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

Details

Parent Category: Products

Category: Amplifier Measurements

Created: 01 January 2025

Link: reviewed by George de Sa on SoundStage! Hi-FI on January 1, 2025

General Information

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

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

The Carina GaN offers one set of line-level and phono analog inputs (RCA, switchable), left/right pre-outs, two digital coaxial (RCA) S/PDIF inputs, one optical (TosLink) S/PDIF input, one USB digital input, one set of speaker-level output, and two headphone outputs, one over 1/4″ TRS connector and the other 4.4mm balanced TRRRS. A Bluetooth input is also offered. For the purposes of these measurements, the following inputs were evaluated: digital coaxial, analog line-level and phono, and the balanced 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 achievable output power of 100W into 8 ohms. (NOTE: despite the 200Wpc into 8/4-ohm rating, the Carina GaN could not sustain more than approximately 100Wpc into 8/4 ohms without inducing the fault protection circuit. According to Peachtree, this is abnormal behaviour and may indicate a fault with our unit under test. The issue is being investigated by Peachtree). For comparison, on the line-level input, an SNR measurement was also made with the volume at maximum.

The Carina GaN offers four different digital filters that are applied only when using the pre-out or headphone outputs. These are: linear phase fast (default), hybrid fast, minimum phase slow, and NOS.

Based on the accuracy and repeatability of the left/right volume-control channel matching (see table below), the Carina GaN volume control is operating fully in the digital domain, meaning all incoming signals are digitized. The Carina GaN overall volume range is from -62dB to +27.9dB (line-level input, speaker output). It offers 1dB increments throughout the volume range.

Our typical input bandwidth filter setting of 10Hz-22.4kHz was used for all measurements except FFTs and where a bandwidth of 10Hz-90kHz was used. Frequency-response measurements utilize a DC to 1 MHz input bandwidth. Because the Carina GaN is a digital amplifier technology that exhibits considerable noise above 20kHz (see FFTs below), the 22.4kHz bandwidth setting was maintained for THD versus frequency sweeps as well. For these sweeps, the highest frequency was 6kHz, to adequately capture the second and third signal harmonics with the restricted bandwidth setting.

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

Published specifications vs. our primary measurements

The table below summarizes the measurements published by Peachtree for the Carina GaN compared directly against our own. The published specifications are sourced from Peachtree’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.

* protection circuit enabled after a few seconds

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

* protection circuit enabled after a few seconds

For the continuous dynamic power test, the Carina GaN was able to sustain 170W into 4 ohms (~1.5% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (17W) for 5 seconds, for 206 seconds of the 500-second test before inducing the fault-protection circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the Carina GaN was slightly warm to the touch.

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

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Our primary measurements revealed the following using the coaxial digital input at the balanced headphone output (unless specified, assume a 1kHz sinewave, 24/96 0dBFS input/2Vrms 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 Carina GaN is essentially perfectly flat within the audioband (20Hz to 20kHz). Just beyond 20kHz, however, there is brickwall filtering, followed by a peak at 30kHz, then beyond 30kHz, brickwall filtering again. This frequency response behavior, along with the behavior of the volume control, indicates that incoming analog signals are digitized within the Carina GaN. The Carina GaN is roughly -0.4dB at 5Hz.

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 Carina GaN yields an enormous amount of absolute input-to-output phase shift, which includes the time delay inherent with the digitization and processing of analog signals. Here we see roughly 17,000 degrees of phase shift at 20kHz. Below . . .

. . . is the same plot but shown “wrapped,” where each 360 degrees of phase shift just wraps back inside the plot area.

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

The chart above shows the Carina GaN’s frequency response (relative to 1kHz) as a function of input type measured across the speaker outputs at 10W into 8 ohms. The two green traces are the same analog input data from the speaker-level frequency-response graph above. The blue and red traces are for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz using the coaxial input, the purple and green traces are for a 24/96 dithered digital input signal from 5Hz to 48kHz, and the pink and orange traces are for a 24/192 dithered digital input signal. At low frequencies, the digital signals yielded a flat or slight over-response at 5Hz, whereas the analog input is -0.4dB at 5Hz. All signals show the same brickwall-type behavior just past 20kHz.

Frequency response vs. MQA (16/44.1)

The chart above shows the Carina GaN’s frequency response (relative to 1kHz) as a function of filter type measured at the pre-outs (left channel only), from 1kHz to 30kHz for a dithered 16/44.1 input signal. Please note that these filters only affect the pre-out and headphone outputs. They have no effect on the speaker-level outputs. The blue trace is the linear phase fast filter, the purple trace hybrid fast, pink is minimum phase slow, and orange is NOS. The linear phase fast filter exhibits brickwall-type filtering just past 20kHz, the hybrid fast filter is -8dB at 20kHz, the minimum phase slow filter is -4dB at 20kHz, and the NOS filter is -30dB at 20kHz, -10dB at 10kHz, and -3dB at 8kHz.

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 maximum deviations within ±0.2dB or so from 20Hz to 20kHz, and worst-case channel-to-channel deviations of roughly 0.1dB. Here again we find sharp attenuating just past 20kHz, meaning the phono input is also digitized. While a very strict adherence to the RIAA curve such as this may be an indication that EQ is applied in the digital domain, Peachtree have assured us that equalization is applied in the analog domain.

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 same extreme phase shift seen here was also seen for the line-level analog input.

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 Carina GaN, where 0dBFS was set to yield 2Vrms. The digital input is swept with a dithered 1kHz input signal from -120dBFS to 0dBFS, and the output is analyzed by the APx555. The ideal response would be a straight flat line at 0dB. The 16/44.1 data were essentially perfect as of -110dBFS down to 0dBFS, while the 24/96 data were near perfect down to -120dBFS. We all also extended the sweep down to -140dBFS, to . . .

. . . see how well the 24/96 would perform. We can see here, that below -120dBFS, the 16/44.1 data significantly over-responds (over 10dB), while the 24/96  significantly under-responds (below -10dB).

Impulse response (24/44.1 data, linear phase fast filter)

The graph above shows the impulse response for the Carina GaN, fed to the coaxial digital input, measured at the line-level pre-outputs, using the Transfer Function measurement in the APx500 software, for the linear phase fast filter. We find a reconstruction filter with symmetrical pre/post ringing. A typical sinc function response.

Impulse response (24/44.1 data, hybrid fast filter)

The graph above shows the impulse response for the Carina GaN, fed to the coaxial digital input, measured at the line-level pre-outputs, using the Transfer Function measurement in the APx500 software, for the hybrid fast filter. We find a reconstruction filter that minimizes pre-ringing, but with obvious post-ringing.

Impulse response (24/44.1 data, minimum phase slow filter)

The graph above shows the impulse response for the Carina GaN, fed to the coaxial digital input, measured at the line-level pre-outputs, using the Transfer Function measurement in the APx500 software, for the minimum phase slow filter. We find a reconstruction filter that minimizes pre-ringing but exhibits some post-ringing.

Impulse response (24/44.1 data, NOS

The graph above shows the impulse response for the Carina GaN, fed to the coaxial digital input, measured at the line-level pre-outputs, using the Transfer Function measurement in the APx500 software, for the NOS filter. We find a reconstruction filter that minimizes all ringing, emulating a true non-oversampling (NOS) DAC.

J-Test (coaxial, MQA off)

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 Carina GaN 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 strong J-test result, with only very low-level peaks below the -150dBrA level. This is an indication that the Carina GaN 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 Carina GaN. The optical input yielded similar but slightly worse results compared to the coaxial input, with peaks flanking the 12kHz fundamental at the -130dBrA level.

J-Test with 10ns of injected jitter (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 Carina GaN, with an additional 10ns of 2kHz sinewave jitter injected by the APx555. The results are strong, with only a few extra spurious peaks at the -150dBrA level.

J-Test with 100ns of injected jitter (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 Carina GaN, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The results are strong again, this time with the tell-tale peaks at 10kHz and 14kHz, but highly suppressed at the -140dBrA level. This is further indication that the DAC in the Carina GaN has strong jitter immunity.

J-Test with 100ns of injected jitter (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 Carina GaN, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The results are strong again, but slightly worse than with the coaxial input. Here the 10/14kHz peaks are higher, at the -125dBrA level.

Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (coaxial input, linear phase fast filter)

The chart above shows a fast Fourier transform (FFT) of the Carina GaN’s line-level pre-outputs with white noise at -4dBFS (blue/red) and a 19.1 kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1, using the linear phase fast filter. The steep roll-off around 20kHz in the white-noise spectrum shows the brickwall-type characteristic of this filter. There is only one clear low-level aliased image peaks within the audioband at -125dBrA at roughly 18kHz. The primary aliasing signal at 25kHz is highly suppressed at -120dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are at roughly the same level.

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

The chart above shows RMS level (relative to 0dBrA, which is 1W into 8ohms or 2.83Vrms) as a function of frequency, for the analog line-level input swept from 5Hz to 50kHz. The blue plot is into an 8-ohm load, the purple is into a 4-ohm load, the pink plot is an actual speaker (Focal Chora 806, measurements can be found here), and the cyan plot is no load connected. The chart below . . .

. . . is the same but zoomed in to highlight differences. Here we see that the deviations between no load and 4 ohms are around 1dB. This is a poor result and an indication of a high output impedance, or low damping factor. With a real speaker load, deviations measured lower at roughly the 0.4dB level.

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

The chart above shows THD ratios at the speaker-level outputs into 8 ohms as a function of frequency for a sinewave stimulus at the analog line-level input. The blue and red plots are for left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at 60W. The power was varied using the Carina GaN volume control. The 1W THD ratios were the lowest, with a constant 0.005% from 50Hz to 6kHz (0.01% at 20Hz). The 10W THD ratios were higher, from 0.2% at 20Hz, down to roughly 0.01% from 1kHz to 6kHz. At 60W, THD ratios ranged from 2% at 20Hz, down to 0.07% from 1kHz to 6kHz.

THD ratio (unweighted) vs. frequency at 10W (MM 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 0.01% 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 speaker-level outputs of the Carina GaN 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). Note: the protection circuit would engage and shut down the unit at roughly 100W into 4 ohms, and just past 100W into 8 ohms. From 50mW to 3W, both THD plots track relatively closely, from 0.02% down to 0.005%. Above 3W, THD ratios into 4 ohms are higher, from 0.02% at 5W to a plateau of 0.2% from 30W to 100W. Into 8 ohms, THD ratios ranged from 0.01% at 5W up to 0.1% from 50W to 100W.

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 Carina GaN 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). Note: the protection circuit would engage and shutdown the unit at roughly 100W into 4 ohms, and just past 100W into 8 ohms. From 50mW to 5W, both THD plots track relatively closely, from 0.2% down to 0.02%. Above 5W, THD+N ratios into 4 ohms are higher, from 0.02% at 5W to a plateau of 0.2% from 30W to 100W. Into 8 ohms, THD+N ratios ranged from 0.02% at 5W up to 0.1% from 50W to 100W.

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 Carina GaN 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. We find a roughly 20dB increase (0.01% to 0.2%) in THD from 8 to 4 ohms from 400Hz to 6kHz. From 4 to 2 ohms, there is only a roughly 5dB increase in THD, with the 2-ohm data yielding a relatively steady 0.5 to 0.3% across the measured audio band.

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 Carina GaN 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 0.15% at 20Hz for the two-way speaker versus 0.006% for the resistive load, and 0.01% at 100-150Hz into the three-way speaker versus 0.005% for the resistive load. At higher frequencies (1.5kHz to 6kHz), the THD ratios measured across all three loads are similar, at around the 0.005% level.

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 Carina GaN 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 the IMD ratios into the three-way speaker were the highest, ranging from 0.03% to 0.05%, compared to the resistive load which was a constant 0.008%. The two-way speaker ranged from 0.02%, down to 0.005%, then up to 0.03%.

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 Carina GaN as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here, the SMPTE IMD method was used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). We find very similar IMD ratios into all three loads, between 0.02 and 0.03% from 40Hz to 250Hz, then down to 0.005% upt 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 third (3kHz) harmonic dominates at a significant -80dBrA, or 0.01%, while the second (2kHz), fourth (4kHz) and fifth (5kHz) harmonics are around -95dBrA, or 0.002%. These are high THD results for a modern solid-state amplifier. On the right side of the signal peak, we do not see any power-supply-related noise peaks (e.g., 60/120/180Hz); however, the overall noise floor is relatively high at -120dBrA.

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 essentially the same result as with the analog FFT above. Given that analog signals are very likely digitized inside the Carina GaN, this should come as no surprise.

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, just below the correct amplitude, with no other peaks above the noise floor. We can also see that the left channel (blue) is quieter than the right channel by more than 5dB throughout the audioband.

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, just below the correct amplitude, with no other significant peaks above the noise floor. Once again, the left channel is quieter than the right channel.

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 MM phono input. We see that the signal’s third (3kHz) harmonic dominates at a significant -80dBrA, or 0.01%, while the second (2kHz), fourth (4kHz) and fifth (5kHz) harmonics are around -95dBrA, or 0.002%. On the right side of the signal peak, we find power-supply related noise peaks at 60/120/180/240Hz etc, ranging from -90dBrA, or 0.003%, down to -110dBrA, or 0.0003%.

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 third (150Hz) signal harmonic at a high -60dBrA, or 0.1%. Other peaks can be seen at -90dBRA, or 0.003%. Again, this represents high levels of THD for a modern solid-state amplifier.

FFT spectrum – 50Hz (MM phono input)

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the MM phono input. The X axis is zoomed in from 40 Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most predominant (non-signal) peak is the third (150Hz) signal harmonic at a high -60dBrA, or 0.1%. The highest power-supply related noise harmonic can be seen at 60Hz at -90dBrA, or 0.003%.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the analog line-level input. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -110dBRa, or 0.0003%, while the third-order modulation products, at 17kHz and 20kHz, are much higher at -85dBrA, or 0.006%.

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

Shown above is the FFT of the speaker-level output of the Carina GaN with the APx 32-tone signal applied to the analog input. The combined amplitude of the 32 tones is the 0dBrA reference, and corresponds to 10W into 8 ohms. The intermodulation products—i.e., the “grass” between the test tones—are distortion products from the amplifier and are at and below the -100dBrA, or 0.001%, level.

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

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 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 -110dBRa, or 0.0003%, while the third-order modulation products, at 17kHz and 20kHz, are much higher at -85dBrA, or 0.006%.

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 -110dBRa, or 0.0003%, while the third-order modulation products, at 17kHz and 20kHz, are much higher at -85dBrA, or 0.006%.

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

Shown above is an FFT of the intermodulation (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the MM phono input. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at around -100dBrA, or 0.001%, while the third-order modulation products, at 17kHz and 20kHz, are higher at -85dBrA, or 0.006%.

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 Carina GaN’s slew-rate performance. Rather, it should be seen as a qualitative representation of the Carina GaN’s extremely restricted bandwidth. An ideal squarewave can be represented as the sum of a sinewave and an infinite series of its odd-order harmonics (e.g., 10kHz + 30kHz + 50kHz + 70kHz . . .). A limited bandwidth will show only the sum of the lower-order harmonics, which may result in noticeable undershoot and/or overshoot, and softening of the edges. In this case, we see the 400Hz switching frequency from the digital amplifier riding on top of a distorted 10kHz fundamental sinewave.

Square-wave response (10kHz, restricted 500kHz bandwidth)

Above is the 1kHz squarewave response using the analog line-level input, at roughly 10W into 8 ohms, this time with a 90kHz input bandwidth on the analyzer to filter out the 400kHz switching frequency, as well as other high-frequency artifacts. We see more evidence here, in the overshoot/undershoot and soft corners of the squarewave, of the Carina GaN’s very limited bandwidth.

FFT spectrum (1MHz bandwidth)

The Carina GaN’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 Carina GaN 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 -20dBrA. There are also two peaks at 800kHz and 1.2MHz (the second and third harmonic of the 400kHz peak), at -50dBrA. In addition, there is a very significant rise in the noise floor from 25kHz to 300kHz, peaking at -70dBrA. Those peaks—the fundamental and its harmonics—are direct results of the switching oscillators in the Carina GaN amp modules. The noise around those very-high-frequency signals are in the signal, but all that noise is far above the audioband—and therefore inaudible—and so high in frequency that any loudspeaker the amplifier is driving should filter it all out anyway.

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

The final graph above is the damping factor as a function of frequency. We can see here a constant damping factor right around 18, from 20Hz to roughly 2kHz, then a dip down to around 7 at 20kHz. This is a very poor damping factor result for a modern solid-state amplifier.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Amplifier Measurements

Created: 01 December 2024

Link: reviewed by Killain Jones on SoundStage! Hi-Fi on December 1, 2024

General Information

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

The T+A R 2500 R was conditioned for 1 hour at 1/8th full rated power (~17W into 8 ohms) before any measurements were taken. All measurements were taken with both channels driven, using a 120V/20A dedicated circuit, unless otherwise stated.

The R 2500 R under test offered one set each of balanced (XLR) and single-ended (RCA) line-level analog inputs, one RCA moving-coil (MC) phono input (moving-magnet and no phono input is also available), one digital coaxial (RCA) input, two digital optical (TosLink) inputs, one USB digital input, one HDMI input, left/right pre-outs, two sets of speaker level outputs (A and B), and one headphone output over a balanced 4.4mm TRRS connector. 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 (MC), as well as the headphone output. The balanced line-level input offers 6dB less gain than the unbalanced input, and about 10dB less distortion in the 3rd signal harmonic (see FFTs in this report).

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 achievable output power of 140W into 8 ohms. For comparison, on the line-level input, a SNR measurement was also made with the volume at maximum. The R 2500 R offers six digital filters for the digital inputs, labeled: long FIR, short FIR, Bezier/FIR, Bezier, NOS 1, NOS 2 . Unless otherwise noted, the long FIR filter was used.

Based on the accuracy and randomness of the left/right volume channel matching (see table below), the R 2500 R volume control is digitally controlled but operating in the analog domain. The R 2500 R overall volume range is from -51dB to +33.2dB (balanced line-level input, speaker output). It offers 1dB increments over 85 steps.

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 T+A  for the R 2500 R compared directly against our own. The published specifications are sourced from T+A’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 R 2500 R was able to sustain 285W into 4 ohms (~3% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (28.5W) for 5 seconds for 5 continuous minutes without triggering 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 R 2500 R were only slightly warm to the touch.

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 frequency-response plots above (relative to 1kHz), measured across the speaker outputs at 10W into 8 ohms, the R 2500 R is essentially perfectly flat within the audioband (20Hz to 20kHz, 0/-0.1dB). The -3dB point is at roughly 100kHz, and 0dB at 5Hz. The R 2500 R appears to be DC-coupled. In the graph above and most of the graphs below, only a single trace may be visible. This is because the left channel (blue or purple trace) is performing identically to the right channel (red or green trace), and so they perfectly overlap, indicating that the two channels are ideally matched.

Frequency response (8-ohm loading, line-level analog input, bass and treble at min and max)

Above is a frequency-response (relative to 1kHz) plot measured at the speaker-level outputs into 8 ohms, with the bass and treble controls set to maximum (blue/red plots) and minimum (purple/green plots). We see that for the bass and treble controls, roughly +7/-5dB of gain/cut is available at 20Hz, and 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 R 2500 R does not invert polarity and yields only about -20 degrees of phase shift at 20kHz.

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

The chart above shows the frequency response (relative to 1kHz) for the MC phono input. What is shown is the deviation from the RIAA curve, where the input signal sweep is EQ’d with an inverted RIAA curve supplied by Audio Precision (i.e., zero deviation would yield a flat line at 0dB). We see a very flat response from 20Hz to 20kHz, within roughly +/-0.2dB of the RIAA target. Below 20Hz, there is a significant rise in the frequency response (+2dB at 10Hz).

Phase response (MC input)

Above is the phase response plot from 20Hz to 20kHz for the MC phono input, measured across the speaker outputs at 10W into 8 ohms. The R 2500 R phono input 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 5-6kHz.

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

The chart above shows the R 2500 R’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 a flat response down to 5Hz, same as the analog response. The -3dB points are: 21.1kHz for the 16/44.1 data, 45.8kHz for the 24/96, 73.2kHz for the 24/192 data, and 100kHz for the analog input. Also of note, the 16/44.1 data showed brickwall-type high-frequency filtering, while the 24/96, 24/192, and analog data did not.

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

The chart above shows the R 2500 R’s frequency response (relative to 1kHz) as a function of filter type measured across the speaker outputs at 10W into 8 ohms for a 16/44.1 digital input (left channel only). The blue plot is the default long FIR filter, the purple trace is the short FIR filter, the pink trace is Bezier/FIR, red is Bezier, orange NOS 1, and green NOS 2. We can see how the long FIR filter offers true brickwall filtering just past 20kHz (21kHz), while all the other filters yielded varying degrees of softer filtering between 10kHz and 20kHz. The Bezier/FIR filter yielded a +0.7dB boost centered around 12/13kHz. The -3dB points are: long FIR: 21.1kHz, short FIR: 19.3kHz, Bezier/FIR: 20.4kHz, Bezier: 17.6kHz (-0.5dB at 10kHz), NOS 1: 18.3kHz (-0.8dB at 10kHz), NOS 2: 19.0kHz (-0.8dB at 10kHz).

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 R 2500 R, where 0dBFS was set to yield 1Vrms. 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 -100dBFS down to 0dBFS. The 24/96 data were at +1dB at -120dBFS, while the 16/44.1 data were +4/+2dB 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 pre-outs of the R 2500 R. The blue trace is for the long FIR filter, which yielded a typical symmetrical sinc function response. The purple trace is for the short FIR filter, which also yielded a symmetrical sinc function response but with less pre/post-ringing.

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 R 2500 R. The pink trace is for the Bezier/FIR filter, which yielded an asymmetrical response with more post versus preringing. The red trace is for the Bezier filter, which yielded close to the same response as the short FIR filter.

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 R 2500 R. The orange trace is for the NOS 1 filter, which yielded a typical symmetrical sinc function response, much like the long FIR filter.

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 R 2500 R. The green trace is for the NOS 2 filter, which yielded a response with almost no pre/post-ringing, approximating that of a true non-oversampling DAC.

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 R 2500 R where 0dBFS is set to 1Vrms. J-Test was developed by Julian Dunn on 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 below the -130dBFS level. This is an indication that the R 2500 R DAC should 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 R 2500 R. The optical input yielded essentially the same result compared to the coaxial 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 R 2500 R, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The result is identical to the result without the jitter injected. This is another indication of the R 2500 R DAC’s strong jitter immunity.

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 R 2500 R, 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 (long FIR filter, coaxial input)

The chart above shows a fast Fourier transform (FFT) of the R 2500 R’s line-level pre-outputs with white noise at -4dBFS (blue/red) and a 19.1 kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1 using the long FIR filter. The steep roll-off around 20kHz in the white-noise spectrum shows that the long FIR filter is of the brickwall-type variety. There are no aliased image peaks within the audioband. The primary aliasing signal at 25kHz is suppressed at -90dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are near or above 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 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 0.04dB. This is a very strong result and an indication of a very low output impedance, or very high damping factor. With a real speaker load, deviations measured lower at roughly 0.03dB.

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 near the rated output at 130W. The power was varied using the R 2500 R volume control. The 11W THD ratios were the lowest, ranging from 0.003% from 20Hz to 2kHz, then up to 0.02% at 20kHz. The 10W THD ratios were just slightly higher by a few dB. At 130W, THD ratios ranged from 0.005% at 20Hz to 1kHz, then up to 0.2% 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 MC phono input measured across an 8-ohm load at 10W. For this test, the input sweep is EQ’d with an inverted RIAA curve. The THD values for the MC configuration vary from around 0.05% (20Hz) down to 0.005% (80Hz to 3kHz), up to 0.02% at 20kHz.

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

The chart above shows THD ratios measured at the speaker-level outputs of the R 2500 R 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 8 ohms are roughly 5-8dB lower than the THD ratios into 4 ohms. THD data into 8 ohms range from 0.002% at 50mW, down to 0.004-0.005% in the 2 to 130W range. The “knee” into 8 ohms can be found just past 130W, while the 4-ohm knee can be seen around 230W. The 1% THD marks were hit at 152W and 278W 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 R 2500 R 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 8 ohms are roughly 3-6dB lower than the THD+N ratios into 4 ohms. THD+N data into 8 ohms range from 0.02% at 50mW, down to 0.005% in the 2 to 130W 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 R 2500 R as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yielded 20W at the output into 8 ohms (and roughly 40W into 4 ohms, and 80W into 2 ohms) for the analog line-level input. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the pink trace the 2-ohm load. We find a roughly 5dB increase in THD from 8 to 4 to 2 ohms across the sweep. The 8-ohm data ranged from 0.004% from 20Hz to 2kHz, then up to 0.02% at 20kHz. Even into 2 ohms, the R 2500 R yielded reasonably low THD ratios from 0.02% to 0.05%.

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 R 2500 R 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 more variable versus frequency than those measured across the resistive dummy load, hovering both above and below the resistive dummy load data. The differences ranged from 0.03% at 20Hz down to 0.0004% at 1.5kHz for the 2-way speaker versus a steady 0.003% for the resistive load (up to 2kHz). The three-way speaker ranged from a low of 0.0015% at 3kHz and a high of 0.02% at 20kHz. This is a relatively 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 R 2500 R 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 generally, the IMD data into real speakers were lower (0.001 to 0.003%) than the steady 0.004% into the resistive load. The three-way speaker IMD data did reach 0.007% from 10kHz to 20kHz.

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 R 2500 R 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 1kHz 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, 0.01% from 40Hz to almost 500Hz, then down to 0.001% from 500Hz to 1kHz.

FFT spectrum – 1kHz (line-level input)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the balanced analog line-level input. We see that the signal’s even-order harmonics (2/4/6/8/10kHz) dominate, with ratios at -90/-100/-110/-115/-120dBrA. This corresponds to a range between 0.003 and 0.0001%. The odd-order harmonics (3/5/7kHz) are lower, with ratios at -115/-120/-130dBrA. This corresponds to a range between 0.0002 and 0.00003%. On the right side of the signal peak, we find only two small power-supply-related noise peaks (left channel only) at -125dBrA (180Hz) and -130dBrA (300Hz).

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 unbalanced analog line-level input. The result is very similar to the FFT above for the balanced input except for a 10dB higher 3kHz signal harmonic.

FFT spectrum – 1kHz (MC phono input)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the phono (MC) analog line-level input. We see that the dominant signal harmonics are at 2kHz, with a level of -85dBrA, or 0.006%, and 4kHz, with a level of -100dBrA, or 0.001%. Power-supply related noise peaks can be seen at 60/180/300Hz, at -70 to -85dBrA, or 0.03% to 0.006%.

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

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 16/44.1. Here the 2/3/4kHz signal harmonic peaks dominate at -90/-95/-105dBrA. This corresponds to a range between 0.003 and 0.0006%. There are no noise peaks visible above the -130dBrA noise floor.

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

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 24/96. We see essentially the same result as with the 16/44.1 FFT above, but with a lower noise floor due to the increased bid 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.

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

Shown above is the FFT for a 1kHz -90dBFS dithered 24/96 input sinewave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, and signal harmonic peaks at a very low -130dBrA, or 0.00003%, and below level.

FFT spectrum – 50Hz (line-level input)

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the analog line-level input. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most predominant (non-signal) peak is the second (100Hz) signal harmonic at -90dBrA, or 0.003%. Subsequent signal harmonics can be seen at and below the -100dBrA, or 0.001%, level.

FFT spectrum – 50Hz (MC phono input)

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the MC phono input. The X axis is zoomed in from 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 -70dBrA, or 0.03%, and -80dBrA, or 0.01%. The signal harmonic peaks (e.g., 100/200Hz) are difficult to discern and very low, at below the -100dBrA, or 0.001%, level.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the analog line-level input. The input RMS values 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 around the -110dBrA, or 0.0003%, level.

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

Shown above is the FFT of the speaker-level output of the A25 with the APx 32-tone signal applied to the analog input. The combined amplitude of the 32 tones is the 0dBrA reference, and 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 -115dBrA, or 0.0002%, 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 -95dBrA, or 0.002%, while the third-order modulation products, at 17kHz and 20kHz, are at -100dBrA, or 0.001%.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 24/96 (-1dBFS). We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -95dBrA, or 0.002%, while the third-order modulation products, at 17kHz and 20kHz, are at -100dBrA, or 0.001%.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the MC phono input. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at around -55dBrA, or 0.2%, while the third-order modulation products, at 17kHz and 20kHz, are much lower at -110dBrA, or 0.0003%.

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 R 2500 R’s slew-rate performance. Rather, it should be seen as a qualitative representation of the R 2500 R’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 relatively clean corners, with only mild softening and no 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 around 450 and above through most of the audioband. This is a very strong result for a medium-powered solid-state integrated amplifier.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Amplifier Measurements

Created: 15 September 2024

Link: reviewed by Phil Gold on SoundStage! Ultra on September 15, 2024

General information

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

The Electrocompaniet AW 300 M was conditioned for 1 hour at 1/8th full rated power (~35W into 8 ohms) before any measurements were taken. All measurements were taken using a 120V/20A dedicated circuit.

The AW 300 M is a one-channel amplifier with one balanced (XLR) input and two sets of speaker-level outputs. An input of 305mVrms 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 utilized a DC to 1MHz input bandwidth.

Published specifications vs. our primary measurements

The table below summarizes the measurements published by Electrocompaniet for the AW 300 M compared directly against our own. The published specifications are sourced from Electrocompaniet’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:

* 327k ohms per differential input

Our primary measurements revealed the following (unless specified, assume a 1kHz sinewave at 305mVrms at the input, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

For the continuous dynamic power test, the AW 300 M was able to sustain about 532W into 4 ohms (~3% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (34.2W) for five seconds, for five continuous minutes without inducing a fault or the initiation of a protective circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the sides and top of the AW 300 M were slightly warm to the touch.

Frequency response (8-ohm loading)

In our frequency-response (relative to 1kHz) plot above, measured across the speaker outputs at 10W into 8 ohms, the AW 300 M exhibits a near-flat frequency response across the audioband (0/-0.1dB at 20Hz/20kHz). The AW 300 M appears to be DC-coupled, as it is perfectly flat down to 5Hz. The -3dB point is at 200kHz.

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 AW 300 M 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, one 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 around 0.02dB up to 2kHz. Beyond 2kHz, the deviations are as high as 0.07dB 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 2kHz were roughly the same (0.02dB) from 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 for a sinewave stimulus at the analog line-level input. The blue plot is at 1W output into 8 ohms, purple at 10W, and pink is near the rated power (260W). The 1W and 10W data are close (within 5dB from 20Hz to 2kHz and 10dB up to 20kHz), with the 1W data outperforming the 10W data and ranging from 0.0003% from 20Hz to 2kHz, then up to 0.001% at 20kHz. The 260W THD data are higher but still very low, ranging from 0.003% from 20Hz to 2kHz, then up to 0.02% at 20kHz.

THD ratio (unweighted) vs. output power at 1kHz into 8, 4, and 2 ohms

The chart above shows THD ratios measured at the output of the AW 300 M as a function of output power for the analog line-level input for an 8-ohm load (blue), 4-ohm load (purple), and 2-ohm load (pink). The 8-ohm data ranged from 0.001% at 50mW, down to 0.0003% from 1-2W, then up to 0.002% at the “knee,” at roughly 250W. The 4-ohm data ranged from 0.0015% at 50mW, down to 0.0005% from 0.5-2W, then up to 0.003% at the “knee,” at roughly 420W. The 2-ohm data ranged from 0.002% at 50mW, down to 0.001% from 0.2-4W, then up to 0.01% at the “knee,” at roughly 700W. The 1% THD marks were reached at 289/515/814W into 8/4/2 ohms.

THD+N ratio (unweighted) vs. output power at 1kHz into 8, 4, and 2 ohms

The chart above shows THD+N ratios measured at the output of the AW 300 M as a function of output power for the analog line-level input for an 8-ohm load (blue), 4-ohm load (purple), and 2-ohm load (pink). The 8-ohm data ranged from 0.01% at 50mW, down to a low of 0.0007% from 10-50W, then up to the “knee.” The 4-ohm data ranged from 0.015% at 50mW, down to a low of 0.001% from 20-100W, then up to the “knee.” The 2-ohm data ranged from 0.02% at 50mW, down to a low of 0.002% from 5-10W, then up to the “knee.”

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

The chart above shows THD ratios measured at the output of the AW 300 M 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 8-ohm data ranged from 0.0007-8% at 20-1kHz, then up to 0.005% at 20kHz. The 4-ohm THD data ranged from 0.0009% at 20Hz to 1kHz, then up to 0.007% at 20kHz. The 2-ohm data yielded a steady climb from 0.0015% at 20Hz up to nearly 0.02% at 20kHz.  This shows that the AW 300 M is perfectly stable into 2-ohms, with low THD ratios even at 200W.

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

The chart above shows THD ratios measured at the output of the AW 300 M 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 all-important 300Hz to 5kHz range, THD ratios into all three loads were extremely close, hovering around the 0.0002-0.0003% level. At the highest frequencies, the three-way speaker yielded the highest THD ratios (0.005% at 20kHz).

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

The chart above shows intermodulation distortion (IMD) ratios measured at the output of the AW 300 M 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 2.5kH, 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 are fairly consistent, from 0.0003 to 0.0005% across the sweep. The results were higher into real speakers, ranging from 0.0005% to 0.003%.

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

The chart above shows IMD ratios measured at the output of the AW 300 M as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input in stereo mode. Here, the SMPTE IMD method was used, where the primary frequency (F1) is swept from 250Hz down to 40Hz and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). The IMD results into the resistive load remained constant between 0.001% and 0.002%. All three plots are essentially identical and constant at 0.002%.

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 -110dBrA and -115dBrA, or 0.0003% and 0.0002%. Other signal harmonics can be seen but below the extremely low -135dBrA level, or 0.00002%, level. There are power-supply noise-related harmonics, but these are below the -125dBrA level, or 0.00006%. This is a clean FFT result.

FFT spectrum – 50Hz (line-level input)

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the balanced analog line-level input. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most dominant (non-signal) peaks are again the signal’s second (100Hz) and third (150Hz) harmonics at -110dBrA and -115dBrA, or 0.0003% and 0.0002%. There are power-supply noise-related harmonics, but these are below the -125dBrA level, or 0.00006%.

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 the very low -120dBrA, or 0.0001%, level, while the third-order modulation products, at 17kHz and 20kHz, are a little higher at -115dBrA, or 0.0002%.

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

Shown above is the FFT of the speaker-level output of the AW 300 M with the APx 32-tone signal applied to the input. The combined amplitude of the 32 tones is the 0dBrA reference, corresponding to 10W into 8 ohms. The intermodulation products—i.e., the “grass” between the test tones—are distortion products from the amplifier and are below the very low -130dBrA, or 0.00003%, level.

Square-wave response (10kHz)

Above is the 10kHz squarewave response using the balanced analog line-level input, at roughly 10W into 8 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the AW 300 M’s slew-rate performance. Rather, it should be seen as a qualitative representation of the AW 300 M’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, from 600-700 from 20Hz to 2kHz. Above 2kHz, there is a dip in damping factor, reaching 250 at 20kHz. This is a very strong damping factor result.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Amplifier Measurements

Created: 15 August 2024

Link: reviewed by Philip Beaudette on SoundStage! Hi-Fi on August 15, 2024

General Information

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

The Hegel Music Systems H400 was conditioned for one 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 H400 offers three sets of line-level analog inputs (two unbalanced over RCA, one balanced over XLR), six digital inputs (three S/PDIF optical, two S/PDIF BNC, one S/PDIF RCA, one USB), left/right unbalanced line-level outputs (fixed and variable over RCA), and one set of speaker level outputs. For the purposes of these measurements, the following inputs were evaluated: digital coaxial (RCA), balanced analog (XLR) line-level. There were no appreciable differences in terms of gain, THD, and noise between the unbalanced and balanced analog inputs.

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 250W into 8 ohms. For comparison, on the line-level input, a SNR measurement was also made with the volume at maximum.

Based on the accuracy and randomness of the left/right volume channel matching (see table below), the H400 volume control is digitally controlled but operating in the analog domain. The H400 overall volume range is from -59dB to +28dB (line-level input, speaker output) using 100 volume steps. It offers 2 to 3dB increments from position 0 to 10, 1dB increments from positions 10 to 56, and 0.5dB from 57 to 100.

Our typical input bandwidth filter setting of 10Hz to 22.4kHz was used for all measurements except FFTs and THD versus frequency, where a bandwidth of 10Hz to 90kHz was used. Frequency-response measurements utilize a DC to 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 Hegel for the H400 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.

* measured at speaker terminals

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 H400 was able to sustain 440W into 4 ohms (~2% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (44W) for 5 seconds, for 5 continuous minutes without inducing a fault protection circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the H400 was warm to the touch.

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 H400 is near flat within the audioband (20Hz to 20kHz, -0.25/-0.1dB). The -3dB point is near 180kHz, validating Hegel’s frequency-response claim. The H400 appears to be AC coupled, yielding just under -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, 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 H400 yielded just under +20 degrees of phase shift at 20Hz, and -20 degrees at 20kHz.

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

The chart above shows the H400’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 as the analog input (-2.2dB at 5Hz). All three digital input data yielded brick-wall-type responses. The -3dB points are: 21.1kHz for the 16/44.1 data, 46.2kHz for the 24/96 data, and 92.4kHz for the 24/192 data. Also of note, the digital input data response show a rise in frequency response above 20kHz while the analog data did not.

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 H400, where 0dBFS yielded 2.6Vrms. 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 -100dBFS down to 0dBFS. The 24/96 data were at -1dB just under -110dBFS, while the 16/44.1 data were +2dB at -120dBFS. We also extended the sweep down to -140dBFS, where . . .

. . . we see that both input data grossly overresponded. Above +10dB at -140dBFS for the 16/44.1 data, and at +10dBFS for the 24/96 data.

Impulse response (24/44.1 data)

The graph above shows the impulse response for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s) for one sample period then back to digital silence, measured at the fixed line-level outputs of the H400. We see that the digital reconstruction filter has no pre-ringing and sustained post-ringing.

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 H400 where 0dBFS yielded about 2.6Vrms. 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 virtually no peaks in the audioband above the -150dBFS noise floor. The peaks at very low frequencies at -110 to -120dBFS are due to power-supply related harmonics (60/120/240Hz, etc.). This is an indication that the H400 DAC should have strong jitter immunity through this input.

J-Test (optical)

The chart above shows the results of the J-Test test for the optical digital input measured at the fixed line-level outputs of the H400. The optical input yielded essentially the same 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 outputs of the H400, with an additional 10ns of 2kHz sinewave jitter injected by the APx555. There are no peaks visible at the telltale 10kHz and 12kHz positions.

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 H400, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. Here we see the telltale peaks at 10kHz and 12kHz, but at the very low -135dBFS level. More evidence of the strong jitter immunity in the H400 DAC.

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 H400, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The optical input yielded essentially the same results compared to the coaxial input.

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

The chart above shows a fast Fourier transform (FFT) of the H400’s fixed 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 the brick-wall-type behavior of the reconstruction filter. There are no aliased image peaks within the audioband above the -135dBrA noise floor. The primary aliasing signal at 25kHz is highly suppressed at -110dBrA, 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 8 ohms or 2.83Vrms) as a function of frequency, for the analog line-level input swept from 5Hz to 50kHz. The blue plot is into an 8-ohm load, the purple is into a 4-ohm load, the pink plot is an actual speaker (Focal Chora 806, measurements can be found here), and the cyan plot is no load connected. The chart below . . .

. . . is the same but zoomed in to highlight differences. Here we see that the deviations between no load and 4 ohms are extremely small at roughly 0.03dB. This is a strong result and an indication of a very low output impedance, or very high damping factor. With a real speaker load, deviations measured at roughly the same level.

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

The chart above shows THD ratios at the speaker-level outputs into 8 ohms as a function of frequency for a sinewave stimulus at the analog line-level input. The blue and red plots are for left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at 220W (near the rated output of 250W). The power was varied using the H400’s volume control. The 1W THD ratios were the lowest, ranging from 0.003% from 20Hz to 3kHz, then up to roughly 0.01% at 20kHz. The 10W THD ratios were only about 5dB higher than the 1W data. At 220W, THD ratios ranged from 0.01-0.02% from 20Hz to 1kHz, then up to 0.2% at 20kHz.

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

The chart above shows THD ratios measured at the speaker-level outputs of the H400 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 remarkably close (within 3-5dB). For the 8-ohm load, THD ratios ranged from 0.002% at 50mW, up to 0.015% at the “knee” at roughly 220W, then up to the 1% THD mark at 259W. For the 4-ohm load, THD ratios ranged from 0.003% at 100mW, up to 0.015% at the “knee” at roughly 380W, then up to the 1% THD mark at 429W.

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 H400 as a function of output power for the analog line level-input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). THD+N ratios into 4 and 8 ohms are remarkably close (with 2-3dB). They range from 0.02% at 50mW, down to 0.004% in the 10 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 H400 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. The 8- and 4-ohm data are extremely close, ranging from 0.005% from 20Hz to 2kHz, then up to 0.03% at 20kHz. Remarkably, the 2-ohm THD data is only roughly 3-5dB above these levels. This is a very strong result, and shows that Hegel has prioritized a robust power supply and output stage in the H400.

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 H400 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 2-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a 3-way speaker (Paradigm Founder Series 100F, measurements can be found here). Generally, THD ratios into the real speakers were similar (higher at some frequencies, lower at others) to those measured across the resistive dummy load. The differences were generally within the 5dB range, and the results were generally in the 0.002% to 0.02% range. This is also a very strong result and shows that the H400 is largely speaker load invariant.

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

The chart above shows intermodulation distortion (IMD) ratios measured at the output of the H400 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 at 20kHz, but 5dB lower IMD results at 3 to 4kHz. Generally, the IMD results ranged from 0.003 to 0.02%.

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 H400 as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here, the SMPTE IMD method was used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). We find very similar IMD ratios into all three loads, between 0.02 and 0.005% across the sweep. Another strong result.

FFT spectrum – 1kHz (balanced 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 that the signal’s second (2kHz) and third (3kHz) harmonics dominate at roughly -90dBrA, or 0.003% (-100dBrA for the left channel at 2kHz). There are subsequent signal harmonics visible between -100dBrA, or 0.001%, and -120dBrA, or 0.0001%. On the left side of the signal peak, we find power-supply related noise peaks (60/120/180/240/300Hz etc) at the -110dBrA, or 0.0003%, and below level. Overall, this is an average FFT result for a modern solid-state amplifier.

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

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 effectively the same result as compared to the analog input FFT above, but for a higher noise floor due to the 16-bit depth.

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

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 24/96. We see essentially the same result as with the 16/44.1 FFT above, but with a lower noise floor due to the increased bit depth.

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

Shown above is the FFT for a 1kHz -90dBFS dithered 16/44.1 input sinewave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, with no signal harmonics above the -135dBrA noise floor, and power-supply-related noise peaks at -105dBrA, or 0.0006%, 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 at -105dBrA, or 0.0006%, 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) peaks are the second (100Hz) and third (3kHz) signal harmonics at -90dBrA, or 0.003%. Other peaks (both signal harmonics and power-supply noise related harmonics) can be seen at -100dBrA 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 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 -105/-90dBrA (left/right), or 0.0006/0.003%, while the third-order modulation products, at 17kHz and 20kHz are at -90dBrA, or 0.003%. Like the 1kHz FFT, this is an average IMD result.

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

Shown above is the FFT of the speaker-level output of the H400 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, 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 -110/-95dBrA (left/right), or 0.0003/0.002%, while the third-order modulation products, at 17kHz and 20kHz, are at -90dBrA, or 0.003%.

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 -110/-95dBrA (left/right), or 0.0003/0.002%, while the third-order modulation products, at 17kHz and 20kHz, are at -90dBrA, or 0.003%.

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 H400’s slew-rate performance. Rather, it should be seen as a qualitative representation of the H400’s relatively 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 only very mild softening and no over/undershoot.

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

The final graph above shows the damping factor as a function of frequency. We can see damping factors ranging from about 600 to 200 for the left channel and 400 to 100 for the right channel. This is a very strong result for an integrated solid-state amplifier.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Amplifier Measurements

Created: 15 August 2024

Link: reviewed by Roger Kanno on SoundStage! Simplifi on August 15, 2024

General Information

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

The Uniti Nova PE was conditioned for one 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 Uniti Nova PE offers four set of line-level analog inputs (two over RCA, two over unbalanced 5-pin DIN connectors), six digital inputs (two S/PDIF over RCA, one S/PDIF over BNC, two S/PDIF over TosLink optical, one over HDMI), an ethernet port for streaming, left/right pre-outs (RCA and unbalanced 4-pin DIN connector), one set of speaker-level outputs, and one headphone output over a 1/8″ TRS connector. A Bluetooth input is also offered. For the purposes of these measurements, the following inputs were evaluated: digital coaxial (RCA), analog line-level (RCA), and 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 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 Uniti Nova PE volume control is digitally controlled but operating in the analog domain. The Uniti Nova PE overall volume range is from -54dB to +27.9dB (line-level input, speaker output). It offers 2dB increments from position 0 to 27, 1dB increments from positions 28 to 84, and 0.5dB from 85 to 100. Also noteworthy is that not every volume step on the display offers a change in gain. That is to say, despite the display showing 100 “steps,” only 85 of those “steps” (default setting) offer an actual change in volume.

Our typical input bandwidth filter setting of 10Hz to 22.4kHz was used for all measurements except FFTs, where a bandwidth of 10Hz to 90kHz was used. Frequency-response measurements utilize a DC to 1MHz input bandwidth. Because the Unity Nova PE uses digital amplifier technology that yields considerable noise above 20kHz, THD vs frequency sweeps were restricted to 6kHz to capture the second and third uppermost signal harmonics with the 22.4kHz analyzer 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 Naim for the Uniti Nova PE compared directly against our own. The published specifications are sourced from Naim’s website, either directly or from the manual available for download, or a combination thereof. 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 Uniti Nova PE was able to sustain 330W into 4 ohms (~3% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (33W) 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 sides of the Uniti Nova PE were only slightly warm to the touch.

Our primary measurements revealed the following using the analog input at the headphone output (unless specified, assume a 1kHz sinewave, 2Vrms 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 Uniti Nova PE is not flat within the audioband (+0.25dB at 30Hz, -1.5dB at 20kHz). The -3dB point is at roughly 23kHz, and the low-frequency response is -1.6dB at 5Hz. The Uniti Nova PE appears to be AC coupled. What is very unusual and must be pointed out is the (what we assume to be) purposeful tilt (bass boost/treble cut) to the response. We can only surmise that this was done to impart a “sound” to the Uniti Nova PE. Also noteworthy is the near brick-wall-type attenuation at high frequencies around 20kHz. 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 Uniti Nova PE does not invert polarity and yields -20000 degrees of phase shift at 20kHz due to the extreme high-frequency filtering.

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

The chart above shows the Uniti Nova PE’s frequency response (relative to 1kHz) as a function of input type measured across the speaker outputs at 10W into 8 ohms. The two green traces are the same analog input data from the speaker-level frequency response graph above. The blue and red traces are for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz using the coaxial input, 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 as the analog response, as well as the same overall bass-to-treble tilt. The -3dB points are: 20.9kHz for the 16/44.1 data, 24.8kHz for the 24/96 and 24/192 data, and 23kHz for the analog input.

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 Uniti Nova PE, where 0dBFS was set to yield 1Vrms at the pre-outs. 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 -100dBFS down to 0dBFS. Both data sets were at roughly +2dB at -120dBFS. Below -120dBFS . . .

. . . both data sets grossly over-responded (beyond +10dB at -140dBFS).

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 Uniti Nova PE. The Uniti Nova PE DAC uses a reconstruction filter that has no pre-ringing and sustained post-ringing.

J-Test (coaxial)

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level pre-outputs of the Uniti Nova PE where 0dBFS is set to 1Vrms. J-Test was developed by Julian Dunn the 1990s. It is a test signal—specifically, a -3dBFS undithered 12kHz squarewave sampled (in this case) at 48kHz (24 bits). Since even the first odd harmonic (i.e., 36kHz) of the 12kHz squarewave is removed by the bandwidth limitation of the sampling rate, we are left with a 12kHz sinewave (the main peak). In addition, an undithered 250Hz squarewave at -144dBFS is mixed with the signal. This test file causes the 22 least significant bits to constantly toggle, which produces strong jitter spectral components at the 250Hz rate and its odd harmonics. The test file shows how susceptible the DAC and delivery interface are to jitter, which would manifest as peaks above the noise floor at 500Hz intervals (e.g., 250Hz, 750Hz, 1250Hz, etc.). Note that the alternating peaks are in the test file itself, but at levels of -144dBrA and below.  The test file can also be used in conjunction with artificially injected sinewave jitter by the Audio Precision, to show how well the DAC rejects jitter.

Here we see a strong J-test result, with only a few peaks in the audioband, at the -130dBFS and below level. This is an indication that the Uniti Nova PE 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 Uniti Nova PE. The optical input yielded essentially the same results as the coaxial 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 Uniti Nova PE, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The telltale peaks at 10kHz and 12kHz cannot be seen above the -145dBFS noise floor. A strong result.

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 Uniti Nova PE, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The optical input yielded essentially the same results as the coaxial input.

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

The chart above shows a fast Fourier transform (FFT) of the Uniti Nova PE’s line-level pre-outputs with white noise at -4dBFS (blue/red) and a 19.1 kHz sinewave at -1dBFS fed to the coaxial digital input, sampled at 16/44.1. The roll-off around 20kHz in the white-noise spectrum shows the implementation of a reconstruction filter that is steep but not of the brick-wall-type variety. There are no aliased image peaks within the audioband above the -135dBrA noise floor. The primary aliasing signal at 25kHz is at -70dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are at and below 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 8 ohms or 2.83Vrms) as a function of frequency, for the analog line-level input swept from 5Hz to 50kHz. The blue plot is into an 8-ohm load, the purple is into a 4-ohm load, the pink plot is an actual speaker (Focal Chora 806, measurements can be found here), and the cyan plot is no load connected. The chart below . . .

. . . is the same but zoomed in to highlight differences. Here we see that the deviations between no load and 4 ohms are relatively large at 0.4dB. This is a poor result and an indication of a high output impedance, or low damping factor, for a solid-state amplifier. With a real speaker load, deviations measured lower at roughly 0.3dB.

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 just at 140W (near the rated output of 150W). The power was varied using the Uniti Nova PE volume control. The 10W THD ratios were the lowest, with a fairly constant 0.003% to 0.005% across the sweep. The 1W THD ratios were slightly higher with a fairly constant 0.005% to 0.006% across the sweep.  At 140W, THD ratios remained low, from 0.005% to 0.01%.

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 Uniti Nova PE 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 remarkably close (within 2-3dB). Beyond 10W, the left channel outperformed the right by as much as 10dB. THD ratios into 8 ohms (left channel) ranged from 0.01% at 50mW down to 0.001% at 30W, then up to 0.002% at the “knee” at roughly 140W, and up to the 1% THD mark at 157W. THD ratios into 4 ohms (left channel) ranged from 0.01% at 60mW down to 0.0007% at 50W to the “knee” at roughly 210W, and up to the 1% THD mark at 261W.

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 Uniti Nova PE as a function of output power for the analog line-level input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). THD+N ratios into 4 and 8 ohms are remarkably close (within 2-3dB). They range from 0.1% at 50mW, down to 0.003% at the “knees.”

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 Uniti Nova PE 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. All three THD plots are remarkably close, and in fact essentially identical at between 0.003% and 0.006% from 20Hz to 500Hz. From 3kHz to 6kHz, there is roughly a 5dB increase in THD every time the load is halved. At 6kHz into 2 ohms, the THD ratio is 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 Uniti Nova PE 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). THD ratios into the real speakers were higher than those measured across the resistive dummy load from 20Hz to 200-300Hz. The differences ranged from 0.3% at 20Hz for the two-way speaker and 0.02% for the three-way speaker versus 0.005% for the resistive load. Between the important frequencies of 400Hz to 6kHz, all three THD traces are essentially identical at 0.005%.

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 Uniti Nova PE 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 essentially identical, ranging from 0.01% at 2.5kHz up to 0.15% at 20kHz.

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 Uniti Nova PE as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here, the SMPTE IMD method was used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). We find very similar IMD ratios into all three loads, between 0.02% 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 -90dBrA, or 0.003%. The third (3kHz) and fifth (5kHz) signal harmonics can be seen at -110dBrA, or 0.0003%. On the left side of the signal peak, we find power-supply related noise peaks, with the third harmonic (180Hz) dominating at just above -110dBrA (left channel), or 0.0003%. Other noise peaks can be seen below 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. Here the second (2kHz) and third (3rd) signal harmonics dominate at -85dBrA and -90dBrA, or 0.006% and 0.003%. The fourth (4kHz) and fifth (5kHz) signal harmonics can be seen at roughly -110dBrA, or 0.0003%. Noise peaks are at and below the -120dBrA, or 0.0001%, level.

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 signal harmonics visible (right channel) at the same level as the signal. The noise floor for the right channel is elevated, as high as -100dBrA, approaching the signal peak in amplitude. The left channel noise floor is much lower at -125dBrA to -145dBrA.

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 essentially the same result as with the 16/44.1 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 a low -90dBrA, or 0.003%. Other peaks (both signal harmonics and power-supply noise related harmonics) can be seen at -110dBrA 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 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 just below the -70dBrA, or 0.3%, level. This is a poor IMD result.

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

Shown above is the FFT of the speaker-level output of the Uniti Nova PE 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  -115dBrA, or 0.0002%, 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 -95dBrA, or 0.002%.

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

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 digital coaxial input at 24/96 (-1dBFS). We see essentially the same result as with the 16/44.1 IMD FFT above.

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 Uniti Nova PE’s slew-rate performance. Rather, it should be seen as a qualitative representation of the Uniti Nova PE’s low 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 only see the fundamental 10kHz sinewave, along with a 600kHz high frequency signal (from the switching oscillator in the digital amp) riding on top. 

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

Above is the 1kHz squarewave response using the analog line-level input, at roughly 10W into 8 ohms, this time with a 250kHz bandwidth filter on the analyzer to filter out the 600kHz oscillator. We see a poor squarewave reproduction, with ringing in the corners.

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

The Uniti Nova PE’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 Uniti Nova PE oscillator switches at a rate of about 600kHz, and this graph plots a wide bandwidth FFT spectrum of the amplifier’s output at 10W into 8 ohms as it’s fed a 1kHz sinewave. We can see that the 600kHz peak is quite evident, and at -50dBrA. There is also a peak at 1.2MHz (the second harmonic of the 600kHz peak), at -80dBrA. Those peaks--the fundamental and its harmonic—are direct results of the switching oscillators in the Uniti Nova PE amp modules. The noise around those very-high-frequency signals are in the signal, but all that noise is far above the audioband–and therefore inaudible—and so high in frequency that any loudspeaker the amplifier is driving should filter it all out anyway.

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

The final graph above shows the damping factor as a function of frequency. We can see here a constant damping factor of 46 through the audioband. This is a poor result for a solid-state amplifier.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Amplifier Measurements

Created: 01 August 2024

Link: reviewed by Matt Bonnaccio on SoundStage! Hi-Fi on August 1, 2024

General information

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

The Starkrimson was conditioned for one 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 Starkrimson is a one-channel amplifier with one balanced (XLR) input and one set of speaker level outputs. An input of 740mVrms was required to achieve the reference 10W into 8 ohms.

Our typical input bandwidth filter setting of 10Hz to 22.4kHz was used for all measurements except the FFTs, where a bandwidth of 10Hz-90kHz was used. Frequency response measurements utilize a 10Hz to 1MHz input bandwidth. Because the Starkrimson is a pulse-density modulated (PDM) amplifier that exhibits considerable noise above 20kHz (see FFTs below), the 22.4kHz bandwidth setting was maintained for THD versus frequency sweeps as well. For these sweeps, the highest frequency was 6kHz, to adequately capture the second and third signal harmonics with the restricted-bandwidth setting.

Published specifications vs. our primary measurements

The table below summarizes the measurements published by Orchard Audio for the Starkrimson compared directly against our own. The published specifications are sourced from Orchard Audio’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 740mVrms at the input, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

For the continuous dynamic power test, the Starkrimson was able to sustain about 342W into 4 ohms (~1.5% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (34.2W) for five seconds, for five continuous minutes without inducing a fault or the initiation of a protective circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the Starkrimson was barely warm to the touch.

Frequency response (8-ohm loading)

In our frequency-response (relative to 1kHz) plot above, measured across the speaker outputs at 10W into 8 ohms, the Starkrimson exhibits a near-flat frequency response across the audioband (0/+0.1dB at 20Hz/20kHz). The dip at low frequencies is due to the 10Hz low-pass filter we used inside the AP analyzer (DC coupling the Starkrimson caused issues). There is a rise at high frequencies, peaking at +1dB at about 80kHz (into 4 ohms, there is a dip instead of a rise—see RMS level versus load plots below) . The -3dB point is beyond 150kHz.

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 Starkrimson does not invert polarity and exhibits, at worst, about -10 degrees of phase shift at 20kHz. The phase shift at lower frequencies is likely due to the 10Hz low-pass filter used inside the AP analyzer.

RMS level vs. frequency vs. load impedance (1W)

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 4-ohm load and no-load to be around 0.04dB. Beyond 2kHz, the deviations increase significantly. This is an indication of a very high damping factor or low output impedance below 2kHz. With a real speaker, the deviations from 20Hz to 2kHz were roughly the same (0.04dB), and about 0.25dB between 4-5kHz and 20kHz.

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

The chart above shows THD ratios at the output into 8 ohms as a function of frequency for a sinewave stimulus at the analog line-level input. The blue plot is at 1W output into 8 ohms, purple at 10W, and pink is just past the rated power (164W with a 3Vrms input). The 1W and 10W data are close, ranging from 0.0002% to 0.0003% from 20Hz to 1kHz. Beyond 1kHz, the 1W data remained around 0.0002%, while the 10W data rose to 0.0007% at 6kHz. The 164W remained impressively low, at 0.003% from 20Hz to 1kHz, then up to 0.02% at 6kHz.

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

The chart above shows THD ratios measured at the output of the Starkrimson as a function of output power for the analog line-level input, for an 8-ohm load (blue) and a 4-ohm load (purple). The 8-ohm data ranged from about 0.001% at 50mW down to 0.0002% from 1-5W, then up to 0.003% at the “knee,” at roughly 150W. The 4-ohm THD data were 5-10dB higher, with a “knee” at roughly 250W. The 1% THD thresholds were reached at 203W and 352W into 8 and 4 ohms.

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

The chart above shows THD+N ratios measured at the output of the Starkrimson as a function of output power for the analog line-level-input, for an 8-ohm load (blue) and a 4-ohm load (purple). The 8-ohm data ranged from about 0.01% down to 0.0005% at 30W. The 4-ohm data ranged from about 0.015% down to 0.001% at 10-20W.

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

The chart above shows THD ratios measured at the output of the Starkrimson as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yields roughly 50W at the output into 8 ohms (blue), 100W into 4 ohms (purple), and 200W into 2 ohms (pink). The 8-ohm data ranged from 0.0008% at 20-200Hz, down to 0.0005% at 1-2kHz, then up to 0.0015% at 6kHz. The 4-ohm THD data ranged from 0.002% at 20Hz up to 0.03% at 6kHz. The 4-ohm data results were somewhat inconsistent compared with the measured THD versus output power plots above, which indicate a potential issue with the measurement (we could not repeat the measurement due to a failure of the amplifier during a subsequent test). The 2-ohm data ranged from 0.005% from 20Hz to 1kHz, then a steady rise to 0.01% at 6kHz. This shows that the Starkrimson is perfectly stable into 2-ohms, with very low THD ratios even at 200W.

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

The chart above shows THD ratios measured at the output of the Starkrimson 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 (0.025%). Generally, from 40Hz to 6kHz, THD ratios into the real speakers were higher than the resistive load, varying widely from 5 to 30dB, but remaining, in absolute terms, low and below the 0.01% level.

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

The chart above shows intermodulation distortion (IMD) ratios measured at the output of the Starkrimson 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 ranges from 0.0003% at lower frequencies, up to 0.002% at 20kHz. The results were much higher into real speakers, ranging from 0.002% to 0.02%.

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

The chart above shows IMD ratios measured at the output of the Starkrimson as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here, the SMPTE IMD method was used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). The IMD results into the resistive load remained constant between 0.001% and 0.002%. Into real speakers the IMD results were higher, from 0.002% up to nearly 0.01% for the three-way speaker.

FFT spectrum – 1kHz

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 sixth (6kHz) harmonics dominate at -115dBrA to -120dBrA, or 0.0002% to 0.0001%. Other signal harmonics can be seen below the -130dBrA level, or 0.00003%. There are essentially no noise related harmonics above the very low -150dBrA noise floor. This is a very clean FFT result.

FFT spectrum – 50Hz

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the balanced analog line-level input. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most dominant (non-signal) peaks are again the signal’s second (100Hz), third (150Hz), and sixth (300Hz) harmonics at -115dBrA to -120dBrA, or 0.0002% to 0.0001%. There are no noise-related harmonics above the very low -160dBrA 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 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 the very low -120dBrA, or 0.0001%, level, while the third-order modulation products, at 17kHz and 20kHz, are higher at -100dBrA, or 0.001%.

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

Shown above is the FFT of the speaker-level output of the Starkrimson with the APx 32-tone signal applied to the input. The combined amplitude of the 32 tones is the 0dBrA reference, and corresponds to 10W into 8 ohms. The intermodulation products—i.e., the “grass” between the test tones—are distortion products from the amplifier and are below the very low -130dBrA, or 0.00003%, level.

Square-wave response (10kHz)

Above is the 10kHz squarewave response using the balanced analog line-level input, at roughly 10W into 8 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the Starkrimson’s slew-rate performance. Rather, it should be seen as a qualitative representation of the Starkrimson’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 the 750kHz switching frequency from the pulse-density modulation riding on top of the 10kHz squarewave.

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

Above is the 10kHz squarewave response using the analog line-level input, at roughly 10W into 8 ohms, this time with a 250kHz input bandwidth on the analyzer to filter out the 750kHz switching frequency, as well as other high-frequency artifacts. Now we see a relatively clean squarewave reproduction, with only some mild over/undershoot in the corners.

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

The Starkrimson’s amplifier relies on a switching oscillator to convert the input signal to a pulse-density modulated (PDM) signal before sending the signal through a low-pass filter to generate an output signal. The oscillator switches at a rate of about 750kHz, 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 750kHz peak is quite evident, and at -40dBrA. In addition, there is a rise in the noise floor from 25kHz to 200kHz, peaking at -120dBrA. The peak at 750kHz is a direct result of the switching oscillators in the Starkrimson GaN amp module. The noise around those very-high-frequency signals are in the signal, but all that noise is far above the audioband—and therefore inaudible—and so high in frequency that any loudspeaker the amplifier is driving should filter it all out anyway.

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

The final graph above is the damping factor as a function of frequency. We find very high damping factor values, nearing 600 from 20Hz to 2kHz. Above 2kHz, there is a dip in damping factor, reaching 40 at 20kHz. This is a strong damping factor.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Amplifier Measurements

Created: 01 August 2024

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

General Information

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

The Peachtree Audio Carina 300 was conditioned for one hour at 1/8th full rated power (~35W 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 Carina 300 offers one set of line-level and phono analog inputs (RCA, switchable), left/right pre-outs, two coaxial (RCA) digital inputs, one optical (TosLink) digital input, one USB digital input, one set of speaker-level outputs, and two headphone outputs over 1/4″ TRS and 4.4mm balanced TRRRS connectors. A Bluetooth input is also offered. For the purposes of these measurements, the following inputs were evaluated: digital coaxial, analog line-level and phono, and the 4.4mm balanced 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 300W into 8 ohms. For comparison, on the line-level input, an SNR measurement was also made with the volume at maximum. The Carina 300 DAC offers three different reconstruction filters: Linear Phase Fast, Hybrid Fast, and Minimum Phase Slow. Unless otherwise stated, the Linear Phase Fast filter was used for the digital measurements.

The Carina 300 offers two types of volume controls: digital and hybrid. Unless otherwise stated, the hybrid volume control was used for all measurements. Based on the accuracy and repeatability of the left/right volume channel matching (see table below), the Carina 300 hybrid volume control is operating partially in the digital domain, partially in the analog domain. The Carina 300 overall volume range is from -56dB to +32.3dB (line-level input, speaker output). It offers 1dB increments throughout the volume range.

Our typical input bandwidth filter setting of 10Hz to 22.4kHz was used for all measurements except FFTs and where a bandwidth of 10Hz to 90kHz was used. Frequency response measurements utilize a DC to 1MHz input bandwidth. Because the Carina 300 uses digital amplifier technology that exhibits considerable noise above 20kHz (see FFTs below), the 22.4kHz bandwidth setting was maintained for THD versus frequency sweeps as well. For these sweeps, the highest frequency was 6kHz, to adequately capture the second and third signal harmonics with the restricted-bandwidth setting.

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

Published specifications vs. our primary measurements

The table below summarizes the measurements published by Peachtree for the Carina 300 compared directly against our own. The published specifications are sourced from Peachtree’s website, either directly or from the manual available for download, or a combination thereof. With the exception of frequency response, where the Audio Precision bandwidth was extended to 1MHz, assume, unless otherwise stated, 10W into 8ohms and a measurement input bandwidth of 10Hz to 22.4kHz, and the worst-case measured result between the left and right channel.

* protection circuit engages at 5Vrms output into 30 or 32 ohms

Our primary measurements revealed the following using the line-level analog and digital coaxial inputs (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 Carina 300 was able to sustain 550W into 4 ohms (~1.8% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (17W) for five seconds, for five 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 Carina 300 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 balanced headphone output (unless specified, assume a 1kHz sinewave, 24/96 0dBFS input/2Vrms output, 300 ohms loading, 10Hz to 22.4kHz bandwidth):

* protection circuit engages at 5Vrms output into 30 or 32 ohms

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 Carina 300 is near flat within the audioband (-0.1dB at 20Hz, -0.6dB at 20kHz). The -3dB high frequency point is at roughly 40kHz. The Carina 300 is at roughly -0.4dB at 5Hz.

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 Carina 300 appears to invert polarity, as we see -180 degrees of phase shift at 20Hz, and more than -1400 degrees at 10kHz.

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). Here we see maximum deviations within ±0.5dB or so from 20Hz to 20kHz, and worst-case channel-to-channel deviations of roughly 0.3dB.

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. What is shown is the excess phase shift, to show the phase shift differences between the MM input and the line-level input. We find +40 degrees at 20Hz, and +20 degrees at 1kHz.

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

The chart above shows the Carina 300’s frequency response (relative to 1kHz) as a function of input type measured across the speaker outputs at 10W into 8 ohms. The two green traces are the same analog input data from the speaker-level frequency-response graph above. The blue and red traces are for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz using the coaxial input, the purple and green traces are for a 24/96 dithered digital input signal from 5Hz to 48kHz, and the pink and orange traces are for a 24/192 dithered digital input signal. At low frequencies, the digital signals yielded a flat response down to 5Hz, whereas the analog input is -0.4dB at 5Hz. The 16/44.1 data yields a brick-wall type response just past 20kHz. The 24/96 and 24/192 data yielded very similar high-frequency responses compared to the analog input, but with slightly higher -3dB points (roughly 45kHz).

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

The plots above show frequency response for a 0dBFS input signal sampled at 16/44.1kHz for the Linear Phase Fast filter (blue), the Hybrid Fast filter (purple), and the Minimum Phase Slow filter (pink) into an 8-ohm load for the left channel only. The graph is zoomed in from 1kHz to 22kHz to highlight the various responses of the three filters. We can see that the Linear Phase Fast filter provides the most “brick-wall” type of response, the Minimum Phase Slow filter shows the gentlest attenuation around the corner frequency (-1dB at 17.1kHz), and the Hybrid Fast filter is very similar to the Minimum Phase Slow filter. The -3dB points for are 20.9kHz for Linear Phase Fast and 18.8kHz for Hybrid Fast and Minimum Phase Slow.

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 Carina 300, where 0dBFS was set to yield 1Vrms at the line-level pre-outs. The digital input was swept with a dithered 1kHz input signal from -120dBFS to 0dBFS, and the output was analyzed by the APx555. The ideal response would be a straight flat line at 0dB. The 16/44.1 data were essentially perfect as of -110dBFS down to 0dBFS, while the 24/96 data were near perfect down to -120dBFS. We all also extended the sweep down to -140dBFS, to . . .

. . . see how well the 24/96 would perform. We can see here that below -120dBFS, the 16/44.1 data significantly over-responds (over 10dB), while the 24/96  significantly under-responds (less than -10dB).

Impulse response (24/44.1 data)

The graph above shows the impulse responses for the Carina 300, fed to the coaxial digital input, measured at the line-level pre-outputs, using the Transfer Function measurement in the APx500 software. We find that the Linear Phase Fast filter (blue) yields a sinc function response with symmetrical pre- and post-ringing, the Hybrid Fast filter (purple) yields little pre-ringing but exhibits post-ringing, while the Minimum Phase Slow filter (pink) yields virtually no pre-ringing and more significant post-ringing.

J-Test (coaxial)

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level pre-outputs of the Carina 300 where 0dBFS was set to 1Vrms. J-Test was developed by Julian Dunn in the 1990s. It is a test signal—specifically, a -3dBFS undithered 12kHz squarewave sampled (in this case) at 48kHz (24 bits). Since even the first odd harmonic (i.e., 36kHz) of the 12kHz squarewave is removed by the bandwidth limitation of the sampling rate, we are left with a 12kHz sinewave (the main peak). In addition, an undithered 250Hz squarewave at -144dBFS is mixed with the signal. This test file causes the 22 least significant bits to constantly toggle, which produces strong jitter spectral components at the 250Hz rate and its odd harmonics. The test file shows how susceptible the DAC and delivery interface are to jitter, which would manifest as peaks above the noise floor at 500Hz intervals (e.g,. 250Hz, 750Hz, 1250Hz, etc.). Note that the alternating peaks are in the test file itself, but at levels of -144dBrA and below.  The test file can also be used in conjunction with artificially injected sinewave jitter by the Audio Precision, to show how well the DAC rejects jitter.

Here we see an above average test result, with low-level peaks below the -130dBrA level. This is an indication that the Carina 300 DAC should have relatively 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 Carina 300. The optical input yielded essentially the same result as the coax 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 Carina 300, with an additional 10ns of 2kHz sinewave jitter injected by the APx555. The results are strong, with no visible peaks at the 10kHz and 14kHz positions.

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 Carina 300, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The results are strong again, this time with the tell-tale peaks at 10kHz and 14kHz, but highly suppressed at the -140dBrA level. This is further indication that the DAC in the Carina 300 has strong jitter immunity.

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 Carina 300, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The results are strong again, but slightly worse than with the coaxial input. Here the 10/14kHz peaks are higher, at the -125dBrA level.

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 Carina 300’s line-level pre-outputs with white noise at -4dBFS (blue/red) and a 19.1 kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1 using the Linear Phase Fast filter. The steep roll-off around 20kHz in the white-noise spectrum shows that the Linear Phase Fast filter is of the brick-wall-type variety. There is only one clear low-level aliased image peak within the audioband at -115dBrA at roughly 18kHz. The primary aliasing signal at 25kHz is highly suppressed at -120dBrA, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are at roughly the same level.

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

The chart above shows RMS level (relative to 0dBrA, which is 1W into 8 ohms or 2.83Vrms) as a function of frequency, for the analog line-level input swept from 5Hz to 50kHz. The blue plot is into an 8-ohm load, the purple is into a 4-ohm load, the pink plot is an actual speaker (Focal Chora 806, measurements can be found here), and the cyan plot is no load connected. The chart below . . .

. . . is the same but zoomed in to highlight differences. Here we see that the deviations between no load and 4 ohms are around 0.1dB. This is a strong result and an indication of a very low output impedance, or high damping factor. With a real speaker load, deviations measured lower at roughly the 0.04dB level.

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

The chart above shows THD ratios at the speaker-level outputs into 8 ohms as a function of frequency for a sinewave stimulus at the analog line-level input. The blue and red plots are for left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange just at 285W (near the rated output power). The power was varied using the Carina 300 volume control. The 1W THD ratios were the lowest, with a constant 0.001% from 20Hz to 2kHz, then down to 0.0003% up to 6kHz. At 10W, the right channel outperformed the left by as much as 10dB, yielding THD ratios from 0.002% at 20Hz, down to 0.0005% from 100Hz to 5kHz. At 285W, THD ratios were fairly constant at around 0.3-0.5%.

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 was EQ’d with an inverted RIAA curve. The THD values for the MM configuration vary from around 0.01% (20Hz) down to 0.0003% from 3kHz to 5kHz.

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 Carina 300 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). Into 8 ohms, THD ratios ranged from 0.004% at 50mW down to 0.0005% at 10W, then up to 0.004% at the “knee” at roughly 200W, then up to the 1% THD mark at 314W. Into 4 ohms, THD ratios for the right channel ranged from 0.005% at 50mW down to 0.002%  from 1W to 10W, then a rise to 0.005% from 20W to 50W, a dip down to 0.001% from 100W to the “knee” at roughly 400W, then up to the 1% THD mark at 573W. The left channel performed considerably worse. This test was one of the last performed, and we began to see intermittent high THD and noise behavior from the left channel. For example, at 200W, there was almost a 40dB difference in THD between channels. We feel that this result for the left channel should not be considered representative for a typical Carina 300 sample since something might’ve gone wrong with our unit during these bench tests.

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 Carina 300 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). Into 8 ohms, THD+N ratios ranged from 0.02% at 50mW down to 0.002% at 10-30W, then up to 0.005% at the “knee” at roughly 200W. Into 4 ohms, THD+N ratios for the right channel ranged from 0.04% at 50mW down to 0.001% at 200-300W.

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 Carina 300 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. We find a roughly 15dB increase (0.001% to 0.005%) in THD ratios from 8 to 4 ohms across most of the sweep. From 4 to 2 ohms, there is a roughly 20dB increase in THD, with the 2-ohm data yielding THD ratios from 0.02% to 0.3%.

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

The chart above shows THD ratios measured at the output of the Carina 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). Generally, THD ratios into the real speakers were close to those measured across the resistive dummy load. The differences ranged from 0.02% at 20Hz for the two-way speaker versus 0.002% for the resistive load, and 0.0003% at 1kHz-4kHz for both speakers compared to 0.0007% for the resistive load. This is a very strong result and shows that the Carina 300 will maintain low THD into real-speaker loads.

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

The chart above shows intermodulation distortion (IMD) ratios measured at the output of the Carina 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). We find that the IMD ratios are all similar (within 5dB), ranging from 0.0003% to 0.001%. Another strong result.

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

The chart above shows IMD ratios measured at the output of the Carina 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). We find very similar IMD ratios into all three loads, between 0.002 and 0.003%.

FFT spectrum – 1kHz (line-level input, hybrid volume control)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the analog line-level input. We see that the signal’s second (2kHz) and third (3kHz) harmonics dominate at a relatively low -110dBrA, or 0.0003% (the left channel at 2kHz measured -130dBrA, or 0.00003%). Subsequent signal harmonics were at the -120dBrA, or 0.0001%, and below level. On the right side of the signal peak, we see power-supply-related noise peaks (60/180/300/420Hz, etc.) around the relatively low -120dBrA, or 0.0001%, level.

FFT spectrum – 1kHz (line-level input, digital volume control)

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, this time with the volume control set to digital. The differences here between the FFT above where the hybrid volume control was used are a slightly higher noise floor (-140dBrA as opposed to -150dBrA) and higher signal harmonics at 5kHz and 7kHz, measuring -110dBrA, or 0.0003%.

FFT spectrum – 1kHz (MM phono input)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the MM phono input.  We see that the signal’s second (2kHz) and third (3kHz) harmonics are difficult to distinguish amongst the noise-realted peaks, but are below the -110dBrA, or 0.0003%, level (although the left channel reached -105dBrA at 3kHz). On the right side of the signal peak, we see power-supply-related noise peaks (60/180/300/420Hz, etc.) at the -85dBrA, or 0.006%, and below level.

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

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 16/44.1. We see essentially the same result as with the analog FFT above using the digital volume control, but with a higher noise floor (-135dBrA) due to the restricted bit depth.

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

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the coaxial digital input, sampled at 24/96. We see essentially the same result as with the analog FFT above using the digital volume control.

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 noise peaks at the -110dBrA and below level. The left channel noise floor and signal harmonic peaks are nearly 10dB higher than the right channel.

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 noise peaks at the -110dBrA and below level. The left channel noise floor and signal harmonic peaks are 5-10dB higher than the right channel.

FFT spectrum – 50Hz (line-level input)

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the analog line-level input. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most predominant (non-signal) peaks are the second (100Hz) and third (150Hz) signal harmonics at a -110dBrA, or 0.0003%. Other peaks can be seen at -120dBrA, or 0.0001%, 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 noise related at 60/180/300/420Hz, etc., at the -85dBrA, or 0.006%, level. The second (100Hz) signal harmonic can be seen at -105dBrA, or 0.0006%.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the analog line-level input. The input RMS values 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 -110dBRa, or 0.0003%, while the third-order modulation products, at 17kHz and 20kHz, are at -100dBrA, or 0.001%.

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

Shown above is the FFT of the speaker-level output of the Carina 300 with the APx 32-tone signal applied to the analog input. The combined amplitude of the 32 tones is the 0dBrA reference, and corresponds to 10W into 8 ohms. The intermodulation products—i.e., the “grass” between the test tones—are distortion products from the amplifier and are at and below the -120dBrA, or 0.0001%, level.

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 -105dBrA, or 0.0006%, while the third-order modulation products, at 17kHz and 20kHz, are at -100dBrA, or 0.001%.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 24/96 (0dBFS). We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -105dBrA, or 0.0006%, while the third-order modulation products, at 17kHz and 20kHz, are at -100dBrA, or 0.001%.

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

Shown above is an FFT of the intermodulation (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 just above the noise floor at around -105dBrA, or 0.0006%, while the third-order modulation products, at 17kHz and 20kHz, are at -100dBrA, or 0.001%.

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 Carina 300’s slew-rate performance. Rather, it should be seen as a qualitative representation of the Carina 300’s mid-tier bandwidth. An ideal squarewave can be represented as the sum of a sinewave and an infinite series of its odd-order harmonics (e.g., 10kHz + 30kHz + 50kHz + 70kHz . . .). A limited bandwidth will show only the sum of the lower-order harmonics, which may result in noticeable undershoot and/or overshoot, and softening of the edges. In this case, we see the 400Hz switching frequency from the digital amplifier riding on top of a distorted 10kHz fundamental sinewave.

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

Above is the 10kHz squarewave response using the analog line-level input, at roughly 10W into 8 ohms, this time with a 250kHz input bandwidth on the analyzer to filter out the 400kHz switching frequency. Here we see an average squarewave response with soft corners.

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

The Carina 300’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 Carina 300 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 -35dBrA. There are also two peaks at 800kHz and 1.2MHz (the second and third harmonic of the 400kHz peak), at -75/-85dBrA. In addition, there is a rise in the noise floor above 30kHz, peaking at -80dBrA. Those peaks—the fundamental and its harmonics—are direct results of the switching oscillators in the Carina 300 amp modules. The noise around those very-high-frequency signals are in the signal, but all that noise is far above the audioband—and therefore inaudible—and so high in frequency that any loudspeaker the amplifier is driving should filter it all out anyway.

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

The final graph above is the damping factor as a function of frequency. We can see here a constant damping factor right around 320 (left channel) and 560 (right channel), from 20Hz to 20kHz. Although there is a significant difference between channels, this is nonetheless a very strong damping factor result.

Diego Estan
Electronics Measurement Specialist