Details

Parent Category: Products

Category: Amplifier Measurements

Created: 01 September 2025

Link: reviewed by Jason Thorpe on SoundStage! Ultra on September 1, 2025

General Information

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

The Marantz Model 10 was conditioned for 1 hour at 1/8th full rated power (~30W 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 10 offers five analog line-level inputs (three RCA, two XLR), one set of phono inputs (RCA, configurable for MM or MC), line-level pre-outs (RCA and XLR), line-level power-amp inputs (RCA and XLR), and two pair of speaker level outputs. In addition, a ¼″ TRS headphone jack can be found on the front panel. For the purposes of these measurements, the following inputs were evaluated: analog line-level balanced (XLR) input, phono (MM and MC), and the headphone output. There were no appreciable differences between the RCA and XLR inputs in terms of THD and noise, but 1kHz FFTs for both are shown in this report. The balanced inputs offer 6dB less gain than the unbalanced inputs (i.e., the designers expect balanced incoming signals to have twice the voltage as unbalanced signals).

Most measurements were made with a 4Vrms line-level analog input, 5mVrms MM input and 0.5mVrms MC input. For the MC configuration, the Model 10 offers three settings with different input impedances (Low at 33 ohms, Mid at 100 ohms, and High at 390 ohms). For the purposes of these measurements, the Mid setting was used. The signal-to-noise ratio (SNR) measurements were made with the same input signal values but with the volume set to achieve the rated output power of 250W. For comparison, on the analog input, a SNR measurement was also made with the volume at maximum.

Based on the accuracy and randomness at various volume levels of the left/right channel matching (see table below), the Model 10 volume control is likely digitally controlled but operating in the analog domain. The volume control offers a total range from -62dB to +36.4dB (XLR line-level input to speaker level outputs). The range is -99.5dB to 0dB, in 0.5dB increments.

Our typical input bandwidth filter setting of 10Hz-22.4kHz was used for all measurements except FFTs, where a bandwidth of 10Hz-90kHz was used. Frequency response measurements utilize a DC to 1 MHz input bandwidth. Because the Model 10 is a digital amplifier technology 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.

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 10 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 set at its maximum (DC to 1MHz), assume, unless otherwise stated, a measurement input bandwidth of 10Hz to 22.4kHz, and the worst-case measured result between the left and right channels.

Our primary measurements revealed the following using the analog input (unless specified, assume a 1kHz sinewave at 4Vrms, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

For the continuous dynamic power test, the Model 10 was able to sustain 750W (3% THD) into 4 ohms using an 80 Hz tone for 500ms, alternating with a signal at -10 dB of the peak (75W) 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 Model 10 was only slightly warm to the touch.

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

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

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

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

In our measured frequency-response (relative to 1kHz) chart above, the Model 10 is essentially perfectly flat within the audioband (20Hz to 20kHz). At the extremes the Model 10 is 0dB at 5Hz, and -3dB at 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.

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

Above are two frequency-response plots (relative to 1kHz) for the analog input, measured at 10W (8-ohm) at the speaker outputs, with the treble/balance controls set at both minimum and maximum. They show that the Model 10 will provide a maximum gain/cut of approximately 11dB at 20Hz, and a maximum gain/cut of approximately 10dB at 20kHz.

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

Above is the phase response plot from 20Hz to 20kHz for the analog input. The Model 10 does not invert polarity and exhibits just past -20 degrees of phase shift at 20kHz.

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

The chart above shows the frequency response for the phono input (MM configuration) measured across the speaker outputs at 10W into 8 ohms. 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 +0.2/+0.25dB (150Hz and 10kHz-20kHz) from 20Hz to 20kHz for the left channel. The right channel performed better and was essentially perfectly flat within the audioband. Below 20Hz, there’s a significant rise in response, peaking at +2.5dB at 6-7Hz. The high frequency response (above 20kHz) is the same as the line-level response above.

Phase response (MM input)

Above is the phase response plot from 20Hz to 20kHz for the phono input (MM configuration) measured across the speaker outputs at 10W into 8 ohms. The Model 10 does not invert polarity. For the phono input, since the RIAA equalization curve must be implemented, which ranges from +19.9dB (20Hz) to -32.6dB (90kHz), phase shift at the output is inevitable. Here we find a worst case of about -60 degrees at 200Hz, and -120 degrees at 20kHz.

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

The chart above shows the frequency response for the phono input (MC configuration) measured across the speaker outputs at 10W into 8 ohms. We see essentially the same response as with the MM configuration above.

Phase response (MC input)

Above is the phase response plot from 20Hz to 20kHz for the phono input (MC configuration) measured across the speaker outputs at 10W into 8 ohms. We see essentially the same response as with the MM configuration above.

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 input swept from 10Hz to 100kHz. The blue plot is into an 8-ohm load, the purple is into a 4-ohm load, the pink plot is an actual speaker (Focal Chora 806, measurements can be found here), and the cyan plot is no load connected. The chart below . . .

. . . is the same but zoomed in to highlight differences. Zoomed in, we can see a maximum deviation within the audio band of just above 0.02dB from 4 ohms to no load, which is an indication of a very high damping factor, or low output impedance. The maximum variation in RMS level when a real speaker was smaller, deviating by about 0.01dB within the flat portion of the curve (20Hz to 10kHz).

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

The chart above shows THD ratios at the output into 8 ohms as a function of frequency (20Hz to 6kHz) for a sinewave stimulus at the analog input. The blue and red plots are for left and right channel at 1W output into 8 ohms, purple/green at 10W, and pink/orange at 250W (rated power). The 10W data exhibited the lowest THD values, 0.0001% from 20Hz to 1kHz, then up to 0.00025% at 6kHz. The 1W data hovered around the 0.0002% across the sweep, and the 250W THD data ranged from 0.0001-0.0002% at 20Hz to 200Hz, then a steady rise to 0.001% at 6kHz.

THD ratio (unweighted) vs. frequency at 10W (MM and MC phono 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 for the MM (blue/red) and MC (purple/green) configurations. The input sweep is EQ’d with an inverted RIAA curve. The MM THD values vary from around 0.005% at 20Hz then a steady decline down to 0.0003% at 6kHz. The MC THD values vary from around 0.05% at 20Hz then a steady decline down to 0.0005% at 6kHz. The decline in THD values as a function of frequency is a function of the noise floor reduction at higher frequencies due to the implementation of RIAA equalization. The analyzer cannot assign a THD value for a harmonic peak it cannot see below the noise floor.

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 Model 10 as a function of output power for the analog line level-input, for an 8-ohm load (blue/red for left/right) and a 4-ohm load (purple/green for left/right), with the volume set to maximum. The 8 and 4-ohm data are closely matched (with 2-3dB). The 8-ohm THD data range from 0.003% at 50mW, down to 0.0002% just before the “knee,” at roughly 220W. The 4-ohm THD data range from 0.005% at 50mW, down to 0.0003% just before the “knee,” at roughly 500W. The 1% THD marks were seen at 340W and 650W.

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 10 as a function of output power for the analog line level-input, for an 8-ohm load (blue/red for left/right) and a 4-ohm load (purple/green for left/right), with the volume set to maximum. The 4-ohm data yielded a consistent 3-4dB higher THD+N result across the sweep compared to the 8-ohm data. The 8-ohm data ranged from 0.03% at 50mW down to 0.0006% at the “knee.”  The 4-ohm data ranged from 0.05% at 50mW down to 0.0006% at the “knee.”

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

The chart above shows THD ratios measured at the output of the Model 10 as a function of load (8/4/2 ohms) for a constant input voltage that yielded 100W at the output into 8 ohms (and roughly 200W into 4 ohms, and 400W into 2 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. We find increasing levels of THD from 8 to 4 (2-3dB) to 2 ohms (6-7dB). Overall, even with a 2-ohm load at roughly 400W, THD values were fairly low and flat within the audioband, between 0.0004% and 0.001%.

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 10 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). The measured THD ratios for the real speakers were higher than for the 8-ohm resistive load between 20Hz and 400Hz. The highest result, as is usually the case, was at 20Hz into the two-way speaker at 0.01%, compared to 0.0002% into the dummy load. At 100Hz, both speakers yielded THD ratios of 0.0006%, compared to 0.0002% into the dummy load. In the important midrange frequencies of 400Hz to 6kHz, all THD ratios were essentially the same, between 0.0002% and 0.0001%.

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 10 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 IMD results are similar, hovering from 0.0005% to 0.001% across the measured frequency range.

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 10 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here, the SMPTE IMD method was used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). All IMD results are effectively the same, hovering just below 0.002% across the sweep.

FFT spectrum – 1kHz (XLR 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 XLR input. We see that the signal’s second (2kHz) and third (3kHz) harmonics dominate at -140/-130dBrA (left/right), or 0.00003/0.00001%, and -120dBrA, or 0.0001%. Subsequent signal harmonics can be seen at -135dBrA and below. Below 1kHz, we see traditional noise peaks from the implementation of a linear power supply at the odd-harmonic positions (60/180/300/420/540Hz etc). Given the enormous size of the power supply, however, the peaks are low in level, at -130/-120dBrA (left/right) and below. We also see a rise in the noise floor above 30kHz, indicative of digital amplifier technology.

FFT spectrum – 1kHz (RCA 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 RCA input. The FFT is almost identical to the balanced FFT above, except for a slightly higher peak at the second (2kHz) harmonic position.

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 (MM configuration). We see the second (2kHz) signal harmonic dominating at around -110dBrA, or 0.0003%. Other signal harmonics are difficult to identify amongst the power-supply-related noise peaks. The most significant power-supply-related noise peak can be seen at 180Hz at -90dBrA, or 0.003%. Higher-order power-supply-related peaks can also be seen at lower amplitudes.

FFT spectrum – 1kHz (MC phono input)

Shown above is the FFT for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the phono input (MC configuration). We see the second (2kHz) signal harmonic dominating at around -100dBrA, or 0.001%. Other signal harmonics are difficult to identify amongst the power-supply-related noise peaks. The most significant power-supply-related noise peak can be seen at 180Hz at -70dBrA, or 0.03%. Higher order power-supply-related peaks can also be seen at lower amplitudes.

FFT spectrum – 50Hz (line-level input)

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the analog 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 signal third (150Hz) signal harmonic and the power-supply-related third (180Hz) harmonic, both around -120dBrA or 0.0001%. Subsequent power-supply-related noise peaks can be seen just below the -120dBrA 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 (MM configuration). 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 signal second (100Hz) harmonic and the power-supply-related third (180Hz) harmonic, at -95dBrA, or 0.002%, and -90dBrA, or 0.003%.

FFT spectrum – 50Hz (MC phono input)

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the phono input (MC configuration). The X axis is zoomed in from 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 power-supply-related primary (60Hz) and third (180Hz) harmonics, at -75dBrA, or 0.02%, and -70dBrA, or 0.03%. Signal harmonics are difficult to identify above the higher noise-floor.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the analog input. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -120dBrA, or 0.0001%, while the third-order modulation products, at 17kHz and 20kHz, are just below -110dBrA, or 0.0003%.

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

Shown above is the FFT of the speaker-level output of the Model 10 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 below the very low -140dBrA, or 0.00001%, 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 (MM configuration). We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -90dBRa, or 0.003%, while the third-order modulation products, at 17kHz and 20kHz, are just below -110dBrA, or 0.0003%.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the phono input (MC configuration). We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -90dBRa, or 0.003%, while the third-order modulation products, at 17kHz and 20kHz, are just below -110dBrA, or 0.0003% (right channel only).

Squarewave response (10kHz)

Above is the 10kHz squarewave response using the analog input, at roughly 10W into 8 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the Model 10’s slew-rate performance. Rather, it should be seen as a qualitative representation of its reasonably extended bandwidth. An ideal squarewave can be represented as the sum of a sinewave and an infinite series of its odd-order harmonics (e.g., 10kHz + 30kHz + 50kHz + 70kHz . . .). A limited bandwidth will show only the sum of the lower-order harmonics, which may result in noticeable undershoot and/or overshoot, and softening of the edges. Due to Model 10’s bandwidth, we can see visible over-shoot in the corners of the waveform. In addition, we can see the 700kHz switching oscillator frequency used in the digital amplifier section visibly modulating the waveform.

Squarewave response (10kHz, 250kHz bandwidth)

Above is the same 10kHz squarewave response using the analog input as seen in the graph above, but this time applying a 250kHz bandwidth filter in the analyzer to remove the effect from the switching oscillator. We find the same visible over-shoot in the corners of the waveform.

FFT spectrum of 700kHz switching frequency relative to a 1kHz tone

The Model 10’s class-D amplifier relies on a switching oscillator to convert the input signal to a pulse-width-modulated (PWM) squarewave (on/off) signal before sending the signal through a low-pass filter to generate an output signal. The oscillator switches at a rate of about 700kHz, 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 700kHz peak is quite evident at -50dBrA. We also see a clear rise in the noise floor above 30kHz all the way to the 700kHz peak. This very-high-frequency noise is in the signal, but is far above the audio band—and is therefore inaudible—and so high in frequency that any loudspeaker the amplifier is driving should filter it all out anyway.

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

The final plot above is the damping factor as a function of frequency. Both channels show a relatively constant damping factor from 20Hz to 20kHz. The damping factor for the left channel ranges from just over 1000 down to 700 at 20kHz, while the right channel ranges from 900 down to 600 at 20kHz. These are very high damping factor results, and they explain the Model 10’s exemplary flat frequency-response results into different loads.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Amplifier Measurements

Created: 01 August 2025

Link: reviewed by Doug Schneider on SoundStage! Hi-Fi on August 1, 2025

General information

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

The Anthem P2 was conditioned for 1 hour at 1/8th full rated power (~40W 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 P2 is a two-channel amplifier with two sets each of balanced (XLR) and unbalanced (RCA) inputs and two sets of speaker level outputs. An input of 320mVrms was required to achieve the reference 10W into 8 ohms. There is a third input option—XLR -6dB—which is balanced but reduces gain from 29dB to 23dB. Unless otherwise stated, the XLR input was used (29dB of gain); however, 1kHz 10W FFTs are provided in this report for all three input selections.

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 1MHz input bandwidth.

Published specifications vs. our primary measurements

The table below summarizes the measurements published by Anthem for the P2 compared directly against our own. The published specifications are sourced from Anthem’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:

* 9.6k ohms for each individual differential input

Our primary measurements revealed the following (unless specified, assume a 1kHz sinewave at 320mVrms at the input, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

For the continuous dynamic power test, the P2 was able to sustain about 580W into 4 ohms (~3% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (58W) 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 P2 was warm to the touch.

Frequency response (8-ohm loading)

In our frequency-response plot (relative to 1kHz) above, measured across the speaker outputs at 10W into 8 ohms, the P2 exhibits a close-to-flat frequency response across the audioband (0/-0.2dB at 20Hz/20kHz). The P2 is only about -0.1dB down at 5Hz. The -3dB point is at roughly 150kHz. 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 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 P2 does not invert polarity and exhibits, at worst, only -10 degrees of phase shift at 20kHz, due to its extended bandwidth.

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 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 4-ohm load and no-load to be just under 0.04dB up to 2kHz. Beyond 2kHz, the deviations are as high as 0.18dB at 20kHz. This is an indication of a very high damping factor or low output impedance. With a real speaker, the deviations from 20Hz to 4kHz were lower at roughly 0.02dB.

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 at 1W output into 8 ohms, purple and green at 10W, and pink and orange at 300W. All THD results below about 1kHz are tightly grouped (within 5dB), hovering around the 0.0005-0.001% level. The 1W and 10W data rise to the 0.005-0.01% level at 20kHz, while the 300W data rise to 0.03% 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 P2 as a function of output power for the analog line-level input for an 8-ohm load (blue/red) and a 4-ohm load (purple/green). The 8-ohm data were fairly constant at 0.001% from 50mW to the “knee” at 300W, then up to the 1% THD mark at 351W. The 4-ohm data were fairly constant at 0.002% from 50mW to the “knee” at 500W, then up to the 1% THD mark at 573W.

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 P2 as a function of output power for the analog line-level input for an 8-ohm load (blue/red) and a 4-ohm load (purple/green). The 8-ohm data ranged from 0.01% at 50mW, down to a low of 0.001% from 20W to 300W, then up to the “knee.” The 4-ohm data ranged from 0.02% at 50mW, down to a low of 0.002% from 20-500W, then up to the “knee.”

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

The chart above shows THD ratios measured at the output of the P2 as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yielded roughly 100W at the output into 8 ohms (blue), 200W into 4 ohms (purple), and 400W into 2 ohms (pink). The 8-ohm and 4-ohm data track closely (within 2-3dB), ranging from 0.0005% at 20-200Hz, then up to 0.04% at 20kHz. The 2-ohm data yielded 0.001% at 20Hz with a steady climb to 0.04% at 20kHz. This shows that the P2 is perfectly stable into 2 ohms, with low THD ratios even at 400W.

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 P2 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 frequencies, the two-way speaker yielded the highest THD ratios (0.02%). In the 100Hz to 6kHz range, THD ratios into all three loads ranged from 0.0004% at 2kHz (two-way speaker) to 0.001% from 150Hz to 5kHz (three-way speaker) to a steady rise from 0.0006% (100Hz) to 0.002% (6kHz) for the resistive load. The highest THD result at 20kHz was from the three-way speaker at just over 0.01%.

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 P2 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here the CCIF IMD method was used, where the primary frequency is swept from 20kHz (F1) down to 2.5kHz, and the secondary frequency (F2) is always 1kHz lower than the primary, with a 1:1 ratio. The CCIF IMD analysis results are the sum of the second (F1-F2 or 1kHz) and third modulation products (F1+1kHz, F2-1kHz). The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). The IMD results into the resistive load range from 0.001 to 0.002% across the sweep. The results into the two-way speaker range from 0.0006% to 0.004%, while the three-way speaker results range from 0.001% to 0.007%.

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 P2 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here, the SMPTE IMD method was used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). All three plots are within 4dB of one another with a constant 0.003-0.005% across the sweep.

FFT spectrum – 1kHz (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 balanced analog line-level input. We see that the signal’s second (2kHz), third (3kHz) and fourth (4kHz) signal harmonics dominate at -100dBrA (2kHz) and -110dBrA (3/4kHz), or 0.001% and 0.0003%. Other signal harmonics can be seen at and below the -120dBrA level, or 0.0001%. There are power-supply noise-related harmonics at and below the -120dBrA, or 0.0001%, level throughout most of the audioband.

FFT spectrum – 1kHz (XLR -6dB 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 using the -6dB (23dB of gain versus 29dB) setting. The signal harmonic profile using this setting is worse, although it’s not clear whether this is due to the setting itself or the doubling of the input signal to achieve the same 10W at the output. Higher-order signal harmonics (5kHz and above) reach the -110dBrA, or 0.0003%, level all the way up to 100kHz. This is not seen in the FFT above using the standard XLR input. Power-supply noise-related harmonics are the same as the standard XLR FFT above.

FFT spectrum – 1kHz (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 analog line-level input. The FFT is very similar to the FFT using the RCA input. The main differences between RCA and XLR inputs are: a -110dBrA versus -120dBrA noise peak at 60Hz; smaller higher-order power-supply related peaks at -140dBrA instead of -120dBrA; a slightly lower noise floor (-150dBrA instead of -145dBrA), likely overall due to fewer components used and therefore less uncorrelated noise; a more prominent cluster of noise peaks centered around 16-17kHz reaching -120dBrA instead of -130dBrA.

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) peak is the signal’s second (100Hz) signal harmonic at -105dBrA, or 0.0006%. Subsequent signal harmonics are at the -120dBrA, or 0.0001% level, while power-supply-related noise peaks are at and below the same 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 products (i.e., the difference signal of 1kHz) are at -110dBrA, or 0.0003%, level, while the third-order modulation products, at 17kHz and 20kHz, are a little higher at just under-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 P2 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 just below -120dBrA, or 0.0001%.

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 P2’s slew-rate performance. Rather, it should be seen as a qualitative representation of the P2’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. In this case, we see a very clean result, with no ringing in the corners and only very mild softening.

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

The final graph above is the damping factor as a function of frequency. We find very high damping factor values, around 500 from 20Hz to 2kHz. Above 2kHz, there is a dip in damping factor, reaching 100 at 20kHz. This is a very strong damping factor result.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Amplifier Measurements

Created: 01 July 2025

Link: reviewed by Dennis Burger on SoundStage! Access on July 1, 2025

General Information

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

The NAD C 700 V2 was conditioned for 1 hour at 1/8th full rated power (~10W into 8 ohms) before any measurements were taken. All measurements were taken with both channels driven, using a 120V/20A dedicated circuit, unless otherwise stated.

The C 700 V2 offers two single-ended RCA analog inputs (one phono MM, one line-level), two digital S/PDIF inputs (coaxial and optical), an HDMI input, an ethernet connection for streaming, line-level subwoofer and pre-outs (RCA), and a pair of speaker-level outputs. For the purposes of these measurements, the following inputs were evaluated: coaxial digital (RCA), and the analog line-level and phono MM unbalanced (RCA).

Most measurements were made with a 1Vrms line-level analog input or 0dBFS digital input depending on the input. The volume control is variable from 0 to 100. The signal-to-noise ratio (SNR) measurements were made with the same input signal values but with the volume set to achieve the rated output power of 80W. For comparison, on the analog input, an SNR measurement was also made with the volume at maximum.

Based on the accuracy and repeatability at various volume levels of the left/right channel matching (see table below), the C 700 V2 volume control is likely operating in the digital domain. Consequently, all analog signals are digitized at the C 700 V2’s inputs so the unit may apply volume, bass management, and tone controls. The volume control offers a total range from -46dB to +32.6dB (speaker-level outputs). Volume increments are in 1dB steps.

Because the C 700 V2 is a digital amplifier technology that exhibits considerable noise above 20kHz (see FFTs below), our typical input bandwidth filter setting of 10Hz-90kHz was necessarily changed to 10Hz-22.4kHz for all measurements, except for frequency response and for FFTs. In addition, THD versus frequency sweeps were limited to 6kHz to adequately capture the second and third signal harmonics with the restricted bandwidth setting.

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

Published specifications vs. our primary measurements

The table below summarizes the measurements published by NAD for the C 700 V2 compared directly against our own. The published specifications are sourced from NAD’s website, either directly or from the manual available for download, or a combination thereof. With the exception of frequency response, where the Audio Precision bandwidth was set at its maximum (DC to 1MHz), assume, unless otherwise stated, a measurement input bandwidth of 10Hz to 22.4kHz, and the worst-case measured result between the left and right channels.

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

For the continuous dynamic power test, the C 700 V2 was able to sustain 107W (2% THD) into 4 ohms using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (10.7W) 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 C 700 V2 was only slightly warm to the touch.

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

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

In our measured frequency response (relative to 1kHz) chart above, the C 700 V2 is nearly flat within the audioband (20Hz to 20kHz). At the extremes the C 700 V2 is -0.04dB at 20Hz, and -0.2dB at 20kHz. The C 700 V2 cannot be considered a high-bandwidth audio device as the -3dB point is just past 20kHz. That’s because incoming analog signals are digitally sampled at 44.1kHz. 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 are two frequency-response plots for the analog input, measured at 10W (8 ohms) at the speaker outputs, with the treble/balance controls set at both minimum and maximum. They show that the C 700 V2 will provide a maximum gain/cut of approximately 6dB at 20Hz, and a maximum gain/cut of approximately 6dB at 10kHz.

Frequency response (subwoofer output engaged, 80Hz crossover)

Above are two frequency-response plots for the analog input, measured at 10W (8 ohms) at the speaker outputs, and at the line-level subwoofer output, with the crossover set at 80Hz. The C 700 V2 DSP crossover uses a slope of 18dB/octave, and the subwoofer output is flat down to 10Hz.

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

Above is the phase-response plot from 20Hz to 20kHz for the analog input. The C 700 V2 appears to invert polarity (not evident in graph due to scale) and due to the sampling by the ADC and the inherent delays associated with this process, the overall phase shift is significant at 1.5 million degrees at 20kHz.

Frequency response (MM input)

The chart above shows the frequency response (relative to 1kHz) 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 50Hz to 1kHz. There is a 0.5dB rise at 20Hz, then a steep dip below 20Hz (roughly -3dB at 10Hz). There is a slow 0.5dB (at 20kHz) high frequency rise starting at 2kHz, then brickwall filtering just past 20kHz.

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

The chart above shows the C 700 V2’s frequency response as a function of input type. The green traces are the same analog input data from the analog line-level previous graph. The red/blue traces are for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz, the purple/green traces are for a 24/96 dithered digital input signal from 5Hz to 48kHz, and finally pink/orange is 24/192 from 5Hz to 96kHz. The analog-in frequency response is identical to the 16/44.1 digital input (but for slightly more low frequency roll-off), with brickwall filtering just above 20kHz. The behavior at low frequencies is the same across all digital input types: -0.15dB at 10Hz. The behavior at high frequencies for all digital input types is typical. The 24/96 data shows brickwall-type filtering right around 48kHz, while the 24/192 data shows a gentler slope with a -3dB point at 77kHz.

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

The chart above shows the results of a linearity test for the coaxial digital input for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the line-level pre-outs of the C 700 V2. For this test, the digital input is swept with a dithered 1kHz input signal from -120dBFS to 0dBFS, and the output is analyzed by the APx555. The ideal response would be a straight flat line at 0dB. Both digital input types performed similarly, approaching the ideal 0dB relative level at -100dBFS, then yielding perfect results to 0dBFS. At -120dBFS, the 16/44.1 input data overshot the ideal output signal amplitude by 2-3dB, while the 24/96 data overshot by only 0.5dB. The above results were good, so we extended . . .

. . . the test to -140dB. In this instance both the 16/44.1 and 24/96 deviated considerably from the ideal of a flat line at 0dB.

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

The graph above shows the impulse response for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s) for one sample period then back to digital silence, measured at the line-level pre-outs of the C 700 V2. We can see that the C 700 V2 utilizes a typical sinc function reconstruction filter, though this test again shows that it appears to invert polarity.

J-Test (coaxial input)

The plot above shows the results of the J-Test test for the coaxial digital input measured at the line-level pre-outs of the C 700 V2. 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. In addition, an undithered 250Hz squarewave at -144dBFS is mixed with the signal. This test file causes the 22 least-significant bits to constantly toggle, which produces strong jitter spectral components at the 250Hz rate and its odd harmonics. The test file shows how susceptible the DAC and delivery interface are to jitter, which would manifest as peaks above the noise floor at 500Hz intervals (e.g., 250Hz, 750Hz, 1250Hz, etc). Note that the alternating peaks are in the test file itself, but at levels of -144dBFS and below. The test file can also be used in conjunction with artificially injected sinewave jitter by the Audio Precision, to show how well the DAC rejects jitter.

We see very small peaks in the audioband at -140dBFS around 10kHz and 14kHz. This is a very good J-Test result, and an indication that the C 700 V2 DAC has good jitter immunity.

J-Test (optical input)

The plot above shows the results of the J-Test test for the optical digital input measured at the line-level pre-outs of the C 700 V2. We see essentially the same result as with the coaxial input above.

J-Test (coaxial input, jitter 10ns)

The plot above shows the results of the J-Test test for the coaxial digital input, measured at the line-level pre-outs of the C 700 V2 with sinewave jitter injected at 2kHz at the 10ns level. We see the same result as without the extra injected jitter. The optical input yielded a similar result.

J-Test (coaxial input, jitter 100ns)

The plot above shows the results of the J-Test test for the coaxial digital input measured at the line-level pre-outs of the C 700 V2 with sinewave jitter injected at 2kHz at the 100ns level. We see the tell-tale peaks at 10kHz and 14kHz peaking just above the very low -140dBFS level. More evidence of how strong the jitter immunity is for the C 700 V2 DAC. The optical input yielded a similar result.

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

The plot above shows a fast Fourier transform (FFT) of the C 700 V2’s line-level pre-outs with white noise at -4 dBFS (blue/red) and a 19.1 kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1. The sharp roll-off above 20kHz in the white-noise spectrum shows the implementation of a brickwall-type reconstruction filter. There are effectively no aliased image peaks in the audioband above the -130dBrA noise floor. The main 25kHz alias peak is near -75dBrA. The second, third, and fourth distortion harmonics (i.e., 38.2, 57.3, 76.4kHz) of the 19.1kHz tone are between -75dBrA and -95dBrA.

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 input swept from 10Hz to 100kHz. The blue plot is into an 8-ohm load, the purple is into a 4-ohm load, the pink plot is an actual speaker (Focal Chora 806, measurements can be found here), and the cyan plot is no load connected. The chart below . . .

. . . is the same but zoomed in to highlight differences. Zoomed in, we can see a maximum deviation within the audio band of less than 0.2dB from 4 ohms to no load, which is an indication of a relatively high damping factor, or low output impedance. The maximum variation in RMS level when a real speaker was used is less, deviating by about 0.1dB within the flat portion of the curve (100Hz to 5kHz), with the lowest RMS level, which would correspond to the lowest impedance point for the load, exhibited around 200Hz, and the highest RMS level, which would correspond to the highest impedance point for the load, at around 2kHz.

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

The chart above shows THD ratios at the output into 8 ohms as a function of frequency (20Hz to 6kHz) for a sinewave stimulus at the analog input. The blue and red plots are for the left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at 71W. The power was varied using the volume control. All three THD plots are relatively flat. The 1W data exhibited the lowest THD values, with values varying around 0.002-0.003%. The 10W data shows THD values around 0.004-0.005%. At 71W, THD values were around 0.05%.

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

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. For this test, the input sweep is EQ’d with an inverted RIAA curve. THD ratios ranged from roughly 0.02% at 20Hz, down to as low as 0.01% at 300-400Hz, then up to 0.02% from 1kHz to 6kHz.

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

The chart above shows THD ratios measured at the output of the C 700 V2 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). Although there are fluctuations before the “knee,” both the 4-ohm and 8-ohm data are close to the same, ranging from 0.002% to 0.05%. The “knee” in the 8-ohm data occurs around 80W, hitting the 1% THD mark at 83W. For the 4-ohm data, the “knee” occurs around 100W, hitting the 1% THD mark at 108W.

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 C 700 V2 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). There’s a distinct 5dB jump in THD+N (also visible in the THD plot above, but to a lesser degree) when the output voltage is around 1Vrms (i.e., 0.15W into 8 ohms, 0.3W into 4 ohms). This behavior was repeatable over multiple measurement trials. Overall, THD+N values before the “knee” ranged from around 0.01% (3 to 20W into 8 ohms and 10 to 30W into 4 ohms) to 0.05/0.03% (8/4 ohms at the knee).

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

The chart above shows THD ratios measured at the output of the C 700 V2 as a function of load (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 increasing levels of THD from 8 to 4 to 2 ohms, with about a 5dB increase from 8 to 4 ohms, and a 2-3dB rise from 4 to 2 ohms. Overall, even with a 2-ohm load at roughly 40W, THD values were fairly flat within the audioband at between 0.01 and 0.02%.

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 C 700 V2 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), 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 at frequencies below 400Hz than those measured across the resistive dummy load. The differences ranged from 0.1/0.006% at 20/150Hz for the two-way speaker versus a constant 0.003% for the resistive load, and 0.01/0.006% at 25/150Hz into the three-way speaker. The three-way speaker did dip as low as 0.001% at 250Hz.

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 C 700 V2 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here the CCIF IMD method 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). Generally, IMD ratios were similar for all three loads, from 0.001 to 0.003%.

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 C 700 V2 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here, the SMPTE IMD method was used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). We find very similar IMD ratios into all three loads, a constant 0.01% from 40Hz to 500Hz, then down to 0.006% 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 -95dBrA and -85dBrA, or 0.002% and 0.006%. The remaining signal harmonics are below -110dBrA, or 0.0003%. Below 1kHz, we do not see traditional peaks from linear power supplies (60/120Hz) because of the switching power supply. All other noise-related peaks are near or below -120dBrA, or 0.0001% (an improvement from the original C700). It appears that the analog signal is digitized with a 44.1kHz sample rate, as peaks can be seen at 44.1kHz, as well as the IMD products with the main signal at 43.1 and 45.1kHz.

FFT spectrum – 1kHz (phono MM 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 phono MM input. Signal harmonics are difficult to distinguish from the numerous noise peaks that range in level from -60dBrA, or 0.1%, down to -110dBrA, or 0.0003%, at high frequencies. The signal’s second (2kHz) and third (3kHz) harmonics can be seen, however, at just below and above -80dBrA, or 0.01%.

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 close to the same signal harmonics at 2kHz and 3kHz as with the analog input, as well as the same lower-level signal harmonics at and below -110dBrA, or 0.0003%. The noise floor is low at -130dBrA, and spurious noise peaks are below -120dBrA, or 0.0001%.

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 signal harmonic profile as with the 16/44.1 FFT above, but with a slightly 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, and the second (2kHz) and third signal harmonics (3kHz) dominating at around -120dBrA, or 0.0001%. The noise floor on the left channel is roughly 10dB lower than the right channel at -150dBrA.

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. The rest of the FFT is very similar to the 16/44.1 FFT above, including the different noise floors between channels.

FFT spectrum – 50Hz (line-level input)

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the analog input. The X axis is zoomed in from 40 Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most predominant (non-signal) peaks are the signal second (100Hz) and third (150Hz) harmonics at around -100dBrA and -85dBrA, or 0.001% and 0.006%, with other signal harmonics seen below the -110dBrA level. Spurious noise peaks are generally below the -120dBrA, or 0.0001%, level.

FFT spectrum – 50Hz (phono MM 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 MM input. The X axis is zoomed in from 40 Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. We see a multitude of noise peaks, signal harmonics, and IMD products between the two, at the -60dBrA, or 0.1%, 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 analog input. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (i.e., the difference signal of 1kHz) are at -95/-110dBrA (left/right), or 0.002/0.0003%, while the third-order modulation products, at 17kHz and 20kHz, are just under -90dBrA, or 0.003%. We also see the main aliased peaks at 25.1kHz and 26.1kHz around -65dBrA, indicating that the C 700 V2 ADC is digitizing the incoming analog signal at 44.1kHz (i.e., 44.1kHz-19kHz = 25.1kHz).

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

Shown above is the FFT of the speaker-level output of the C 700 V2 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 low -120dBrA, or 0.0001%, level.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, phono MM 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 MM 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 products (i.e., the difference signal of 1kHz) are at -90/-100dBrA (left/right), or 0.003/0.001%, while the third-order modulation products, at 17kHz and 20kHz, are around -80dBrA, or 0.01%.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 16/44.1. We find that the second-order modulation products (i.e., the difference signal of 1kHz) are at -90/-100dBrA (left/right), or 0.003/0.001%, while the third-order modulation products, at 17kHz and 20kHz, are just under -90dBrA, or 0.003%.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 24/96. We find that the second-order modulation products (i.e., the difference signal of 1kHz) are at -90/-100dBrA (left/right), or 0.003/0.001%, while the third-order modulation products, at 17kHz and 20kHz, are just under -90dBrA, or 0.003%.

Square-wave response (10kHz)

Above is the 10kHz squarewave response using the analog input, at roughly 10W into 8 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the C 700 V2’s slew-rate performance. Rather, it should be seen as a qualitative representation of its very limited 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. Due to C 700 V2’s very limited bandwidth, only the square wave’s fundamental (10kHz) sinewave is reproduced here. In addition, we can see the 400kHz switching oscillator frequency used in the digital amplifier section visibly modulating the waveform.

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

Above is the 1kHz squarewave response using the analog input, at roughly 10W into 8 ohms, with a 250kHz restricted bandwidth to remove the modulation from the 400kHz oscillator. We see more evidence here, in the over and undershoot at the squarewave corners, of the C 700 V2’s limited bandwidth with an analog input.

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

The C 700 V2’s class-D amplifier relies on a switching oscillator to convert the input signal to a pulse-width-modulated (PWM) squarewave (on/off) signal before sending the signal through a low-pass filter to generate an output signal. The C 700 V2 oscillator switches at a rate of about 400kHz, and this graph plots a wide bandwidth FFT spectrum of the amplifier’s output at 10W into 8 ohms as it’s fed a 1kHz sinewave. We can see that the 400kHz peak is quite evident, and at -40dBrA. There is also a peak at 800kHz and 1200kHz (the second and third harmonics of the 400kHz peak) at -65/-90dBrA. Those three peaks—the fundamental and its second/third harmonics—are direct results of the switching oscillators in the C 700 V2 amp modules. Also seen are the 43.1/44.1/45.1kHz peaks due to the ADC sampling the incoming signal at 44.1kHz. The noise around those very-high-frequency signals are in the signal, but all that noise is far above the audioband—and therefore inaudible—and so high in frequency that any loudspeaker the amplifier is driving should filter it all out anyway.

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

The final plot above is the damping factor as a function of frequency. Both channels show a relatively constant damping factor from 20Hz to 20kHz. The damping factor for the left and right channels are just above and below 100 from 20Hz to 20kHz.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Amplifier Measurements

Created: 01 April 2025

Link: reviewed by Matt Bonaccio on SoundStage! Hi-Fi on April 1, 2025

General Information

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

The Hegel Music Systems H190v was conditioned for 1 hour at 1/8th full rated power (~18W 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 H190v offers three set of line-level analog inputs (two single-ended RCA, one balanced XLR), one MM phono input (single-ended RCA), one digital coaxial (RCA) S/PDIF input, three digital optical (TosLink) S/PDIF inputs, one USB input, left/right line-level pre-outs (single-ended RCA) and fixed-outs (single-ended RCA), one set of speaker level outputs, and on the front panel, one headphone output over 1/4″ TRS connector. An ethernet network input is also offered. For the purposes of these measurements, the following inputs were evaluated: digital coaxial, analog (XLR) line-level and phono, as well as the headphone output. There were no appreciable differences between the XLR and RCA line-level inputs, nonetheless, 1kHz FFTs for each are included in this report.

Most measurements were made with a 2Vrms line-level analog input, 5mVrms phono-level 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 achievable output power of 150W into 8 ohms. For comparison, on the line-level input, a signal-to-noise ratio (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 H190v volume control is digitally controlled but operating in the analog domain. The H190v overall volume range is from -70dB to +38dB (line-level input, speaker output). It offers 2-3dB increments from position 0 to 9, and 1dB increments from positions 9 to 100. Also noteworthy is that several step positions do not actually change the volume (e.g., steps 84 and 85 yield the same volume level).

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 Hegel for the H190v compared directly against our own. The published specifications are sourced from Hegel’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 H190v was able to sustain 250W into 4 ohms (~2% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (16.1W) for 5 seconds, for 5 continuous minutes without 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 H190v was very 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 H190v is near flat within the audioband (20Hz to 20kHz, -0.2/-0.1dB). The -3dB point is at roughly 120-130kHz, and -2dB at 5Hz. The H190v appears to be AC-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 H190v does not invert polarity and yields only about +15 degrees of phase shift at 20Hz and -20 degrees 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 relatively flat (+/-0.5dB) response from 35Hz to 20kHz and a worst-case channel-to-channel deviations of roughly 0.1dB at 100 to 300Hz. Below 35Hz, there is steep attenuation (-3dB at ~17Hz), as Hegel 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 H190v does not invert polarity. For the phono input, since the RIAA equalization curve must be implemented, which ranges from +19.9dB (20Hz) to -32.6dB (90kHz), phase shift at the output is inevitable. Here we find a worst case of about +40 degrees at 20Hz and -100 degrees at 20kHz.

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

The chart above shows the H190v’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, 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 the same response down to 5Hz (-2dB) as the analog response. The -3dB points are: 21kHz for the 16/44.1 data, 46kHz for the 24/96, 50.5kHz for the 24/192 data, and 130kHz for the analog input. Also of note, all three digital input data showed brick-wall-type high-frequency filtering and a rise in output (up to +0.5dB) past 20kHz.

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

The chart above shows the results of a linearity test for the coaxial digital input for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the fixed line-level outputs of the H190v, where 0dBFS yielded approximately 2Vrms. For this measurement, 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 +2/3dB at -120dBFS, while the 16/44.1 data were +4/5dB at -120dBFS.

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 fixed outputs of H190v. We see a typical symmetrical sinc-function response.

J-Test (coaxial)

The chart above shows the results of the J-Test test for the coaxial digital input measured at the fixed line-level outputs of the H190v where 0dBFS is just over 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 a relatively strong J-test result, with several peaks in the audioband but at low levels, just above and below -130dBFS. This is an indication that the H190v DAC may have good jitter immunity.

J-Test (optical)

The chart above shows the results of the J-Test test for the optical digital input measured at the line-level pre-outputs of the H190v. The optical input yielded essentially the same result 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 H190v, with an additional 10ns of 2kHz sinewave jitter injected by the APx555. The telltale peaks at 10kHz and 14kHz cannot be seen in the FFT. The performance of the optical input with 10ns of jitter was similar.

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 H190v, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The telltale peaks at 10kHz and 14kHz can be seen, but are at the relatively low -100dBFS level.

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 H190v, 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 H190v’s line-level 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. The steep roll-off around 20kHz in the white-noise spectrum shows that the filter is of the brickwall-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 and buried in the noise floor, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are around -100dBrA.

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

The chart above shows RMS level (relative to 0dBrA, which is 1W into 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 0.04dB. This is a strong result and an indication of a low output impedance, or very high damping factor. With a real speaker load, deviations measured at roughly the same level from 60Hz to 8kHz.

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 103W. The power was varied using the H190v volume control. The 1W and 10W THD ratios were close, hovering around the 0.01% level from 20Hz to 4kHz, then up to 0.03% at 20kHz. The 103W THD ratios were higher and relatively flat across the audioband at 0.03% to 4Khz, then up to 0.05% 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. For this measurement, the input sweep was EQ’d with an inverted RIAA curve. The THD values for the MM configuration vary from around 1% (20Hz) down to 0.02% at 4Khz to 20kHz. The limiting factor in the measured THD values is the noise floor (the analyzer cannot assign a THD value to a harmonic peak it cannot see below the noise floor), and since the RIAA curve applies more gain at low frequencies than high frequencies, we find the THD plots above roughly following the shape of the noise floor (higher to lower from low to high frequencies).

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 H190v 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 5dB). The 8-ohm THD ratios are relatively constant to the “knee,” ranging from 0.005% to 0.01%. The “knee” into 8 ohms can be found just past 100W, while the 4-ohm knee can be seen around 200W. The 1% THD marks were hit at 149W and 240W 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 H190v 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 close (within 5dB). The 8-ohm data range from 0.02% at 50mW, down to 0.005% in the 50 to 50W 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 H190v 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. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. Here again we see the 8 and 4-ohm THD data are close together (within 5dB). Below 1kHz, the 4-ohm data yielded lower THD ratios whereas above 1kHz, the 8-ohm data were lower. These ranged from 0.006% at 20Hz, down to 0.003% from 60Hz to 200Hz, then up to 0.02-0.03% at 20kHz. The 2-ohm load ranged from 0.01% at 20Hz, down to 0.004% at 50-100Hz, then up to 0.06% 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 H190v 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 all three loads were close (mostly within 5dB), which is a strong result. As is typical with this test, the worst results were at 20Hz into the two-way speaker (0.04%), and at 20kHz into the 3-way speaker (0.04%). Generally, most of the measured THD ratios hovered around the 0.005% to 0.01% range below 4kHz.

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 H190v 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 real speakers yielding 4-5dB lower results in the 2.5-5kHz range, and 2dB higher results from 10kHz to 20kHz. Most of the IMD results are hovering around the 0.01%-0.02% 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 H190v 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, 0.03% from 40Hz to 250Hz, and 0.006% from 300Hz to 1kHz. Another strong result.

FFT spectrum – 1kHz (XLR analog 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) harmonic dominate at -80dBrA, or 0.01%. There are subsequent signal harmonics visible at and below -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 -105/-110dBrA (left/right), or 0.0006/0.0003%. Other noise peaks can be seen below the -110dBrA level.

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

FFT spectrum – 1kHz (MM phono input)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the phono (MM) input. We see that the signal’s second (2kHz) and fourth (4kHz) harmonics dominate at -65dBrA, or 0.06%, and -85dBrA, or 0.006%, respectively. There are subsequent signal harmonics visible at and below the -90dBrA, or 0.003%, level. On the right side of the signal peak, we find significant power-supply-related noise peaks, with the second harmonic (120Hz) dominating at -45dBrA, or 0.6%, and the fourth (240Hz) harmonic reaching -50dBrA, or 0.3%. Other noise peaks can be seen throughout the audioband, down to the -120dBrA 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. The results are very similar to the analog line-level FFTs 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.

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 -130dBrA noise floor, and power-supply noise-related peaks at the sub -100dBrA level.

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 effectively the same FFT as with the 16/44.1 sampled data 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 (150Hz) signal harmonics at just below -80dBrA, or 0.01%. Other peaks (both signal harmonics and power-supply noise related harmonics) can be seen at -100dBrA 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 second (120Hz) and fourth (240Hz) power-supply noise peaks at roughly -45/-50dBrA, or 0.6/0.3%, and the second (100Hz) signal harmonic at -50dBrA, or 0.3%.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the analog line-level input. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -90dBRa, or 0.003%, while the third-order modulation products, at 17kHz and 20kHz are at the -85dBrA, or 0.006%, level.

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

Shown above is the FFT of the speaker-level output of the H190v 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 -105dBrA, or 0.0006%, 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 -90dBRa, or 0.003%, while the third-order modulation products, at 17kHz and 20kHz, are at the -85dBrA, or 0.006%, level.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 24/96 (-1dBFS). We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -90dBRa, or 0.003%, while the third-order modulation products, at 17kHz and 20kHz, are at the -85dBrA, or 0.006%, level.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the MM phono input. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -70dBRa, or 0.03%, while the third-order modulation products, at 17kHz and 20kHz, are at the -90dBrA, or 0.003%, 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 H190v’s slew-rate performance. Rather, it should be seen as a qualitative representation of the H190v’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 only mild softening in the corners.

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

The final graph above is the damping factor as a function of frequency. We can see here very high damping factor ranging from roughly 500 to 250 (left) and 400 to 185 (right). 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: 01 March 2025

Link: reviewed by Jason Thorpe on SoundStage! Ultra on March 1, 2025

General information

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

The Balanced Audio Technology (BAT) REX 300 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 REX 300 is a two-channel amplifier with two balanced (XLR) inputs and two sets of speaker level outputs. An input of 500mVrms was required to achieve the reference 10W into 8 ohms.

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 1MHz input bandwidth.

Of note is that BAT claims no global negative feedback for the REX 300. Our measurements corroborate this claim, as two clear consequences of this design can be seen: a low damping factor (high output impedance) and high THD.

Published specifications vs. our primary measurements

The table below summarizes the measurements published by BAT for the REX 300 compared directly against our own. The published specifications are sourced from BAT’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 500mVrms at the input, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

For the continuous dynamic power test, the REX 300 was able to sustain about 250W into 4 ohms (~1.5% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (25W) 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 and top of the REX 300 were hot to the touch. Of note, just above the 250W mark, the REX 300’s protection circuit was engaging almost immediately.

Frequency response (8-ohm loading)

In our frequency response (relative to 1kHz) plots above, measured across the speaker outputs at 10W into 8 ohms, the REX 300 exhibits a near-flat frequency response across the audioband (0/-0.1dB at 20Hz/20kHz). The REX 300 appears to be DC-coupled, as it is perfectly flat down to 5Hz. The -3dB point is at 150kHz.  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 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 balanced line-level input, measured across the speaker outputs at 10W into 8 ohms. The REX 300 does not invert polarity and exhibits, at worst, only -10 degrees of phase shift at 20kHz, due to its extended bandwidth.

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 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 nearly 1dB. This is an indication of a very low damping factor, or high output impedance. With a real speaker, the maximum deviation from 20Hz to 20kHz was roughly 0.6dB, which may be audible.

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 at 1W output into 8 ohms, purple and green at 10W, and pink and orange at 150W. At 1W and 10W, the left channel outperformed the right by as much as 10dB from 300Hz to 20kHz. The 1W left channel data ranged from 0.05% at 20Hz, down to 0.02% from 100Hz to 20kHz. The 10W left channel data ranged from 0.06% from 20Hz to 4kHz, then up to 0.15% at 20kHz. The 150W THD data are higher, ranging from 0.2% from 20Hz to 100Hz, then up to a very high 7% 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 REX 300 as a function of output power for the analog line level-input, for an 8-ohm load (blue/red) and a 4-ohm load (purple/green). The left channel outperformed the right up to the “knee” for both loads by as much as 10dB. The 8-ohm data for the left channel ranged from 0.003% at 50mW, with a steady climb to 0.2% at the “knee,” at roughly 100W. The 1% THD mark was hit at 165W, and at the rated output of 200W, THD ratios measured around 3%. The 4-ohm data for the left channel ranged from 0.005% at 50mW, with a steady climb to 0.4% at the “knee,” at roughly 200W. The 1% THD mark was hit at 284W, and at the rated output of 400W, THD ratios would have (the plot stops just shy of 400W) measured around 4%.

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 REX 300 as a function of output power for the analog line level-input, for an 8-ohm load (blue/red) and a 4-ohm load (purple/green). The left channel outperformed the right up to the “knee” for both loads by as much as 5dB. The 8-ohm data for the left channel ranged from 0.05% from 50mW to 2W, then a steady climb to 0.2% at the “knee,” at roughly 100W. The 4-ohm data for the left channel ranged from 0.1% from 50mW to 5W, then a steady climb to 0.4% at the “knee,” at roughly 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 REX 300 as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yielded roughly 50W at the output into 8 ohms (blue), 100W into 4 ohms (purple), and 200W into 2 ohms (pink). The 2-ohm data is not present because the protection circuit was initiated almost immediately after the start of the sweep. The 8-ohm data ranged from 0.1% at 20-2kHz, then up to 0.4% at 20kHz. The 4-ohm THD data ranged from 0.2% at 20-2kHz, then up to 2% 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 REX 300 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 frequencies, the two-way speaker yielded the highest THD ratios (0.6%). Between 40Hz and 10kHz, the THD ratios into all three loads were within roughly 5dB of one another, ranging from roughly 0.01% to 0.1%. At the highest frequencies, the three-way speaker yielded the highest THD ratios (0.08% at 20kHz), nearly 15dB higher than the two-way speaker and the resistive load.

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

The chart above shows intermodulation distortion (IMD) ratios measured at the output of the REX 300 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here the CCIF IMD method was used, where the primary frequency is swept from 20kHz (F1) down to 2.5kHz and the secondary frequency (F2) is always 1kHz lower than the primary, with a 1:1 ratio. The CCIF IMD analysis results are the sum of the second (F1-F2 or 1kHz) and third modulation products (F1+1kHz, F2-1kHz). The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). The IMD results into the resistive load range from 0.03% at low frequencies, down to 0.002% at high frequencies. The two-way speaker IMD results were flatter, ranging from 0.01% to 0.006%, while the three-way speaker ranged from 0.02% 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 REX 300 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here, the SMPTE IMD method was used, where the primary frequency (F1) is swept from 250Hz down to 40Hz and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). All three plots are essentially identical and constant right around 0.1%.

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 a very high -60dBrA and -80dBrA, or 0.1% and 0.01%. Power-supply noise-related harmonics, and what are likely IMD products between those noise peaks and the signal and its harmonics, are significant and can be seen throughout the FFT at levels of -70dBrA, or 0.03%, and below. This is an extremely poor FFT result. It should be noted, however, that the noise floor and noise peaks are far more significant with the REX 300 when a signal is present. This can be seen in our main measurement table where signal-to-noise ratios are respectable because the noise is measured separately from the signal. It can also be seen by comparing the noise levels in the table with and without a signal. Noise levels with the signal present are very high for a modern solid-state amplifier using a line-level input, and even higher that an average noise level from a solid-state amplifier’s phono input. Noise levels with a signal are 20 to 30 times higher than the noise measured without a signal present.

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) peak is the signal’s second (100Hz) harmonic at -70dBrA, or 0.03%. Again, power-supply noise-related harmonics and IMD peaks can be seen throughout the FFT at 10Hz intervals at -80dBrA, or 0.01%, and below.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the balanced analog line-level input. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -70dBrA, or 0.03%, level, while the third-order modulation products, at 17kHz and 20kHz, cannot be distinguished from the densely packed noise peaks rising up to -70dBrA, or 0.03%. This is an extremely poor IMD result.

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

Shown above is the FFT of the speaker-level output of the REX 300 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 around the -80dBrA, or 0.01%, level and below.

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 REX 300’s slew-rate performance. Rather, it should be seen as a qualitative representation of the REX 300’s 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. In this case, we see a very clean result, with no ringing in the corners and only very mild softening.

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

The final graph above is the damping factor as a function of frequency. We find very low damping factor values, hovering around 18 to 19 from 20Hz to 15kHz, and 17 at 20kHz. This is a poor damping factor result for a solid-state amplifier.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Amplifier Measurements

Created: 15 February 2025

Link: reviewed by Thom Moon on SoundStage! Access on February 1, 2025

General Information

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

The Advance Pari X-i75 was conditioned for 1 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 X-i75 offers seven sets of line-level analog inputs (RCA), one moving-magnet (MM) phono input (RCA), two digital S/PDIF coaxial (RCA) inputs, one digital S/PDIF optical (TosLink) input, one USB digital input, left/right pre-outs (RCA), and rec-outs (RCA), one sub-out (RCA), one set 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 (RCA) 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 ratio (SNR) measurements were made with the default input signal values but with the volume set to achieve the rated output power of 75W into 8 ohms. For comparison, on the line-level input, a SNR measurement was also made with the volume at maximum.

The X-i75 also offers a Hi Bias (for high bias) switch on the rear panel. No appreciable differences (THD, noise, gain) were seen with this switch in the on or off position; however, comparative FFTs can be found in this report. Unless otherwise stated, the high-bias switch was left in the off position because slightly lower levels of odd-ordered signal harmonics were observed in this configuration.

Based on the accuracy and randomness of the left/right volume channel matching (see table below), the X-i75 volume control is digitally controlled but operating in the analog domain. The X-i75 overall volume range is from -51dB to +38dB (line-level input, speaker output). It offers 2dB increments from positions 1 to 30, and 1dB increments from positions 31 to 60.

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 Advance Paris for the X-i75 compared directly against our own. The published specifications are sourced from Advance Paris’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 X-i75 was able to sustain 120W into 4 ohms (~3% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (12W) 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 X-i75 was 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 X-i75 is close to flat within the audioband (20Hz to 20kHz, -0.3/-0.1dB). The -3dB point is at roughly 150kHz, and -2.5dB at 5Hz. The X-i75 appears to be AC 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.

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

Above are the frequency-response plots (relative to 1kHz) measured across the speaker outputs at 10W into 8 ohms, with the bass and treble controls set to minimum and maximum. We find roughly +/-8.5dB of bass boost/cut centerd at 100Hz, and +/-8.5dB of treble boost/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 X-i75 yielded only about +20 degrees of phase shift at 20Hz, and at worst -10 degrees at 20kHz.

Frequency response (8-ohm loading, subwoofer output)

Above is the frequency-response plot (relative to 20Hz) measured at the line-level subwoofer output. We find an essentially perfectly flat response down to 5Hz (-0.2dB), a -3dB point at 200Hz, and a 9dB/octave high-frequency roll-off.

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 deviations as large as +0.5dB (30Hz and 20kHz) and -0.4dB (200Hz) within the audioband. We also see what appears to be the implementation of a rumble filter (-3dB at 8Hz).

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 X-i75 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 +20 degrees at 20Hz and -80 degrees at 20kHz.

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

The chart above shows the X-i75’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, the digital signals yielded similar results as the analog response (between -2.5 and -3.5dB at 5Hz). The -3dB points are: 21kHz for the 16/44.1 data, 46.5kHz for the 24/96, 93kHz for the 24/192 data, and 150kHz for the analog input. Also of note, all digital frequency responses exhibit brickwall-type behavior around their respective high-frequency cut-offs.

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 X-i75, where 0dBFS was set to yield 2Vrms. For this test, the digital input is swept with a dithered 1kHz input signal from -120dBFS to 0dBFS and the output is analyzed by the APx555. The ideal response would be a straight flat line at 0dB. Both data were essentially perfect as of -110dBFS down to 0dBFS, with the exception of the right channel at 24/96, which was -9dB down at -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 X-i75. We find a typical, symmetrical sinc function response.

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 X-i75 where 0dBFS is set to 2Vrms. 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 an elevated noise floor (-120dBFS) around the main 12kHz signal peak, and peaks at -120dBFS flanking the main signal peak. This is an indication that the X-i75 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 X-i75. The optical input yielded similar 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 X-i75, with an additional 10ns of 2kHz sinewave jitter injected by the APx555. The telltale peaks at 10kHz and 12kHz can easily be seen at -70dBFS. More evidence of the poor jitter immunity. The optical input showed a similar result.

J-Test (coaxial, 100ns jitter)

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-evel output of the X-i75, 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 -50dBFS. The optical input show a similarly poor result.

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 X-i75’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. The steep roll-off around 20kHz in the white-noise spectrum shows the implementation of a brickwall-type filter. There are no visible low-level aliased image peaks within the audioband; however, there is a rise in the noise floor around the signal peak up to -110dBFS. The primary aliasing signal at 25kHz is highly suppressed at -85dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are near the same level.

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

The chart above shows RMS level (relative to 0dBrA, which is 1W into 8ohms or 2.83Vrms) as a function of frequency, for the analog 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 at roughly 0.25dB. This is a poor result for a solid-state amp and an indication of a relatively high output impedance, or low damping factor. With a real speaker load, deviations measured lower at roughly 0.2dB.

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 65W. The power was varied using the X-i75’s volume control. The 1 and 10W THD ratios were similar, ranging from as low as 0.001% (right channel) from 60 to 400Hz, and up to 0.03% (left channel) at 20kHz (the right channel was at 0.015%). At 65W, THD ratios were higher (0.009%) and relatively flat across most of the audioband (20Hz to 2kHz), then up to 0.03% (left channel) at 20kHz (the right channel was at 0.015%).

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 0.2% (20Hz) down to 0.002% (300-500Hz), up to 0.03% (left channel) at 20kHz (the right channel was at 0.015%).

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 X-i75 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 vary by about 5dB, the same as between channels (the right channel and 8-ohm data yielded lower THD ratios). They range (for the right channel into 8 ohms) from 0.005% at 50mW, down to 0.0015% in the 1 to 5W range, with the “knee” at 0.007% just past 60W, while the 4-ohm knee can be seen at 0.02% just shy of 100W. The 1% THD marks were hit right at the rated levels of 75W and 110W 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 X-i75 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 2-5dB). They range from 0.03% at 50mW, down to 0.003% (right channel, 8 ohms) in the 10W 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 X-i75 as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yields 10W at the output into 8 ohms (and roughly 20W into 4 ohms, and 40W into 2 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. We find a roughly 10dB increase in THD from 8 to 4 to 2 ohms. These ranged from 0.002% at 20Hz to 400Hz, then up to 0.03% at 20kHz for the 8-ohm load. The 4-ohm load ranged from 0.005% at 20Hz to 400Hz, then up to 0.06% at 20kHz. The 2-ohm load ranged from 0.015% at 20Hz to 400Hz, then up to 0.1% 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 X-i75 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 0.2% at 20Hz for the two-way speaker versus 0.005% for the resistive load, and 0.05% at 20kHz into the three-way speaker versus 0.03% for the resistive load. Between the important frequencies of 500Hz to 6kHz, all three THD traces were close, with lower THD ratios into the real speakers (0.001-0.003%) compared to the dummy load (0.002-0.01%).

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 X-i75 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 across the sweep. Most of the IMD results are hovering around the 0.003-0.005% 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 X-i75 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 (the three-way speaker was up to 5dB higher than the two-way speaker and resistive load), between 0.007% and 0.015% across the sweep.

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 roughly -90dBrA, or 0.003%, while the third (3kHz) and fourth (4kHz) harmonics can be seen at -100dBrA, or 0.001%. Higher-order harmonics are also visible at lower levels. On the right side of the signal peak, we find power-supply-related noise peaks, with the first (60Hz) and third (180Hz) harmonics dominating at -100dBrA, or 0.001%, for the left channel, and -110dBrA, or 0.0003%, for the right channel. Overall, the noise from the left channel is roughly 10dB higher than the right channel. High-order power-supply-related noise peaks can be seen from the left channel up to nearly 10kHz.

FFT spectrum – 1kHz (line-level input, Hi Bias turned on)

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, with Hi Bias turned on. The results are very similar to the FFT above without Hi Bias on. The differences are in the high odd-ordered signal harmonics (5kHz, 7kHz), which are about 10dB higher with Hi Bias on.

FFT spectrum – 1kHz (MM phono input)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the phono MM input. We see that the signal harmonics, while difficult to distinguish amongst the power-supply related noise peaks, are similar in amplitude as seen in the analog line-level FFT above. Power-supply-related noise peaks dominate throughout the audioband, ranging from -55dBrA, or 0.2%, at 60Hz, down to the -120dBrA, or 0.0001%, 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. Results are very similar to the analog FFT above within the audioband.

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 slightly 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 powers-supply-related noise peaks (mostly from the left channel) at -110dBrA, or 0.0003%, 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 the correct amplitude, with no signal harmonics above the -140dBrA noise floor, and power-supply-related noise peaks (mostly from the left channel) at -110dBrA, or 0.0003%, and below.

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 -95dBrA, or 0.002%. Other peaks (both signal harmonics and power-supply noise-related harmonics) can be seen at -100dBrA 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 and 120Hz power-supply noise peaks at -55dBrA and -65dBrA, or 0.2% and 0.02%, respectively. Signal harmonics are much lower, at the -90dBrA, or 0.003%, level and below.

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

Shown above is an FFT of the intermodulation (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the 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 -100dBrA, or 0.001%, while the third-order modulation products, at 17kHz and 20kHz, are also at -100dBrA.

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

Shown above is the FFT of the speaker-level output of the X-i75 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 -110dBrA, or 0.0003%, level.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the MM phono input. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at around -105dBrA, or 0.0006%, while the third-order modulation products, at 17kHz and 20kHz, are lower at -110dBrA, or 0.0003%.

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 products (i.e., the difference signal of 1kHz) are at -90dBrA, or 0.003%, while the third-order modulation products, at 17kHz and 20kHz, are at the same level.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 24/96 (-1dBFS). We find that the second-order modulation products (i.e., the difference signal of 1kHz) are at -90dBrA, or 0.003%, 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 X-i75’s slew-rate performance. Rather, it should be seen as a qualitative representation of the X-i75’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 very clean corners, with no softening or overshoot.

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 of around 60 through most of the audioband. This is a mid-tier result for a medium-powered integrated solid-state amplifier.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Amplifier Measurements

Created: 01 February 2025

Link: reviewed by Roger Kanno on SoundStage! Simplifi on February 1, 2025

General Information

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

The Caspian 4G Streaming Amplifier was conditioned for 1 hour at 1/8th full rated power (~13W 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 Caspian offers three set of line-level analog inputs (two RCA, one XLR), one moving-magnet (MM) phono input, two digital coaxial (RCA) S/PDIF inputs, two digital optical (TosLink) S/PDIF inputs, one HDMI eARC connection, left/right analog pre-outs (RCA and XLR), and one set of speaker level outputs a. A Bluetooth input is also offered. For the purposes of these measurements, the following inputs were evaluated: digital coaxial, analog (XLR) line-level and phono.

Most measurements were made with a 4Vrms line-level analog input and 0dBFS digital input. The RCA line-level input offers 6dB more gain than the XLR input (i.e., 2Vrms in over RCA yields the same speaker-level output as 4Vrms in over XLR). The signal-to-noise ratio (SNR) measurements were made with the default input signal values but with the volume set to achieve the achievable output power of 105W 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 repeatability of the left/right volume channel matching (see table below), the Caspian volume control is digital through the lower range (steps 1 through 40). Above 40 up to the maximum step (100), the volume appears to be digitally controlled but operating in the analog domain. To achieve this, the Caspian must digitize incoming analog signals, including the phono input. The Caspian overall volume range is from -70dB to +29dB (line-level XLR input, speaker output). It offers 1dB increments throughout the range.

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 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 Roksan for the Caspian 4G compared directly against our own. The published specifications are sourced from Roksan’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.

* Roksan specifics power output with 235VAC mains level, whereas our measurements reflect the North American standard of 120VAC

Our primary measurements revealed the following using the line-level XLR analog input and digital coaxial input (unless specified, assume a 1kHz sinewave at 4Vrms or 0dBFS, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

For the continuous dynamic power test, the Caspian 4G was able to sustain 210W into 4 ohms (~6% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (21W) for 5 seconds, for 5 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 Caspian was 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):

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 Caspian 4G is near flat within the audioband (20Hz to 20kHz, +0.07,-0.77dB). The -3dB point is at roughly 40kHz, and it is +1.7dB at 5Hz. The Caspian appears to digitize the incoming analog signal as we see high-frequency brickwall-type filtering just below 50kHz. 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 Caspian yields significant phase shift, more than -9000 degrees at 20kHz. The phase shift is so significant because the plot shows total phase shift, including any timing delays from input to output due to digitization. As a point of comparison, the plot below . . .

. . .shows only the excess phase shift (beyond the frequency independent timing delays), where we find +20 degrees at 20Hz and 0 degrees 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 50Hz to 10kHz. Below 30Hz, there is steep attenuation (-1dB at 20Hz then a brickwall below 15Hz), as Roksan appears to have implemented an anti-rumble filter on their phono input, likely in the digital domain. The adherence to the RIAA curve is so strict between 50Hz and 10kHz that we may conclude that RIAA EQ is likely implemented in the digital domain as well.

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 Caspian does not invert polarity. Again, because the input is digitized, which introduces significant timing delays, phase shift is -9500 degrees at 20kHz. Below is . . .

. . . the same phase-shift plot but only showing excess phase shift (beyond the frequency independent timing delays). With it displayed this way, we see a fairly typical phono RIAA phase shift response.

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

The chart above shows the Caspian 4G’s frequency response (relative to 1kHz) as a function of input type measured across the speaker outputs at 10W into 8 ohms. The two dark 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, 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 near-flat response down to 5Hz (-0.1dB), which differs from the +1.7dB at 5Hz response seen with the analog response. The -3dB points are roughly: 21kHz for the 16/44.1 data, 46kHz for the 24/96, 90kHz for the 24/192 data, and 40kHz 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 24/192 does not. The analog input frequency response, which is digitized, oddly, does not look like the 24/96 response.

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 XLR pre-outputs of the Caspian, 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. Both data were essentially perfect as of -90dBFS down to 0dBFS. The 24/96 data were above +10dB at -120dBFS, while the 16/44.1 data were +3dB at -120. This is a poor result.

Impulse response (24/44.1 data)

The graph above shows the impulse response for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s) for one sample period then back to digital silence, measured at the line-level XLR pre-outs of Caspian 4G. We see a typical, symmetrical sinc-function response.

J-Test (coaxial)

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level XLR pre-outputs of the Caspian where 0dBFS is set to 2Vrms. The J-Test was developed by Julian Dunn the 1990s. It is a test signal—specifically, a -3dBFS undithered 12kHz squarewave sampled (in this case) at 48kHz (24 bits). Since even the first odd harmonic (i.e., 36kHz) of the 12kHz squarewave is removed by the bandwidth limitation of the sampling rate, we are left with a 12kHz sinewave (the main peak). In addition, an undithered 250Hz squarewave at -144dBFS is mixed with the signal. This test file causes the 22 least-significant bits to constantly toggle, which produces strong jitter spectral components at the 250Hz rate and its odd harmonics. The test file shows how susceptible the DAC and delivery interface are to jitter, which would manifest as peaks above the noise floor at 500Hz intervals (e.g,. 250Hz, 750Hz, 1250Hz, etc.). Note that the alternating peaks are in the test file itself, but at levels of -144dBrA and below.  The test file can also be used in conjunction with artificially injected sinewave jitter by the Audio Precision, to show how well the DAC rejects jitter.

Here we see a strong J-Test result, with some lower frequency peaks likely due to power-supply noise, and two very small peaks below -130dBFS flanking the 12kHz fundamental. This is an indication that the Caspian DAC should have strong 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 Caspian 4G. The optical input yielded effectively the same result as the coax input.

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 Caspian, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The result is identical to the original J-Test result without the added jitter, with no signs of the tell-tale peaks at 10kHz and 14 kHz due to the added jitter. This is further evidence of the strong jitter immunity in the Caspian 4G DAC. The optical input yielded the same result.

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 Caspian 4G’s line-level XLR 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. The steep roll-off around 20kHz in the white-noise spectrum shows the implementation of a brickwall-type reconstruction filter. There are no low-level aliased image peaks within the audioband above the -135dBrA noise floor. The primary aliasing signal at 25kHz is highly suppressed at -130dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are at -110dBrA and below.

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

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

. . . is the same but zoomed in to highlight differences. Here we see that the deviations between no load and 4 ohms are very small at roughly 0.08dB. 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 0.04dB.

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 roughly 95W. The power was varied using the Caspian 4G’s volume control. Between 20Hz and 3kHz, all three THD results are closely clustered together, ranging from roughly 0.0006% to 0.005%. Above 3kHz we find clear deviations between the three power levels. At 20kHz, the 1W data was at 0.01%, the 10W data at 0.02%%, and the 95W data at 1.5%.

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. THD ratios below 400Hz vary wildly (40dB swings); however, this is likely due to sporadic and significant rises in the noise floor that were observed during the measurements. From 400Hz to 20kHz, THD ratios ranged from roughly 0.002% up to 0.02%.

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 Caspian 4G 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 close (within 3-5dB, the 8-ohm data outperformed the 4-ohm data). They range from 0.01% at 50mW, down to 0.001% in the 10 to 90W range for the 8-ohm data. The “knee” into 8 ohms can be found at roughly 95W, while the 4-ohm knee can be seen around 170W. The 1% THD marks were hit at 107W and 182W 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 Caspian 4G 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 (within 2-3dB). They range from 0.1% at 50mW, down to 0.003% at the “knee” for the 8-ohm data, and 0.2% down to 0.005% at the “knee” for the 4-ohm data.

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 Caspian 4G 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. The 8-ohm load is the blue trace and the 4-ohm load the purple trace and the 2-ohm load the pink trace. We find a roughly 5dB increase in THD from 8 to 4 ohms, and a 5-10dB increase from 4 to 2 ohms. The 2-ohm load ranged from 0.01% at 20Hz down to 0.003% at 50-200Hz, then up to 0.07% 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 Caspian 4G 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 0.004% for the resistive load, and 0.02% at 20kHz into the 3-way speaker versus 0.01% for the resistive load. Between the important frequencies of 300Hz to 6kHz, all three THD traces were close (within 5dB), around the 0.001-0.002% 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 Caspian 4G 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). Generally, IMD ratios into the real speakers were higher than those measured across the resistive dummy load. IMD results into the dummy load ranged from 0.001% to 0.005%, while the highest IMD ratios came from the three-way speaker, from 0.003% to 0.008%.

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 Caspian 4G 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, a constant 0.007%.

FFT spectrum – 1kHz (XLR analog 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 XLR line-level input. We see that the signal’s second (2kHz) and third (3kHz) harmonics dominate at -100dBrA, or 0.001%, and just above -110dBrA, or 0.0003%. On the right and left side of the signal peak, we find power-supply-related noise peaks, ranging in amplitude from -100dBrA, or 0.001%, down to -120dBrA, or 0.0001%. We also see strong peaks around 96kHz, likely due to the ADC’s sampling frequency of the analog signals.

FFT spectrum – 1kHz (RCA analog 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 RCA line-level input. We see essentially the same result as the FFT above for the XLR input.

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 analog phono MM input. We see that the signal’s second (2kHz) and third (3kHz) harmonics, while difficult to discern amongst the power supply related noise peaks, are around the -100dBrA, or 0.001%, level. On the right and left side of the signal peak, we find power-supply related noise peaks, ranging in amplitude from -65dBrA, or 0.06%, down to -120dBrA, or 0.0001%. 

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 a very similar result as the FFT above for the XLR analog input, except for the 96kHz peaks due to the ADC sampling not occurring here.

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.

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 below the correct amplitude, with no obvious signal harmonics amongst the numerous power-supply noise-related harmonics.

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 below the correct amplitude, with no obvious signal harmonics amongst the numerous power-supply noise related harmonics.

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 many power-supply noise-related harmonics at -100dBrA, or 0.001%, and below. The second (100Hz) and third (150Hz) signal-related harmonics are just above and below -110dBrA, or 0.0003%.

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 third (180Hz) harmonic at -65dBrA, or 0.06%. The highest signal harmonic is at 100Hz, at -90dBrA (left channel), 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 XLR 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 -80dBrA, or 0.01%, while the third-order modulation products, at 17kHz and 20kHz are at -100dBrA, or 0.001%, level. This is a mediocre IMD result.

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

Shown above is the FFT of the speaker-level output of the Caspian 4G 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 other peaks are related to power-supply noise harmonics.

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 -90dBrA, or 0.003%, while the third-order modulation products, at 17kHz and 20kHz, are at -105dBrA, or 0.0006%.

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 -90dBrA, or 0.003%, while the third-order modulation products, at 17kHz and 20kHz, are at -105dBrA, or 0.0006%.

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. Here we experienced the same issue as seen in our THD vs Frequency sweep for the phono input—sporadic rises in the noise floor. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at around -80dBrA, or 0.01%, while the third-order modulation products, at 17kHz and 20kHz, cannot be seen above the rise in the noise floor up to -90dBrA.

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 Capsian 4G’s slew-rate performance. Rather, it should be seen as a qualitative representation of the Caspian 4G’s limited 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 digitization of the analog input and brickwall behaviour above 50kHz, we find a very poor 10kHz square wave reproduction.

Squarewave response (1kHz)

Above is the 1kHz squarewave response using the analog line-level input, at roughly 10W into 8 ohms. At this lower frequency, the squarewave reproduction is much cleaner than at 10kHz; however, significant ringing can be seen in the corners.

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 of roughly from 20Hz to 3kHz, then down to 80 at 20kHz. 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 January 2025

Link: reviewed by Thom Moon on SoundStage! Access on January 15, 2025

General information

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

The Dayton Audio A400 was conditioned for 1 hour at 1/8th full rated power (~20W 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.

Although marketed as a power amplifier, the A400 was evaluated on the test bench as an integrated amplifier because it offers a prominent, non-defeatable volume control. It offers two line-level analog inputs (balanced XLR and single-ended RCA, switchable on the rear panel), left/right fixed line-level outputs (single-ended RCA and balanced XLR, both with no gain), and one set of speaker-level outputs (configurable for bridged operation).

For the purposes of these measurements, the following input was evaluated: balanced analog line-level. There were no appreciable differences in terms of THD, noise, and gain between the unbalanced and balanced analog inputs (FFTs provided in this report for comparison).

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 150W into 8 ohms. For comparison, on the line-level input, an 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 A400 volume control is a potentiometer operating in the analog domain. The A400 overall volume range is from -62dB to +38dB (balanced line-level input, speaker output).

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 Dayton Audio for the A400 compared directly against our own. The published specifications are sourced from Dayton Audio’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, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

For the continuous dynamic power test, the A400 was able to sustain 310W into 4 ohms (~3% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (31W) 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 and sides of the A400 were 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 A400 is nearly flat within the audioband (-0.2/-0.1dB at 20Hz/20kHz). The -3dB point is just past the 100kHz mark. The A400 appears to be AC coupled, yielding roughly -2dB 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 A400 yielded just under +20 degrees of phase shift at 20Hz, and -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 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 see that the deviations between no load and 4 ohms are relatively small at roughly 0.1dB. This is a mid-tier result and an indication of a low to average output impedance, or mid-tier damping factor. With a real speaker load, deviations were smaller, at roughly 0.05dB.

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 160W (just above the rated output of 150W). The power was varied using the A400 volume control. All data are fairly closely lumped together, an indication of a strong result for this test, except for the high THD ratios overall. THD ratios ranged from 0.015% to 0.07%. While these THD ratios are well below the threshold of audibility, they are nonetheless one to two orders of magnitude higher than many modern solid-state amplifiers.

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 A400 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 close (within roughly 5-8dB). For the 8-ohm load, THD ratios ranged from 0.05% at 50mW, down to 0.015% from 10W to the “knee” at roughly 170W, then up to the 1% THD mark at 190W. For the 4-ohm load, THD ratios ranged from 0.06% at 50mW, down to 0.03% from 1W to the “knee” at roughly 270W, then up to the 1% THD mark at 296W.

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 A400 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 close (within 3-6dB—note that since THD ratios are relatively high, these dominate the data in this graph). THD+N ratios range from just under 0.1% (50mW) to 0.015% at the “knee” for the 8-ohm load, and to just over 0.1% (50mW) to 0.03% to the “knee” for the 4-ohm load.

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 A400 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 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. There is roughly a 5dB increase in THD every time the load is halved. Into 2 ohms, THD ratios ranged from 0.05% at 20Hz up to 0.15% 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 A400 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, which is a good result, except that THD ratios are all relatively high. The two-way speaker yielded THD ratios from 0.06% (20Hz) to 0.01% (80/1.5kHz), and up to 0.06% (20kHz). The three-way speaker yielded THD ratios from 0.015% (20Hz) to 0.03% (100Hz), and up to 0.08% (20kHz).

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 A400 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 two-way speaker (Paradigm Founder Series 100F, measurements can be found here). We find that all three IMD traces are close to one another, ranging from 0.02% to 0.05%.

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 A400 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; 0.05% up to 500Hz, then down to 0.005% up 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 balanced input. We see significant signal harmonic peaks up to the limits of the FFT (90kHz), ranging from the highest at 2kHz (-75dBrA, or 0.02%) down to the -120dBrA, or 0.0001%, level. On the right side of the signal peak, we find significant power-supply-related noise peaks up to the limits of the FFT (90kHz), ranging from the highest at 60/120/180/240Hz (-90 to -100dBrA, or 0.003-0.001%) down to the -130 to -140dBrA, or 0.00003-0.00001%, level.

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

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) peak is the second (100Hz) signal harmonic at -80dBrA, or 0.01%, and subsequent signal harmonics can be seen at the -90dBrA, or 0.003%, and below level. Power-supply-related noise peaks are prevalent through the FFT at the -90dBrA, or 0.003%, and below level.

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. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -80dBrA, or 0.01%, while the third-order modulation products, at 17kHz and 20kHz, are at roughly the -90dBrA, or 0.003%, level.

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

Shown above is the FFT of the speaker-level output of the A400 with the APx 32-tone signal applied to the analog input. The combined amplitude of the 32 tones is the 0dBrA reference, which 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 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 A400’s slew-rate performance. Rather, it should be seen as a qualitative representation of the A400’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 some mild softening and no over/undershoot.

Damping factor vs. frequency (20Hz to 20kHz, two-channel mode)

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 190 from 20Hz to 2kHz, then down to just above 100 at 20kHz. This is a mid-tier result for an integrated solid-state amplifier.

Diego Estan
Electronics Measurement Specialist