Bryston BR-20 Network/DAC Preamp Lab Report

Lab Report

'Precision' is the watchword for this preamplifier, defining both its engineering and technical performance. The digitally-governed volume control, for example, precisely indicates the gain of the BR-20. So, '+12.0dB' represents a gain of 12dB, '0.0dB' is unity gain and '–30.0dB' is a gain of –29.5dB (an error of just ±0.5dB over the top 42dB of its range and ±1dB over a 72dB range). Maximum (balanced) output is 13.5V from a 70ohm source impedance and distortion is lowest at 2-6V through the midrange at ~0.00004%, and only slightly 'higher' at 0.00009-0.0002% for 0dBV (20Hz-20kHz). The S/N is a wide 100dB (A-wtd, re. 0dBV) while the analogue in/out frequency response is flat to within ±0.01dB from 20Hz-20kHz and extends from 3Hz-100kHz at –0.3dB. Importantly, and in contrast with many amps/preamps, the volume circuit is correctly buffered and so the HF response does not change with volume position.

Used as a DAC/preamp, the BR-20 clips at volume '+10.5dB' for a full scale 0dBFs input, realising a 12.4V output at '+10.0dB'. Distortion is ~0.0011% at this full scale and only slightly lower at ~0.0009% if the volume is reduced to '+6.0dB' or '+0.0dB'. Over the top 30dB of its (digital) dynamic range, however, distortion falls to as low as 0.00005% through the midrange and 0.00015% at 20kHz [see Graph 1, below]. The A-wtd S/N is fabulously wide at 118.4dB, linearity good to ±0.2dB over a 110dB range and channel separation all but 'absolute' at 145dB! Jitter rejection is also nearly absolute at <5psec [see Graph 2] while Bryston's choice of minimum phase/fast roll-off digital filter for the AK4490 DACs defines the 69dB stopband rejection and response of –0.2dB/20kHz, –3.5dB/45kHz and –10.2dB/90kHz with 48kHz, 96kHz and 192kHz media, respectively. PM


Distortion vs. USB 24-bit digital signal level over a 120dB range at 1kHz (black) and 20kHz (blue)


High resolution jitter spectrum via USB input with 48kHz/24-bit data

Maximum output / Impedance 13.5V / 70-77ohm (balanced)
Input sensitivity (re. 0dBV) 250mV (balanced)
Freq. resp. (20Hz-20kHz/100kHz) +0.0 to –0.01dB/–0.26dB (pre)
Freq. resp. (20Hz-20k/45k/90kHz) +0.0 to –0.2dB/–3.5dB/–10dB (DAC)
Digital jitter (USB at 48kHz/96kHz) <5psec / <5psec
A-wtd S/N ratio (re. 0dBV/0dBFs) 99.6dB (Analogue) / 118.5dB (Dig)
Distortion (20Hz-20kHz; 0dBV/0dBFs) 0.00009-0.0002%/0.0011-0.012%
Power consumption 22W (2W standby)
Dimensions (WHD) / Weight 430x116x330mm / 5.5kg
Prices £7500 (HDMI module, £1200; phono module, £950)

Bryston Ltd
Supplied by: PMC Ltd, Luton
0870 4441044