How can unwanted ringing and audio instability be prevented in an op-amp audio filter?
Why In an active (op-amp) filter, high Q means the feedback network is very lightly damped, so any transient rings for a long time before decaying, and high stage gain adds to the loop gain that keeps that ringing alive. Excess loop gain combined with phase shift in the RC network can turn the filter into an oscillator. The cure is to keep both the per-stage gain and the Q modest, cascading several low-Q, low-gain sections when a sharp response is needed.
Watch out The choices that raise one parameter while restricting the other miss the point: gain and Q both feed the same loop, so pushing either one up brings the stage closer to oscillation, and a very high Q alone will ring even at unity gain.
Both knobs down: high gain plus high Q equals ringing. Cascade several gentle stages instead of one sharp one.