Details

Parent Category: Products

Category: Amplifier Measurements

Created: 01 August 2020

Link: reviewed by Doug Schneider on SoundStage! Hi-Fi on August 1, 2020

General Information

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

The H95 was conditioned for 30 minutes at 10W (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 H95 offers two sets of line-level unbalanced (RCA) inputs, one set of unbalanced variable line outputs, and six digital inputs (three optical, one coaxial, one USB, one Ethernet). For the purposes of these measurements, the following inputs were evaluated: digital coaxial, analog (RCA) line-level.

We attempted to optimize the volume position to achieve the best signal-to-noise ratio (SNR) and THD+N measurements at the speaker outputs (8 ohms) for both analog and digital inputs. For all analog input primary measurements (unless otherwise specified), the best measurements were achieved with the volume was set to 99. At a volume setting of 99, 240mVrms was required at the input for 10W (8 ohms) at the output. For the digital input, we found a volume setting of 59 yielded 10W (8 ohms) at the output for a 0dBFS input. We found essentially no differences between the optical and coaxial S/PDIF inputs, as well as the USB input, in terms of THD+N.

Based on the accuracy of the left/right volume channel matching (see table below), the H95 volume control is likely digitally controlled in the analog domain. The volume range is 0 to 99, in increments of 1-3dB from 0 to 9, and of 1dB from 9 to 99. Beyond volume level 58, every second volume increment has no effect. When the volume is set to 99 (maximum), at the variable RCA outputs, there is a gain of -0.57dB (almost unity) for the analog inputs. For the digital inputs, 2.35Vrms was measured at the variable RCA outputs (volume at maximum) for a 0dBFS input, with a 16-bit and 24-bit input bit depth dynamic range (AES17 method, A-weighted) of 96dB and 110dB, respectively.

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 H95 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 is set at its maximum (DC to 1MHz), assume, unless otherwise stated, 10W into 8ohms and a measurement input bandwidth of 10Hz to 90kHz, and the worst-case measured result between the left and right channel.

Our primary measurements revealed the following using the analog line-level input, and the coaxial digital input (unless specified, assume a 1kHz input sinewave at 240mVrms or 0dBFS, 10W output, 8-ohm loading, 10Hz to 90kHz bandwidth):

For the continuous dynamic power test, the H95 was able to sustain 96W (1% THD) into 4 ohms using an 80Hz tone for 500ms, alternating with a signal at -10dB of the peak (9.6W) 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 H95 was quite warm to the touch, but not hot enough to induce pain.

Our primary headphone measurements revealed the following using the analog line-level input (unless specified, assume volume at 99, 1kHz sinewave, 2Vrms output, 300-ohm loading, 10Hz to 90kHz bandwidth):

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

In our measured frequency response plots above, the H95 is just under -1dB at 5Hz (better than -0.2dB at 20Hz), and just under -2dB at 100kHz (better than -0.2dB at 20kHz). While Hegel does not include “-dB” points in their specifications, this measurement clearly demonstrates that the H95 is a wide-bandwidth (in audio terms) product, corroborating the manufacturer’s claim of a frequency response of 5Hz to 100kHz. In the chart above and most of the charts 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)

Shown above is the phase response of the H95 from 20Hz to 20kHz, using the analog input measured across the speaker outputs at 10W into 8 ohms. The H95 does not invert polarity. The plot is clean, with only +20 degrees of phase shift at 20kHz, and less than +10 degrees at 20Hz.

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

The chart above shows the H95’s frequency response as a function of input type. The blue trace is the same analog input data from the previous chart. The red trace is for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz, the purple trace is for a 24/96 dithered digital input signal from 5Hz to 48kHz, and finally green is 24/192 from 5Hz to 96kHz. The behavior at low frequencies is the same across input types—better than -0.2dB at 20Hz. The 16/44.1 digital input exhibits a sharp brick-wall-type attenuation near the limit of its theoretical frequency range (22.05kHz), with the “knee” at roughly 18kHz (-1.5dB at 20kHz). The 24/96 digital input also exhibits a sharp brick-wall-type attenuation near the limit of its frequency range (48kHz), with the “knee” at roughly 35kHz. The 24/192 digital input frequency response is nearly identical to the 24/96 plot, despite the extended theoretical range up to 96kHz, which indicates that the H95 may be downsampling 24/192 data to 24/96.

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

The chart above shows the results of a linearity test for the coaxial digital input (the optical input performed identically) for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the line level output. The digital input is swept with a dithered 1kHz input signal from -120dBFS to 0dBFS, and the output is analyzed by the APx555. The ideal response would be a straight flat line at 0dB. Both digital input types performed similarly, approaching the ideal 0dB relative level at -100 dBFS, then yielding perfect results from -96dBFS to 0dBFS. At -120dBFS, both channels at 16/44.1 overshot the ideal output signal amplitude by about 4dB, while the left/right channels at 24/96 undershot by 3 and 1dB respectively.

Impulse response (24/44.1 data)

The chart 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 outputs of the H95. We can see that the H95 utilizes a typical sinc function reconstruction filter.

J-Test (coaxial input)

The chart above shows the results of the J-test test for the coaxial digital input measured at the line-level outputs of the H95. The J-Test 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. In addition, an undithered 250Hz squarewave at -144dBFS is mixed with the signal. This test file causes the 22 least significant bits to constantly toggle, which produces strong jitter spectral components at the 250Hz rate and its odd harmonics. The test file shows how susceptible the DAC and delivery interface are to jitter, which would manifest as peaks above the noise floor at 500Hz intervals (e.g., 250Hz, 750Hz, 1250Hz, etc). Note that the alternating peaks are in the test file itself, but at levels of -144dBFS and below. The test file can also be used in conjunction with artificially injected sinewave jitter by the Audio Precision, to show how well the DAC rejects jitter.

We see a few peaks in the audioband just below -110dbFS, the rest are below -130dBFS. This is a good J-Test result, and an indication that the H95 DAC has good jitter immunity. When sinewave jitter was injected at 2kHz, which would manifest as sidebands at 10kHz and 14kHz without any jitter rejection, no further peaks, or worsening of existing peaks, were observed up to a significant 600ns of jitter level, beyond which the H95 DAC lost sync with the signal.

J-Test (optical input)

The chart above shows the results of the J-Test test for the optical digital input measured at the line-level outputs of the H95. We see very small peaks in the audioband at -120to 130dBFS. This result and the results of the jitter-rejection test are essentially identical to the coaxial input.

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

The chart above shows a fast Fourier transform (FFT) of the H95’s line-level outputs with white noise at -4dBFS (blue/red), plus a 19.1kHz sinewave at 0dBFS, fed to the coaxial digital input, sampled at 16/44.1. The sharp roll-off above 20kHz in the white-noise spectrum shows the implementation of a brick-wall-type reconstruction filter. The aliased image at 24kHz and the reciprocal alias at 15kHz are down below -110 dBrA, or 0.0003%. The second, third, and fourth distortion harmonics (38.2, 57.3, 76.4kHz) of the 19.1kHz tone are much higher in amplitude, lying between -70 and -80dBrA, or 0.003% and 0.001%, respectively.

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

The plots above show RMS level (relative to 0dBrA, which is 1W into 8ohms or 2.83Vrms) as a function of frequency, for the analog 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 is an actual speaker (Focal Chora 806, measurements can found here), and the cyan is no load connected. The chart below . . .

. . . is the same but zoomed in to highlight differences. Zoomed in, within the flat portion of the plot, at 1kHz, the deviation from a 4-ohm load to no load is about 0.03dB. At the frequency extremes (20Hz and 20kHz), the spread is larger, between 0.06 to 0.08dB. This is an indication of a high damping factor, or low output impedance The maximum variation in RMS level when a real speaker was used as a load is also very small, deviating by just under 0.04dB within the flat portion of the curve (100Hz to 5kHz), with the lowest RMS level, which would correspond to the lowest impedance point for the load, exhibited at 100Hz, and the RMS highest level, which would correspond to the highest impedance point for the load, at around 4kHz.

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

The chart above shows THD at the H95’s output as a function of frequency (20Hz to 20kHz) for a sinewave stimulus at the analog input. The blue and red plots are for the left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange at the full rated power of 60W. The power was varied using the H95’s volume control. At 1W and 10W, the THD values are quite close, with the 10W figures slightly outperforming the 1W figures, especially at the lowest frequencies (0.01% vs 0.02% for the left channel). The general trend of the lowest THD figures appearing between about 300Hz to 1kHz (around 0.005%), with higher figures at both low and high frequencies (0.025% at 20kHz at worst) was consistent for both the 1W and 10W data. The 60W data showed much higher THD values, with a general trend of lower figures at 20Hz (0.3%), then rising with frequency and peaking at just below 2% near 20kHz.

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

The chart above shows THD ratios measured at the output as a function of output power, for an 8-ohm load (blue/red for left/right) and a 4-ohm load (purple/green for left/right). The 4-ohm data shows consistently higher THD values compared to the 8-ohm data (about a 5 dB difference). THD ratio values are fairly steady from 10mW to the “knee” for both 8-ohm and 4-ohm data. The 8-ohm values hover between 0.01% and 0.005%, trending towards lower values with increased output power, while the 4-ohm values are largely between 0.02% and 0.01%. The “knee” in the 8-ohm data occurs around 40W, hitting the 1% THD mark at 69W, just above the rated output of 60W. For the 4-ohm data, the “knee” occurs just above 60W, hitting the 1% THD at 97W.

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 as a function of output power, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right). The 4-ohm data shows consistently higher THD values compared to the 8-ohm data (about a 4-5 dB difference). THD+N ratio values start at 0.1/0.15% (8/4 ohms) at 10mW, then down to 0.006/0.008% (8/4 ohms) at 30/40W (8/4ohms).

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 H95 as a function of load (8/4/2 ohms), for a constant input voltage that yielded 5W at the output into 8 ohms (and roughly 10W into 4 ohms, and 20W into 2 ohms). The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. We find increasing levels of THD from 8 to 4 to 2 ohms, with about a 5dB difference between 8 and 4 ohms above 1kHz (and very close tracking below 1kHz), and a 40-15dB difference between 4 and 2 ohms from 20Hz to 20kHz, with the largest differences in THD exhibited at lower frequencies, where at 2 ohms and roughly 20W, the H95 exhibits 2% THD at 20Hz.

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 H95 as a function of load (8/4/2 ohms), for a constant input voltage that yielded 5W at the output into 8 ohms (and roughly 10W into 4 ohms, and 20W into 2 ohms). The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. We find increasing levels of THD from 8 to 4 to 2 ohms, with about a 5dB difference between 8 and 4 ohms above 1kHz (and very close tracking below 1kHz), and a 40-15dB difference between 4 and 2 ohms from 20Hz to 20kHz, with the largest differences in THD exhibited at lower frequencies, where at 2 ohms and roughly 20W, the H95 exhibits 2% THD at 20Hz.

THD+N (unweighted) vs. output level at 1kHz for line outputs (analog and digital)

The chart above shows THD+N versus output voltage measured at the variable line-level outputs of the H95, with the volume set to 99 (-0.5dB of gain at the line outputs). The blue/red traces (left/right channels) are for the analog input, swept from 0.2mVrms to 2.4Vrms, while the purple/green traces (left/right) are for a dithered 24/96 digital signal fed to the coaxial input swept from -90dBFS to 0dBFS. We find that the analog input outperformed the DAC section by about 8dB up until about 650mVrms at the output. Above this point, THD+N values jump up from 0.002% to 0.06% (left channel) for the analog input, and from 0.005% to the same 0.06% (left channel) for the DAC input. The right channel faired better at about 0.03% at 2Vrms out. This behaviour of more than a 20dB increase in THD+N between 0.6 and 2Vrms is curious; however, in most home-use cases, analog levels from the variable line outputs of the H95 driving most power amplifiers would not exceed 0.6Vrms.

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

Shown above are FFTs for a 1kHz 0dBFS dithered 16/44 input sinewave stimulus at the coaxial digital input, measured at the output across an 8-ohm load at 10W. We see that the second through fifth harmonics, at 2,3,4, and 5kHz, are between -80dBrA, or 0.01%, and -100dBrA, or 0.001%. The highest peak is for the odd third harmonic, just below -80dBrA. The other harmonics within the audio band measured lower, below -100dBrA, down to about -125dBRa, or 0.00006% at 20kHz. Below 1kHz, we see noise artifacts, with the 60Hz peak reaching -85dBrA (left), or 0.006%, and -120dBrA (right), or 0.0001%. The second noise harmonic (120Hz) is at -105dBrA (left), or 0.0006%, and -95dBrA (right), or 0.002%. The higher harmonics of these two peaks can also be seen at lower levels.

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

Shown above are FFTs for a 1kHz 0dBFS dithered 24/96 input sinewave stimulus at the coaxial digital input, measured at the output across an 8-ohm load at 10W. We see effectively 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 an 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 at 10W. We see the peaks from noise artifacts on the left side of the main signal dominating (with respect to amplitude) the peaks due to the harmonics of the signal on the right side. The 60Hz peak due to power-supply noise is nearing -80dBrA, or 0.01%, above the signal peak at -90dBrA.

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

Shown above is an 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 at 10W. We see effectively the same result as with the 16/44.1 FFT above.

FFT spectrum – 50Hz (line-level input)

Shown above is an FFT for a 50Hz input sinewave stimulus at the analog input, measured at the output across an 8-ohm load at 10W. 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 peak is from the third signal harmonic at 150Hz, reaching -85dBrA, or 0.006%. The second largest peak is from power-supply noise at 120Hz, reaching almost -90dBrA, or 0.003%, followed by the second signal harmonic at 100Hz on the left channel, reaching -95dBrA, or 0.002%.

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

Above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone at the analog input. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 10W (0dBrA) into 8 ohms at the output. Here we find that the second-order modulation product (i.e., the difference signal of 1kHz) is just above -100dBrA, or 0.001%, while the third-order modulation products, at 17kHz and 20kHz, are are both just above -90dBrA, or 0.003%.

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

Above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone at the digital input, where the top plot is for a dithered 16/44.1 digital input. The input digital values are set at -6.02dBFS so that, if summed for a mean frequency of 18.5kHz, would yield 0dBFS at the input and 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%, so slightly better than the analog input, while the third-order modulation products, at 17kHz and 20kHz, are both at -85dBrA, or 0.008%, so slightly worse than the analog input.

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

Above is an FFT of the intermodulation (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone at the digital input, where the top plot is for a dithered 24/96 digital input. There is very little difference between the 16/44.1 and 24/96 IMD FFTs, other than a lower noise floor on the 24-bit spectrum below 22kHz.

Square-wave response (10kHz)

Above is the 10kHz squarewave response of the H95 using the analog input, at roughly 10W into 8 ohms. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the H95’s slew-rate performance. Rather, it should be seen as a qualitative representation of the H95’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. The H95’s reproduction of the 10kHz squarewave is reasonably clean, and although the edges are slightly rounded, they are nonetheless devoid of undershoot and overshoot.

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

The final chart above is the damping factor of the H95 as a function of frequency. Both channels show a general trend of a higher damping factor in the midrange frequencies, and lower damping factors at both the lowest and highest frequencies. The left channel generally outperformed the right channel, with a peak value around 520 between 300Hz and 2kHz, while the right channel peaked around 400 between 200 and 300Hz. At 20Hz, the damping factor for the left channel measured 220, while for the right channel it was around 300. At 20kHz, the damping factor for the left channel measured 340, for the right channel it was around 190.

Diego Estan
Electronics Measurement Specialist

Details

Parent Category: Products

Category: Amplifier Measurements

All amplifier measurements are performed independently by BHK Labs. All measurement data and graphical information displayed below are the property of the SoundStage! Network and Schneider Publishing Inc. Reproduction in any format is not permitted.

Measurements were taken at both channels’ Coaxial S/PDIF, Line 2, and Phono inputs, at 120V AC line voltage, both channels driven.

All unless otherwise noted: the volume control was set for 5W output into 8 ohms, for an input level into Line 2 of 500mV; the results discussed below are for the left channel only; and an Audio Precision AUX-0025 external low-pass filter was used for the speaker-output measurements.

Power output

• Power output at 1% THD+N: 64.1W @ 8 ohms, 76.7W @ 4 ohms
• Power output at 10% THD+N: 75.0W @ 8 ohms, 82.5W @ 4 ohms

Additional data

• Input/output polarity (analog and digital): noninverting
• AC-line current draw
  • Idle: <0.5W
  • Operating: 14.1W, 0.22A, 0.54PF
• Gain: output voltage divided by input voltage, 8-ohm load, volume at +10dB
  
  • Speaker output, Line 2 input: 60.2X, 35.6dB
  • Speaker output, Phono input: 3810.0X, 71.6dB
  • Pre/Sub output, Line 2 input: 6.16X, 15.8dB
  • Pre/Sub putput, Phono input: 390.6X, 51.8dB
• Input sensitivity for 1W output into 8 ohms
  
  • Line 2 input: 47.0mV
  • Phono input: 0.74mV
• Output impedance @ 50Hz
  • Speaker output: 0.016 ohm
  • Pre/Sub output: 440 ohms
• Input impedance @ 1kHz
  • Line 2 input: 18.0k ohms
  • Phono: 44.0k ohms
• Output noise, speaker output, 8-ohm load, input terminated with 1k ohm, Lch/Rch
  
  • Without AUX-0025 measurement filter (high-frequency switching)
    • Wideband: 165.2mV / 158.6mV, -24.7dBW / -25.0dBW
  • With AUX-0025 filter, volume at -3.5dB (ref 5W output for 500mV input)
    
    • Wideband: 486.1uV / 382.1uV, -75.3dBW / -77.4dBW
    • A weighted: 58.4uV / 53.0uV, -93.7dBW / -94.6dBW
  • With AUX-0025 filter, volume at -90dB
    
    • Wideband: 197.8uV / 175.9uV, -83.1dBW / -84.1dBW
    • A weighted: 32.1uV / 32.2uV, -98.9dBW / -98.9dBW
  • With AUX-0025 filter, volume at +10dB
    
    • Wideband: 1970.0uV / 1390.0uV, -63.1dBW / -66.2dBW
    • A weighted: 196.5uV / 149.7uV, -83.2dBW / -85.5dBW

Measurements summary

The NAD D 3045 is a feature-laden little integrated amplifier offering digital inputs as well as analog line and phono inputs.

Chart 1 shows the D 3045’s frequency response with varying loads, with and without the Audio Precision AUX-0025 external low-pass filter. The output LC filtering must have been included in the overall feedback loop to produce a response so invariant with load. Most impressive!

Chart 2 illustrates how the D 3045’s total harmonic distortion plus noise (THD+N) vs. power varies for 1kHz and SMPTE intermodulation test signals and amplifier output load for 8- and 4-ohm loads.

The D 3045’s THD+N as a function of frequency at several different power levels is plotted in Chart 3. The amount of increase of distortion with frequency is admirably low, if not absent -- in my career of measuring many amplifiers, this is very rare.

The damping factor vs. frequency of the D 3045 is shown in Chart 4. Like the unchanging THD+N vs. frequency, the damping factor remains high at a much higher frequency than most power amplifiers.

Chart 5 plots the spectrum of the D 3045’s harmonic distortion and noise residue of a 10W, 1kHz test signal. The AC-line harmonics are low and simple, with some 120Hz visible. The signal harmonics are dominated by third-order harmonics, with second- and higher-order harmonics of much lower magnitude.

Chart 6 is a measure of the phono section’s RIAA equalization error. It shows extremely good accuracy.

Chart 7 is the frequency response of the D 3045’s digital input for sample rates of 44.1, 96, and 192kHz. Of interest is the gentle rolloff of the high frequencies for the two higher rates, which implies less ringing of the leading edges of transient signals.

Chart 8 shows the D 3045’s input/output linearity. This is usually done with a bandpass filter, to exclude noise and see only the signal amplitude. It is also instructive to take the same measurement within an audioband bandwidth, as that shows the ultimate noise level when the signal level descends into the noise.

I also looked briefly at the performance of the D 3045’s headphone amplifier. With a 32-ohm load, hard clipping began at about 1.5W, and low distortion below about 1.3W. With a 600-ohm load, clipping began at about 115mW.

Chart 1 - Frequency response of output voltage as a function of output loading

Red line = with AUX-0025 measuring filter
Magenta line = without AUX-0025 measuring filter
(Note: these responses are representative of 4-, 8-, and open-load curves)

Chart 2 - Distortion as a function of power output and output loading

(Line up at 20W to determine lines)
Top line = 8-ohm SMPTE IM distortion
Second line = 4-ohm SMPTE IM distortion
Third line = 8-ohm THD+N
Bottom line = 4-ohm THD+N

Chart 3 - Distortion as a function of power output and frequency

(8-ohm loading)
Cyan line = 1W
Magenta line = 10W
Blue line = 30W
Red line = 60W

Chart 4 - Damping factor as a function of frequency

Damping factor = output impedance divided into 8

Chart 5 - Distortion and noise spectrum

1kHz signal at 10W into an 8-ohm load

Chart 6 - Phono RIAA equalization response

Chart 7 - Digital-input frequency response

Red line = 44.1kHz sample rate
Magenta line = 96.0kHz sample rate
Blue line - 192.kHz sample rate

Chart 8 - Digital input-output linearity

Magenta line = with usual bandpass filter
Red line = 10Hz - 20kHz

Details

Parent Category: Products

Category: Amplifier Measurements

All amplifier measurements are performed independently by BHK Labs. All measurement data and graphical information displayed below are the property of the SoundStage! Network and Schneider Publishing Inc. Reproduction in any format is not permitted.

Measurements were made at a line voltage of 120V AC, both channels driven, and were taken on both channels using the Hegel H590’s AES, Analog 1, and BNC digital inputs. Unless otherwise noted, the data reported below are for the left channel.

Power output

• Power output at 1% THD+N: 322.7W @ 8 ohms, 524.9W @ 4 ohms
• Power output at 10% THD+N: 400.0W @ 8 ohms, 648.6W @ 4 ohms

Additional data

• Input/output polarity (analog and digital): noninverting
• AC-line current draw at idle: 98.0W, 1.3A, 0.64PF
• Gain: output voltage divided by input voltage, 8-ohm load, Lch/Rch
  
  • Balanced inputs: 42.7X, 32.6dB / 42.6X, 32.6dB
  • Unbalanced inputs: 42.9X, 32.7dB / 42.7X, 32.6dB
• Input sensitivity for 1W output into 8 ohms, Lch/Rch
  
  • Balanced inputs: 66.2mV / 66.4mV
  • Unbalanced inputs: 65.9mV / 66.2mV
• Output impedance @ 50Hz: 0.013 ohm
• Input impedance @ 1kHz
  • Balanced inputs: 9.3k ohms
  • Unbalanced inputs: 7.0k ohms
• Output noise, 8-ohm load, balanced inputs terminated with 600 ohms, Lch/Rch
  
  • At reference volume setting
    • Wideband: 0.646mV / 0.629mV, -72.8dBW / -73.1dBW
    • A weighted: 0.084mV / 0.080mV, -90.6dBW / -91.0dBW
  • At maximum volume
    
    • Wideband: 0.659mV / 0.643mV, -72.6dBW / -72.9dBW
    • A weighted: 0.122mV / 0.120mV, -87.3dBW / -87.5dBW
  • At minimum volume
    
    • Wideband: 1.13mV / 1.07mV, -68.0dBW / -68.4dBW
    • A weighted: 0.107mV / 0.105mV, -88.4dBW / -88.6dBW
• Output noise, 8-ohm load, unbalanced inputs terminated with 1k ohms, Lch/Rch
  
  • At reference volume setting
    • Wideband: 0.633mV / 0.618mV, -73.0dBW / -73.2dBW
    • A weighted: 0.077mV / 0.076mV, -91.3dBW / -91.4dBW
  • At maximum volume
    
    • Wideband: 0.465mV / 0.468mV, -75.7dBW / -75.6dBW
    • A weighted: 0.072mV / 0.075mV, -91.9dBW / -91.5dBW
  • At minimum volume
    
    • Wideband: 1.15mV / 1.06mV, -67.8dBW / -68.5dBW
    • A weighted: 0.106mV / 0.104mV, -88.5dBW / -88.7dBW

Measurements summary

The H590 is Hegel Music Systems’ newest, most powerful integrated amplifier-DAC.

Chart 1 shows the H590’s frequency response with varying loads. The output impedance is low enough that there was negligible variation with the NHT dummy speaker load.

Chart 2 illustrates how the H590’s total harmonic distortion plus noise (THD+N) vs. power varied for 1kHz and SMPTE IM test signals and amplifier output for loads of 8 and 4 ohms. The level of distortion is quite low.

The Hegel’s THD+N as a function of frequency at a number of increasing power levels is plotted in Chart 3. The increase in distortion with frequency is moderate.

Chart 4 plots the H590’s damping factor vs. frequency. The shape of the low-frequency rolloff curve is unusual, and the high-frequency rolloff begins at a lower frequency than the norm.

The Hegel’s spectrum of harmonic distortion and noise residue of a 10W, 1kHz test signal is shown in Chart 5. The AC line harmonics are quite low but relatively complex. The signal harmonics are dominated by the second and third harmonics, with the higher harmonics decreasing quickly.

Some key measurements of the Hegel H590’s digital section were taken. Its BNC input was fed with a full-scale, 0dBFS digital signal level, and, using the volume control, the main amplifier outputs were set as close as possible to 5W/8 ohms. The frequency response is shown in Chart 6.

Chart 7 shows the results of a revealing measurement that I always do on a DAC: a test of its input/output linearity. This measures the amplitude of a decreasing 1kHz signal for both channels with a 1kHz bandpass filter, in order to track the signal down into the noise. The results for sample rates of 44.1, 96, and 192kHz were about the same; for clarity, I’ve shown here only the result for the 44.1kHz sample rate. I additionally changed the measurement bandwidth to 22kHz; the resulting curve shows the residual noise level in the audioband, which in this case is at about CD resolution.

Chart 1 - Frequency response of output voltage as a function of output loading

Red line = open circuit
Magenta line = 8-ohm load
Blue line = 4-ohm load

Chart 2 - Distortion as a function of power output and output loading

(Line up at 200W to determine lines)
Top line = 8-ohm SMPTE IM distortion
Second line = 4-ohm SMPTE IM distortion
Third line = 8-ohm THD+N
Bottom line = 4-ohm THD+N

Chart 3 - Distortion as a function of power output and frequency

(8-ohm loading)
Red line = 1W
Magenta line = 10W
Blue line = 70W
Cyan line = 200W
Green line = 270W
Yellow line = 290W

Chart 4 - Damping factor as a function of frequency

Damping factor = output impedance divided into 8

Chart 5 - Distortion and noise spectrum

1kHz signal at 10W into an 8-ohm load

Chart 6 - Frequency response of AES/EBU digital input at amplifier output

Red line = 44.1kHz
Magenta line = 96kHz
Blue line = 192kHz

Chart 7 - DAC input/output linearity of both channels

24-bit/44.1kHz resolution with 1kHz bandwidth filter
Red line = left channel
Magenta line = right channel

24-bit/44.1kHz resolution with 22kHz bandwidth filter
Cyan line = left channel
Blue line = right channel

Details

Parent Category: Products

Category: Amplifier Measurements

All amplifier measurements are performed independently by BHK Labs. All measurement data and graphical information displayed below are the property of the SoundStage! Network and Schneider Publishing Inc. Reproduction in any format is not permitted.

These measurements were taken at 120V AC line voltage, both channels driven. Measurements were taken on both channels, using inputs 1 and 2. Unless otherwise noted, the data reported below are for the left channel.

Power output

• Power output at 1% THD+N: 133.3W @ 8 ohms, 241.3W @ 4 ohms
• Power output at 10% THD+N: 179.2W @ 8 ohms, 318.0W @ 4 ohms

Additional data

• Input/output polarity (analog and digital): noninverting
• AC-line current draw at idle: 95.0W, 1.06A, 0.65PF
• Gain: output voltage divided by input voltage, 8-ohm load, Lch/Rch
  
  • Balanced inputs: 69.9X, 36.9dB / 69.7X, 36.9dB
  • Unbalanced inputs: 71.4X, 37.1dB / 71.1X, 37.0dB
• Input sensitivity for 1W output into 8 ohms, Lch/Rch
  
  • Balanced inputs: 40.4mV / 40.6mV
  • Unbalanced inputs: 39.6mV / 36.7mV
• Output impedance @ 50Hz: 0.2 ohm
• Input impedance @ 1kHz
  • Balanced inputs: 37.5k ohms
  • Unbalanced inputs: 260.0k ohms
• Output noise, 8-ohm load, balanced inputs terminated with 600 ohms, Lch/Rch
  
  • At reference volume setting
    • Wideband: 1.69mV / 0.815mV, -64.5dBW / -70.8dBW
    • A weighted: 0.161mV / 0.0764mV, -84.9dBW / -91.3dBW
  • At maximum volume
    
    • Wideband: 2.28mV / 2.09mV, -61.9dBW / -62.6dBW
    • A weighted: 0.407mV / 0.389mV, -76.6dBW / -77.2dBW
  • At minimum volume
    
    • Wideband: 4.23mV / 1.01mV, -56.5dBW / -68.9dBW
    • A weighted: 0.423mV / 0.106mV, -76.5dBW / -88.5dBW
• Output noise, 8-ohm load, unbalanced inputs terminated with 1k ohms, Lch/Rch
  
  • At reference volume setting
    • Wideband: 1.67mV / 0.773mV, -64.6dBW / -71.3dBW
    • A weighted: 0.161mV / 0.0774mV, -84.9dBW / -91.3dBW
  • At maximum volume
    
    • Wideband: 1.40mV / 1.03mV, -66.1dBW / -68.8dBW
    • A weighted: 0.145mV / 0.0999mV, -85.0dBW / -91.0dBW
  • At minimum volume
    
    • Wideband: 4.24mV / 1.02mV, -56.5dBW / -68.9dBW
    • A weighted: 0.393mV / 0.106mV, -77.1dBW / -88.5dBW

Measurements summary

Gryphon Audio Designs’ Diablo 120 integrated amplifier builds on the ten-year-long success of Gryphon’s Diablo 300 model.

Chart 1 shows the frequency response of the Diablo 120 with varying loads. The output impedance is low enough that there was negligible variation with the NHT dummy speaker load.

Chart 2 illustrates how the Diablo 120’s total harmonic distortion plus noise (THD+N) vs. power varied for 1kHz and SMPTE IM test signals and amplifier output for 8- and 4-ohm loads. Note that Gryphon claims to use zero overall feedback in the Diablo 120; the levels of distortion, though higher than in most feedback designs, are still reasonable.

The Diablo 120’s THD+N as a function of frequency at a number of increasing power levels is plotted in Chart 3. The levels of increase are moderate.

The Gryphon’s damping factor vs. frequency, plotted in Chart 4, is unusual in its relative flatness. This is a natural consequence of the absence of any overall negative feedback being used, and of not having a series inductor in an output-stabilizing network.

Chart 5 plots the Diablo 120’s spectrum of THD+N residue of a 10W, 1kHz test signal. The AC line harmonics are very low but relatively complex. The signal harmonics are dominated by the second and third harmonics, with higher harmonics of decreasing magnitude.

Some key measurements of the Diablo 120’s digital section were taken. Its AES input was fed with a full-scale 0dBFS digital signal level, and the main amplifier outputs were set as close to 5W/8 ohm as possible with the volume control. Chart 6 shows the frequency response with both of the filter settings, Slow and Fast.

Chart 7 plots the results of a revealing test that I always do on DACs: measure the output amplitude of a 1kHz signal with a 1kHz bandpass filter at full-scale digital level with decreasing input signal level, down to where the output level meets the noise floor. This reveals that the Diablo 120’s noise floor in this test was about -110dBFS, which is pretty good for 24-bit input data.

Chart 1 - Frequency response of output voltage as a function of output loading

Red line = open circuit
Magenta line = 8-ohm load
Blue line = 4-ohm load
Cyan line = NHT dummy-speaker load

Chart 2 - Distortion as a function of power output and output loading

(Line up at 30W to determine lines)
Top line = 4-ohm SMPTE IM distortion
Second line = 8-ohm SMPTE IM distortion
Third line = 4-ohm THD+N
Bottom line = 8-ohm THD+N

Chart 3 - Distortion as a function of power output and frequency

(8-ohm loading)
Red line = 1W
Magenta line = 10W
Blue line = 30W
Cyan line = 70W
Green line = 120W

Chart 4 - Damping factor as a function of frequency

Damping factor = output impedance divided into 8

Chart 5 - Distortion and noise spectrum

1kHz signal at 10W into an 8-ohm load

Chart 6 - Frequency response of AES/EBU digital input at amplifier output

Slow filters
Red line = 44.1kHz
Magenta line = 96kHz
Yellow line = 192kHz

Fast filters
Cyan line = 44.1kHz
Green line = 96kHz
Blue line = 192kHz

Chart 7 - DAC input/output linearity of both channels

24-bit/44.1kHz resolution with 1kHz bandwidth filter
Red line = left channel
Magenta line = right channel

Details

Parent Category: Products

Category: Amplifier Measurements

All amplifier measurements are performed independently by BHK Labs. All measurement data and graphical information displayed below are the property of the SoundStage! Network and Schneider Publishing Inc. Reproduction in any format is not permitted.

Notes: The PS Audio Stellar M700 was measured at 120V AC line voltage at its balanced input, unless otherwise noted. The Audio Precision AUX-0025 external filter was used for all measurements -- again, except as noted.

Power output

• Power output at 1% THD+N: 357.0W @ 8 ohms, 712.0W @ 4 ohms
• Power output at 10% THD+N: 465.0W @ 8 ohms, 930.0W @ 4 ohms

Additional data

• Input/output polarity: noninverting
• AC-line current draw
  • Operate: 20.0W, 0.28A, 0.56PF
  • Standby: 11.0W, 0.18A, 0.52PF
• Gain: output voltage divided by input voltage, 8-ohm load
  • Balanced input: 33.9X, 30.6dB
  • Unbalanced input: 33.9X, 30.6dB
• Input sensitivity for 1W output into 8 ohms
  • Balanced input: 83.4mV
  • Unbalanced input: 83.4mV
• Output impedance @ 50Hz (see text): 0.022/0.0081 ohm
• Input impedance @ 1kHz
  • Balanced input: 98.8k ohms
  • Unbalanced input: 50.0k ohms
• Output noise, 8-ohm load, balanced/unbalanced inputs without AUX-0025 filter
  
  • Wideband: 0.98V, -9.2dBW
• Output noise, 8-ohm load, unbalanced input terminated with 1k ohms
  
  • Wideband: 1.58mV, -65.1dBW
  • A weighted pin 3 of B input open: 179.0uV, -84.0dBW
  • A weighted pin 3 of B input connected to pin 1 (ground): 147.7uV, -85.6dBW
• Output noise, 8-ohm load, balanced input terminated with 600 ohms
  
  • Wideband: 1.57mV, -65.1dBW
  • A weighted: 151.6uV, -85.4dBW

Measurements summary

The M700 mono power amp is a member of PS Audio’s new Stellar line of models. Its circuitry comprises a combination of a special PS Audio Gain Cell front end and a powerful class-D power amp section.

Chart 1 shows the M700’s frequency response with varying loads. Like most class-D circuits, this one has some out-of-band high-frequency peaking. Note that these data were taken without the AUX-0025 external filter, to reveal the amp’s true out-of-band HF response. Note also that the level at the high-frequency end of the chart does not continue to attenuate, due to the almost 1V of switching output noise.

Chart 2 illustrates how the M700’s total harmonic distortion plus noise (THD+N) vs. power varied for 1kHz and SMPTE intermodulation test signals and amplifier output into loads of 8 and 4 ohms. The amount of distortion is low, and is dominated by noise up to about 10W, above which it rises smoothly to the onset of clipping.

The PS Audio’s THD+N as a function of frequency at several different power levels is plotted in Chart 3. Here, the increase in distortion with frequency is rather pronounced.

The M700’s damping factor vs. frequency is shown in Charts 4A and 4B. The amplifier has two sets of output terminals, the wire pairs of each going back to the actual single output of the class-D amplifier. When the damping factor measurement is driven and measured at one of these outputs, the damping factor is lower with a higher output impedance than when measured at the other, undriven output terminals. This difference is due to the resistance of the internal wire pair being driven and measured.

Chart 5 plots the spectrum of the Stellar M700’s harmonic distortion and noise residue of a 10W, 1kHz test signal. The AC line harmonics are below the level of the noise, and the signal harmonics are dominated by low amounts of the second and third harmonics.

Chart 1 - Frequency response of output voltage as a function of output loading

Red line = open circuit
Magenta line = 8-ohm load
Blue line = 4-ohm load
Cyan line = NHT dummy-speaker load

Chart 2 - Distortion as a function of power output and output loading

(Line up at 100W to determine lines)
Top line = 8-ohm SMPTE IM distortion
Second line = 4-ohm SMPTE IM distortion
Third line = 8-ohm THD+N
Bottom line = 4-ohm THD+N

Chart 3 - Distortion as a function of power output and frequency

(4-ohm loading)
Red line = 1W
Magenta line = 10W
Blue line = 100W
Cyan line = 300W
Green line = 600W

Chart 4 - Damping factor as a function of frequency

Chart 4A - measured at output terminals

Damping factor = output impedance divided into 8

Chart 4B - measured at internal output

Damping factor = output impedance divided into 8

Chart 5 - Distortion and noise spectrum

1kHz signal at 10W into an 8-ohm load

Details

Parent Category: Products

Category: Amplifier Measurements

All amplifier measurements are performed independently by BHK Labs. All measurement data and graphical information displayed below are the property of the SoundStage! Network and Schneider Publishing Inc. Reproduction in any format is not permitted.

Notes: All measurements were made at 120V AC line voltage, both channels driven -- and, unless otherwise noted, through the Direct (DIR) balanced input.

Power output

• Power output at 1% THD+N: 595.0W @ 8 ohms, 988.0W @ 4 ohms
• Power output at 10% THD+N: 777.0W @ 8 ohms, 1324.0W @ 4 ohms

Additional data

• Input/output polarity: noninverting
• AC-line current draw
  • Idle: 125W, 1.52A, 0.67PF
  • Standby: 4.0W, 0.06A, 0.52PF
• Gain: output voltage divided by input voltage, 8-ohm load
  • BAL input: 18.21X, 25.2dB
  • RCA input: 18.23X, 25.2dB
  • DIR input: 3.996X, 12.0dB
• Input sensitivity for 1W output into 8 ohms
  • BAL input: 155.3mV
  • RCA input: 155.2mV
  • DIR input:  707.8mV
• Output impedance @ 50Hz: 0.014 ohm
• Input impedance @ 1kHz
  • BAL input: 792k ohms
  • RCA input: 534k ohms
  • DIR input: 78.6k ohms
• Output noise, 8-ohm load, BAL input terminated with 600 ohms
  
  • Wideband: 193.2uV, -83.3dBW
  • A weighted: 72.8uV, -91.8dBW
• Output noise, 8-ohm load, RCA input terminated with 1k ohms
  
  • Wideband: 208.1uV, -82.7dBW
  • A weighted: 74.8uV, -91.6dBW
• Output noise, 8-ohm load, DIR input terminated with 600 ohms
  
  • Wideband: 124.8uV, -87.1dBW
  • A weighted: 67.4uV, -92.5dBW

Measurements summary

The Taurus Mono is a high-powered amplifier in Constellation Audio’s new Revelation Series of models. All Constellation power amps use a unique circuit design comprising MOSFET and JFET devices. The power-output stage uses only N-type devices, driven symmetrically.

Chart 1 shows the frequency response for both the Direct (DIR) and Balanced (BAL) inputs. Since the response deviation for open circuit, 8 ohms, and 4 ohms were virtual overlays, due to the Taurus Mono’s low output impedance, these curves are for an 8-ohm loading.

Chart 2A illustrates how, in DIR mode, the Taurus Mono’s total harmonic distortion plus noise (THD+N) vs. power varies for 1kHz and SMPTE IM test signals and amplifier output load for loads of 8 and 4 ohms. Chart 2B shows the results for BAL mode.

The DIR input’s THD+N as a function of frequency at several different power levels is plotted in Chart 3. The rise in distortion at high frequencies is fairly pronounced.

The Taurus Mono’s damping factor vs. frequency, shown in Chart 4, is relatively high, remaining at 2-3kHz before declining with increasing frequency.

Chart 5 plots the spectrum of harmonic distortion and noise residue of a 10W, 1kHz test signal. The magnitude of the AC-line harmonics is relatively complex and the signal harmonics are dominantly the third harmonic -- a mark of the symmetry of the plus and minus half-cycles of the signal.

Chart 1 - Frequency response of output voltage as a function of output loading

Red line = DIR input 8-ohm loading
Magenta line = BAL input 8-ohm loading

Chart 2 - Distortion as a function of power output and output loading

Chart 2A - DIR input

(Line up at 100W to determine lines)
Top line = 4-ohm SMPTE IM distortion
Second line = 8-ohm SMPTE IM distortion
Third line = 4-ohm THD+N
Bottom line = 8-ohm THD+N

Chart 2B - BAL input

(Line up at 20W to determine lines)
Top line = 4-ohm SMPTE IM distortion
Second line = 4-ohm THD+N
Third line = 8-ohm SMPTE IM distortion
Bottom line = 8-ohm THD+N

Chart 3 - Distortion as a function of power output and frequency

(8-ohm loading)
Red line = 1W
Magenta line = 10W
Blue line = 30W
Green line = 100W
Yellow line = 400W

Chart 4 - Damping factor as a function of frequency

Damping factor = output impedance divided into 8

Chart 5 - Distortion and noise spectrum

1kHz signal at 10W into an 8-ohm load

Details

Parent Category: Products

Category: Amplifier Measurements

All amplifier measurements are performed independently by BHK Labs. All measurement data and graphical information displayed below are the property of the SoundStage! Network and Schneider Publishing Inc. Reproduction in any format is not permitted.

Note: Unless otherwise noted, measurements were taken at the balanced left-channel input, at a line voltage of 120V AC.

Power output

• Power output at 1% THD+N: 60.4W @ 8 ohms, 39.6W @ 4 ohms
• Power output at 10% THD+N: 79.3W @ 8 ohms, 104.5W @ 4 ohms

Additional data

• Input/output polarity: noninverting
• AC-line current draw
  • Operate: 242W, 2.4A, 0.84PF
  • Standby: 1.2W, 0.03A, 0.29PF
• Gain: output voltage divided by input voltage, 8-ohm load (Lch/Rch)
  • Balanced inputs: 17.55X, 24.9dB / 17.43X, 24.8dB
  • Unbalanced inputs: 34.45X, 30.7dB / 34.11X, 30.7dB
• Input sensitivity for 1W output into 8 ohms (Lch/Rch)
  • Balanced inputs: 161.1mV / 162.2mV
  • Unbalanced inputs: 82.1mV / 82.9mV
• Output impedance @ 50Hz: 0.99 ohm
• Input impedance @ 1kHz
  • Balanced inputs: 196k ohms
  • Unbalanced inputs: 92k ohms
• Output noise, 8-ohm load, balanced inputs terminated with 600 ohms, Lch/Rch
  
  • Wideband: 231.3uV/85.5uV, -81.8dBW/-90.3dBW
  • A weighted: 33.8uV/29.8uV, -98.5dBW/-99.6dBW
• Output noise, 8-ohm load, unbalanced inputs terminated with 1k ohms, Lch/Rch
  
  • Wideband: 970.0uV/1000.0uV, -69.3dBW/-69.0dBW
  • A weighted: 200.2uV/200.2uV, -83.0dBW/-83.0dBW

Measurements summary

The VT80 is a power amplifier in Audio Research’s new Foundation Series, which is said to have a new auto-bias arrangement for the output tubes. These tubes are large KT120s, each operated conservatively at a plate dissipation of about 25W.

Chart 1 shows the frequency response of the VT80 with varying loads. An output impedance of about 1 ohm, which is typical of tubed power amps, causes considerable variation of the output level with load. With the NHT dummy speaker load, the variation in output level with frequency is about +0.5/-1.0dB. The high-frequency, -3dB bandwidth is about 60kHz.

Chart 2 illustrates how the VT80’s total harmonic distortion plus noise (THD+N) vs. power varies for 1kHz and SMPTE intermodulation test signals and amplifier output load for 8- and 4-ohm loads at the 8-ohm output tap. The distortion in this plot starts to rise quickly above 10-20W, depending on the load. Interestingly, the distortion with a 4-ohm load at the 8-ohm tap begins to rise at about 10W, and at 20W for an 8-ohm load on the 8-ohm tap. Note that a load of 4 ohms on the 4-ohm tap would produce a level of distortion similar to that produced by an 8-ohm load on the 8-ohm tap in the chart.

Chart 3 plots the VT80’s THD+N as a function of frequency at several different power levels. The increase of distortion with frequency is reasonable, and the very-low-frequency region shows more distortion at higher power levels.

Chart 4 plots the VT80’s damping factor vs. frequency. The quite low damping factor is typical of tubed power amplifiers, is constant over quite a wide frequency range, and begins to decrease at about 4kHz.

A spectrum of the residue of harmonic distortion and noise of a 10W, 1kHz test signal is plotted in Chart 5. AC-line harmonics are quite complex in frequency content. The signal harmonics are dominated by the second and third harmonics, with decreasing amounts of lower-level higher harmonics.

Chart 1 - Frequency response of output voltage as a function of output loading

Red line = open circuit
Magenta line = 8-ohm load
Blue line = 4-ohm load
Cyan line = NHT dummy speaker load

Chart 2 - Distortion as a function of power output and output loading

(Line up at 20W to determine lines)
Top line = 4-ohm SMPTE IM distortion
Second line = 4-ohm THD+N
Third line = 8-ohm SMPTE IM distortion
Bottom line = 8-ohm THD+N

Chart 3 - Distortion as a function of power output and frequency

(8-ohm loading)
Red line = 1W
Magenta line = 10W
Blue line = 30W
Cyan line = 60W
Green line = 75W

Chart 4 - Damping factor as a function of frequency

Damping factor = output impedance divided into 8

Chart 5 - Distortion and noise spectrum

1kHz signal at 10W into an 8-ohm load

Details

Parent Category: Products

Category: Amplifier Measurements

All amplifier measurements are performed independently by BHK Labs. All measurement data and graphical information displayed below are the property of the SoundStage! Network and Schneider Publishing Inc. Reproduction in any format is not permitted.

Note: Measurements were taken of both channels of the Parasound Halo A 23+ at 120V AC line voltage, both channels driven, at the balanced and unbalanced inputs. Except as noted, discussed below are the results for the unbalanced inputs and the left channel.

Power output (stereo mode) @ 1kHz

• Power output at 1% THD+N: 191.9W @ 8 ohms, 275.1W @ 4 ohms
• Power output at 10% THD+N: 229.3W @ 8 ohms, 337.6W @ 4 ohms

Power output (mono mode) @ 1kHz

• Power output at 1% THD+N: 526.1W @ 8 ohms
• Power output at 10% THD+N: 693.4W @ 8 ohms

Additional data

• Input/output polarity: noninverting
• AC-line current draw at idle: 60.0W, 0.73A, 0.68PF
• Gain: output voltage divided by input voltage, 8-ohm load
  • Stereo mode
    • Balanced input: 28.5X, 29.1dB
    • Unbalanced input: 29.2X, 29.3dB
  • Mono mode
    • Balanced input: 57.6X, 35.2dB
    • Unbalanced input: 56.4X, 34.7dB
• Input sensitivity for 1W output into 8 ohms
  • Stereo mode
    • Balanced input: 99.2mV
    • Unbalanced input: 96.9mV
  • Mono mode
    • Balanced input: 49.1mV
    • Unbalanced input: 50.1mV
• Output impedance @ 50Hz
  • Stereo mode: 0.005 ohm
  • Mono mode: 0.009 ohm
• Input impedance @ 1kHz
  • Stereo mode
    • Balanced inputs: 97.0k ohms
    • Unbalanced inputs: 50.0k ohms
  • Mono mode
    • Balanced input: 97.0k ohms
    • Unbalanced input: 50.0k ohms
• Output noise (stereo mode), 8-ohm load, balanced inputs terminated with 600 ohms, Lch/Rch
  • Wideband: 0.335mV/0.244mV, -78.5dBW/-82.0dBW
  • A weighted: 0.116mV/0.085mV, -87.7dBW/-90.4dBW
• Output noise (stereo mode), 8-ohm load, unbalanced inputs terminated with 1k ohms, Lch/Rch
  
  • Wideband: 0.322mV/0.228mV, -78.9dBW/-81.9dBW
  • A weighted: 0.116mV/0.082mV, -87.7dBW/-90.8dBW
• Output noise (mono mode), 8-ohm load, balanced inputs terminated with 600 ohms
  • Wideband: 0.454mV, -75.9dBW
  • A weighted: 0.189mV, -83.5dBW
• Output noise (mono mode), 8-ohm load, unbalanced inputs terminated with 1k ohms
  • Wideband: 0.438mV, -76.2dBW
  • A weighted: 0.179mV, -84.0dBW

Measurements summary

The Halo A 23+, an update of the Halo A 23, is the lowest-powered amplifier model in Parasound’s Halo line. Because the A 23+ can be switched between stereo and bridged mono, some measurements were taken in both modes. In the charts below, the suffix A indicates measurements taken in stereo mode, the suffix B measurements taken in bridged mono.

Charts 1A and 1B show the Halo A 23+’s frequency response with varying loads. Chart 1A shows both channels, as between them there is a small difference in gain. Because the A 23+’s output regulation is so tight, only the 8-ohm loading is shown; the other loadings look the same. Note the greater high-frequency rolloff in bridged mode, due to the series connected nature of the load in bridged-mono mode.

Chart 2A illustrates how the Halo A 23+’s total harmonic distortion plus noise (THD+N) vs. power varies for 1kHz and SMPTE intermodulation test signals and amplifier output load with loads of 8 and 4 ohms. Chart 2B shows only the results in bridged mode for a load of 8 ohms -- the Halo A 23+ is not specified for use with 4-ohm loads in bridged mode.

The Halo A 23+’s THD+N as a function of frequency at several different power levels is plotted in Charts 3A and 3B. The increase in high-frequency distortion with frequency is moderate, and distortion remains reasonably low through most of the power range in both stereo and bridged-mono modes.

Chart 4 shows that the Parasound’s damping factor vs. frequency is of a value and nature typical of many solid-state amplifiers: high up to 1-2kHz, then rolling off with frequency. Not unexpectedly, the damping factor was lower in bridged mono, due to the fact that in this mode each channel’s output impedance is doubled.

Chart 5, the spectrum of the residue of harmonic distortion and noise of a 10W, 1kHz test signal, reveals a lot of line-frequency harmonics of significant amplitude. The signal harmonics are dominated by the second harmonic, with higher harmonics of significantly lower amplitude.

Chart 1 - Frequency response of output voltage as a function of output loading

Chart 1A - stereo mode

Stereo mode
Red line = Lch 8-ohm load (open circuit and 4-ohm loading look the same)
Blue line = Rch 8-ohm load (open circuit and 4-ohm loading look the same)

Chart 1B - mono mode

Mono mode
Red line = 8-ohm load (open circuit and 4-ohm loading look the same)

Chart 2 - Distortion as a function of power output and output loading

Chart 2A - stereo mode

Stereo mode
(Line up at 70W to determine lines)
Top line = 8-ohm SMPTE IM distortion
Second line = 4-ohm THD+N distortion
Third line = 8-ohm THD+N
Bottom line = 4-ohm SMPTE IM distortion

Chart 2B - mono mode

Mono mode
(Line up at 70W to determine lines)
Top line = 8-ohm SMPTE IM distortion
Second line = 8-ohm THD+N

Chart 3 - Distortion as a function of power output and frequency

Chart 3A - stereo mode

Stereo mode
(8-ohm loading)
Red line = 1W
Magenta line = 10W
Blue line = 30W
Cyan line = 160W

Chart 3B - mono mode

Mono mode
(8-ohm loading)
Red line = 1W
Magenta line = 10W
Blue line = 30W
Green line = 200W
Yellow line = 400W
Cyan line = 600W

Chart 4 - Damping factor as a function of frequency

Stereo mode
Damping factor = output impedance divided into 8

Chart 5 - Distortion and noise spectrum

Stereo mode
1kHz signal at 10W into an 8-ohm load