Memory Man Pedal volume pot behaving strangely.

September 14, 2006 10:49 AM

Help with a volume pot that won't turn off.

I have one of these:



Lately, the pot that controls the vibrato/chorus has gone all wonky. If it is even the smallest bit on, it behaves as though it is on ten. I can counteract this by turning it violently toward "-1" and hoping that the vibrating stage doesn't jostle it any.

I don't even use that part of the effect, so I don't care if it doesn't work. I just don't want it popping on in the middle of a set. Does anyone have experience with a pot behaving like this? Workarounds and quick fixes are appreciated, as I need it for the next month of shows.

posted by jon_kill to media & arts (7 comments total)

Have you tried taking it apart and blasting it with compressed air? Since that probably won't work, have you considered taking it apart and desoldering one of the leads from the pot? That should bypass it completely.

IANAElectrician. Seems like it would work though.
posted by quin at 10:56 AM on September 14, 2006

Get some contact-cleaner spray (Radio Shack sells a version) and spray it into the pot while you rotate it back & forth.
posted by Kirth Gerson at 10:57 AM on September 14, 2006

Quin, I thought of that. And then I realized it might kill the circuit. And then I thought of finding the resistance of the pot turned to 0 and replacing it with a resistor. And then I realized that I didn't really know what the hell I was doing and decided to ask here.

Thanks, Keith.
posted by jon_kill at 11:08 AM on September 14, 2006

seconding kirths suggestion. I've had nasty wonky pots work great for years after a quick burst of pot cleaner
posted by cosmicbandito at 11:17 AM on September 14, 2006

D5 contact cleaner is the best. Radio Shack sells liquid, but I am not sure that they have the spray. Guitar Center sells the spray.
posted by caddis at 11:18 AM on September 14, 2006

You'll need to get access to the pots, which means taking it at least partially apart.

I notice a three-wire AC power cord on the unit, so first let me explicitly recommend unplugging it before ANY disassembly.

There are no lethal voltages in this thing, unless you leave it plugged in.

Pots have a mechanical wiper that moves in concert with the knob across a conductive element. The symptom you describe can just as easily be duplicated by one of the two leads on the pot being open.... such as from a broken/loose wire or a cold solder joint. I'd check those items first. Cold solder joints look grainy, not shiny.

It is easy to replace pots, functionally, but they are highly specific mechanically. They also come in different tapers, meaning the relationship between rotation and resistance can be non-linear (usually logarithmic) or linear. For chorus, I am betting linear. Measure the two outer terminals to get an approximation of resistance in case you can't decipher the value.

it is also possible to disassemble/repair a pot.. You just have to diddle around with it and figure how it goes together. Either take a picture or make a sketch of reassebly and have at it.

It is ALSO possible to deactivate the pot. Remove the center (wiper) lead and solder to one or the other of the end terminals. One will give you full on and the other, full off, providing their leads aren't the ones at fault.

If you have trouble, take a digital pix and email it to me (in contact info) and I'll help you analyze what you've got.

Good luck.
posted by FauxScot at 2:18 PM on September 14, 2006

I've had problems with pots on musical equipment in the past and upon investigation the pots were sealed and there was nowhere to squirt the pot cleaner! The recommendation was to replace it since the sealed pots are not fix-able. I bet a musical instrument repair place would be able to replace the pot with a new identical copy.
posted by tdogboy at 2:54 PM on September 14, 2006