July 2008

Bryston 2B SST C-Series 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 and 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 the left channel and the unbalanced inputs unless otherwise noted.
• This amplifier does not invert polarity.
• AC line current draw at idle: 0.37A.
• Input impedance @ 1kHz: 9.9k ohms.
• Output impedance at 50Hz: 0.026 ohms.
• Input sensitivity for 1W output into 8 ohms:
• 1V sensitivity: 99.6mV
• 2V sensitivity: 197.8mV
• Gain (8-ohm load), unbalanced and balanced inputs:
  • 1V sensitivity: 28.4X, 29.1dB.
  • 2V sensitivity: 14.3X, 23.1dB.
• Output noise, 8-ohm load, unbalanced input, 1k-ohm input termination, Lch/Rch:
  • 1V sensitivity: wideband - 0.21mV, -82.6dBW / 0.18mV, -83.9dBW
  • 2V sensitivity: wideband - 0.18mV, -83.9dBW / 0.13mV, -86.8dBW
  • 1V sensitivity: A weighted - 0.11mV, -88.2dBW / 0.046mV, -95.8dBW
  • 2V sensitivity: A weighted - 0.10mV, -89.0dBW / 0.032mV, -98.9dBW
• Output noise, 8-ohm load, balanced input, 600-ohm input termination, Lch/Rch:
  • 1V sensitivity: wideband - 0.29mV, -79.8dBW / 0.28mV, -80.1dBW
  • 2V sensitivity: wideband - 0.21mV, -82.6dBW / 0.16mV, -85.0dBW
  • 1V sensitivity: A weighted - 0.11mV, -88.2dBW / 0.069mV, -92.3dBW
  • 2V sensitivity: A weighted - 0.10mV, -89.0dBW / 0.040mV, -97.0dBW

Power output with 1kHz test signal

• 8-ohm load at 1% THD: 127W
• 8-ohm load at 10% THD: 163W
  
  
• 4-ohm load at 1% THD: 213W
• 4-ohm load at 10% THD: 235W

General

The Bryston 2B SST C-Series is a medium-power solid-state stereo power amplifier, the lowest-powered unit in Bryston’s SST C-Series line.

Chart 1 shows the frequency response of the amp with varying loads. The high-frequency response is moderately wide with an approximate 3dB down point of 100kHz. 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 display. The variation with the NHT dummy load in the audio range is of the order of +/-0.05dB -- a negligible amount.

Chart 2 illustrates how total harmonic distortion plus noise vs. power varies for 1kHz and SMPTE IM test signals and amplifier output load. The amount of distortion is low right up to clipping --- the behavior of most solid-state power amplifiers. The distortion performance was essentially identical with unbalanced and balanced connections.

Total harmonic distortion plus noise as a function of frequency at several different power levels is plotted in Chart 3 for 4-ohm loading. The amount of rise in distortion at low and high frequencies is admirably low, except at the 180W level where distortion started to rise abruptly below 20Hz, most likely due to power-supply limitations. This didn’t happen with the 8-ohm loads at the rated 100W power output.

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 about 1kHz and then rolling off with frequency.

The left channel of this unit had somewhat more power-supply line harmonics due to rectifier conduction-pulse ground currents than the quieter right channel. Therefore, the spectrum of both channels is shown in charts 5A and 5B for a 10W 1kHz test signal with 8-ohm loading. As can be seen, the left-channel spectrum has many line harmonics that extend way up into the test-signal area, whereas the right-channel spectrum is more normal looking with low amounts of line harmonics and a tapering-off spectrum of test-signal harmonics.

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

(line up at 70W to determine lines)
Top line: 4-ohm THD+N
Second line: 8-ohm SMPTE IM
Third line: 8-ohm THD+N
Bottom line: 4-ohm SMPTE IM

4-ohm output loading
Grey line: 180W
Cyan line: 100W
Blue line: 30W
Magenta line: 10W
Red line: 1W

Damping factor = output impedance divided into 8

5A - left channel

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

5B - right channel

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

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