Taper Control for Volume Pedals

Tom Bradshaw · From: Walnut Creek, California, USA

In another post here, I indicated that I'd provide information on how to rig up a taper control pot for volume pedals. I've concluded that it would be appropriate to make this a Forum prject.

I've learned that all electronic experts have different ideas on how to get something done and done best. For example, I asked a very competent electronics technician what capacitor to use between a Dunlop 470K audio pot to achieve maximum extremes of bass and treble in the excusion of a tone pot. He told me pointedly. I followed his recommendation and the result was awful. I had to experiment, finally settling on something different for the capacitor value, as well as ending up using a linear pot for the tone control.

So, to all the electronics fellows on the Forum, if you have an idea for the best connection, resisitor, pot, etc., please provide your idea here or email it to me and I'll test it against all the ideas that are presented. ...Tom (tbradshaw@california.com)

Steve Feldman · From: Central MA USA

Tom -

I assume by 'taper control' (with resistors/caps, etc.) you mean something to prevent loss of highs as the volume increases? I do this on my single coil guitars (strats/teles) with a 'treble bleed' circuit, which actually should be called a 'treble pass', or 'high pass' circuit. For the single coils which have 250K volume pots, I use a 0.001uF cap in parallel with a ~130K, 1/4 watt resistor, and it works great for me. Some folks use different values of cap, with or without resistor, and either in series or in parallel.

I guess part of all this is to find a formula that works well with 500K pots. But then I guess it would also vary with cable capacitance and other things that are beyond me.

There are lots of options and speculation about all this. Here are some references from the guitar world that you may find useful.

http://www.dominocs.com/AshBassGuitar/modtreble.html
http://www.bothner.co.za/articles/volumepot2.shtml
http://www.kinman.com/html/toneWorkshop/perfectGuitar.htm#volumePots

Anyway, I hope this is of some help.
_________________
"...An admission of interest in protracted commentary is certainly no reason to capitalize on surmised aberations that do not exist." - BH

Greg Cutshaw · From: Corry, PA, USA

Here's some links to Ernie Ball schematics. They have some with a taper pot that later were redesigned to use a taper switch. Also they have a tone pot version. It would be helpful to plot the frequency response of these with a nominal input and load impedance and also plot the volume level as a function of pedal position to show the differences in taper. It would not be a big deal to change these 250K pot designs to 500k pot designs or to add a "taper switch" to the taper pot designs which would return the circuit back to a normal pot pedal.

All the Ernie Ball Mono designs are referenced here:

Ernie Ball Schematic1

Ernie Ball Schematic2

Ernie Ball Schematic3

Ernie Ball Schematic4

Ernie Ball Schematic5

Ernie Ball Schematic6

Ernie Ball Schematic7

Greg

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Tom your post is a little confusing. Taper of a potentiometer, in terms of a volume pedal, is how the pedal comes on during travel from off to full on.
If you want to keep the frequency the same throughout the travel of the pedal, you will need a pre-amp, because a pot is a voltage divider. When you divide voltage you change frequency. I don't think there is any way to just use a capacitor and make the frequency stay the same throughout the travel. What are you after, making the pot come on different, or having the frequency stay the same all the way through the travel? Can't help you unless I know what you want.

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