Tracking Down Scratchy Pots

One of the most common faults in audio equipment is noisy pots - potentiometers that introduce scratching or crackling noises into the signal as they are adjusted. The problem is that sometimes a perfectly good pot will sound scratchy or crackly because of an intermittent connection or because DC is getting into it through a faulty capacitor or an out of balance direct-coupled stage. So how can you determine whether a pot really is scratchy before going to the trouble of finding and fitting a physically compatible replacement?

Tracking down scratchy pots circuit schematic

This solution is simple and involves a test setup which can be done with the pot still in circuit (but with the power off). Using clip leads or temporarily soldered wires connected directly to the pot's terminals, connect the pot as a volume control between a signal generator and a signal tracer (or audio amplifier), as shown. Then adjust the pot up and down. If the signal tracer gives scratchy noises on top of the tone from the signal generator, then the pot is faulty.
Author: Andrew Partridge - Copyright: Silicon Chip Electronics