In fact, pretty new to upright. I had some lessons years ago, and was recently given a bass in need of some tlc. Still working on the tlc part... but I picked up an MB112 combo (GK) to use it with, and played a couple Sundays at the church my wife's been handling the music for over the summer. We did some old-timey gospel, bluegrass, etc., and I found that if I turned the amp up a good bit I got feedback from the bass. That may be obvious... but being I just had a little piezo p'up on the bridge, I don't get the energy coming back to the string that way. On electric I presume it's the pickup acting on the steel string in a loop of increasing energy. But my doghouse is just a big box, no magnet of any consideration really. How does this work? How do you guys stop it? Thanks for taking the time, much appreciated.