SoundStageNetwork.com | SoundStage.com - BHK Labs Measurements: Bryston 4B3 Stereo/Mono Amplifier

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 4B³’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
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
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
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
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
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
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

Measurements summary

The Bryston 4B³ 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 4B³’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 4B³’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 4B³’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

Chart 1

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