Motor Boating?

[lefizz]

My amp setup uses a 100 watt class T amp and the TL071 based preamp many people here have help me with.

The issue is this, at high gain setting, i.e. when i want to play loud, the amp ocassionally gets stuck it a sort of weird feedback loop with the Bass driver pumping in and out slowly with no input from the guitar. Is that called motor-boating? Even totally dampening the strings doesnt stop it, the only way to control is it to either turn of the amp or cut the volume right down for a moment.

I was wondering what causes this and what could be done to reduce/eliminate it.

Any feedback(no pun intented!) greatfully recieved.

Phil

[LJ King]

Motorboating is almost always caused by a low frequency feedback path through the power supply.

Increase the value of the power supply decoupling caps, or replacing old ones that have lost some capacitance usually corrects the problem.

[joecool85]

Motorboating is almost always caused by a low frequency feedback path through the power supply.

Increase the value of the power supply decoupling caps, or replacing old ones that have lost some capacitance usually corrects the problem.

I would try replacing the old caps first, electrolytic caps only last for 15-25 years anyway.