Quality Control

Guitarsmith Richard Stanley says: Most pots are made for applications where variance is not critical. Nobody makes pots truly geared for use in passive circuit electric guitars, where you want a specific value for the overall resistance. Manufacturers tolerance specs on pots was always +/- 25% which is unbelievable because that means a nominal 500KΩ (ohm) pot could be anywhere between 400KΩ to 625KΩ. Suppose you had a 500KΩ pot in a guitar, and you put in a 625KΩ pot. It's going to sound enough brighter that the player will think you swapped his pickup in the process rather than his pot. Or if you go down in value a lot, the guitar will sound dead and lifeless in the upper end. When I'm replacing pots in a guitar, I don't use any that are more than +/- 10KΩ away from the original pot I'm replacing to maintain the instrument’s present voicing. Because anything more tham +/- 10KΩ is enough to hear the difference.

When I get potentiometers in, I measure them all with an ohm meter. For example, here are three pots that were sold to me as nominal 250KΩ pots, and I've marked them with the values I took off of them with the meter. Here's one that's 219, one that's 248, one that's 270. That's a pretty fair spread.

The other thing that's important is minimum wiper resistance. I reject any pot with a wiper resistance of over 40Ω and I would rather they be not more than 10Ω. This sounds counter-intuitive when you consider that the D.C. resistance of most pickups is at least 6,000Ω, but a minimum wiper resistance of 100Ω can definitely produce audible problems and I lke to stay well below that. On the lower end, it prevents the pot from closing down to ground (that is, being able to roll volume all the way off). This can be a problem mostly with high output metal type pickups.