Secret life of pots, extra tidbit

[Greg Moss]

I don't remember seeing this on the GEOFEX Secret life of pots article, maybe it's in there...  I got this off of a Circuit bending page, probably
//http://www.anti-theory.com/soundart/circuitbend/

but maybe not.

Anyway,You can open up the back of the pot and, using a pin or x-acto or simular, completely scratch away a thin line in the resistive material of the pot.  In my particular case, I was creating distortion in a cheap keyboard by feeding an audio op-amps output back into it's input.  The problem was, I liked the control I had of the distorted sound with a 100k pot, but I would still get a quiet squeal at the pot's maximum resistance.  So I scratched the resistive material in the pot, sectioning of the small area the pot's wiper sits on when the knob is turned "fully down" so that a the "minimum" setting, the connection had infinite resistance, but beyond that it behaved like fine tuning for the distorted sound.

I wonder if you could make a cut halfway across the pot, so that you could use one knob to choose variable resistances to two separate circuits, filter ciruits, for example.....

I'm sure somebody here has does this before, I just wanted to vent my enthusiasm for how well this trick solved my problem....

OK,

Greg

[BillyJ]

That is the coolest site ever. I am off to get me a speak and spell!!! :O)

[Peter Snowberg]

That's a cool site!  

along the same lines, check out:

http://www.carrionsound.com/

I wanted to mention that if you're going to that kind of extent to get a custom pot, you can also use a Chemtronics circuit repair pen to draw a conductor at the edge of the resistive material to take things in the other direction. With this trick and a double pot you can make a balance control with very low resistance in one half between 0 and 50% and very low resistance in the other half between 50 and 100%. With some careful scratching and the right pot, you can also use the trick above to get infinite resistance at one end, but still retain contacts with both end of the resistor element.

-Peter

[Mark Hammer]

Scratching the resistive element of a pot is a secret weapon for some guitar builders.  Note that volume and tone controls are always in-circuit, hence bleeding off signal or loading things down.  By scraping the resistive element at the appropriate extreme of rotation, one can create what's referred to as a "no-load pot".  Most effective in the case of tone controls on SC-equipped guitars.  Roll the tone up full and it's as if the tone pot is removed from the circuit.  No drilling, no switches, no problem.  Start to roll stuff off a bit and the wiper now makes contact again and allows you to bleed off high end.