Guitar Volume Question

[New Frontier]

Hello All

I'm trying to find a circuit to avoid the loss of drive when you lower the guitar volume..

My guitar has a very nice tone  ( strat with a hot rails on the bridge) when its volume is maximized , but it loses the drive when I need to lower the volume..
Can anybody explain what happens and tell me what to do to avoid it ?

Tkx

[Ansil]

its the impeadance.  put a 330pf cap from across the input and output lugs of the vol pot  prblem solved

[New Frontier]

I heard there is a whole circuit to avoid it.. And I heard it keeps the same drive even when the volume is very low..

When you use the cap, is the tone changed ??

[Mark Hammer]

First, what you call "drive" is not drive but brightness or treble, although losing a lot of treble can make it seem softer too.

What Ansil describes IS the "whole circuit", although there are variations on it that different people use depending on the kind of tone they like.

A bit of theory....

The guitar signal goes into the pot and the level of the output depends on the ratio of the resistance on one side of the wiper (the middle contact of the pot) to the other side.  Lets call the resistance between the input and the wiper Ra, and the resistance between the wiper and ground Rb.

When Ra is small and Rb big (pot is now turned up "full"), very little signal is lost.  AS Ra gets bigger and Rb gets smaller, you lose more and more signal until there is none left.

Okay, lets stick in the capacitor Ansil describes.  This goes in parallel with Ra.  Capacitors work partly like a resistor that big for low frequencies and small for high frequencies, so just for argument, we will call it Rc.

For low frequencies, Rc is always big.  When Ra is small (volume turned up), low freqs and high freqs can always go through Ra, and Rc makes no difference.  As Ra gets bigger, though, Rc starts to matter more, especially for high frequencies.  In fact, when you turn down a bit, it is as if Ra were still small, but just for high frequencies.

I will say this a different way.  What the capacitor does is make the volume pot turn down the bass "faster" than it turns down the treble.  This way, when you turn down a bit, you can still here the "bite" in the note even though it is quieter.

Your stereo amplifier at home (if you have one) may have a "loudness" button/switch.  This does the same thing but also includes bass as well.  So, instead of turning down mids and bass faster than treble, a stereo amp's "loudness" function turns down the mids faster than it turns down bass and treble.

As I mentioned, there are different versions of this "compensating capacitor" on the volume control in guitars.  Some people put in a resistor in series with the cap (e.g., 120K), and other people use just the cap, but use a larger or smaller value (I like to use 1000pf), but they all work the same way, just sounding a little different.