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?

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


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