Last Thursday, I was jamming on my amp and it sounded perfect as usual. When I'm playing by myself before I meet with others I usually set the volume controls pretty low with the master at 1 and the clean gain at about 4-5 to get a mild breakup, but still very clean sounding. When I'm jamming with others, my controls have the master volume at 3 and the clean gain at 6-7 or the overdrive right on 6 so I get a pretty good grumble going but still pretty clean. Yesterday afternoon, I turn it on my low volume settings and the gain is extremely high with virtually all clean headroom gone; the overdrive channel is essentially a Big Muff with it's nuts caught in a sling. Before looking at the amp, I looked over everything else to see if I set up something wrong. I checked my bass' batteries, changed them out for new ones, all cables are good, so it is the amp itself causing this. Could it be something wrong with the tubes? I swapped them all out last year and I never experienced a problem since. I do play with ALOT of fuzz/dirt pedals though, I don't think that would be the problem though. Any thoughts?