The Volume Control in the Bryston B135 Cubed

Dear Diego Estan,

I have a question about your measurements report on the Bryston B1353, where you wrote: “Based on the accuracy of the left/right channel matching (see table below), and 0.5dB volume-step resolution throughout its range, the B1353 volume knob is not a potentiometer in the signal path, but, rather, provides digital control (analog domain) over a proprietary or integrated volume circuit.” To understand it correctly, is the potentiometer only used to trigger a digital volume control, like the solution Yamaha is using in its A-S3200 and A-S2200 models? Or like Denon is doing recently in its PMA-A110 model?

This point is very important for me, because I listen to music mostly at a lower level. Most amplifiers with normal potentiometers are not very easy to adjust with the remote control at a lower level.

It would be great if you can answer my question.

Best regards,

Hi Matthias,

Thank you for your question, and for reading my measurement report. While I don’t know exactly what components Bryston uses for the volume control in the B1353 (aka B135 Cubed), I can assure you that the volume knob is not a potentiometer in the signal path—but first, let me explain a little bit about volume controls.

There are two main types of volume controls: ones that operate in the digital domain, and those that operate in the analog domain. A purely digital volume control consists of an analog-to-digital-converter to digitize the signal (if the signal is not in the digital domain already), and a bit-depth truncation circuit to reduce volume. Most home-theater receivers operate this way, and so do some high-end two-channel integrated amps. The Technics SU-R1000 that I measured in January is a case in point, mostly because it processes all signals in the digital domain.

Within analog-domain volume controls, we have two main types: old-fashioned potentiometers, which can suffer from noise over time and have poor channel tracking at low volumes, and the more popular digitally controlled analog volume controls. The latter typically uses an integrated circuit (IC), such as the Muses 72320 or Crystal CS3310, or a discrete solution using relays. These ICs or discrete solutions change the volume—or rather, the amplitude of the signal—using digital control to toggle switches (transistors or relays) within a resistor-attenuation ladder.

The measurements show that the Bryston has very low channel-to-channel deviation—but not the exact same deviation across the entire volume range like you’d see with a purely digital volume control, so that means it’s operating in the analog domain. But it’s also clear from the measurements that the Bryston B1353 offers consistent 0.5dB volume increments throughout the range—something that’s not possible with a potentiometer in the signal path—so that’s how I know it’s using a digitally controlled solution.

In summary: like the Yamaha A-S3200, the Bryston B1353 has a digitally controlled analog volume control—it’s not an in-signal potentiometer, but neither is it a purely digital volume control.

I hope that clears things up.