The history of volume controls

October 2, 2021
 by Paul McGowan

12 comments on “The history of volume controls”

  1. And what is now the technical effect having degraded the fine input signal by those “cheap” resistors? Is it the resulting impedance mismatch between preamp and power amp or is there an effect by leaving the linear region of the response curve of the amplifying transistor/vacuum tube?????? Or what kind of degradation is added by a cheap resistor compared to a top end Vishay resistor?

  2. I’d be curious about Paul’s attitude towards the volume controls that used a single light sensitive resistor where the resistance varied depending on how much light hit the resistor. The volume is then controlled by varying the light intensity. But there is only one resistor and it is hard wired eliminating mechanical contacts.

      1. You’re correct. Melos Electronics used them in some pre amps designed by Mark Porzilli and Mark told me it took him about an hour to set up a volume control.

    1. The circuit design of the original Hammond organs is always a useful reference. The swell pedal is made from a lamp, and LDR and a vane that progressively covers the LDR. Laurence Hammond had an almost pathological aversion to moving contacts and particularly potentiometers. The drawbars are actually switches that select one of 10 different taps on an autotransformer.

  3. And if that’s at the pre-amp level, what’s the affect of pumping post-amp power through a resistor (or two) at the tweeter?

    Of course, less is more

  4. This is topic that’s been discussed several times on Ask Paul. I don’t doubt for one moment what Paul says about the sonic results from different configurations he’s tried, but the conclusions are most surprising. A few comments:

    – Resistors are used throughout the circuitry. If resistors were non-linear, or had a “sound” then it would be almost impossible to design any high-end audio equipment. For example, what about the resistors that set the gain in a feedback loop?

    – I don’t understand why potentiometers are a problem in a properly designed circuit, given the use of materials like conductive plastic, or the option for switched fixed resistors.

    – The Studer mixer has hundreds of potentiometers, and Octave recordings will have been through dozens of them.

    – Recently Paul showed some mechanics for an automated fader for a mixer, where a potentiometer was used. Why do this if potentiometers are a no-no?

    – A Gilbert cell is a very complex solution to the simple need for a volume control. A multiplier is inherently a non-linear device, and enormous care is needed to minimise distortion in a voltage controlled amplifier application. Transistors need to be very closely matched, so this is generally a great place to use an IC. VCAs are tolerated as a unwelcome necessity in automated mixers.

  5. Very good questions. Let me see if I can answer at least a few:

    – Resistors are used throughout the circuitry. If resistors were non-linear, or had a “sound” then it would be almost impossible to design any high-end audio equipment. For example, what about the resistors that set the gain in a feedback loop?

    They are critical and you are correct. We learned years ago the importance of the resistors in a circuit. The first version of the PerfectWave DAC had to be scrapped before it went to production to change out all the resistor types. We had for years depended on an excellent sounding metal film brand that had been selected after hours of listening. When we finished work on the PWD I had just learned about an entirely new brand of resistor, PRP, that was so much better sounding than our trusted brand that I halted production, threw away thousands of dollars of already stuffed boards and retooled to use PRPs. The difference was that big.

    – I don’t understand why potentiometers are a problem in a properly designed circuit, given the use of materials like conductive plastic, or the option for switched fixed resistors.

    For the same reason as the above story of resistors. Think of the pot as a resistor for a moment. And consider what I just said about their importance. If a key signal path resistor were made of conductive plastic or some of the crapier materials we’re stuck with in pots, we’d be in real sonic trouble. Or, reverse your thinking to say it another way. What if we could get a potentiometer made in the same way a PRP resistor is made? Of course we can’t. With respect to fixed resistors as in a stepped attenuator, indeed, this is an excellent sounding solution just kind of klunky to use and a nightmare to make remote controllable. Just look at the contraption Charlie Hanson came up with in the Ayre preamp where he employed a belt drive and motor arrangement for the switch.

    – The Studer mixer has hundreds of potentiometers, and Octave recordings will have been through dozens of them.

    Actually, no. Each channel only has volume and balance to go through before the summing amplifier and then one more pot for the master. But, we agree, even three is too many.

    – Recently Paul showed some mechanics for an automated fader for a mixer, where a potentiometer was used. Why do this if potentiometers are a no-no?

    Because that potentiometer does not contain the signal. It is used only for DC to measure the position of the slider. What we are building is a control fader that operates a lossless digital pot in the DAW with a 64 bit signal. Think of it like the volume control in the DirectStream DAC where only math is used and there’s zero resolution lost.

    – A Gilbert cell is a very complex solution to the simple need for a volume control. A multiplier is inherently a non-linear device, and enormous care is needed to minimise distortion in a voltage controlled amplifier application. Transistors need to be very closely matched, so this is generally a great place to use an IC. VCAs are tolerated as a unwelcome necessity in automated mixers.

    Indeed, VCAs were crap compared to a quality pot in most mixers. There was a whole period during the introduction of automated control boards where VCAs were the thing and they just didn’t get it right.

    A VCA done right is a little better sounding than the best pots we’ve played with. That doesn’t mean it’s the be all to end all, but at least it’s better than listening through crappy conductive plastic.

Leave a Reply

Stop by for a tour:
Mon-Fri, 8:30am-5pm MST

4865 Sterling Dr.
Boulder, CO 80301
1-800-PSAUDIO

Join the hi-fi family

Stop by for a tour:
4865 Sterling Dr.
Boulder, CO 80301

Join the hi-fi family

linkedin facebook pinterest youtube rss twitter instagram facebook-blank rss-blank linkedin-blank pinterest youtube twitter instagram