I am trying to troubleshoot some fuzz coming out of my Mesa Bass 400. I am kind of new to tube amps and tube distortion. Basically I am at 7-8 preamp, 7-8 master and get fuzz on low notes. If I turn up the volume more, I get fuzz on more notes. Using a Mesa Powerhouse 4x10 cabinet, with an active bass (plugged into the channel suited for active basses). Is this about the normal breakup point for tube amps? Does the breakup point occur earlier if the tubes are going? If this is because I am driving the amp to the breakup point, how can I reduce this problem and still have high/clear output?