I have a single channel combo amp. By turning the "volume" (preamp stage) up to about 5, I used to have a great clean tone with just a touch of distortion on the peaks.
One night at a show, somebody borrowed my amp and had everything cranked to 10 for an entire set. Now I'm getting really bad distortion (with the overdrive turned off) unless I turn that volume down to 1 or 2 and turn up the master volume. At first I thought the speaker was blown, because that's almost exactly what it sounds like, but that's not the case. My observations lead me to believe that the problem is with the preamp or somewhere in the preamp stage. Any ideas?