The Secret Life of Pots
For a few months, my wife’s old Pioneer amplifier has given us bad volume control at lower volumes. Unless it’s turned up pretty loud, the volume will jump up and down even though the know isn’t being moved.
But now I’ve found an article that might explain what’s going on. The volume knob is just attached to a potentiometer, and the potentiometer, or “pot” has just worn out.
The wiper literally wears a path through the conductive strip. When all three contacts get all the way through, they don’t make contact any more, and the pot quits functioning. During the normal life of the pot (that is, the wear-out process) the bits of resistive material gouged and work from the resistive strip stay around and can actually lift the wipers from the resistive strip. If there is a DC voltage across the pot when this happens, the wiper loses and then regains contact at a different DC level than it left, so it makes a scratch or click.
