My Peavey Ecoustic 112, a 2-channel amp which I am generally very happy with, has a "feedback control", notch filter type. It consists of a horizontal slider marked "Frequency" with a range of 40 Hz > 2K, and a dial-type "Notch" control with values of -27 up to 0.

What I would like to figure out is: how do you actually use this thing to reduce/eliminate feedback? Documentation is completely unhelpful. The only thing I have figured out, is that if you sweep the slider across the frequency range while playing, there is a point where the volume drops perceptibly, then it goes back up. OK, is that the notch? Is there a feedback-prone frequency or something that I should be tweaking? I was having feedback problems at my last gig, at which I didn't bother using pickups since constant instrument-switching made it handier just to mike the guitars/mandola.

This amp has other controls that drastically affect the sound, especially a switch for either active or passive pickups. I usually set it to passive, which gives much more volume, so I don't have to use a separate preamp.

I have yet to find a description of notch filters that is written for musicians rather than for electrical engineers. Anyone want to have a go?

W-O