Best way to adjust the volume level

April 3, 2021
 by Paul McGowan

3 comments on “Best way to adjust the volume level”

  1. I’m always surprised that PS Audio prefers variable gain to a simple potentiometer. Conductive plastic controls are used quite widely and, as we can see, there are an enormous number of potentiometers in the Studer mixer. If we don’t trust variable potentiometers, even the conductive plastic type, then it would be straightforward to create a switched potentiometer using miniature relays and fixed resistors.

    By contrast, electronically-variable gain is essentially a multiplier, which is inherently a non-linear function. It’s very difficult (maybe not impossible) to make a low distortion gain cell. Electonically-variable gain is a necessary evil in a compressor or in an automated mixer, but why make things more complicated than needed in high-end replay equipment?

    1. Thanks, Mark. We’ve listen tested so many potentiometers over the years that I think I can “smell” what they are going to sound like just from their composition. And yes, conductive plastic is good but certainly has a distinct sonic signature.

      One way to think about an electronic control is to imagine the circuit and what’s in the path. In one version we built we used a very expensive Vishay resistor in series and a CMOS activated shunt group of switches. That was excellent sounding as the signal only really went through the fixed Vishay resistor. It had the challenge of limited volume range (big first step from zero to on).

      Or, think about the BHK preamp. Here we have its vacuum tube gain stage which I think we can all agree is an excellent and necessary component in the signal chain. Now imagine we implement various combinations of fixed resistors switched in and out by CMOS switches that change the vacuum tube’s gain.

      I can assure you that these steps sound remarkably better than running ther signal through the variable element of a pot.

      And we haven’t yet discussed stepped attenuators…..

      1. Thanks Paul for the response. If the electronic gain control is implemented by electronically switching fixed resistors around a tube or semiconductor amplifier then that makes perfect sense. I imagined that you were varying the bias current in the tube. That sounds wonderful in the tremolo circuit of a guitar amplifier, but it wouldn’t have enough control range to replace a volume control.

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