August 2006

Bryston B100 SST Integrated Amplifier: Measurements

All  amplifier measurements are performed independently by BHK Labs. Please click to learn more about how we test amplifiers there. All measurement data, including graphical information displayed below, are the property of SoundStage! and Schneider Publishing Inc. Reproduction in any format is not permitted.

• Measurements were made at 120V AC line voltage with both channels being driven; measurements made on left channel unless otherwise noted.
• This integrated amplifier does not invert polarity.
• AC line current draw:
• at idle: 0.76A
• in standby: 0.00A
• Input sensitivity for 1W output into 8 ohms, volume at maximum: 24.8mV
• Input impedance @ 1kHz: 47.6k ohms
• Output impedance at 50Hz: 0.026 ohms
• Gain, output voltage divided by input voltage, volume at maximum: 114.2X, 41.2dB
• Output noise, 8-ohm load, 1k-ohm input termination, Lch/Rch
  • Volume control at reference position
    • wideband: 0.70mV, -72.1dBW / 0.66mV, -72.6dBW
    • A weighted: 0.37mV, -77.7dBW / 0.33mV, -78.7dBW
  • Volume control full clockwise
    • wideband: 1.86mV, -63.6dBW / 1.84mV, -63.7dBW
    • A weighted: 0.67mV, -72.5dBW / 0.65mV, -72.8dBW
  • Volume control full counterclockwise
    • wideband: 0.63mV, -73.0dBW / 0.59mV, -73.6dBW
    • A weighted: 0.36mV, -77.9dBW / 0.32mV, -78.9dBW

Power output with 1kHz test signal

• 8-ohm load at 1% THD: 140W
• 8-ohm load at 10% THD: 165W
  
  
• 4-ohm load at 1% THD: 191W
• 4-ohm load at 10% THD: 213W

General

The Bryston B100 SST is a medium-power solid-state integrated amplifier. The overall gain of this unit is on the high side for an integrated amplifier of the type so popular these days -- the kind with a passive selector switch and volume control preceding a power amplifier. The B100 SST has an active line-level preamp stage within, and the overall gain is appropriate for this topology.

Chart 1 shows the frequency response of the amp with varying loads. The high-frequency response is moderately wide with an approximate -3dB point of 80kHz. Output impedance, as judged by the closeness of spacing between the curves of open-circuit, 8-ohm and 4-ohm loading, is quite low in the audio band. The usual NHT-dummy-load curve is not shown as the variations in the response would not appear. The variation with the NHT dummy load in the audio range is less than +/-0.05dB -- a negligible amount. The frequency response was quite independent of volume-control setting. This plot was made with the reference volume-control position as set for 0.5V input to produce 5W output into an 8-ohm load.

Chart 2 illustrates how total harmonic distortion plus noise vs. power varies for 1kHz and SMPTE IM test signals and amplifier output load. Amount of distortion is satisfactorily low in this design, rising out of the noise at 10-20W.

Total harmonic distortion plus noise as a function of frequency at several different power levels is plotted in Chart 3. Amount of rise in distortion at high frequencies is admirably low -- practically non-existent.

Damping factor vs. frequency is shown in Chart 4 and is of a value and nature typical of many solid-state amplifiers, being high up to mid-hundreds of Hz and then rolling off with frequency.

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 low and simple, and intermodulation components of line harmonics with signal harmonics are also low. Visible signal harmonics consist of second, third, and fourth harmonics.

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

(line up at 50W to determine lines)
Top line: 8-ohm SMPTE IM
Second line: 4-ohm SMPTE IM
Third line: 8-ohm THD+N
Bottom line: 4-ohm THD+N

8-ohm output loading
Cyan line: 100W
Blue line: 30W
Magenta line: 10W
Red line: 1W

Damping factor = output impedance divided into 8

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

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