eric coleridge wrote:All you need is a 10K, 50k, or 100k log potentiometer (they come in log/audio or linear variety-- log is probably what you want). I believe the pots in the expression pedals are 50k... but one of the other values might work better for you, depending on what you want. They're generally all the same size, and will fit in the space you mentioned (because there are pots in that space already). You can get a rotary/knob pot, or a slider/fader type pot. Either will work, as long as you get the right value. You just need a stereo type cable and connect it to a male jack to access your MF.
You'll then have 2 cables trailing your guitar--which might not be an ideal solution. You might also consider replacing the existing 1/4" audio jack on yr guitar with some other type of connector that could carry/connect all of these wires at one locale. On the other end of this connector's cable, you could split the wire back into two 1/4" male phonos for use with your amp and/or MFs.
Eric - I would reccomend against using a log pot. That is because all of the control is at one end, and then the response increases expontentially. A linear pot, on the other hand, has an even response throughout, and so is more suited for control.
Log pots are generally used when the scale is logarithmic, for example audio volume. The deciBell scale is log, so it makes sense to use this type there.
Jim - have you ever considered using an expression pedal? That would leave your hands free for playing. Or is it more the image you want? I guess Tom Morello made great use of his faulty pickup switch.
Sliders are much more (but not impossibly so) painful to mount than pots.
I think all the Moog manuals reccomend a 50 or 100K pot for use in expression pedals, so do the same for your extension.
FWIW, I once built a little extension box for my MF-102. It comprised of four TRS jacks connected with two trailer light cables (5 core, common ground (sleeve)) to two 5 pin DIN (MIDI) connectors on a little box. Then, I attached these to 100K sliders. The cables were long enough that I could sit the box up quite high, and slide whilst playing.
But soon I gave up and just turned the Moog knobs instead
