Volume Pots

[Lee Baucum]

The only way to avoid it is to get an electronic volume pedal...ie. Hilton, Telonics, H10k, etc. They are built to have a constant output impedance, so that, basically, what goes in is what comes out.

Or, you could purchase an impedance matching device, such as a Sarno FreeLoader, Hilton Digital Sustain, or Goodrich Matchbox. All three are excellent products.

[Will Cowell]

I'm always surprised at the misconceptions that are out there about "woolly" top-end with volume pots.

Mike says:
At full volume, the pot is showing the amp input(or pedal input) about 500k ohms. As you lower the volume with the pedal, that resistance becomes lower and lower, and bleeds off high frequencies (due to the mismatch with the amp's input impedance).

This is not correct, although it sounds like a workable explanation. You can't go into it in detail without looking at a little math, and it helps to understand how a potential divider works.

Fundamentally, the problem is mainly in the pickup. it has an internal impedance which rises with frequency - because it's an inductor first and foremost. Double the frequency, double the impedance, roughly. I say "roughly", because actually impedance is the vector sum of the resistance, which is constant, and the reactance, which is frequency related.

Add to that, that some of the signal is "lost" across that impedance - it doesn't get presented to the pot for the amp to see, not even at full throttle. So it has nothing to do with whether your pedal is at low volume or high, it never gets there anyway. The higher the resistance of the pot in the pedal, the less the loss of high frequencies.

So buffer it by going straight into a high impedance input on the amp, then out through the FX loop to the pedal etc, then back to the amp. Or put it through a high impedance pre-amp, internal or external, or use an electronic pot, as advised here. Then you'll really hear what that pickup can do! (No offence guys, but yes, I do have a Master's in electronic engineering just in case anyone thinks I'm making it up.)

Will Cowell
Huntingdon, England

[Mike Wheeler]

Thanks, Will, for the explanation.

There are few electronics engineers here on the forum, so it's not useful to a player to go into theoretical discussions here. The point of my description is that the changing output resistance of the pot, changes the impedance characteristics of the signal path from the pickup to the amp input, such that, at lower pedal levels, the high frequencies are somewhat attenuated. At full pedal they are affected the least.

Any more "in-depth" than that is not helpful to most players. I'm just trying to keep it simple.