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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.

Unless otherwise noted, these measurements were taken at the left-channel unbalanced analog inputs of the Exogal Ion PowerDAC at 120V AC line voltage, both channels driven. I used the old IHF standard for integrated amplifiers, in which the volume control is set so that a 500mV analog input signal produces a nominal output of 5W into 8 ohms. Unless stated otherwise, I used Audio Precision’s Aux-0025 external filter.

- Power output at 1% THD+N: 80.0W @ 8 ohms, >100.0W @ 4 ohms
- Power output at 10% THD+N: 100.0W @ 8 ohms, >100.0W @ 4 ohms

- Input/output polarity
- Analog input: inverting
- Digital input: noninverting

- AC-line current draw
- Standby: 9.0W, 0.17A, 0.44PF
- Operating: 25.0W, 0.31A, 0.68PF

- Gain: output voltage divided by input voltage, 8-ohm load (Lch/Rch)
- Unbalanced inputs: 36.70X, 37.7dB / 36.18X, 37.7dB

- Input sensitivity for 1W output into 8 ohms (Lch/Rch)
- Unbalanced inputs: 77.1mV / 78.3mV

- Output impedance @ 50Hz: 0.065 ohm
- Input impedance @ 1kHz
- Unbalanced inputs: 1.87k ohms

- Output noise at reference conditions, 8-ohm load, unbalanced inputs terminated with 1k ohms, Lch/Rch

- Wideband: 0.352mV/0.350mV, -78.1dBW/-78.2dBW
- A weighted: 0.142mV/0.142mV, -86.0dBW/-86.0dBW

- Output noise with volume at maxium, 8-ohm load, unbalanced inputs terminated with 1k ohms, Lch/Rch

- Wideband: 127.2mV/128.3V, -26.9dBW/-26.8dBW
- A weighted: 1.95mV/1.89mV, -63.2dBW/-63.5dBW

- Output noise with volume at minimum, 8-ohm load, unbalanced inputs terminated with 1k ohms, Lch/Rch

- Wideband: 0.352V/0.350V, -78.1dBW/-78.2dBW
- A weighted: 0.142mV/0.142mV, -86.0dBW/-86.0dBW

Exogal’s Ion PowerDAC is an unusual combination of a DAC and line stage (the Comet) coupled to a DAC and switching power amp (the Ion). I used the unbalanced analog inputs of the Comet to test the combination as an integrated amplifier.

It was difficult to measure some things on the Ion PowerDAC, including its maximum power and damping factor. The Exogal’s very sensitive protection circuit frequently shut it down, requiring a restart, and the damping factor was affected by some interference from the untested right channel.

Chart 1A shows the frequency response of the Ion PowerDAC with varying loads and with my usual vertical scale. The FR is strongly dependent on the load, as is typical of switching-amp designs. With resistive loading, the -3dB bandwidth for an 8-ohm load extends slightly higher than 20kHz; with a 4-ohm load, the bandwidth is 11-12kHz. Chart 1B shows the Exogal’s high-frequency response out to 30kHz: It rolls off pretty quickly and, with the open circuit loading, peaks at over +10dB. This will probably not be a problem with non-inductive tweeters, but with a typical moving-coil tweeter, the Ion PowerDAC may produce a high-frequency rise in the top octave of the audioband: 10-20kHz.

To test the tracking of the Exogal’s volume control, I used a 1kHz test tone; the reference volume was the 5W output with a 500mV input signal. The volume-control tracking was within a few tenths of a dB down to -60dB.

Chart 2 illustrates how the Ion PowerDAC’s total harmonic distortion plus noise (THD+N) vs. power varied for 1kHz and SMPTE intermodulation (IM) test signals and amplifier output for 8- and 4-ohm loads. As mentioned above, it was not possible to get full distortion data because of the behavior of the Exogal’s protection circuit. The THD+N of the 1kHz test signal was pretty good, but the IM distortion was unusually high throughout the range I was able to measure.

The Ion PowerDAC’s THD+N as a function of frequency at different power levels is plotted in Chart 3. To reduce the out-of-band noise, I had to use the regular Audio Precision low-pass filter set to 30kHz instead of the usual 80kHz, and a 40kHz sharp cutoff filter to keep the distortion measurement uncontaminated by noise throughout most of the audioband. Any rise in high-frequency distortion is therefore masked above about 10kHz. At the 70W level, the amount of distortion rises precipitously below 100Hz and above about 15kHz.

It wasn’t possible to take my usual measurements of damping factor vs. frequency. What can be deduced from Chart 1A is that the damping factor is reasonably high at low frequencies, at around 123, and decreases rapidly above about 1kHz -- as can be seen in the divergence of the curves above that frequency.

Chart 5 plots the spectrum of the harmonic distortion and noise residue of a 10W, 1kHz test signal sent through the Exogal. The magnitudes of the AC line harmonics are not visible in what is a relatively high level of background noise throughout the audioband. The signal harmonics are mainly the third, fifth, and seventh, with lower-level, higher-order harmonics above 10kHz.

1A

Red line = open circuit

Magenta line = 8-ohm load

Blue line = 4-ohm load

Cyan line = NHT dummy-speaker load

1B

Red line = open circuit

Magenta line = 8-ohm load

Blue line = 4-ohm load

Cyan line = NHT dummy-speaker load

(Line up at 20W 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

(8-ohm loading)

Red line = 1W

Magenta line = 10W

Blue line = 30W

Cyan line = 70W

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

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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 a line voltage of 120V AC at the left-channel balanced input, with the Audio Precision AUX-0025 filter engaged.

- Power output at 1% THD+N: 164.7W @ 8 ohms, 302.4W @ 4 ohms
- Power output at 10% THD+N: 230.0W @ 8 ohms, 395.0W @ 4 ohms

- Input/output polarity: noninverting
- AC-line current draw at idle: 14.0W, 0.23A, 0.51PF
- Gain: output voltage divided by input voltage, 8-ohm load (Lch/Rch)
- Balanced inputs: 15.36X, 23.7dB / 15.28X, 23.7dB
- Unbalanced inputs: 30.81X, 29.8dB / 30.48X, 29.7dB

- Input sensitivity for 1W output into 8 ohms (Lch/Rch)
- Balanced inputs: 184mV / 185mV
- Unbalanced inputs: 91.8mV / 92.8mV

- Output impedance @ 50Hz: 0.018 ohm
- Input impedance @ 1kHz
- Balanced inputs: 21.4k ohms
- Unbalanced inputs: 10.3k ohms

- Output noise, 8-ohm load, balanced inputs terminated with 600 ohms, Lch/Rch

- Wideband: 0.849mV/0.857mV, -70.5dBW/-70.4dBW
- A weighted: 0.050mV/0.050mV, -95.0dBW/-95.0dBW

- Output noise, 8-ohm load, unbalanced inputs terminated with 1k ohms, Lch/Rch

- Wideband: 0.882mV/0.890mV, -70.1dBW/-70.0dBW
- A weighted: 0.065mV/0.066mV, -92.8dBW/-92.6dBW

- Output noise, 8-ohm load, without AP AUX-0025 filter, unbalanced and balanced inputs

- Wideband: 498mV, -15.1dBW

The Wadia a315 is a medium-power, two-channel, switching power amplifier that includes the latest Hypex Electronics Ncore technology.

Chart 1, which shows the a315’s frequency response into varying loads, was not sent through the Audio Precision AUX-0025 low-pass measuring filter. One of the interesting aspects of the Ncore technology is that the out-of-band high-frequency response is controlled by an output LCR filter in the overall feedback loop. Of interest in the shapes of the curves is that, just above 20kHz, the output impedance goes from normal positive (output drops with increasing load) to negative, with the greatest deviation of response at 40kHz, then passes through a close-to-zero output-impedance point at 60kHz, above which the output impedance becomes positive again. Within the audioband, the output impedance is low enough that there is negligible variation with the NHT dummy speaker load.

Chart 2 illustrates how the a315’s total harmonic distortion plus noise (THD+N) vs. power varies with 1kHz and SMPTE intermodulation test signals, and with 8- and 4-ohm loads. The level of distortion indicated is reasonably low.

THD+N as a function of frequency at different power levels is plotted in Chart 3. The increase in distortion with frequency is moderate. Still, the level of distortion is low over most of the power and frequency range.

Damping factor vs. frequency is shown in Chart 4. The damping factor remains moderately high throughout the audioband, and, unlike with most power amps, does not roll off severely above 500-1000Hz.

Chart 5 plots the spectrum of the harmonic distortion and noise residue of a 10W, 1kHz test signal. The AC line harmonics are low, their principal component being 60Hz. The signal harmonics are dominated by the second and third harmonics, with higher harmonics of rapidly decreasing magnitude.

Red line = open circuit

Magenta line = 8-ohm load

Blue line = 4-ohm load

(Line up at 50W 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

(8-ohm loading)

Red line = 1W

Magenta line = 10W

Blue line = 30W

Cyan line = 70W

Green line = 130W

Yellow line = 150W

Stereo mode

Damping factor = output impedance divided into 8

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

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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 on the left-channel balanced input at 120V AC line voltage.

- Power output at 1% THD+N: 130.0W @ 8 ohms, 195.9W @ 4 ohms
- Power output at 10% THD+N: 157.1W @ 8 ohms, 241.0W @ 4 ohms

- Power output at 1% THD+N: 405.0W @ 8 ohms
- Power output at 10% THD+N: 480.0W @ 8 ohms

- Input/output polarity: noninverting
- AC-line current draw at idle: 31.0W, 0.53A, 0.48PF
- Gain: output voltage divided by input voltage, 8-ohm load (balanced/unbalanced inputs)
- Stereo mode: 32.2X, 30.2dB
- Mono mode: 64.5X, 36.2dB

- Input sensitivity for 1W output into 8 ohms (balanced/unbalanced inputs)
- Stereo mode: 87.7mV
- Mono mode: 43.8mV

- Output impedance @ 50Hz
- Stereo mode: 0.003 ohm
- Mono mode: 0.0035 ohm

- Input impedance @ 1kHz (stereo/mono modes)
- Balanced input: 90.0k ohms
- Unbalanced input: 45.0k ohms

- Output noise (stereo mode), 8-ohm load, balanced inputs terminated with 600 ohms, Lch/Rch

- Wideband: 0.15mV/0.15mV, -85.6dBW/-85.8dBW
- A weighted: 0.069mV/0.060mV, -92.3dBW/-93.5dBW

- Output noise (stereo mode), 8-ohm load, unbalanced inputs terminated with 1k ohms, Lch/Rch

- Wideband: 0.18mV/0.15mV, -83.9dBW/-85.5dBW
- A weighted: 0.12mV/0.062mV, -87.4dBW/-93.1dBW

- Output noise (mono mode), 8-ohm load, balanced inputs terminated with 600 ohms

- Wideband: 0.20mV, -82.9dBW
- A weighted: 0.083mV, -90.7dBW

- Output noise (mono mode), 8-ohm load, unbalanced inputs terminated with 1k ohms
- Wideband: 0.23mV, -81.9dBW
- A weighted: 0.13mV, -84.0dBW

The Simaudio Moon Neo 330A is a medium-power stereo amplifier with a conventional linear power supply and bipolar output devices. It can be bridged to function as a mono power amp by using Simaudio’s special balanced bridge cable, which reverses the signal phase of the left channel to make the outputs of the two stereo channels out of phase. As usual in mono mode, the load is connected between the two plus outputs of the stereo channel outputs.

Chart 1 shows the frequency response of the Moon Neo 330A with varying loads. The output impedance is low enough that there was negligible variation with the NHT dummy speaker load.

Chart 2A illustrates how total harmonic distortion plus noise (THD+N) vs. power varies for 1kHz and SMPTE intermodulation (IM) test signals and amplifier output load for loads of 8 and 4 ohms. The output power is a bit shy of specification into 4 ohms. In contrast to most amplifier measurements at the lower levels that are noise dominated, the Moon Neo 330A has actual distortion at 100mW that remains reasonably constant over most of the power range.

Chart 2B is a plot of THD+N for 1kHz and SMPTE IM test signals into 8 ohms. The Moon Neo 330A was not measured into 4 ohms in mono mode, as the load per channel would have been 2 ohms. This surely would have triggered its protection circuit, and the stock 5A, normal-blow AC line fuse would likely have blown.

THD+N as a function of frequency at several different power levels is plotted in Chart 3. The amount of increase in distortion with frequency is typical of many amplifiers. Also, the low-frequency region begins to be more distorted at the higher power levels. The protection circuit was triggered at the points on the graph at the low-frequency area where the trace stops shy of reaching 10Hz -- these sweeps begin at the high-frequency end and end up at 10Hz.

The Moon Neo 330A’s damping factor vs. frequency (Chart 4A) is of a shape typical of most power amplifiers. Measured in mono mode, the shape was quite a bit different for reasons I don’t understand (Chart 4B).

A spectrum of the harmonic distortion and noise residue of a 10W, 1kHz test signal is plotted in Chart 5. The AC line harmonics are a bit high and complex. The right channel (not shown) was quite a bit better. Signal harmonics are dominated by the second, third, fourth, and fifth harmonics, with higher harmonics of decreasing magnitude.

Stereo mode

Red line = open circuit

Magenta line = 8-ohm load

Blue line = 4-ohm load

Chart 2A

Stereo mode

(Line up at 100W to determine lines)

Top line = 8-ohm SMPTE IM distortion

Second line = 8-ohm SMPTE IM distortion

Third line = 8-ohm THD+N

Bottom line = 4-ohm THD+N

Chart 2B

Mono mode

(Line up at 100W to determine lines)

Top line = 8-ohm SMPTE IM distortion

Second line = 8-ohm THD+N

Stereo mode

(4-ohm loading)

Red line = 1W

Magenta line = 30W

Blue line = 75W

Cyan line = 150W

Yellow line = 200W

Chart 4A

Stereo mode

Damping factor = output impedance divided into 8

Chart 4B

Mono mode

Damping factor = output impedance divided into 8

Stereo mode

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

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Note: Unless otherwise noted, measurements were taken at 120V AC line voltage, at the balanced input, and with the Audio Precision AUX-0025 measurement filter.

- Power output at 1% THD+N: 380.0W @ 8 ohms, 643.0W @ 4 ohms
- Power output at 10% THD+N: 489.0W @ 8 ohms, 841.0W @ 4 ohms

- Input/output polarity: noninverting
- AC line current draw at idle: 25.0W, 0.44A, 0.47PF
- Gain: output voltage divided by input voltage, 8-ohm load
- Unbalanced input: 24.1X, 27.6dB
- Balanced input: 24.1X, 27.6dB

- Input sensitivity for 1W output into 8 ohms
- Unbalanced input: 117.3mV
- Balanced input: 117.3mV

- Output impedance @ 50Hz: 0.0033 ohm
- Input impedance @ 1kHz
- Unbalanced input: 92.5k ohms
- Balanced input: 92.5k ohms

- Output noise, 8-ohm load, unbalanced inputs terminated with 1k ohms

- Wideband: 0.600mV, -73.5dBW
- A weighted: 0.0264mV, -100.6dBW

- Output noise, 8-ohm load, balanced inputs terminated with 600 ohms

- Wideband: 0.597mV, -73.5dBW
- A weighted: 0.026mV, -100.7dBW

- Output noise, 8-ohm load, unbalanced inputs terminated with 1k ohms, without the AP AUX-0025 filter

- Approx. 450kHz: 448.0mV, -16.0dBW

- Output noise, 8-ohm load, balanced inputs terminated with 600 ohms, without the AP AUX-0025 filter

- Approx. 450kHz: 448.0mV, -16.0dBW

The Mola Mola Kaluga is a switching power amplifier that uses the latest Hypex Electronics Ncore technology.

Chart 1 shows the Kaluga’s frequency response with varying loads. One of the interesting aspects of the Ncore technology is its amazing independence from load in the high-frequency region; this is in contrast to many switching-amplifier designs. Here, though, there is a significant anomaly between 50 and 60kHz. Of interest is the regulation of the output -- which, as indicated by the closeness of the three curves, is very good before the anomaly and uniformly poorer after. The output impedance within the audioband is low enough that there was negligible variation with the NHT dummy speaker load.

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

Chart 3 plots the Mola Mola’s THD+N as a function of frequency at different power levels. The increase in distortion with frequency is pronounced. Also, the low-frequency region begins to distort more at higher power levels. Still, the levels of distortion are very low through most of the power and frequency ranges.

The Kaluga’s damping factor vs. frequency is shown in Chart 4. The damping factor is very high, and is still about 1000 even at 20kHz. Fantastic! However, as mentioned in the description of Chart 1, things are quite different above the audioband, especially above about 50kHz.

Chart 5 shows the spectrum of the residue of harmonic distortion and noise of a 10W, 1kHz test signal. The AC-line harmonics are very low, and are mostly odd harmonics of 60Hz. The signal harmonics are dominated by the third harmonic, with higher harmonics of rapidly decreasing magnitude.

Red line = open circuit

Magenta line = 8-ohm load

Blue line = 4-ohm load

(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

(8-ohm loading)

Red line = 1W

Magenta line = 10W

Blue line = 70W

Cyan line = 150W

Yellow line = 300W

Stereo mode

Damping factor = output impedance divided into 8

Stereo mode

1kHz signal at 10W into a 4-ohm load

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Unless otherwise noted, measurements were taken at the balanced input and at 120V AC line voltage, with the Audio Precision AUX-0025 measurement filter.

- Power output at 1% THD+N: 358.4W @ 8 ohms, 658.4W @ 4 ohms
- Power output at 10% THD+N: 452.7W @ 8 ohms, 852.4W @ 4 ohms

- Input/output polarity: noninverting
- AC line current draw at idle: 16.0W, 0.32A, 0.44PF
- Gain: output voltage divided by input voltage, 8-ohm load
- Unbalanced input: 22.5X, 27.0dB
- Balanced input: 22.3X, 27.0dB

- Input sensitivity for 1W output into 8 ohms
- Unbalanced input: 125.7mV
- Balanced input: 126.9mV

- Output impedance @ 50Hz: 0.03 ohm
- Input impedance @ 1kHz
- Unbalanced input: 92.5k ohms
- Balanced input: 92.5k ohms

- Output noise, 8-ohm load, unbalanced inputs terminated with 1k ohms

- Wideband: 0.471mV, -75.6dBW
- A weighted: 0.022mV, -102.2dBW

- Output noise, 8-ohm load, balanced inputs terminated with 600 ohms

- Wideband: 0.476mV, -75.5dBW
- A weighted: 0.0206mV, -102.8dBW

- Output noise, 8-ohm load, unbalanced inputs terminated with 1k ohms, without the AP AUX-0025 filter

- 462kHz: 423.0mV, -16.5dBW

- Output noise, 8-ohm load, balanced inputs terminated with 600 ohms, without the AP AUX-0025 filter

- 462kHz: 423.0mV, -16.5dBW

The Bel Canto Design REF600M mono power amp is a switching design using the latest Hypex Ncore technology.

Chart 1 shows the REF600M’s frequency response with varying loads. One of the interesting aspects of the Ncore technology, in contrast to many other switching-amplifier designs, its amazing independence from load in the high frequencies. Here, though, there is a little anomaly between 50 and 60kHz. The output impedance is low enough that there was negligible variation with the NHT dummy speaker load.

Chart 2 illustrates how the REF600M’s total harmonic distortion plus noise (THD+N) vs. power varies for 1kHz and SMPTE intermodulation test signals and amplifier output for loads of 8 and 4 ohms. The amount of distortion visible in this plot is quite low.

The Bel Canto’s THD+N as a function of frequency at different power levels is plotted in Chart 3. The rise in distortion with increasing frequency is quite pronounced, and the low-frequency region also shows more distortion at higher power levels.

The REF600M’s damping factor vs. frequency (Chart 4) is somewhat lower than Bel Canto’s specified >1000. My measurements of some other amplifiers have resulted in values higher than 1000, so I know the measurement technique is valid. However, of considerable interest is that the damping factor’s “bandwidth” is quite a bit wider than with most amplifiers.

Chart 5 plots a spectrum of the Bel Canto’s harmonic distortion and noise residue of when fed a 10W, 1kHz test signal. The AC line harmonics are extremely low and relatively simple. The signal harmonics are dominated by the third and second harmonic, with higher harmonics of decreasing magnitude.

Red line = open circuit

Magenta line = 8-ohm load

Blue line = 4-ohm load

(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

(4-ohm loading)

Red line = 1W

Magenta line = 10W

Blue line = 70W

Cyan line = 150W

Green line = 300W

Yellow line = 500W

Stereo mode

Damping factor = output impedance divided into 8

Stereo mode

1kHz signal at 10W into a 4-ohm load

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Measurements were taken at 120V AC line voltage with both channels driven, and on both channels using balanced inputs. Unless otherwise noted, all results cited are for the left channel. The integrated amplifier reference volume setting was 500mV input (5W/8-ohm power output).

- Output power at 1% THD+N: 231.1W @ 8 ohms, 468.3 @ 4 ohms
- Output power at 10% THD+N: 281.3W @ 8 ohms, 564.7W @ 4 ohms

- This amplifier does not invert polarity.
- AC line current draw at idle: 1.02A, 0.63PF, 78.0W
- Gain: output voltage divided by input voltage
- Unbalanced inputs: 44.5X, 33.0dB
- Balanced inputs: 44.5X, 33.0dB

- Input sensitivity for 1W output into 8 ohms
- Unbalanced inputs: 43.5mV
- Balanced inputs: 43.5mV

- Output impedance @ 50Hz: 0.015 ohm
- Input impedance @ 1kHz
- Unbalanced inputs: 6.7k ohms
- Balanced inputs: 9.7k ohms

- Output noise, reference conditions, balanced inputs, termination 600 ohms, Lch/Rch
- Wideband: 0.561mV/0.580mV, -74.1dBW/-73.8dBW
- A weighted: 0.0745mV/0.0862mV, -91.6dBW/-90.3 dBW

- Output noise, reference conditions, unbalanced inputs, termination 1k ohm, Lch/Rch
- Wideband: 0.546mV/0.569mV, -74.3dB/-73.9dBW
- A weighted: 0.0706mV/0.0803mV, -92.1dBW/-90.4dBW

- Output noise, 8-ohm load, volume at maximum, balanced inputs, termination 600 ohms, Lch/Rch
- Wideband: 0.652mV/0.707mV, -72.4dBW/-72.0dBW
- A weighted: 0.155mV/0.141mV, -87.8dBW/-86.1dBW

- Output noise, 8-ohm load, volume at maximum, unbalanced inputs, termination 1k ohm, Lch/Rch
- Wideband: 0.410mV/0.457mV, -76.8dBW/-75.8dBW
- A weighted: 0.0618mV/0.0784mV, -93.2dBW/-91.1dBW

- Output noise, 8-ohm load, volume at minimum, balanced inputs, termination 600 ohms, Lch/Rch
- Wideband: 0.403dBW/0.422mV, -76.9dBW/-76.5dBW
- A weighted: 0.0533mW/0.0655mV, -94.5dBW/-92.7dBW

- Output noise, 8-ohm load, volume at minimum, unbalanced inputs, termination 1k ohm, Lch/Rch
- Wideband: 0.405mV/0.422mV, -76.9dBW/-75.5dBW
- A weighted: 0.0533mV/0.0645mV, -94.5dBW/-92.8dBW

The H360 DAC-integrated amplifier builds on the success of Hegel’s H300, adding network-playing capability and AirPlay. The power outputs of the two models are similar.

Chart 1 shows the frequency response of the H360 with varying impedance loads. The output impedance is low enough that there was negligible variation with the NHT dummy speaker load.

Chart 2 illustrates how the H360’s total harmonic distortion plus noise (THD+N) vs. power varies for 1kHz and SMPTE intermodulation test signals and amplifier output for 8- and 4-ohm loads.

Chart 3 plots the THD+N as a function of frequency at several different power levels. As the power level is increased, the increase in distortion with frequency is quite pronounced.

The H360’s damping factor vs. frequency is shown in Chart 4. Like the H300, the H360 shows a typical decrease as the frequency increases, but with a surprising decrease at low frequencies. Perhaps Hegel has discovered something by having this characteristic -- that it possibly improves the sound?

A spectrum of the harmonic distortion and noise residue of a 10W, 1kHz test signal is plotted in Chart 5. The AC-line harmonics are low but relatively complex. The signal harmonics are dominated by the third harmonic, with second and higher harmonics of decreasing magnitude.

Some key measurements were taken of the H360’s digital section. The Coax 1 input was fed a full-scale, 0dBFS digital signal and the main amplifier outputs were set as close to 5W/8 ohms as possible with the volume control. At a sample rate of 192kHz, the frequency response was the same as at a sample rate of 96kHz. I have seen this behavior in a few other DACs. This means that files at sample rates of 176.4 and 192kHz won’t be played back with the extended high-frequency response such files can contain. Chart 6 is a plot of this response.

A revealing test that I always do on a DAC is to measure the THD+N of a 1kHz signal in a 20Hz-22kHz bandwidth at full-scale digital level with decreasing input signal level, down to where the distortion disappears into the noise floor. Doing this revealed that the H360’s noise floor was about -84dBFS, which is equivalent to about 0.42mV, -76.6dBW of output noise dominated by AC-line harmonics. This is somewhat more than with the analog inputs.

Red line = open circuit

Magenta line = 8-ohm load

Blue line = 4-ohm load

(Line up at 10W 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

(8-ohm loading)

Red line = 1W

Magenta line = 10W

Blue line = 30W

Cyan line = 70W

Green line = 200W

Damping factor = output impedance divided into 8

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

Red line = 44.1kHz

Magenta line = 96 and 192kHz

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Notes: The Cyrus Stereo 200 power amplifier was measured at 120V AC line voltage, both channels driven, using its balanced inputs. Measurements were taken for both channels, but unless noted otherwise, the results reported below are for the left channel only. Because the Stereo 200 is a switching amplifier, measurements were made with the Audio Precision AUX-0025’s low-pass filter, except as noted.

- Power output at 1% THD+N: 174.3W @ 8 ohms, 262.4W @ 4 ohms
- Power output at 10% THD+N: 220.0W @ 8 ohms, 345.0W @ 4 ohms

- Input/output polarity: noninverting
- AC-line current draw at idle: 26.3W, 0.30A, 0.74PF
- Gain: output voltage divided by input voltage, 8-ohm load (Lch/Rch): 26.4X/26.2X, 28.4dB/28.4dB
- Input sensitivity for 1W output into 8 ohms (Lch/Rch): 107mV/107mV
- Output impedance @ 50Hz: 0.028 ohm
- Input impedance @ 1kHz (Lch/Rch): 62.8k ohms/60.1k ohms
- Output noise, 8-ohm load, balanced inputs, termination 600 ohms (Lch/Rch)

- Wideband without AUX-0025: 1.86V/1.92mV, -3.64dBW/-3.36dBW
- Wideband with AUX-0025: 3.94mV/4.0mV, -57.1dBW/-57.0dBW
- A weighted: 0.114mV/0.124mV, -87.9dBW/-87.1dBW

The Stereo 200’s switching-amplifier output circuit is powered by a conventional nonswitching power supply. It has a unique circuit for adjusting the output filter to the optimal conditions for the speaker load used.

Chart 1 shows the frequency response of the Stereo 200 with varying loads. This was done by going through the output-filter startup program with 8-ohm resistive loads. As can be seen, the curve for the 8-ohm load is the flattest, with more rolloff for a 4-ohm load, and some pretty bad peaking with an open-circuit load. The NHT dummy speaker load is nicely contained within about +/-0.8dB throughout the audioband.

Chart 2 illustrates how the Stereo 200’s total harmonic distortion plus noise (THD+N) vs. power varies for 1kHz and SMPTE intermodulation (IM) test signals and amplifier output for loads of 8 and 4 ohms. The THD+N curves have some strange kinks on the way up to clipping. The IM curves show significant increases in the amount of distortion in the 5-30W range; these are worse for the 4-ohm load.

THD+N as a function of frequency at several different power levels is plotted in Chart 3. The Cyrus Stereo 200 had some trouble producing high-frequency power. I had to modify the Audio Precision’s settling routines from the normal exponential settling to no settling to get the measurements I did get. The amount of HF rise is pretty substantial; I felt I had to stop at a 30W power level to avoid damaging the review sample.

Chart 4 plots the Stereo 200’s damping factor vs. frequency. Although it seems typical of many amplifiers -- high at low frequencies, then declining over the audioband -- it begins to decrease at 50Hz, which is quite a bit lower than the norm, and declines to a very low value at 20kHz.

A spectrum of the harmonic distortion and noise residue of a 10W, 1kHz test signal is plotted in Chart 5. The magnitudes of the AC line harmonics are about as low as I have seen in any amplifier, showing no really identifiable line frequency harmonics. The signal harmonics are also low, and consist mainly of a declining series of odd harmonics.

Red line = open circuit

Magenta line = 8-ohm load

Blue line = 4-ohm load

Cyan line = NHT dummy-speaker load

(Line up at 50W 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

(8-ohm loading)

Red line = 1W

Magenta line = 5W

Blue line = 10W

Cyan line = 30W

Stereo mode

Damping factor = output impedance divided into 8

Stereo mode

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

- Details
- Parent Category: Products
- Category: Amplifier Measurements

Notes: Measurements of the NAD C 275BEE power amplifier were taken at 120V AC line voltage, both channels driven. Both channels were measured, using the fixed-level inputs. Unless otherwise indicated, the data reported below are for the right channel.

- Power output at 1% THD+N: 192.0W @ 8 ohms, 201.0W @ 4 ohms
- Power output at 10% THD+N: 203.8W @ 8 ohms, 243.8W @ 4 ohms

- Power output at 1% THD+N: 354.1W @ 8 ohms
- Power output at 10% THD+N: 468.7W @ 8 ohms

- Input/output polarity: noninverting
- AC-line current draw at idle: 65.0W, 0.78A, 0.71PF
- Gain (stereo, Lch/Rch): output voltage divided by input voltage, 8-ohm load
- Fixed input: 28.6X/28.5X, 29.1dB/29.1dB
- Variable input, full clockwise: 50.7X/50.0X, 34.1dB/34.0dB

- Gain (mono), output voltage divided by input voltage, 8-ohm load
- Fixed input: 57.2X, 35.2dB
- Variable input, full clockwise: 101.1X, 40.1dB

- Input sensitivity for 1W output into 8 ohms (stereo, Lch/Rch)
- Fixed input: 98.9mV/99.2mV
- Variable input, full clockwise: 55.8mV/56.6mV

- Input sensitivity for 1W output into 8 ohms (mono)
- Fixed input: 59.4mV
- Variable input, full clockwise: 28.0mV

- Output impedance @ 50Hz
- Stereo mode: 0.042 ohm
- Mono mode: 0.084 ohm

- Input impedance @ 1kHz (stereo)
- Fixed input: 10.3k ohms
- Variable input, full clockwise: 205k ohms

- Input impedance @ 1kHz (mono)
- Fixed input: 10.3k ohms
- Variable input, full clockwise: 163k ohms

- Output noise with fixed input (stereo mode), 8-ohm load, termination 1k ohm, Lch/Rch
- Wideband: 0.45mV/0.33mV, -76.0dBW/-78.9dBW
- A weighted: 0.0257mV/0.0264mV, -100.8dBW/-100.6dBW

- Output noise with variable input set full clockwise (stereo mode), 8-ohm load, termination 1k ohm, Lch/Rch
- Wideband: 0.38mV/0.37mV, -77.4dBW/-77.7dBW
- A weighted: 0.0391mV/0.0433mV, -97.2dBW/-96.3dBW

- Output noise with fixed input (mono mode), 8-ohm load, termination 1k ohm
- Wideband: 0.70mV, -72.1dBW
- A weighted: 0.0540mV, -94.4dBW

- Output noise with variable input set full clockwise (mono mode), 8-ohm load, termination 1k ohm
- Wideband: 0.64mV, -72.9dBW
- A weighted: 0.0821mV, -90.7dBW

The C 275BEE appears to be a linear design with load-sensing circuitry that causes it to output about the same amount of power into 4 or 8 ohms; usually, a solid-state power amp produces quite a bit more power into 4 ohms.

Chart 1 shows the frequency response of the C 275BEE with varying loads. In mono mode (not shown), the high-frequency rolloff was about twice that shown in Chart 1. In both cases, the output impedance was low enough that there was negligible variation with the NHT dummy speaker load.

The distortion measured in the C 275BEE’s left channel was quite a bit better than in the right. Chart 2 illustrates how the NAD’s total harmonic distortion plus noise (THD+N) vs. power varied for 1kHz and SMPTE intermodulation test signals, and with amplifier output for 8- and 4-ohm loads. Chart 2A shows the results for 8-ohm loading in mono mode. NAD does not recommend 4-ohm loading for the C 275BEE in mono mode.

Chart 3 plots the C 275BEE’s THD+N as a function of frequency at different power levels. The rise in distortion with frequency in the right channel is quite pronounced. Chart 3A shows the same measurement taken for the left channel.

The NAD’s plot of damping factor vs. frequency, shown in Chart 4, is typical of most solid-state power amplifiers: high at low frequencies, then declining throughout the audioband. In mono mode, the damping factor (not shown) was about half that indicated in Chart 4 -- a normal situation, as the two output channels are in series with the load.

Chart 5 shows a spectrum of the C 275BEE’s harmonic distortion and noise residue in a 10W, 1kHz test signal. AC-line harmonics are low but relatively complex. Signal harmonics are dominated by the third harmonic, with the second and higher harmonics of decreasing magnitude.

Stereo mode

Red line = open circuit

Magenta line = 8-ohm load

Blue line = 4-ohm load

Chart 2A

Stereo mode

(Line up at 50W 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

Mono mode

(Line up at 100W to determine lines)

Top line = 8-ohm SMPTE IM distortion

Second line = 8-ohm THD+N

Chart 3A

Stereo mode

(8-ohm loading, Rch)

Red line = 1W

Magenta line = 10W

Blue line = 30W

Cyan line = 70W

Green line = 150W

Chart 3B

Stereo mode

(8-ohm loading, Lch)

Red line = 1W

Magenta line = 10W

Blue line = 70W

Cyan line = 150W

Stereo mode

Damping factor = output impedance divided into 8

Stereo mode

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

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