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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.

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 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

- 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

- Without AUX-0025 measurement filter (high-frequency switching)

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.

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)

(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

(8-ohm loading)

Cyan line = 1W

Magenta line = 10W

Blue line = 30W

Red line = 60W

Damping factor = output impedance divided into 8

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

Red line = 44.1kHz sample rate

Magenta line = 96.0kHz sample rate

Blue line - 192.kHz sample rate

Magenta line = with usual bandpass filter

Red line = 10Hz - 20kHz

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- 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 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

- 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

- At reference volume setting
- 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

- At reference volume setting

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.

Red line = open circuit

Magenta line = 8-ohm load

Blue line = 4-ohm load

(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

(8-ohm loading)

Red line = 1W

Magenta line = 10W

Blue line = 70W

Cyan line = 200W

Green line = 270W

Yellow line = 290W

Damping factor = output impedance divided into 8

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

Red line = 44.1kHz

Magenta line = 96kHz

Blue line = 192kHz

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

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- 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 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

- 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

- At reference volume setting
- 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

- At reference volume setting

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.

Red line = open circuit

Magenta line = 8-ohm load

Blue line = 4-ohm load

Cyan line = NHT dummy-speaker load

(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

(8-ohm loading)

Red line = 1W

Magenta line = 10W

Blue line = 30W

Cyan line = 70W

Green line = 120W

Damping factor = output impedance divided into 8

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

Slow filters

Red line = 44.1kHz

Magenta line = 96kHz

Yellow line = 192kHz

Fast filters

Cyan line = 44.1kHz

Green line = 96kHz

Blue line = 192kHz

24-bit/44.1kHz resolution with 1kHz bandwidth filter

Red line = left channel

Magenta line = right channel

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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 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

- 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

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.

Red line = open circuit

Magenta line = 8-ohm load

Blue line = 4-ohm load

Cyan line = NHT dummy-speaker 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 = 100W

Cyan line = 300W

Green line = 600W

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

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

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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 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

- 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

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.

Red line = DIR input 8-ohm loading

Magenta line = BAL input 8-ohm 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

(8-ohm loading)

Red line = 1W

Magenta line = 10W

Blue line = 30W

Green line = 100W

Yellow line = 400W

Damping factor = output impedance divided into 8

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

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- Category: Amplifier Measurements

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

- 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

- 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

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.

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 = 4-ohm THD+N

Third line = 8-ohm SMPTE IM distortion

Bottom line = 8-ohm THD+N

(8-ohm loading)

Red line = 1W

Magenta line = 10W

Blue line = 30W

Cyan line = 60W

Green line = 75W

Damping factor = output impedance divided into 8

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

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- Parent Category: Products
- Category: Amplifier Measurements

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

- 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

- Stereo mode
- 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

- Stereo mode
- 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

- Stereo mode
- 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

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 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 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 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

Stereo mode

Damping factor = output impedance divided into 8

Stereo mode

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

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- Parent Category: Products
- Category: Amplifier Measurements

Note: Unless otherwise noted, all measurements were taken using the balanced input of the Bryston 4B^{3}’s left channel, with 120V AC line voltage driving both channels at 29dB gain.

- Power output at 1% THD+N: 354.0W @ 8 ohms, 552.0W @ 4 ohms
- Power output at 10% THD+N: 424.0W @ 8 ohms, 626.0W @ 4 ohms

- Power output at 1% THD+N: 1190W @ 8 ohms
- Power output at 10% THD+N: 1440W @ 8 ohms

- Input/output polarity: noninverting
- AC-line current draw at idle: 81.0W, 1.09A, 0.62PF
- Gain: output voltage divided by input voltage, 8-ohm load
- Stereo mode
- Balanced input (29dB gain): 28.26X, 29.0dB
- Balanced input (23dB gain): 14.13X, 23.0dB
- Unbalanced input (29dB gain): 27.27X, 28.7dB
- Unbalanced input (23dB gain): 14.12X, 23.0dB

- Mono mode
- Balanced input (29dB gain): 27.84X, 28.9dB
- Balanced input (23dB gain): 13.91X, 22.9dB
- Unbalanced input (29dB gain): 27.65X, 28.8dB
- Unbalanced input (23dB gain): 13.79X, 22.8dB

- Stereo mode
- Input sensitivity for 1W output into 8 ohms
- Stereo mode
- Balanced input (29dB gain): 100.1mV
- Balanced input (23dB gain): 203.3mV
- Unbalanced input (29dB gain): 102.3mV
- Unbalanced input (23dB gain): 200.3mV

- Mono mode
- Balanced input (29dB gain): 101.6mV
- Balanced input (23dB gain): 203.3mV
- Unbalanced input (29dB gain): 102.3mV
- Unbalanced input (23dB gain): 205.1mV

- Stereo mode
- Output impedance @ 50Hz
- Stereo mode: 0.008 ohm
- Mono mode: 0.018 ohm

- Input impedance @ 1kHz
- Stereo mode
- Balanced input: 20k ohms
- Unbalanced input: 29k ohms

- Mono mode
- Balanced input: 10.5k ohms
- Unbalanced input: 7.8k ohms

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

- 29dB gain
- Wideband: 413.9uV/406.6uV, -76.7dBW/-76.9dBW
- A weighted: 98.69uV/96.98uV, -89.2dBW/-89.3dBW

- 23dB gain
- Wideband: 215.9uV/209.0uV, -82.4dBW/-82.6dBW
- A weighted: 53.04uV/49.13uV, -95.0dBW/-95.2dBW

- 29dB gain
- Output noise (stereo mode), 8-ohm load, unbalanced inputs terminated with 1k ohms, Lch/Rch

- 29dB gain
- Wideband: 419.7uV/410.5uV, -76.6dBW/-76.8dBW
- A weighted: 99.43uV/98.98uV, -89.1dBW/-89.3dBW

- 23dB gain
- Wideband: 219.8uV/213.0uV, -82.2dBW/-82.5dBW
- A weighted: 54.99uV/51.09uV, -94.2dBW/-94.9dBW

- 29dB gain
- Output noise (mono mode), 8-ohm load, balanced inputs terminated with 600 ohms

- 29dB gain
- Wideband: 413.9uV, -76.7dBW
- A weighted: 98.69uV, -89.2dBW

- 23dB gain
- Wideband: 215.9uV, -82.4dBW
- A weighted: 53.04uV, -94.5dBW

- 29dB gain
- Output noise (mono mode), 8-ohm load, unbalanced inputs terminated with 1k ohms
- 29dB gain
- Wideband: 419.7uV, -76.6dBW
- A weighted: 99.43uV, -89.1dBW

- 23dB gain
- Wideband: 219.8uV, -82.2dBW
- A weighted: 54.99uV, -94.2dBW

- 29dB gain

The Bryston 4B^{3} is a high-power stereo power amplifier capable of operating in bridged-mono mode; most measurements were also made in the mono mode.

Chart 1 shows the 4B^{3}’s frequency response with varying loads. The output impedance over most of the audioband is low enough that the IHF load would not show any appreciable difference within that bandwidth. In mono mode (not shown), the amount of change with load at 200kHz was about double.

Chart 2A illustrates how the 4B^{3}’s total harmonic distortion plus noise (THD+N) vs. power varies for 1kHz and SMPTE IM test signals into 8 and 4 ohms. Chart 2B shows the results for the mono mode into 8 ohms. The levels of distortion are very low.

THD+N as a function of frequency at several different power levels is plotted in Chart 3. The degree of increase in distortion at high frequencies is admirably low.

Chart 4 shows the 4B^{3}’s damping factor vs. frequency: though high at low frequencies, it starts to decline at a lower frequency than in most solid-state designs. The damping factor for the mono mode (not shown) is similar in shape but about half the magnitude.

The spectrum of the harmonic distortion and noise residue of a 10W, 1kHz test signal is plotted in Chart 5. The magnitude of the AC line harmonics is reasonably low, and dominated by odd harmonics of 60Hz. The test-signal harmonics are very low, consisting mostly of the second and third harmonics.

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 = 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 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

(8-ohm loading)

Red line = 1W

Magenta line = 10W

Blue line = 30W

Cyan line = 100W

Green line = 300W

Stereo mode

Damping factor = output impedance divided into 8

Stereo mode

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