Foot controller for variable resistor

This is my first post, so be gentle.

Does anyone remember a product that allowed you to remove a knob from your amplifier and attach a flex cable that connected to a foot controller? You could connect it to any knob you wanted, volume, bass, treble etc and control it with your foot. Way cool. I need one of these little gadgets for an amplifier project that I'm working on.

Thanks,

Tracy aka Stratofreaker

I highly doubt there is any all in one solution to your problem, but its easy enough to do. Pots usually have three lugs and often all three are used. So instead of running the three wires to the three different lugs, you run them to three different connectors (tip/ring/post) on a stereo jack. Plug in a stereo instrument cable and plug the other end into a stereo jack on an expression pedal or volume/wah shell that has been gutted. The three lugs on the jack then connect to their respective lugs on the pot used that the pedal controls. Make sure the pot is the same value as the one its replacing in the amp, and tah dah, the expression pedal does exactly the same job as the pot in the amp. Bonus, use a switching jack at the amp and connect it to the original pot, so it uses the pot in the amp when no cable is plugged in, or the pot in the expression pedal when it isn't. If you wanted, you could do that for every pot in the amp and pick which one you hook it up to. The only problem you really run into is matching the pot values, because its difficult to find wah pots in certain values and because different pots in the amp are different values. You could probably get away with some sort of switching on the expression pedal and use resistors in parallel to change the value a bit and get it close enough for most of your needs.

Further Reading:

http://www.geofex.com/Article_Folders/xprnped.htm

http://www.geofex.com/Article_Folders/potsecrets/potscret.htm

On second thought, I'm sure you could also do it mechanically with an expression pedal controlling a small motor and gear you put on top of the amp to physically rotate the knob, would be cool as hell and probably very complicated, and I'm positive nothing like it exists commercially but I'd love to see someone build it.

EH made one long ago, and i have no idea how hard they are to find.

in current production, there's at least this one: http://www.musictoyz.com/guitar/pedals/tip.php

Wow I never would have guessed something like that existed, but its crazy it does. If its long enough to reach up onto your amp, thats probably the easiest solution.

Hey Clay,

Do you remember what Electro Harmonix called their pedal? I think that's the one I'm thinking about. Maybe I can find one eBay.

But I must admit the idea that pr1son3r had is growing on me. It would be a more permanent solution. Plus gutting some old wah pedal would be a piece of cake and cheap too.

Tracy aka Stratofreaker

the EH pedal was called the hot foot, i think.

rewiring to accomodate an expression pedal is simple, and a more elegant solution than one of those rube-goldberg-knob-turning contraptions. the only problem is that expression pedals are much better suited for control voltages than audio. replacing any pots in the audio path with an expression pedal pot will probably add significant cable length and heaps of noise, plus whatever scratchiness will occur if the exp pedal pot is not the best. try it and see if it works for you.

you could set up the expression pedal to control a vactrol or transistor if you were really set on it. there are a couple of articles at geofex.com that could get you started in that direction.

Ok. What do you do about the other knob?