I am endeavoring to learn some lessons from an awful performance the other night. My longtime originals band performed a twenty-minute set as part of a multi-band show so setup was rushed and there was no real chance to troubleshoot. Anyway, for whatever reason my Markbass amp started feeding back something awful and I had to turn it down so low that I could no longer hear myself or be heard. Things pretty much crashed and burned from there. Is it possible the Fender Downtown Multieffects pedal that I had place on top of the amp is what caused the amp to feed back so badly? I am really chagrined.