Hegel Music Systems H30A Stereo/Mono Amplifier Measurements

Link: reviewed by Jason Thorpe on SoundStage! Hi-Fi on April 15, 2023

General information

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

The Hegel Music Systems H30A was conditioned for 1 hour at 1/8th full rated power (~60W 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 Hegel H30A has both unbalanced (RCA) and balanced (XLR) inputs, and a pair of speaker level outputs. We found no appreciable differences in term of THD and noise between the RCA and XLR inputs. The H30A can be operated in stereo or mono mode, for which the latter uses a third unbalanced or balanced input. Hegel states that the H30A is designed as a mono power amplifier, but that it can also be used as a stereo amplifier. As such, essentially all measurements have been performed in both stereo (two-channel) and mono (single-channel) modes. Unless otherwise stated, the balanced inputs were used for all measurements.

Published specifications vs. our primary measurements

The table below summarizes the measurements published by Hegel for the H30A 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 500kHz, assume, unless otherwise stated, 10W into 8 ohms and a measurement input bandwidth of 10Hz to 90kHz, and the worst-case measured result between the left and right channels.

* Hegel measures damping factor directly at the output stage, whereas we measure at the amp’s output terminals.

Our primary measurements in stereo mode revealed the following using the line-level balanced analog input (unless specified, assume a 1kHz sinewave at 223mVrms, 10W output, 8-ohm loading, 10Hz to 90kHz bandwidth):

For the continuous dynamic power test, the H30A was able to sustain 553W into 4 ohms (~1.5% THD) using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (55.3W) for 5 seconds, for 5 continuous minutes without inducing a fault or the initiation of a protective circuit. This test is meant to simulate sporadic dynamic bass peaks in music and movies. During the test, the top of the H30A was only warm to the touch, without causing any discomfort.

Our primary measurements in mono mode revealed the following using the line-level balanced analog input (unless specified, assume a 1kHz sinewave at 223mVrms, 10W output, 8-ohm loading, 10Hz to 90kHz bandwidth):

Frequency response (8-ohm loading, stereo mode)

In our frequency-response plots (relative to 1kHz) above, measured across the speaker outputs at 10W into 8 ohms, the H30A is near flat within the audioband (-0.2/0dB, 20Hz/20kHz). At the extremes, the H30A is at -1.5dB at 5Hz and +-1.2dB at 200kHz. 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, stereo mode)

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 H30A does not invert polarity and exhibits, at worst, about 30 degrees (at 20kHz) of phase shift within the audioband.

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

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

. . . is the same but zoomed in to highlight differences. Here we find that maximum deviation between no load and a 4-ohm load is very small, at around 0.02dB. This is an indication of a very high damping factor, or low output impedance. With a real speaker, maximum deviations in RMS level were roughly the same.

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

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

. . . is the same but zoomed in to highlight differences. Here we find that maximum deviation between no load and a 4-ohm load is roughly double in mono mode compared to stereo, at around 0.04dB. This is normal for a bridged amplifier, as the output impedance roughly doubles because each speaker output terminal is wired to an amplifier output (but out of phase). In a conventional amplifier, only the positive speaker output terminal is connected to the amplifier output, while the negative speaker output terminal is connected to ground.  Nonetheless, the output impedance is still very low in mono mode by any conventional standard. With a real speaker, maximum deviations in RMS level were roughly the same, at 0.04dB.

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

The chart above shows THD ratios at the output into 8 ohms as a function of frequency for a sinewave stimulus at the analog line-level input in stereo mode. The blue and red plots are for left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at 200W. We find fairly consistent THD ratios at 1W and 10W, from 0.001-0.003% at 20Hz, up to 0.005-0.008% at 20kHz. At 200W, THD ratios were higher, from 0.006% from 20Hz to 2kHz, up to nearly 0.02% at 20kHz.

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

The chart above shows THD ratios at the output into 8 ohms as a function of frequency for a sinewave stimulus at the analog line-level input in mono mode. The blue plot is at 1W output into 8 ohms, purple at 10W, and pink at 600W. THD ratios at 1W were the lowest, from 0.002-0.001% between 20Hz and 5kHz, then up to 0.006% at 20kHz. At 10W, THD values were roughly 5dB higher. At 600W, THD ratios were still commendably low, at 0.003-0.004% from 20Hz to 2kHz, then up to 0.006% near 20kHz.

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

The chart above shows THD ratios measured at the output of the H30A as a function of output power for the analog line-level input in stereo mode, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). The 8-ohm data ranged from about 0.003% at 50mW, down to 0.0015% from 0.5 to 50W, then up to the “knee” just shy of 300W. The 4-ohm data yielded THD ratios 5-10dB higher through the flat portion of the curve up to 200W, and hit the “knee” at nearly 500W. The 1% THD marks were hit at 296W (8 ohms) and 525W (4 ohms).

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

The chart above shows THD+N ratios measured at the output of the H30A as a function of output power for the analog line-level input in stereo mode, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). THD+N values for the 8-ohm data ranged from 0.05% down to 0.002% at 50W. The 4-ohm data yielded THD+N values 3-4dB higher, except at the lowest point, where 0.002% was also reached, but at around 150W.

THD ratio (unweighted) vs. output power at 1kHz into 8 ohms (mono mode)

The chart above shows THD ratios measured at the output of the H30A as a function of output power for the analog line level-input in mono mode into 8 ohms. THD values were at 0.003% at 50mW, down to 0.001% at 1-3W then up to 0.002% up to 500W, then to the “knee” between 800 and 900W. The 1% THD mark was hit at 1060W (8-ohm).

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

The chart above shows THD+N ratios measured at the output of the H30A as a function of output power for the analog line level-input in mono mode into 8 ohms. THD+N values were at 0.05% at 50mW, down to as low as 0.002% between 100 and 500W.

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

The chart above shows THD ratios measured at the output of the HA30 as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yielded 100W at the output into 8 ohms (and roughly 200W into 4 ohms, and 400W into 2 ohms) for the analog line-level input in stereo mode. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. We see increasing levels (5dB) of THD from 8 to 4 to 2 ohms at 3kHz and above. Below 1kHz, are three THD data sets are fairly close, with THD ratios ranging from 0.002% to 0.005%.

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

The chart above shows THD ratios measured at the output of the H30A as a function of frequency into three different loads (8/4/2 ohms) for a constant input voltage that yielded 200W at the output into 8 ohms (and roughly 400W into 4 ohms, and 800W into 2 ohms) for the analog line-level input in mono mode. The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. We see increasing levels (5-10dB) of THD from 8 to 4 to 2 ohms between about 300Hz and 3kHz, with the 8-ohm data as low as 0.001-0.002%. At the frequency extremes, THD ratios were quite similar: 0.002% at 20Hz, and 0.007% near 20kHz.

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

The chart above shows THD ratios measured at the output of the H30A as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the balanced analog line-level input in stereo mode. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). The 8-ohm plot is fairly flat and between 0.001% and 0.002% from 20Hz to 5kHz, but the two speaker plots vary considerably. The two-way speaker ranges from 0.02% at 20Hz, to as low as 0.0005% at 2kHz, then back up to 0.01% at 20kHz. The three-way speaker THD plot ranges from 0.003% at 100Hz, down to as low as 0.0007% at 4kHz, then up to 0.01% at 20kHz.

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

The chart above shows THD ratios measured at the output of the H30A as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the balanced analog line-level input in mono mode. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). The 8-ohm plot ranges from 0.002% at 20Hz down to 0.0008-0.0009% between 100Hz and 3kHz, then up to 0.006% at 20kHz. The two speaker plots vary considerably more. The two-way speaker ranges from 0.03% at 20Hz, to as low as 0.0006% at 2-3kHz, then back up to 0.002% at 10kHz. The three-way speaker THD plot ranges from 0.004% at 100Hz, down to as low as 0.0007% at 2kHz, then up to 0.015% at 20kHz.

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

The chart above shows intermodulation distortion (IMD) ratios measured at the output of the H30A as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for the analog line-level input. Here the CCIF IMD method is used, where the primary frequency is swept from 20kHz (F1) down to 2.5kHz, and the secondary frequency (F2) is always 1kHz lower than the primary, with a 1:1 ratio. The CCIF IMD analysis results are the sum of the second (F1-F2 or 1kHz) and third modulation products (F1+1kHz, F2-1kHz). The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). The 8-ohm IMD data is fairly flat, between 0.002% and 0.003%. The two-way speaker data ranges from 0.001% at 2.5kHz up to 0.003% at 20kHz. The three-way speaker data ranges from 0.001% at 2.5kHz up to 0.007% at 20kHz.

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

The chart above shows intermodulation distortion (IMD) ratios measured at the output of the H30A 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 mono mode. Here the CCIF IMD method is used, where the primary frequency is swept from 20kHz (F1) down to 2.5kHz, and the secondary frequency (F2) is always 1kHz lower than the primary, with a 1:1 ratio. The CCIF IMD analysis results are the sum of the second (F1-F2 or 1kHz) and third modulation products (F1+1kHz, F2-1kHz). The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). The 8-ohm IMD data is fairly flat, between 0.002% and 0.003%. The two-way speaker data ranges from 0.001% at 2.5kHz up to 0.005% at 20kHz. The three-way speaker data ranges from 0.001% at 5.5kHz up to 0.01% at 20kHz.

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

The chart above shows IMD ratios measured at the output of the H30A 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 is used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). All three data sets are close enough to be judged as nearly identical, hovering around the 0.006-0.008% level.

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

The chart above shows IMD ratios measured at the output of the H30A 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 mono mode. Here, the SMPTE IMD method is used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). All three data sets are close enough to be judged as nearly identical, hovering around the 0.006-0.008% level.

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

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the analog line-level input in stereo mode. We see that the signal’s second (2kHz) and third (3kHz) harmonic, are at roughly -100dBrA, or 0.001%. The subsequent harmonics (4/5/6/7/8kHz) are visible but at lower and descending levels below the -110dBrA, or 0.0003% mark. Power supply related noise peaks at the fundamental (60Hz) frequency are evident at -130/-115dBrA (left/right), or 0.00003/0.0002%, as well as both even and odd harmonics at a low -120dBrA, or 0.001%, and below.

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

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the output across an 8-ohm load at 10W for the analog line-level input in mono mode. We see that the signal’s even harmonics are lower than is seen in stereo mode. For example, the 2kHz peak here is at -115dBrA, or 0.0002%, versus -100dBrA in stereo mode. Power-supply-related noise peaks are roughly the same as is seen in the stereo FFT above.

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

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the analog line-level input in stereo mode. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most dominant (non-signal) peaks are the second (100Hz) and third (150Hz) signal harmonic at roughly -100dBrA (right), or 0.001%. Power-supply-related harmonics are generally below the -120dBrA, or 0.0001% level.

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

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the output across an 8-ohm load at 10W for the analog line-level input in mono mode. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. Here again we see that the signal’s even harmonics are lower than is seen in stereo mode. For example, the 200Hz (fourth harmonic) peak here is nearly at -120dBrA, or 0.0001%, versus -110dBrA (left channel) in stereo mode. Power-supply-related noise peaks are roughly the same as is seen in the stereo FFT above.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the analog line-level input in stereo mode. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -100dBrA, or 0.001%, and the third-order modulation products, at 17kHz and 20kHz, are at the same level.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the output across an 8-ohm load at 10W for the analog line-level input in mono mode. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -110dBrA, or 0.0003%, which is lower than is seen in stereo mode, while the third-order modulation products, at 17kHz and 20kHz, are at -95dBrA, or 0.002%, which is higher than is seen in stereo mode.

Squarewave response (10kHz, stereo mode)

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 H30A’s slew-rate performance. Rather, it should be seen as a qualitative representation of the H30A’s extended bandwidth. An ideal squarewave can be represented as the sum of a sinewave and an infinite series of its odd-order harmonics (e.g., 10kHz + 30kHz + 50kHz + 70kHz . . .). A limited bandwidth will show only the sum of the lower-order harmonics, which may result in noticeable undershoot and/or overshoot, and softening of the edges. The H30A’s squarewave response is superb, showing no visible over/undershoot, or ringing near the sharp corners.

Damping factor vs. frequency (20Hz to 20kHz, stereo mode)

The graph above is the damping factor as a function of frequency in stereo mode. We see both channels tracking closely and a very high damping factor, ranging around the 800 mark between 40Hz and 1kHz, then down to 300 at 20kHz.

Damping factor vs. frequency (20Hz to 20kHz, mono mode)

The final graph above is the damping factor as a function of frequency in mono mode. We see roughly the same plot as above in stereo mode, but at half the values, due to each speaker output terminal being connected to an amplifier output (bridged mode), each with its own output impedance.

Diego Estan
Electronics Measurement Specialist