance control does not have a center detent. The balance control was used to balance both channels with the volume control at the center position before the volume table was measured.

The analyzer’s input bandwidth filter was set to 10Hz to 22.4kHz for all measurements, except for frequency response and FFTs. Because the Ultima uses a digital switch-mode power supply that exhibits 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.

One final important note is that because of the unique output stage of the Ultima Integrated, which seems to dynamically adjust to the load it is driving, we could not attrain a reliable damping factory measurement. In fact, using our traditional means we derived a negative damping factor, which is impossible, but is likely because of the way the output stage behaves. As a result, no damping factor chart, which we usually provide, is shown.

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 Chord for the Ultima compared directly against our own. The published specifications are sourced from Chord’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 to 1MHz, 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.

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

For the continuous dynamic power test, the Ultima was able to sustain 265W into 4 ohms (~3.5% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (26.5W) for 5 seconds, for 5 continuous minutes without inducing a fault protection circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the Ultima was quite warm to the touch.

Frequency response (8-ohm loading)

In our frequency-response plots above (relative to 1kHz), measured across the speaker outputs at 10W into 8 ohms, the Ultima is near flat within the audioband (20Hz to 20kHz): 0dB at 20Hz and -2.5dB at 20kHz. At the extremes, the Ultima measured -0.2dB at 5Hz and -3dB at 65kHz. This does not corroborate Chord’s claim of 10Hz to 200kHz, ±3dB. 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)

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 Ultima does not invert polarity and yields little phase shift, with less than +5 degrees at 20Hz (the Ultima is not DC coupled) and roughly -30 degrees at 20kHz.

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 50kHz. 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 see that the deviations between no load and 4 ohms are not only minuscule at less than 0.005dB, but also that the 4-ohm response is higher in amplitude than the 8-ohm data, which would imply a negative output impedance. This is, of course, impossible, but implies some sort of on-the-fly gain adjustments in the Ultima as the load is changed. It also made our typical damping factor measurements impossible to perform. In any event, with a real speaker load, deviations measured just below the 0.01dB level, which is an extraordinary result.

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

The chart above shows THD ratios at the speaker-level outputs 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 at 1W output into 8 ohms, purple/green at 10W, and pink/orange at the rated 125W. The power was varied using the Ultima volume control. Generally, THD ratios are on the high side for a solid state amplifier. The left channel outperformed the right channel by as much as 10dB at lower frequencies. THD ratios, at all power levels, ranged from 0.003%/0.02% at 20Hz, up to 0.03%/0.07% at 6kHz.

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

The chart above shows THD ratios measured at the speaker-level outputs of the Ultima 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). The 8-ohm data outperformed the 4-ohm data by roughly 7-8dB. The 8-ohm THD ratios were steady at roughly 0.02/0.03% from 50mW to the “knee” at roughly 130W. The 4-ohm THD ratios were steady at roughly 0.04/0.05% from 50mW to the “knee” at roughly 200W. The 1% THD marks were hit at 140W and 257W.

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 Ultima as a function of output power for the 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).  The 8-ohm data outperformed the 4-ohm data by roughly 5dB. The 8-ohm THD+N ratios ranged from 0.2% at 50mW down to 0.03% at 50-130W. The 4-ohm THD+N ratios ranged from 0.4% at 50mW down to 0.05% at 20-200W.

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 Ultima as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yielded 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 a roughly 5dB increase in THD every time the load is halved. Into 2 ohms, THD ratios ranged from 0.006% at 20Hz, up to 0.2% at 6kHz.

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 Ultima 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 very similar to the resistive dummy load, although still high for a modern solid-state amplifier. These ranged from 0.006% at 20Hz up to 0.1% at 5kHz. Of note is that the Ultima maintained low THD at 20-30Hz into the two-way speaker, which often yields much higher THD ratios when used with a typical class-AB integrated amp.

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 Ultima 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 3-way speaker (Paradigm Founder Series 100F, measurements can be found here). We find very similar IMD ratios into all three loads up to 7kHz, between 0.007 and 0.02%. Above 7kHz, the three-way speaker yielded the highest IMD results, 0.09% at 20kHz, compared to 0.02/0.03% for the two-way speaker and resistive load.

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 Ultima 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, steady at a high 0.1% from 40Hz to 500Hz, then down to 0.05% to 1kHz.

FFT spectrum – 1kHz (line-level XLR 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 (2kHz) and third/fourth (3/4kHz) harmonics dominate at a fairly high -80dBrA, or 0.01%, and -85dBrA, or 0.006%, while subsequent signal harmonics range from -90dBrA, or 0.003%, down to -110dBrA, or 0.0003%. On the right side of the signal peak, we see the primary (60Hz) noise-related peak at a relatively high -90dBrA, or 0.003%, and its harmonics (120, 180, 240, 300Hz, etc.) at the -100dBrA level, or 0.001%, down to -110dBrA, or 0.0003%. The base noise floor, at -130dBrA to -120dBrA, is also relatively high for a solid-state amplifier.

FFT spectrum – 1kHz (line-level RCA 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 unbalanced (RCA) analog line-level input. We see essentially the same FFT as with the balanced input above.

FFT spectrum – 50Hz (line-level input)

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the balanced 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 most predominant (non-signal) peaks are the second (100Hz), third (150Hz), and fifth (250Hz) signal harmonics and the primary noise peak at 60Hz. These are all at the -80dBrA (right channel), or 0.01%, to -90dBrA, or 0.003%, level. We can also see that the THD ratios for the left channel on the third (150Hz) and fifth (250Hz) signal harmonics are 20dB lower than the right channel.

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 -85dBRa, or 0.006%, while the third-order modulation products, at 17kHz and 20kHz, are at -75dBrA, or 0.02%. This is a weak IMD result for a modern solid state amplifier.

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

Shown above is the FFT of the speaker-level output of the Ultima 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 -100dBrA, or 0.001%, level. The low energy peaks that rise near and above -90dBrA are due to power-supply noise.

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 Ultima’s slew-rate performance. Rather, it should be seen as a qualitative representation of the Ultima’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, due to the Ultima’s use of a digital-type switch mode power-supply, we see an oscillator frequency riding on top of the 10kHz waveform.

Square-wave response (10kHz)—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 switching frequency. We see evidence here, in the soft corners of the squarewave, of the Ultima’s mid-tier bandwidth.

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

The Ultima’s use of a digital swith-mode power supply that yields a rising noise floor above 2kHz, as well as several peaks, as high as -35dBrA, beyond the audioband. Those peaks are direct results of the switching oscillators in the Ultima. 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.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Amplifier Measurements

Created: 01 July 2024

Link: reviewed by Dennis Burger on SoundStage! Access on July 1, 2024

General Information

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

The Arcam Radia A25 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 A25 offers three set of RCA line-level analog inputs, one RCA phono input, two digital RCA coaxial inputs, one digital TosLink optical input, one USB digital input, left/right RCA pre-outs, one set of speaker-level outputs, and one headphone output over a 1/8″ TRS connector. A Bluetooth input is also offered. For the purposes of these measurements, the following inputs were evaluated: digital coaxial, analog line-level, and phono, as well as the headphone output.

Most measurements were made with a 2Vrms line-level analog input and 0dBFS digital input. The signal-to-noise (SNR) measurements were made with the default input signal values but with the volume set to the rated output power of 100W into 8 ohms. For comparison, on the line-level input, a SNR measurement was also made with the volume at maximum. The A25 offers three digital filters for the digital inputs: Linear Phase Fast, Hybrid Fast, Minimum Phase Slow. Unless otherwise noted, the Linear Phase Fast filter was used.

Based on the accuracy and randomness of the left/right volume channel matching (see table below), the A25 volume control is digitally controlled but operating in the analog domain. The A25 overall volume range is from -77dB to +44.dB (line-level input, speaker output). It offers 4dB increments from position 0 to 10, 2dB increments from positions 10 to 20, 1dB from 20 to 50, and 0.5dB from 50 to 99.

Our typical input bandwidth filter setting of 10Hz to 22.4kHz was used for all measurements except FFTs and THD versus frequency, where a bandwidth of 10Hz to 90kHz was used. Frequency response measurements utilize a DC to 1 MHz input bandwidth.

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 Arcam for the A25 compared directly against our own. The published specifications are sourced from Arcam’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 to 1MHz, 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.

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 A25 was able to sustain 161W into 4 ohms (~3% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (16.1W) for 5 seconds, for 200 seconds of the 500-second test before inducing the fault protection circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the A25 was 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 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 frequency response plots above (relative to 1kHz), measured across the speaker outputs at 10W into 8 ohms, the A25 is essentially perfectly flat within the audioband (20Hz to 20kHz, 0/-0.1dB). The -3dB point is at roughly 70kHz, and 0dB at 5Hz. The A25 appears to be DC coupled. 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 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 A25 yielded only about -30 degrees of phase shift at 20kHz.

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

The chart above shows the frequency response for the MM 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 a very flat response from 200Hz to 20kHz, and worst-case channel-to-channel deviations of roughly 0.1dB at 100 to 200Hz. Below 200Hz, there is steep attenuation (-3dB at 20Hz), as Arcam appears to have implemented an anti-rumble filter on their phono input.

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 A25 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 +30 degrees at 20Hz and -100 degrees at 20kHz.

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

The chart above shows the A25’s frequency response (relative to 1kHz) as a function of input type measured across the speaker outputs at 10W into 8 ohms. The two green traces are the same analog input data from the speaker-level frequency-response graph above. The blue and red traces are for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz using the coaxial input, and the purple and green traces are for a 24/96 dithered digital input signal from 5Hz to 48kHz, and the pink and orange traces are for a 24/192 dithered digital input signal. At low frequencies, the digital signals yielded a flat response down to 5Hz, same as the analog response. The -3dB points are: 21kHz for the 16/44.1 data, 46kHz for the 24/96, 78kHz for the 24/192 data, and 72kHz for the analog input. Also of note, the 16/44.1 and 24/96 input data showed brick-wall-type high-frequency filtering, while the 24/912 and analog data did not.

Frequency response vs. filter type (16/44.1, left channel only)

The chart above shows the A25’s frequency response (relative to 1kHz) as a function of filter type measured across the speaker outputs at 10W into 8 ohms for a 16/44.1 digital input (left channel only). The blue plot is the default Linear Phase Fast filter, the purple trace is the Hybrid Fast Filter, while the pink trace is the Minimum Phase Slow filter. We can see how the Linear Phase Fast filter offers true brick-wall filtering just past 20kHz (21kHz), while the Hybrid Fast and Minimum Phase Slow filters yielded -3dB points at 19kHz.

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-outputs of the A25, where 0dBFS was set to yield 1Vrms (2Vrms caused excessive THD). 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. The 24/96 data were at -3dB at -120dBFS, while the 16/44.1 data were +/-1dB at -120 to -110dBFS.

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 A25. The blue trace is for the Linear Phase Fast filter, which yielded a typical symmetrical sinc function response. The purple trace is for the Hybrid Fast filter, which yielded little pre-ringing and extended post-ringing, while the Minimum Phase Slow filter (orange) yielded essentially no pre-ringing and minimized post-ringing.

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-outputs of the A25 where 0dBFS is set to 1Vrms. 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.

Here we see a poor J-Test result, with several peaks in the audioband, ranging from -105dBFS down to -150dBFS. This is an indication that the A25 DAC may have poor 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 pre-outputs of the A25. The optical input yielded similar but slightly worse results compared to the coaxial input.

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 A25, with an additional 10ns of 2kHz sinewave jitter injected by the APx555. The telltale peaks at 10kHz and 12kHz can be seen at -120dBFS.

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 A25, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The telltale peaks at 10kHz and 12kHz can be seen at a higher -100dBFS.

J-Test (optical, 100ns jitter)

The chart above shows the results of the J-Test test for the optical digital input measured at the line-level output of the A25, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The results are essentially the same as with the coaxial input.

Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (Linear Phase Fast filter, coaxial input)

The chart above shows a fast Fourier transform (FFT) of the A25’s line-level pre-outputs with white noise at -4dBFS (blue/red) and a 19.1 kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1 using the Linear Phase Fast filter. The steep roll-off around 20kHz in the white-noise spectrum shows that the Linear Phase Fast filter is of the brick-wall type variety. There are a few low-level aliased image peaks within the audioband at the -115dBrA and below level. The primary aliasing signal at 25kHz is highly suppressed at -80dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are near the same level.

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

The chart above shows a fast Fourier transform (FFT) of the A25’s line-level pre-outputs with white noise at -4dBFS (blue/red) and a 19.1 kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1, using the Hybrid Fast filter. The steep roll-off around 20kHz in the white-noise spectrum shows that the Hybrid Fast filter is of the brick-wall type variety. There are a few low-level aliased image peaks within the audioband at the -120dBrA and below level. The primary aliasing signal at 25kHz is highly suppressed at -80dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are near the same level.

Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (Minimum Phase Slow filter, coaxial input)

The chart above shows a fast Fourier transform (FFT) of the A25’s line-level pre-outputs with white noise at -4dBFS (blue/red) and a 19.1 kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1, using the Minimum Phase Slow filter. The shallower roll-off around 20kHz in the white-noise spectrum shows that the Minimum Phase Slow filter does not use Brick-Wall type of filtering. There are a few low-level aliased image peaks within the audioband at the -120dBrA and below level. The primary aliasing signal at 25kHz is mildly suppressed at -35dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are around the -80 to -90 dBrA 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 line-level input swept from 5Hz to 50kHz. 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 see that the deviations between no load and 4 ohms are very small at roughly 0.09dB. This is a strong result and an indication of a low output impedance, or high damping factor. With a real speaker load, deviations measured lower at roughly 0.07dB.

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

The chart above shows THD ratios at the speaker-level outputs 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 at 1W output into 8 ohms, purple/green at 10W, and pink/orange just at 90W. The power was varied using the A25 volume control. The 10W THD ratios were the lowest, ranging from 0.0005% at 20Hz down to 0.0002-0.0003% from 100Hz to 2kHz, then up to 0.001% at 20kHz. The 1W THD ratios were higher and relatively flat across the audioband, from 0.0005% to 0.001%. At 90W, THD ratios ranged from 0.0005% at lower frequencies, up to 0.01% at 20kHz.

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

The chart above shows THD ratios as a function of frequency plots for the MM phono input 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 0.03% (20Hz) down to 0.0005% (2/3kHz left channel), up to 0.003% at 20kHz.

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

The chart above shows THD ratios measured at the speaker-level outputs of the A25 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). THD ratios into 4 and 8 ohms are remarkably close (with 2-3dB). They range from 0.002% at 50mW, down to 0.0003% in the 5 to 30W range. The “knee” into 8 ohms can be found right around the rated output power of 100W, while the 4-ohm knee can be seen around 150W. The 1% THD marks were hit at 109W and 160W into 8 and 4 ohms.

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

The chart above shows THD+N ratios measured at the speaker-level outputs of the A25 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). THD+N ratios into 4 and 8 ohms are remarkably close (with 2-3dB). They range from 0.02% at 50mW, down to 0.001% in the 20 to 100W range.

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 A25 as a function of frequency into three different loads (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. Note that for the 2-ohm load, the A25’s protection circuit was almost immediately initiated and shut the unit down, so it is not visible. The 8-ohm load is the blue trace and the 4-ohm load the purple trace. We find a roughly 5-10dB increase in THD from 8 to 4 ohms from 400Hz to 20kHz. These ranged from 0.0003% at 20Hz down to 0.0002% at 1-2kHz, then up to 0.0015% at 20kHz for the 8-ohm load. The 4-ohm load ranged from 0.0005% at 20Hz down to 0.0002% at 100-200Hz, then up to 0.002% 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 A25 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 0.06% at 20Hz for the two-way speaker versus 0.0008% for the resistive load, and 0.004% at 20kHz into the three-way speaker versus 0.001% for the resistive load. Between the important frequencies of 500Hz to 6kHz, all three THD traces were very close, around the 0.0006-0.0007% mark. This is a strong result.

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 A25 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 4-5kHz range. Most of the IMD results are hovering around the 0.001% 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 A25 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 0.002 and 0.003% across the sweep. Another strong result.

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 (2kHz) and third (3kHz) harmonics dominate at a very low -115dBrA, or 0.0002%. There are subsequent signal harmonics visible at and below the extremely low -130dBrA, or 0.00003%, level. On the left side of the signal peak, we find power-supply-related noise peaks, with the second harmonic (120Hz) dominating at just above -120dBrA, or 0.0001%. Other noise peaks can be seen below the -120dBrA level. Overall, this is a very clean FFT.

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 MM phono input. We see that the signal’s second (2kHz) harmonic dominates (right channel) at a low -100dBrA, or 0.001%. On the right side of the signal peak, we find power-supply-related noise peaks, with the fundamental (60Hz) and second harmonic (120Hz) dominating at just above -80dBrA, or 0.01%. Other noise peaks can be seen at and below the -90dBrA level.

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. Here the second (2kHz) signal harmonic dominates at a higher -105/-100dBrA (left/right), or 0.0006/0.001%. Subsequent harmonics can be seen at and below the -120dBrA, or 0.0001%, level. Noise peaks are essentially the same as with the analog FFT above.

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 essentially the same result as with the 16/44.1 FFT 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, with no signal harmonics above the -135dBrA noise floor, and the same -120dBrA 120Hz noise peak.

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 a single signal harmonic at 3kHz just barely above the -145dBrA noise floor, and the same -120dBrA 120Hz noise peak. Other power-supply-related noise peaks can be seen below the -120dBrA level.

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. The most predominant (non-signal) peak is the second (100Hz) signal harmonic at a low -110dBrA, or 0.0003%. Other peaks (both signal harmonics and power-supply noise-related harmonics) can be seen at -120dBrA and below.

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. The most predominant (non-signal) peaks are the 60Hz fundamental power-supply noise peak and its second (120Hz) harmonic at -80dBrA, or 0.01% (left channel). The highest signal harmonic is at 100Hz, at -90dBrA, or 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 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%, while the third-order modulation products, at 17kHz and 20kHz, are just below the -110dBrA, or 0.0003%, level. This is a very clean IMD result.

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

Shown above is the FFT of the speaker-level output of the A25 with the APx 32-tone signal applied to the analog input. The combined amplitude of the 32 tones is the 0dBrA reference, and that 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 -135dBrA, or 0.00002%, 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 (0dBFS). We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -110/100dBrA (left/right), or 0.0003/0.001%, while the third-order modulation products, at 17kHz and 20kHz, are very low at -120dBrA, or 0.0001%.

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 (0dBFS). We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -110/100dBrA (left/right), or 0.0003/0.001%, while the third-order modulation products, at 17kHz and 20kHz, are very low at -120dBrA, or 0.0001%.

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 around -100dBrA, or 0.001%, while the third-order modulation products, at 17kHz and 20kHz, are lower at -115dBrA, or 0.0002%.

Squarewave 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 A25’s slew-rate performance. Rather, it should be seen as a qualitative representation of the A25’s mid-to-high 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, we find relatively clean corners, with some softening and overshoot.

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

The final graph above shows the damping factor as a function of frequency. We can see here a constant damping factor just under 200 through most of the audioband. This is a strong result for a medium-powered solid-state integrated amplifier.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Amplifier Measurements

Created: 15 June 2024

Link: reviewed by Roger Kanno on SoundStage! Hi-Fi on June 15, 2024

General information

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

The MXA-8400 was conditioned for 1 hour at 1/8th full rated power (~25W 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 MXA-8400 has eight balanced inputs (XLR), and eight speaker-level outputs (Neutrik speakON). Each pair of inputs (e.g., 1&2 and 3&4, etc) can be independently configured as a single channel in bridge mode. The MXA-8400 was evaluated as a stereo amplifier using channels 1 and 2, as well as a two-channel bridged amplifier using channels 1/2 (bridged) and 3/4 (bridged). The MXA-8400 also offers a low gain mode (6Vrms sensitivity) and a more typical high gain mode (2Vrms sensitivity). Unless otherwise stated, the high gain mode was used.

Because the MXA-8400 uses 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.

Published specifications vs. our primary measurements

The table below summarizes the measurements published by Lyngdorf for the MXA-8400 compared directly against our own. The published specifications are sourced from Lyngdorf’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 to 500kHz, 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 in two-channel mode revealed the following using the line-level balanced analog input (unless specified, assume a 1kHz sinewave at 440mVrms, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

For the continuous dynamic power test, the MXA-8400 was able to sustain 548W into 4 ohms (~1.2% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (54.8W) 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 MXA-8400 was only slightly warm to the touch.

Our primary measurements in bridge mode revealed the following using the line-level balanced analog input (unless specified, assume a 1kHz sinewave at 230mVrms, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

Frequency response (8-ohm loading)

In our frequency-response plots above, measured across the speaker outputs at 10W into 8 ohms, the MXA-8400 is essentially flat within the audioband. At the extremes the MXA-8400 is at 0dB at 5Hz and -3dB just past 60kHz. 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)

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 MXA-8400 does not invert polarity and exhibits at worst, about 30 degrees (at 20kHz) of phase shift within the audioband.

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, in stereo mode. 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 find that maximum deviation between no-load and a 4-ohm load is very small, at around 0.025dB. This is an indication of a very high damping factor, or low output impedance. With a real speaker, the deviations are smaller, at roughly 0.01dB.

THD ratio (unweighted) vs. frequency vs. output power (two-channel mode)

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 in stereo mode. The blue and red plots are for left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at the rated 200W. The 10W data yielded the lowest THD figures, ranging from 0.00004% from 20Hz to 200Hz, then up to 0.0005% at 6kHz. These are extraordinarily low THD ratios, nearing the limits of the APx555 analyzer. At 1W, THD ratios were more constant, from 0.0001% from 20Hz to 1kHz, then up to 0.0003% at 6kHz.  A 200W, THD ratios ranged from 0.00006% from 20Hz to 200Hz, then up to 0.0005% at 6kHz.

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

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 in bridge mode. The blue and red plots are for left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at the rated 450W.  The 1W data yielded the most constant results, ranging from 0.0002% from 20Hz to 2kHz, then down to 0.0001% at 3-4kHz. At 10W, THD ratios ranged from 0.00006% from 20Hz to 1kHz, then up to 0.0006% at 6kHz.  A 450W, THD ratios ranged from 0.00002/0.00003% from 20Hz to 100Hz, then a steady climb to 0.0004% at 6kHz.

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

The chart above shows THD ratios measured at the output of the MXA-8400 as a function of output power for the analog line level-input in two-channel mode, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). The 8-ohm data ranged from about 0.0003% at 50mW, down to 0.00007% from 10 to 50W, then up to the “knee” right around 200W. The 4-ohm data ranged from about 0.0006% at 50mW, down to 0.00007% from 5 to 100W, then up to the “knee” around 350W. The 1% THD marks were hit at 278W (8-ohm loading) and 540W (4-ohm loading).

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 MXA-8400 as a function of output power for the analog line level-input in stereo mode, for an 8-ohm load (blue/red for left/right) and a 4-ohm load (purple/green for left/right channels). THD+N values for the 8-ohm data ranged from 0.003% down to just below 0.0002% at 100-200W. The 4-ohm data yielded THD+N values 3-4dB higher.

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

The chart above shows THD ratios measured at the output of the MXA-8400 as a function of output power for the analog line-level-input in bridge mode for a 4-ohm load (blue/red for left/right channels). THD ratios were not measured into an 8-ohm load because our dummy-load configuration allows for a power handling of only 500W (but 1000W for 4 ohms). Maximum (1% THD) power into 8 ohms was measured in bridge mode with very short 1-second iterative measurements where a staggering 950W with two bridged channels driven was observed. The 4-ohm data ranged from about 0.002% at 300mW, down to 0.0001-0.0002% from 1.5 to 500W, then up to the “knee” around 700-800W. The 1% THD mark was hit at 1040W.

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

The chart above shows THD ratios measured at the output of the MXA-8400 as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yields 50W at the output into 8 ohms (and roughly 100W into 4 ohms, and 200W into 2 ohms) for the balanced analog line-level input in two-channel mode. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. The 8 and 4-ohm THD data are nearly identical, ranging from 0.00002-0.00003% from 20Hz to 100Hz, then up to 0.0004% at 6kHz. The 2-ohm data ranged from 0.0001% to 0.003% across the audioband. It’s clear that these amplifier modules are optimized for 4- and 8-ohm loads. Nonetheless, they are stable into 2 ohms, yielding admirably low THD ratios.

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

The chart above shows THD ratios measured at the output of the MXA-8400 as a function of frequency into two different loads (8/4 ohms) for a constant input voltage that yields 200W at the output into 8 ohms (and roughly 400W into 4 ohms) for the analog line-level input in bridged mode. THD ratios were essentially identical, ranging from 0.00004% at low frequencies, then up to 0.0004% at 4kHz.

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 MXA-8400 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 in stereo mode. 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 8-ohm plot is fairly flat and between 0.0001% and 0.0003% from 20Hz to 6kHz. Between 1kHz and 6kHz, the THD ratios when real speakers were used as loads are identical to the dummy load.  The two-way speaker THD results were as high as 0.02% at 20Hz. Between 40Hz and 200Hz, the speaker THD results were roughly 10-20dB higher than that of the dummy load. While THD ratios remain low and below the threshold of audibility into real-world speaker loads, the NAD M23, using similar amplifier modules, performed better in this regard than the MX-8400.

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 MXA-8400 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 IMD plots are within 10-15dB of one another, hovering between 0.0002% and 0.0008%. The IMD results for the real-world speaker loads can be seen both above an below the resistive dummy load results, depending on frequency.

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 MXA-8400 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 in stereo mode. 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 data sets are close enough to be judged as identical, hovering around the 0.001% level.

FFT spectrum – 1kHz (line-level input, two-channel mode)

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 in two-channel mode. We see that the signal’s third (3kHz) and fifth (5kHz) harmonics are at -125dBrA, or 0.00006%, and -130dBrA, or 0.00003%, respectively. The remaining visible signal harmonics are below the -135dBrA, or 0.00002%, levels. These are extraordinarily low THD levels.  The power-supply-related noise peak at the fundamental (60Hz) frequency is barely seen at just above the -150dBrA, or 0.000003%, level; however, this peak is inherent to the AP’s signal generator. A rise in the noise floor can be seen above 20kHz, indicative of this type of digital amplifier technology. This is an exceptionally clean FFT result.

FFT spectrum – 1kHz (line-level input, two-channel mode, low gain)

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 in two-channel mode, this time with the gain set to low. We see that the signal’s second (2kHz) and third (3kHz) harmonic, are nearing the absurdly low -140dBrA, or 0.00001%, level. As a point of comparison, below is a 1kHz FFT with the AP analyzer in loopback mode (generator internally feeds the analyzer) with the same 9Vrms signal amplitude. The only differences are that the overall noise floor, from uncorrelated thermal noise, is roughly 10dB higher with the MXA-8400 in the signal path (in the audioband), and the 2kHz signal harmonic peak is just below (instead of above) of -140dBrA, and the 3kHz peak is at -150dBrA instead of -140dBrA. In low-gain mode, in can be said that the MXA-8400 adds only a very small amount of uncorrelated noise (hiss), and from a THD perspective, is essentially perfectly transparent. In other words, the very definition of a “straight wire with gain.”

FFT spectrum – 1kHz (loopback, 9Vrms)

Shown above is the fast Fourier transform (FFT) for a 9Vrms 1kHz input sinewave stimulus, measured with the AP analyzer in loopback mode, for comparison to the above MXA-8400 FFT charts. The overall noise floor is around the -165dBrA level, and the only visible peaks are at 60Hz (-150dBrA), 120/240Hz (-155dBrA), 2kHz (-140dBrA), 3kHz (-150dBrA), and 4/6kHz (-160dBrA).

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

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 in bridged mode (high-gain setting). We see that the signal’s third (3kHz) harmonic is at -130dBrA, or 0.00003%, while the second (2kHz) and fifth harmonics (5kHz) are even lower at -135dBrA, or 0.00002%. These THD levels are slightly lower than the already extraordinarily low levels in two-channel mode. The overall noise floor (from uncorrelated thermal noise) is a few dB higher in bridge mode (slightly above versus slightly below -150dBrA), however. This is an unavoidable consequence of using two amplifier modules instead of just one to drive the load.

FFT spectrum – 50Hz (line-level input, two-channel mode)

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 in two-channel mode. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most dominant (non-signal) peaks are the second (100Hz) and third (150Hz) signal harmonics at roughly -145dBrA, or 0.000006%, and -140dBrA, or 0.00001%. THD levels are even lower at 50Hz than the already ultra-low levels at 1kHz. The power-supply-related noise peak at the fundamental (60Hz) frequency is evident at the extremely low -140dBrA, or 0.00001%, level. Another near-perfect FFT.

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

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 in two-channel mode. 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 -125dBrA, or 0.00006%, and the third-order modulation products, at 17kHz and 20kHz, are at roughly -110dBrA, or 0.0003%.

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

Shown above is the FFT of the speaker-level output of the MXA-8400 with the APx 32-tone signal applied to the 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 below the very low -140dBrA, or 0.00001%, level. This is an another ultra-clean IMD FFT.

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 MXA-8400’s slew-rate performance. Rather, it should be seen as a qualitative representation of the MXA-8400’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 the case of the MXA-8400, however, what cn be seen in the plateaus of the squarewave in the top graph is a 500 kHz sinewave, the frequency at which the switching oscillator in the Class D amp is operating (see FFT below).

Square-wave response (10kHz)—250kHz bandwidth

Above is the 10kHz squarewave response using the analog input, at roughly 10W into 8 ohms, with a 250kHz restricted bandwidth to remove the modulation from the 500kHz oscillator. Here we find a relatively clean squarewave, with some overshoot in the corners.

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

The MXA-8400’s 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 MXA-8400 oscillator switches at a rate of about 500kHz, 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 500kHz peak is quite evident, and at -40dBrA. There is also a peak at 1MHz (the second harmonic of the 500kHz peak), at -70dBrA. Those three peaks—the fundamental and its second/third harmonics—are direct results of the switching oscillators in the MXA-8400 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, two-channel mode)

The graph above is the damping factor as a function of frequency in two-channel mode. We see both channels with very high and constant damping factor, around 650 to 780 across the audioband.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Amplifier Measurements

Created: 01 June 2024

Link: reviewed by Jonathan Gorse on SoundStage! Ultra on June 1, 2024

General information

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

The NAP 350 was conditioned for 1 hour at 1/8th full rated power (~25W 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 NAP 350 is a single-channel amplifier with one balanced (XLR) input and one set of speaker level outputs. An input of 330mVrms was required to achieve the reference 10W into 8 ohms.

Published specifications vs. our primary measurements

The table below summarizes the measurements published by Naim for the NAP 350 compared directly against our own. The published specifications are sourced from Naim’s website, either directly or from the manual available for download, or a combination thereof. Assume, unless otherwise stated, 10W into 8 ohms and a measurement input bandwidth of 10Hz to 22.4kHz.

Our primary measurements revealed the following (unless specified, assume a 1kHz sinewave at 330mVrms at the input, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

For the continuous dynamic power test, the NAP 350 was able to sustain about 382W into 4 ohms (~2% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (38.2W) 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 sides of the NAP 350 were warm to the touch.

Frequency response (8-ohm loading)

In our frequency-response (relative to 1kHz) plot above, measured across the speaker outputs at 10W into 8 ohms, the NAP 350 exhibits a near-flat frequency response across the audioband (0/-2dB at 20Hz/20kHz). At low frequencies, the NAP 350 is -0.3dB at 5Hz. The -3dB point is just past 100kHz.

Phase response (8-ohm loading)

Above is the phase-response plot from 20Hz to 20kHz for the balanced line-level input, measured across the speaker outputs at 10W into 8 ohms. The NAP 350 does not invert polarity and exhibits, at worst, about -20 degrees of phase shift at 20kHz, and +5 degrees at 20Hz.

RMS level vs. frequency vs. load impedance (1W, single 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 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 . . .

. . . is the same but zoomed in to highlight differences. Here we find the maximum deviation between an 8-ohm load and no-load to be around 0.5dB. This is an indication of a low damping factor, or high output impedance, for a solid-sate amplifier. With a real speaker, the deviations are lower, at just over 0.3dB.

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 plot is at 1W output into 8 ohms, purple at 10W, and pink at 160W. The 1W data ranges from 0.002% at 20Hz, down to 0.0005% at 200-300Hz, then up to 0.01% at 20kHz. The 10W data ranges from 0.005% at 20Hz, down to 0.002% at 60-2kHz, then up to 0.01% at 20kHz. The 160W data ranges from 0.04% at 20Hz, down to 0.007% at 40-1kHz, then up to 0.1% 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 NAP 350 as a function of output power for the analog line-level input, for an 8-ohm load (blue) and a 4-ohm load (purple). The 8-ohm data ranged from about 0.002% from 50mW to 20W, then up to 0.01% at the “knee,” at roughly 180W. The 4-ohm THD data were close, but 5-6dB higher, with a “knee” at just past 300W. The 1% THD thresholds were reached at 201W and 370W into 8 and 4 ohms.

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 NAP 350 as a function of output power for the analog line-level input, for an 8-ohm load (blue) and a 4-ohm load (purple). The 8-ohm data ranged from about 0.015% down to 0.0025% at 10-30W. The 4-ohm data ranged from about 0.02%% down to 0.004% at 10-30W.

THD ratio (unweighted) vs. frequency at 8 and 4 ohms

The chart above shows THD ratios measured at the output of the NAP 350 as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yields roughly 50W at the output into 8 ohms (blue), 100W into 4 ohms (purple), and 200W into 2 ohms (pink). The 8-ohm data ranged from 0.008% at 20Hz down to 0.003% from 30Hz to 2kHz, then a steady rise to 0.03% at 20kHz. The 4-ohm THD data were only about 5dB higher compared to the 8-ohm data from 20Hz to 2kHz, while above this frequency THD ratios were the same at 4 and 8 ohms. The 2-ohm data ranged from 0.02% at 20Hz down to 0.006% from 200Hz to 2kHz, then a steady rise to 0.04% at 20kHz.This shows that the NAP 350 is perfectly stable into 2 ohms, and it yields THD results that are comparable to those seen at 8 and 4 ohms.

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

The chart above shows THD ratios measured at the output of the NAP 350 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 very low freqencies, the two-way speaker yielded the highest THD ratios (0.4%). Generally, below 500Hz or so, THD ratios into the real speakers were higher than the resistive load, from 5 to 30dB. Above 1kHz, THD ratios into the real speakers were either lower (by up to 5dB) or close to the resistive-load values.

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

The chart above shows intermodulation distortion (IMD) ratios measured at the output of the NAP 350 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). All three IMD plots are close, within about 5dB, most often within a couple dB throughout the frequency sweep. IMD values ranged from 0.01 to 0.03%, which is not a particularly strong result.

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

The chart above shows IMD ratios measured at the output of the NAP 350 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). The IMD results into real speakers were lower than those measured into the resistive load, by about 5dB. IMD values ranged from 0.03 to 0.01%, again, not a particularly strong result for a modern solid-state amplifier.

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 (2kHz) and third (3kHz) harmonics dominate at around -95dBrA, or 0.002%. The subsequent signal harmonics range from the -110dBrA level, or 0.0003%, down to -140dBrA, or 0.00001%. The highest noise-related peaks are at the third (180Hz) and fifth (300Hz) harmonics at a low -125dBrA, or 0.00006%.

FFT spectrum – 50Hz (line-level input)

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the balanced 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 most dominant (non-signal) peaks are the signal’s second (100Hz) and third (150Hz) harmonics at close to -100dBrA, or 0.001%. Noise-related harmonics are much lower, at the -125dBrA, or 0.00006%, and below level.

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 were 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 the relatively high -85dBrA, or 0.006%, level, while the third-order modulation products, at 17kHz and 20kHz, are lower at -95dBrA, or 0.002%.

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

Shown above is the FFT of the speaker-level output of the NAP 350 with the APx 32-tone signal applied to the 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 below the -120dBrA, or 0.0001%, level.

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 NAP 350’s slew-rate performance. Rather, it should be seen as a qualitative representation of the NAP 350’s relatively wide 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 find clean corners with only mild softening.

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

The final graph above is the damping factor as a function of frequency. We find quite low damping factor values, right around 35 across the audioband. This is a poor damping factor result for a modern solid-state amplifier.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Amplifier Measurements

Created: 01 May 2024

Link: reviewed by Dennis Burger on SoundStage! Access on May 1, 2024

General Information

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

The Marantz Model 50 was conditioned for one hour at 1/8th full rated power (~9W 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 Model 50 offers four line-level analog inputs (RCA), one moving-magnet (MM) phono input (RCA), a sub output and left/right variable and fixed pre-outs plus a power amp input (all RCA), two pairs (A and B) of speaker-level outputs, and one headphone output over 1/4" TRS connector. For the purposes of these measurements, the following inputs were evaluated: analog line-level and phono.

Most measurements were made with a 2Vrms line-level analog input and a 5mVrms phono input. The signal-to-noise ratio (SNR) measurements were made with the default input signal values but with the volume set to achieve the rated output power of 70W (8 ohms). For comparison, SNR measurements were also made with the volume at maximum.

Based on the variability and non-repeatability of the left/right volume channel matching (see table below), the Model 50 volume control is digitally controlled operating in the analog domain. The Model 50 overall volume range is from -57.6dB to +41.8dB (line-level input, speaker output). It offers 0.5dB increments throughout the volume range.

Our typical input bandwidth filter setting of 10Hz–22.4kHz was used for all measurements except FFTs and THD vs. frequency sweeps, where a bandwidth of 10Hz –90kHz was used. Frequency response measurements utilized a DC to 1MHz input bandwidth.

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 Marantz for the Model 50 compared directly against our own. The published specifications are sourced from Marantz’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 to 1MHz, 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.

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 Model 50 was able to sustain 145W into 4 ohms (~3.5% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (14.5W) for 5 secondss, for 233 seconds of the 500-second test before inducing the fault-protection circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the Model 50 was warm to the touch.

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

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

In our frequency-response plots above (relative to 1kHz), measured across the speaker outputs at 10W into 8 ohms, the Model 50 is essentially perfectly flat within the audioband (20Hz to 20kHz). At the extremes, the Model 50 is -0.1dB at 5Hz and -0.2dB at 100kHz. The Model 50 can be considered a high-bandwidth audio device. In the graph above and most of the graphs below, only a single trace may be visible. This is because the left channel (blue or purple trace) is performing identically to the right channel (red or green trace), and so 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 (relative to 1kHz) 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 +/-11dB of gain/cut is available at 20Hz, and roughly +/-10dB of gain/cut at 20kHz.

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 Model 50 yields very little phase shift (as expected given the extended frequency response), with less than +5 degrees at 20Hz (the Model 50 is not DC coupled) and less than -5 degrees at 20kHz.

Frequency response (line-level pre and sub outputs)

Above is a frequency response plot measured at the line-level outputs into 8 ohms, where the left/right pre-outs are in purple/green and the sub-out is in blue.  The pre-outs show an extended frequency response, -0.1dB at 5Hz and -0.5dB at 70kHz. The sub-out is low-pass filtered with a -3dB point at around 150Hz.

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

The chart above shows the frequency response (relative to 1 kHz) for the phono input (MM configuration) and shows very small maximum deviations of about +0.25/-0.1dB (100-200Hz/20kHz) from 20Hz to 20kHz. What is shown in this chart 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, measured across the speakers outputs at 10W into 8 ohms. 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 -90 degrees at 20kHz.

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 50kHz. 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 see that the deviations between no load and 4 ohms are around 0.15dB. This is a reasonably strong result for an integrated class-AB amp, and an indication of a low output impedance, or high damping factor. With a real speaker load, deviations measured just below the 0.07dB level—well below the threshold of audibility.

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

The chart above shows THD ratios at the speaker-level outputs 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 the rated 70W. The power was varied using the Model 50 volume control. Between 20Hz and 2kHz, all THD ratios are fairly constant and similar, between 0.004 and 0.006%. Between 2kHz and 20kHz, THD ratios were higher at higher power levels, but not by a significant margin. At 20kHz, we measured around 0.01% at 1W and 10W, and 0.03% at 70W.

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

The graph above shows THD ratio as a function of frequency plot for the phono input measured across an 8-ohm load at 10W. The input sweep was EQ’d with an inverted RIAA curve. The THD values vary from 0.01% (20Hz) down to between 0.001 and 0.002% from 200Hz to 3kHz, then up to 0.006% at 20kHz.

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

The chart above shows THD ratios measured at the speaker-level outputs of the Model 50 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). THD ratios were essentially identical into 8 and 4 ohms up to the 8-ohm “knee” at roughly 70W (the 4-ohm “knee” is at roughly 100W). These ranged from 0.003% at 50mW, down to 0.001% at 1 to 3W, then up to 0.005% at the “knees.” The 1% THD values were hit at 83W and 132W into 8 and 4 ohms, 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 Model 50 as a function of output power for the 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 closely, but the 4-ohm data yielded a couple dB more noise than the 8-ohm data. THD+N ratios into 8 ohms ranged from 0.02% at 50mW, down to 0.002% at 10W, then up to just below 0.005% at the 8-ohm “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 Model 50 as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yielded 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 essentially identical THD ratios (0.005%) into all three loads up to about 1kHz. From 3kHz to 20kHz, there is a roughly 5dB increase in THD between the 2-ohm load and the 8/4-ohm loads. At 20kHz, we measured 0.015% into 8/4 ohms, and 0.025% into 2 ohms. This is a strong result, and shows that the Model 50 is stable into 2 ohms.

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 Model 50 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 similar to the resistive dummy load, with the expection of the two-way speaker at 20 to 30Hz. THD ratios hovered between 0.007 and 0.01% from 40Hz to 20kHz for all three loads. At 20Hz, the THD ratio was 0.07% into the two-way speaker. This is a relatively strong result, and shows that the Model 50 will yield consistently low THD results into real-world speaker loads.

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 Model 50 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 essentially identical IMD ratios into all three loads, at a relatively flat and constant 0.005%.

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 Model 50 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 thee-way speaker (Paradigm Founder Series 100F, measurements can be found here). We find essentially identical IMD ratios into all three loads, at a relatively flat 0.02% from 40Hz to 500Hz, then down to 0.0015% from 500Hz to 1kHz.

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 (2kHz) and third (3kHz) harmonics dominate at -85dBrA, or 0.006%, and -105dBrA, or 0.0006%, while subsequent signal harmonics are below -110dBrA, or 0.0003%. On the right side of the signal peak, we see the primary (60Hz) noise-related peak and its harmonics (120, 180, 240, 300Hz, etc.) at and below the very low -120dBrA, or 0.0001%, level.

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) signal harmonic dominate at -95dBrA, or 0.002%, while subsequent signal harmonics are below the -110dBrA, or 0.0003%, level. The noise related peaks are at and below the -85dBrA, or 0.006%, level.

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. The most predominant (non-signal) peaks are the second (100Hz) and third (150Hz) signal harmonics at a -90dBrA, or 0.003%, and -105dBrA, or 0.0006%. Noise related peaks can be seen below the -110dBRa, or 0.0003%, level.

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 most predominant (non-signal) peaks are that of the power-supply fundamental (60Hz) and third (180Hz) harmonics at -90dBrA, or 0.003%, and -85dBrA, or 0.006%. The signal’s second (100Hz) harmonic is at the -95dBrA, or 0.002%, level.

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 were 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 -95dBRa, or 0.002%, while the third-order modulation products, at 17kHz and 20kHz are at -100dBrA, or 0.001%.

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

Shown above is the FFT of the speaker-level output of the Model 50 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 -120dBrA, or 0.0001%, 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 phono input configured for MM. 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 the same level.

Squarewave 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 Model 50’s slew-rate performance. Rather, it should be seen as a qualitative representation of the Model 50’s extremely high 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, due to the Model 50’s very extended bandwidth, we see a near-perfect squarewave, with sharp corners and no ringing.

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

The final graph above is the damping factor as a function of frequency. We can see here a constant damping factor right around 200, from 20Hz to roughly 20kHz. This is a relatively strong damping factor result for an affordable class AB integrated amp.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Amplifier Measurements

Created: 01 May 2024

Link: reviewed by George de Sa on SoundStage! Simplifi on May 1, 2024

General Information

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

The Rotel RAS-5000 was conditioned for one hour at 1/8th full rated power (~17W 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 RAS-5000 offers one pair of line-level analog inputs (RCA), a sub output (RCA), left/right pre-outs (RCA), one coaxial S/PDIF input (RCA), one optical S/PDIF input (TosLink), one USB digital input, a pair of speaker level outputs, and one headphone output over a 1/4" TRS connector. Bluetooth, streaming, and HDMI (eARC) inputs are also offered. For the purposes of these measurements, the following inputs were evaluated: digital coaxial, analog line-level.

Most measurements were made with a 2Vrms line-level analog input and 0dBFS digital input. The signal-to-noise ratio (SNR) measurements were made with the default input signal values but with the volume set to achieve the rated output power of 140W (8 ohms). For comparison, on the line-level input, an SNR measurement was also made with the volume at maximum.

Based on the variability and non-repeatability of the left/right volume channel matching (see table below), the RAS-5000 volume control is digitally controlled but operating in the analog domain. The RAS-5000 overall volume range is from -69dB to +32.4dB (line-level input, speaker output). It offers 1dB increments up to about the 75% mark, and then 0.5dB steps to full volume.

Our typical input bandwidth filter setting of 10Hz–22.4kHz was used for all measurements except FFTs and THD vs. frequency sweeps where a bandwidth of 10Hz–90kHz was used. Frequency response measurements utilize a DC to 1 MHz input bandwidth.

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 Rotel for the RAS-5000 compared directly against our own. The published specifications are sourced from Rotel’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 to 1MHz, 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.

*protection circuit enabled after a few seconds

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):

*protection circuit enabled after a few seconds

For the continuous dynamic power test, the RAS-5000 was able to sustain 237W into 4 ohms (~2% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (23.7W) for 5 seconds, for 233 seconds of the 500-second test before inducing the fault protection circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the RAS-5000 was warm to the touch.

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

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

In our frequency-response plots above (relative to 1kHz), measured across the speaker outputs at 10W into 8 ohms, the RAS-5000 is essentially perfectly flat within the audioband (20Hz to 20kHz). There’s a +0.4dB rise in the frequency response at 200kHz, and -0.2dB at 10Hz. The RAS-5000 can be considered a high-bandwidth audio device. In the graph above and most of the graphs below, only a single trace may be visible. This is because the left channel (blue or purple trace) is performing identically to the right channel (red or green trace), and so 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 (relative to 1kHz) 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 +/-11dB of gain/cut is available at 20Hz, and roughly +/-9dB of gain/cut at 20kHz.

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 RAS-5000 yields very little phase shift (as expected given the extended frequency response), with +10 degrees at 20Hz (the RAS-5000 is not DC coupled), and less than -5 degrees at 20kHz.

Frequency response (line-level pre and sub outputs)

Above is a frequency response plot measured at the line-level outputs into 8 ohms, where the L/R pre-outs are in blue/red, and the sub-out is in purple.  All three plots overlap perfectly, with a ruler-flat and extended frequency response, as was seen with the speaker outputs. The sub-out is not low-pass filtered in any way, and is likely simply a summed L/R version of the pre-outs.

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

The chart above shows the RAS-5000’s frequency response (relative to 1kHz) as a function of input type measured across the speaker outputs at 10W into 8 ohms. The two green traces are the same analog input data from the speaker-level frequency response graph above, but limited to 80kHz. The blue and red traces are for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz using the coaxial input, and the purple and green traces are for a 24/96 dithered digital input signal from 5Hz to 48kHz, and the pink and orange traces are for a 24/192 dithered digital input signal. At low frequencies, all four plots yield the same -0.2dB at 10Hz. The -3dB points for the 16/44.1, 24/96, and 24/192 digital input data are: 21.0kHz, 35.1kHz, and 71.2kHz.

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-outputs of the RAS-5000, where 0dBFS was set to yield 2Vrms. The digital input was swept with a dithered 1kHz input signal from -120dBFS to 0dBFS, and the output was analyzed by the APx555. The ideal response would be a straight flat line at 0dB. The 16/44.1 data were essentially perfect as of -100dBFS down to 0dBFS, while the 24/96 data were near perfect down to -120dBFS. We all also extended the sweep down to -140dBFS, to . . .

. . . see how well the 24/96 would perform. We can see here, only a +3/+1dB (L/R) overshoot at -140dBFS. This is an exemplary digital-linearity result.

Impulse response (24/44.1 data)

The graph above shows the impulse response for the RAS-5000, fed to the coaxial digital input, measured at the line-level pre-outputs, 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 minimizes pre-ringing, with short post-ringing.

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-outputs of the RAS-5000 where 0dBFS is set to 2Vrms. 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.

Here we see an average J-Test result, with peaks flanking the 12kHz fundamental, as high as -110dBrA. This is an indication that the RAS-5000 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 line-level pre-outputs of the RAS-5000. The optical input yielded similar but slightly worse results compared to the coaxial input.

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 RAS-5000, with an additional 10ns of 2kHz sinewave jitter injected by the APx555. The results are very clear, as we see the sidebands at 10kHz and 14kHz (12kHz main signal +/- 2kHz jitter signal) manifest at near -100dBrA. This is further indication that the DAC in the RAS-5000 has poor jitter immunity. For this test, the optical input yielded effectively the same results.

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 RAS-5000, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The results are very clear, as we see the sidebands at 10kHz and 14kHz (12kHz main signal +/- 2kHz jitter signal) manifest at near -80dBrA. This is further indication that the DAC in the RAS-5000 has poor jitter immunity. For this test, the optical input yielded effectively the same results.

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 RAS-5000’s line-level pre-outputs with white noise at -4dBFS (blue/red) and a 19.1 kHz sinewave at -1dBFS fed to the coaxial digital input, sampled at 16/44.1. The gentle roll-off around 20kHz in the white-noise spectrum shows that the RAS-5000 does not use a brick-wall type reconstruction filter. There are very clear low-level aliased image peaks within the audio band at the -90dBrA and below level. The primary aliasing signal at 25kHz is prominent at -20dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are at -80dBrA.

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 line-level input swept from 5Hz to 50kHz. 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 that the deviations between no load and 4 ohms are around 0.05dB. This is a strong result for a class-AB amp, and an indication of a low output impedance, or high damping factor. With a real speaker load, deviations measured just below the 0.05dB level—well below the threshold of audibility.

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

The chart above shows THD ratios at the speaker-level outputs 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 the left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange just under 137W (just shy of the rated 140W). The power was varied using the RAS-5000 volume control. Between 20Hz and 1kHz, all THD ratios are fairly constant and similar, between 0.001 and 0.002%. Between 1kHz and 20kHz, THD ratios were higher at higher power levels, but not by a significant margin. At 20kHz, we measured 0.002% at 1W, 0.003% at 10W, and 0.01% at 137W.

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

The chart above shows THD ratios measured at the speaker-level outputs of the RAS-5000 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). Into 4 ohms, the right channel outperformed the left by more than 10dB between about 2 and 20W. The right channel THD ratios into 4 ohms ranged from 0.002% at 50mW, down to nearly 0.0002% at 5W, then up to 0.002% at just shy of 200W, where the RAS-5000 protection circuit engaged and shut down the unit. THD ratios into 8 ohms ranged from 0.001% at 50mW, then down to 0.0003-0.0005% between 1 and 10W, then up to 0.002% at the “knee” at roughly 140W, then up to the 1% THD mark at 154W. Note that we were able to achieve 230W into 4 ohms (1% THD) with the RAS-5000 in Bench Mode, but only for a few seconds before the protection circuit engaged and shut down the unit.

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 RAS-5000 as a function of output power for the 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 closely except for the left input into 4 ohms, which yielded about 5dB more THD+N from 10W to over 100W. Otherwise, THD+N ratios ranged from 0.02% at 50mW, down to 0.001% at 20 to 50W, then up to just below 0.002% at the 8-ohm “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 RAS-5000 as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yielded 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 essentially identical THD ratios (0.0015%) into all three loads up to about 200Hz. From 2kHz to 20kHz, there is a roughly 7-8dB increase in THD every time the load is halved. At 20kHz, we measured 0.003% into 8 ohms, 0.009% into 4 ohms, and 0.02% into 2 ohms. This is a strong result, and shows that the RAS-5000 is stable into 2 ohms.

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 RAS-5000 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 similar to the resistive dummy load, with the expection of the two-way speaker at 20 to 30Hz, and the three-way speaker at 10 to 20kHz. THD ratios hovered between 0.001 and 0.003% from 40Hz to 6kHz for all three loads. At 20Hz, the THD ratio was 0.04% into the two-way speaker, and at 20kHz, 0.008% into the three-way speaker. This is a relatively strong result, and shows that the RAS-5000 will yield consistently low THD results into real-world speaker loads.

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 RAS-5000 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 very similar IMD ratios into all three loads, between 0.001 and 0.003% from 2.5kHz to 20kHz. Another strong result.

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 RAS-5000 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 0.002 and 0.005% from 40Hz to 1kHz. Another strong result.

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 (2kHz) and third (3kHz) harmonics dominate at a low -100dBrA, or 0.001%, while subsequent signal harmonics are near and below -120dBrA, or 0.0001%. On the right side of the signal peak, we see the primary (60Hz) noise-related peak and its harmonics (120, 180, 240, 300Hz, etc.) at the -105dBrA, or 0.0006%, and below level.

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. Both the signal and noise-related harmonic peaks are very similar to the analog FFT above, but for a higher noise floor (-135dBFS) due to the 16-bit depth.

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. Both the signal and noise-related harmonic peaks are very similar to the analog FFT above.

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 noise-related peaks below the -110dBrA, or 0.0003%, level. There are no signal related peaks above the -135dBFS noise floor.

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 noise-related peaks below the -110dBrA, or 0.0003%, level. Signal-related peaks are difficult to discern above the -145dBFS noise floor.

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. The most predominant (non-signal) peak is the second (100Hz) and third (150Hz) signal harmonic at a low -100dBrA, or 0.001%. Noise related peaks can be seen at -105dBRA, or 0.0006%.

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 were 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 at -105dBrA, or 0.0006%. This is a strong IMD result.

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

Shown above is the FFT of the speaker-level output of the RAS-5000 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 -120dBrA, or 0.0001%, level. The low frequency peaks that rise near and above -110dBrA, are due to power-supply noise.

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 (-1dBFS). We find that the second-order modulation product (i.e., the difference signal of 1kHz) is just below -100dBrA, or 0.001%, while the third-order modulation products, at 17kHz and 20kHz, are around -95dBrA, or 0.002%.

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 (-1dBFS). We find that the second-order modulation product (i.e., the difference signal of 1kHz) is just below -100dBrA, or 0.001%, while the third-order modulation products, at 17kHz and 20kHz, are around -95dBrA, or 0.002%.

Squarewave 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 RAS-5000’s slew-rate performance. Rather, it should be seen as a qualitative representation of the RAS-5000’s extremely high 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, due to the RAS-5000’s very extended bandwidth, we see a near-perfect squarewave, with sharp corners and no ringing.

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

The final graph above is the damping factor as a function of frequency. We can see here a constant damping factor right around 300, from 20Hz to roughly 15kHz, then a dip down to around 80 at 20kHz. This is a relatively strong damping factor result for an affordable class-AB amp.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Amplifier Measurements

Created: 01 May 2024

Link: reviewed by Philip Beaudette on SoundStage! Hi-Fi on May 1, 2025

General information

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

The Bryston Bi-200 was conditioned for 1 hour at 1/8th full rated power (~25W 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 Bi-200 offers six sets of line-level analog inputs (four unbalanced over RCA, two balanced over XLR), left/right line-level pre-outputs (over RCA and XLR), one set of speaker-level outputs, and a ¼″ TRS headphone output on the front panel. For the purposes of these measurements, the following input was evaluated: balanced analog (XLR) line-level. There were no appreciable differences in terms of THD and noise between the unbalanced and balanced analog inputs. The unbalanced input provides 6dB more gain than the balanced input.

Most measurements were made with a 2Vrms line-level analog input. The signal-to-noise (SNR) measurements were made with the default input signal values but with the volume set to achieve the achievable output power of 200W into 8 ohms. For comparison, on the line-level input, a SNR measurement was also made with the volume at maximum.

Based on the accuracy and randomness of the left/right volume channel matching (see table below), the Bi-200 volume control is digitally controlled but operating in the analog domain. The Bi-200 overall volume range is from -80dB to +34.3dB (balanced line-level input, speaker output). It offers course adjustments from -80dB to -60dB, 2dB increments from -60dB to -51dB, 1dB increments from -51dB to -30dB, and 0.5dB increments from -30dB to 12dB.

Our typical input bandwidth filter setting of 10Hz-22.4kHz was used for all measurements except FFTs and THD versus frequency, where a bandwidth of 10Hz-90kHz was used. Frequency response measurements utilize a DC to 1 MHz input bandwidth.

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 Bryston for the Bi-200 compared directly against our own. The published specifications are sourced from Bryston’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 to 1MHz, 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.

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

For the continuous dynamic power test, the Bi-200 was able to sustain 340W into 4 ohms (~2% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (44W) for 5 seconds, for 5 continuous minutes without inducing a fault protection circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the heatsinks of the Bi-200 were hot to the touch.

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)

In our frequency response plots above (relative to 1kHz), measured across the speaker outputs at 10W into 8 ohms, the Bi-200 is essentially perfectly flat within the audioband (less than -0.1dB at 20Hz). The -3dB point is right around 200kHz. The Bi-200 appears to be AC coupled, yielding roughly -0.8dB 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)

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 Bi-200 yielded just under +10 degrees of phase shift at 20Hz, and less than -20 degrees at 20kHz.

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 line-level input swept from 5Hz to 50kHz. 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 see that the deviations between no load and 4 ohms are extremely small at roughly 0.03dB below 3-4kHz. This is a strong result and an indication of a very low output impedance, or very high damping factor. With a real speaker load, deviations measured at roughly the same level.

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

The chart above shows THD ratios at the speaker-level outputs 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 the left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at 194W (just under  the rated output of 200W). The power was varied using the Bi-200’s volume control. All data are fairly closely lumped together, an indication of a strong result for this test. The lowest THD ratios came from the left channel at 194W, around 0.0005% from 100Hz to 1kHz. At these same frequencies, the 1W data yielded the highest THD ratios, but still low at around 0.001%. The same trend of higher THD ratios at high frequencies was observed at all power levels, with THD ratios reaching just above and below the 0.005% level at 20kHz.

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

The chart above shows THD ratios measured at the speaker-level outputs of the Bi-200 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). THD ratios into 4 and 8 ohms are close (within roughly 5-8dB). The exception was the left channel into 4 ohms between 25W and 250W, where a THD jump of up to 20dB was observed. The sweep was repeated twice, and the effect was reproducible. For the 8-ohm load, THD ratios ranged from 0.005% at 50mW, down to just above 0.0005% at the “knee” at roughly 200W, then up to the 1% THD mark at 217W. For the 4-ohm load, THD ratios ranged from 0.006% at 50mW, down to 0.001% (right channel) at the “knee” at roughly 250W, then up to the 1% THD mark at 342W.

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

The chart above shows THD+N ratios measured at the speaker-level outputs of the Bi-200 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). THD+N ratios into 4 and 8 ohms are remarkably close (within 3-5dB), with the exception of the left channel into 4 ohms between 25W and 200W. They range from 0.05% at 50mW, down to 0.002-0.003% in the 100 to 200W range.

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 Bi-200 as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yielded 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. The 8-ohm data yielded THD ratios roughly 5dB lower than the 4-ohm data, from 0.001% at 20Hz, down to 0.0004% from 100Hz to 1kHz, then up to 0.002% at 20kHz. The 2-ohm data were fairly consistent, at between 0.002% and 0.0003% across the audioband. This is a strong result showing the Bi-200 is stable into low impedance 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 Bi-200 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 close to those measured across the resistive dummy load. The exception is the two-way speaker from 20Hz to 30Hz, where THD ratios reached 0.02%, roughly 20dB higher than the resistive load. Generally, differences in THD ratios were within the 5dB range, and the results were generally in the 0.0007% to 0.005% range. This is also a very strong result and shows that the Bi-200 is largely speaker load invariant.

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 Bi-200 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 from 4kHz to 20kHz. Generally, the IMD results ranged from 0.001% to 0.005%.

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 Bi-200 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 0.003% and 0.005% across the sweep. Another strong result.

FFT spectrum – 1kHz (line-level XLR 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 balanced input. We see that the signal’s second (2kHz) and third (3kHz) harmonic dominate at roughly -110dBrA, or 0.0003%. There are subsequent signal harmonics visible at roughly -120dBrA, or 0.0001%, and below. On the right side of the signal peak, we find power-supply-related noise peaks (60/120/180/240/300Hz etc) at the -100dBrA, or 0.001%, and below level.

FFT spectrum – 1kHz (line-level RCA 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 unbalanced input. We see effectively the same result as with the balanced input FFT above.

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. The most predominant (non-signal) peaks are the second (100Hz) and third (150kHz) signal harmonics at roughly -110dBrA, or 0.0003%, and the power-supply-related noise peaks at 120Hz and 240Hz at -100dBrA, or 0.001%.

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, they 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 at roughly the same level.

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

Shown above is the FFT of the speaker-level output of the Bi-200 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  -120dBrA, or 0.0001%, level. The other larger peaks are from power-supply-related noise.

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 Bi-200’s slew-rate performance. Rather, it should be seen as a qualitative representation of the Bi-200’s high 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, we find clean corners with virtually no softening and no over/undershoot.

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

The final graph above is the damping factor as a function of frequency. Both channels track very closely. We can see damping factors ranging from about 600 from 20Hz to 2kHz, then down to just below 200 at 20kHz. This is a very strong result for a solid-state integrated amplifier.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Amplifier Measurements

Created: 01 March 2024

Link: reviewed by Dennis Burger on SoundStage! Access on March 1, 2024

General Information

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

The Dayton Audio HTA200 was conditioned for one hour at 1/8th full rated power (~4W 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 HTA200 offers one pair of line-level analog inputs (RCA), one pair of moving-magnet (MM) phono inputs (RCA), an RCA sub output, one digital coaxial (RCA) input, one optical (TosLink) input, one USB digital input, a pair of speaker level outputs and one headphone output over 1/4″ TRS connector. A Bluetooth input is also offered. For the purposes of these measurements, the following inputs were evaluated: digital coaxial, analog line-level, as well as phono.

Most measurements were made with a 2Vrms line-level analog input, 5mVrms MM input, and 0dBFS digital input. The signal-to-noise (SNR) measurements were made with the default input signal values but with the volume set to achieve the rated output power of 70W (4 ohms). For comparison, on the line-level input, a SNR measurement was also made with the volume at maximum.

Based on the inaccuracy and non-repeatability of the left/right volume channel matching (see table below), the HTA200 volume control is a potentiometer operating in the analog domain. The HTA200 overall volume range is from -59dB to +28.6dB (line-level input, speaker output).

Our typical input bandwidth-filter setting of 10Hz–22.4kHz was used for all measurements except FFTs and THD vs frequency sweeps where a bandwidth of 10Hz–90kHz was used. Frequency response measurements utilize a DC to 1 MHz input bandwidth.

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 Dayton Audio for the HTA200 compared directly against our own. The published specifications are sourced from Dayton’s manual provided with the review sample (note: the PDF availiable on Dayton's website shows much higher power ratings that are less realistic than those shown here). With the exception of frequency response, where the Audio Precision bandwidth was extended to 1MHz, 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.

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 HTA200 was able to sustain 133W into 4 ohms (~7% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (13.3W) for five seconds, for five continuous minutes without inducing a fault or the initiation of a protective circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the HTA200 (except for the tubes) 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 analog input at the headphone output (unless specified, assume a 1kHz sinewave, 2Vrms output, 300-ohm loading, 10Hz to 22.4kHz bandwidth):

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

In our frequency-response plots above (relative to 1kHz), measured across the speaker outputs at 10W into 8 ohms, the HTA200 is not flat within the audioband (20Hz to 20kHz). There’s a +1dB rise in the frequency response at 40Hz and at nearly 20kHz. There’s also a -0.3dB dip at 5-7kHz. The HTA200 appears to be AC coupled (or at least purposefully high-pass filtered) with a -3dB point at 10Hz. There is extreme brickwall-type filtering at 20kHz, with a -3dB point at around 21.8kHz. There is a high probability that the analog input is digitized, because this type of brickwall filtering is easier to implement in the digital domain. Further evidence for this can be seen in the FFTs in this report. In the graph above and most of the graphs below, only a single trace may be visible. This is because the left channel (blue or purple trace) is performing identically to the right channel (red or green trace), and so they perfectly overlap, indicating that the two channels are ideally matched.

Frequency response (8-ohm loading, 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 +7.5/-6.5dB of gain/cut is available centered at 100Hz/8kHz.

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

Above are the phase-response plots from 20Hz to 20kHz (wrapped, or every time the phase delay exceeds 360 degrees, the plot loops back up to +180 degrees) for the line-level input, measured across the speaker outputs at 10W into 8 ohms. The HTA200 appears to invert polarity and yields an astonishing -60000 degrees of phase shift at 20kHz.

Frequency response (line-level sub out)

Above is the frequency-response plot (relative to 80Hz) measured at the line-level sub out of the HTA200. The same rise at 40Hz that was observed at the speaker-level outputs can be seen here. The -3dB point is just past 2kHz.

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

The chart above shows the HTA200’s frequency response (relative to 1kHz) as a function of input type measured across the speaker outputs at 10W into 8 ohms. The pink 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, and the 24/192 dithered digital input signal is not shown because it yielded the same result as the 24/96 data. Because the HTA200 appears to digitize incoming analog signals, as well as resample all digital signals to 44.1kHz, the same brickwall-type behavior is seen right at 20kHz regardless of the input type. At low frequencies, there is slightly more extension for the analog input, with a -3dB point at 10Hz versus about 12Hz for the digital input. The digital input shows less significant deviations within the audioband, with a rise of only 0.5dB at 50Hz versus the 1dB rise at 40Hz for the analog input. The same is true at 20kHz, where the digital input is at +0.25dB compared to the +0.8dB for the analog signal.

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

The chart above shows the frequency response (relative to 1kHz) for the phono input (MM configuration). 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 a maximum deviation of about -5dB/+0.8dB (20Hz and 20kHz) from 20Hz to 20kHz. The dip at 5-7kHz seen with the line-level input is also seen here; however, with a channel-to-channel deviation of about 0.3dB (from 5kHz to 20kHz).

Phase response (MM input)

Above is the phase-response plot from 20Hz to 20kHz (excess, or above and beyond the true input to output phase delay as seen in the plot for the line-level input above) for the phono input (MM configuration) measured across the speaker outputs at 10W into 8 ohms. 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 +150 degrees at 20Hz.

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 speaker outputs of the HTA200 at 1W into 8 ohms. 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. The 16/44.1 data were essentially perfect as of -90dBFS down to 0dBFS, while the 24/96 data were near perfect down to -100dBFS. Both overshot the mark by over 10dB at -120dBFS. This is a poor linearity-test result, although it should be pointed that the linearity test is measured at the line-level pre-out when available. In this case, there are none, and the speaker outputs will invariably be noisier.

Impulse response (24/44.1 data)

The graph above shows the impulse response for the HTA200, fed to the coaxial digital input, measured at the speaker level output at 1W into 8ohms, 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 adheres to a typical symmetrical sinc function, although the HTA200 does invert polarity.

J-Test (coaxial)

The chart above shows the results of the J-Test test for the coaxial digital input measured at the speaker level output of the HTA200 at 1W into 8 ohms. 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.

It is difficult to assess the results, with the significant rise in the noise floor (-80dBrA) centered on the main peak. We see a peak at -75dBrA at 8kHz, and another at -85dBrA at 16kHz. This is a poor J-Test result, indicating that the HTA200 DAC may be susceptible to jitter. When we attempted to inject artificial jitter at a level of only 10ns, we could not capture a reliable result.

J-Test (optical)

The chart above shows the results of the J-Test test for the optical digital input measured at the speaker-level output of the HTA200 at 1W into 8 ohms. The optical input yielded essentially the same result as the coaxial input.

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 HTA200’s speaker level output at 1W into 8 ohms, with white noise at -4dBFS (blue/red) and a 19.1 kHz sinewave at -1dBFS fed to the coaxial digital input, sampled at 16/44.1. The steep roll-off around 20kHz in the white-noise spectrum shows the brickwall-type behavior of the HTA200’s reconstruction filter. There are low-level aliased image peaks within the audioband at the -100dBrA level. The primary aliasing signal at 25kHz cannot be seen and is completely suppressed, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are at -55dBrA.

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 line-level input swept from 5Hz to 50kHz. 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 find that between 100Hz and 8kHz, the deviations between no load and 4 ohms are around 0.15dB. This is a fair result for a class-AB amp, and an indication of a relatively low output impedance, or high damping factor. Due to the nonlinear nature of the HTA200’s frequency response, it is difficult to assess the fluctuations in response versus frequency for the real speaker load.

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 just under 35W. The power was varied using the HTA200 volume control. At 1W, THD ratios are fairly constant at 0.3% from 20Hz to 20kHz. At 10W, THD ratios are fairly constant across the audioband from 1% to 0.8%, while at 35W, THD ratios are as high as 2% at 20Hz, then a constant 1.5% from 100Hz to 20kHz. The HTA200 is definitely a high-distortion amplifier, considering the class-AB transistor-based output.

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

The chart above shows THD ratio as a function of frequency plots for the phono input measured across an 8-ohm load at 10W. The input sweep is EQ’d with an inverted RIAA curve. The THD values vary from around 0.5% to 0.8% across the audioband.

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 HTA200 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 closely except for maximum power, with the 4-ohm data slightly outperforming (2-3dB) the 8-ohm data at medium power. THD ratios range from as low as 0.1% at 50mW, then a steady linear climb to the “knees” at 80W (2% into 8 ohms) and just past 100W (2% into 4 ohms). The 1% THD marks were reached at just 16.5W (8 ohms) and 32W (4 ohms).

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 HTA200 as a function of output power for the 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 closely except for maximum power, with the 4-ohm data slightly outperforming (2-3dB) the 8-ohm data at lower power. Overall, THD+N values for both loads ranged from 0.2% at 50mW, then a steady linear climb to the “knees” at 80W (2% into 8 ohms) and just past 100W (2% into 4 ohms). Because THD ratios are so high with the HTA200, it’s the THD component of THD+N that dominates in these graphs.

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 HTA200 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 essentially identical THD ratios into all three loads, from 1% to 0.8%. Ordinarily, having all three data sets plot identically would be commendable; however, in this case, THD ratios are very high for a solid-state amplifier output.

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 HTA200 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). We find essentially identical THD ratios into all three loads, just above and below 0.3% to 0.8%. As above, ordinarily, having all three data sets plot identically would be commendable; however, in this case, THD ratios are very high for a solid-state amplifier output.

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 HTA200 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 essentially identical IMD ratios into all three loads, around 0.3%. Once again, having all three data sets plot identically would be commendable; however, in this case, the IMD ratios are very high for a solid-state amplifier output.

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 HTA200 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 essentially identical IMD ratios into all three loads, 1% from 40Hz to almost 500Hz, and then a dip to 0.02% from 500Hz to 1kHz. As mentioned above, having all three data sets plot identically would be commendable; however, in this case, the IMD ratios are very high for a solid-state amplifier output.

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 (2kHz) harmonic dominates at a very high -40dBrA, or 1%, while subsequent signal harmonics are at and below -70dBrA, or 0.03%. On the right side of the signal peak, we see the primary (60Hz), second (120Hz), and fourth (240Hz) noise-related harmonics dominate at -85dBrA to -95dBrA, or 0.006% to 0.002%. While difficult to see in this graph, we did find two peaks at 43.1kHz and 45.1kHz, which are telltale IMD products that are a result of the 1kHz analog signal being digitized and sampled at 44.1kHz.

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) harmonic dominates at a very high -40dBrA, or 1%, while subsequent signal harmonics are at and below -55dBrA, or 0.2%. On the right side of the signal peak, we see the primary (60Hz), second (120Hz), and fourth (240Hz) noise-related harmonics dominate at -85dBrA to -95dBrA, or 0.006% to 0.002%.

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 that the signal’s second (2kHz) harmonic dominates at a very high -45dBrA, or 0.6%, while subsequent signal harmonics are at and below -90dBrA, or 0.003%. On the right side of the signal peak, we see the primary (60Hz), second (120Hz), and fourth (240Hz) noise-related harmonics dominate at -85dBrA to -95dBrA, or 0.006% to 0.002%.

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 just under the correct amplitude, and noise-related peaks at -90dBrA, or 0.003%, and below.

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 just under the correct amplitude, and noise-related peaks at -90dBrA, or 0.003%, and below.

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 (2kHz) harmonic dominates at a very high -40dBrA, or 1%, while subsequent signal harmonics are at and below -70dBrA, or 0.03%. On the right side of the signal peak, we see the primary (60Hz) noise-related peak dominate at -65/-75dBrA (left/right), or 0.06/0.02%.

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. The most predominant (non-signal) peak is the second (100Hz) signal harmonic at a high -40dBrA, or 1%. Several other signal-related harmonic peaks can be seen throughout at -70dBrA, or 0.03%, and below.

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. The most predominant (non-signal) peak is from the second (100Hz) signal harmonic at a high -45dBrA, or 0.6%. The worst-case noise-related peak is from the fundamental (60Hz) for the left channel at -60dBrA, or 0.1%.

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 -45dBRa, or 0.6%, while the third-order modulation products, at 17kHz and 20kHz, are at -80dBrA, or 0.01%.

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

Shown above is the FFT of the speaker-level output of the HTA200 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 -70dBrA, or 0.03%, 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 (-1dBFS). We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -50dBrA, or 0.3%, while the third-order modulation products, at 17kHz and 20kHz, are around -75dBrA, or 0.02%.

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 (-1dBFS). We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -50dBrA, or 0.3%, while the third-order modulation products, at 17kHz and 20kHz, are around -90dBrA, or 0.003%.

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 -50dBrA, or 0.3%, while the third-order modulation products, at 17kHz and 20kHz, are around -60dBrA, or 0.1%.

Squarewave 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 HTA200’s slew-rate performance. Rather, it should be seen as a qualitative representation of the HTA200’s extremely restricted 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 brickwall-type cutoff at 20kHz, we find only the 10kHz fundamental sinewave, with all the upper harmonics filtered out.

Squarewave response (1kHz)

Above is the 1kHz squarewave response using the analog line-level input, at roughly 10W into 8 ohms, We can see significant overshoot/undershoot in the corners of the squarewave, a consequence of the HTA200’s limited bandwidth.

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

The final graph above is the damping factor as a function of frequency. We can see here a constant damping factor right around 100, from 20Hz to 20kHz.

Diego Estan
Electronics Measurement Specialist