Bryston 21B³ Asymmetric 3-channel Class A/B audio power amplifier


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Power output:
1x 600W @8Ω | 1x 900W @4Ω & 2x 300W @8Ω | 2x 500W
Asymmetric Triple mono power amplifier, Patented Salomie ultra linear input stage
Audio channels:
Rack mount:
NO version with rack mount holes
20 Years
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Bryston impressed the audiophile community with an ultimate fully active loudspeaker system that let you choose your own amplifiers. Listeners were free to build 6-channel systems any way they liked. Now Bryston introduces the 21B³-an amplifier dedicated to bringing Cubed Series excellence to an easy to manage package. Each 21B³ has 3 channels. One is rated at 600 watts, the other two are rated at 300 watts each. Active loudspeaker customers will use the high powered channel for the bass section and smaller channels for the midrange and high frequency sections of their 3 way systems. Since the 21B³ is based on our 7B³ and 4B³ amps, it can also be used to power any 3 channels such as the front LCR in a home theatre.




  • Balanced XLR and Single ended RCA input
  • 3 Channels each with fully independent power supplies including transformers
  • 600W into 8 ohms (and up to 900 into 4 ohms) for one channel. Two more channels each rated at 300W into 8 ohms and 500W into 4 ohms.
  • The patented Salomie circuit found in all Cubed Series amplifiers
  • Switchable gain (23dB or 29dB)
  • Fully convection cooled means no noisy fans
  • Machined and anodized aluminum enclosure and dress panel
  • Less than 500mW standby power consumption
  • SoftStart microprocessor controlled startup sequence won't trip circuit breakers
  • DC trigger for automated turn on and turn off
  • Legendary Bryston 20 Year Warranty


  • Silver or black faceplate
  • 17” or 19” faceplate (non-rack mountable) 19" comes with front mounted handles


Dimensions Inches: 17 or 19 W x 8.1 H x 16.8 or 18.4 (with front handles) D
Weight 91 lbs | 41 kg
Frequency Response: <1Hz - 100kHz: -3dB
THD+N (20Hz-20kHz @ Rated Power, 8Ω): <0.005%
Power Output (per channel): CH 1: 600W @ 8Ω | 900W @ 4Ω
  CH 2&3: 300W @ 8Ω | 500W @ 4Ω
Noise: RCA: <-115dB
  XLR: <-116dB
Input Impedance: Unbalanced 7.5kΩ
  Balanced 5kΩ / leg
20 Year Warranty

3 Reviews Hide Reviews Show Reviews

  • 5
    Power amps 21B Cubed

    Posted by Marc Customer on 2nd Jun 2021

    An hour out of the box, these 21B Cubed amps are ABSOLUTELY FANTASTIC!

  • 5
    21B3 amps

    Posted by Suave Kajko NOVO Magazine on 2nd Jun 2021

    The system offered a massively large sonic landscape with a three dimensional soundstage, a warm, natural midrange and a near perfect tonal balance. The dynamic range of this system was also incredible, as was the handling of bass notes. I could have sat here for hours, just hanging out with James and listening to music. This was definitely among the best sounding systems at the show.

  • 5
    Active Bryston with 21B3s

    Posted by Jean-Denis Doyle TED on 2nd Jun 2021

    Don’t be fooled though, as these colossal actives three-way loudspeakers offer a great softness and transport you in a passionate musical universe. The tones are beautiful and the impression of quiet power is definitely there. The stereophonic image is immense, both in width and in height. So, I undoubtedly predict many beautiful listening sessions will occur with this pair of loudspeakers...A heck of an audio system!