KEELEY ELECTRONICS COMPRESSOR PLUS General Troubleshooting

100k-Ohm Linear Potentiometer

The Sustain knob is a potentiometer that uses a physical wiper sliding across a carbon resistive element. Over time, friction causes the carbon to shed or oxidation to form on the contact points, leading to intermittent electrical connection during rotation. Replacing the physical potentiometer restores a clean, continuous resistive path and eliminates the audible artifacts.

Polyester Film Coupling Capacitor

If a coupling capacitor in the signal path fails and 'leaks' DC voltage onto the potentiometer, the wiper will cause a scratchy sound regardless of the pot's cleanliness. Replacing the capacitors upstream of the Sustain control ensures no stray direct current enters the variable resistance stage.

CA3080A Operational Transconductance Amplifier

In Ross-style compressor circuits, the Sustain control interacts with the bias of the OTA IC. If the IC's internal gain-cell is unstable or failing, it can manifest as noise during bias adjustments, though this is significantly less common than mechanical pot failure.