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, 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 (stereo mode) @ 1kHz

- 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 (mono mode) @ 1kHz

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

### Additional data

- 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

### Measurements summary

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.

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

Stereo mode

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

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

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

Stereo mode

(8-ohm loading)

Red line = 1W

Magenta line = 10W

Blue line = 30W

Cyan line = 100W

Green line = 300W

### 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