Zakk-w

I play a Epi LP Custom I have standard pickups a the minute but it cant get a good distortion sound out of this at all it sounds great clean which makes me think its not the speakers but it sounds terible distorted i can get a quite nice sound for solos but power chords and such sound horrible very unclear sounding if that makes any sence is there somthing i can do? Iv tried loadsa diffrent settings btw or is it just a crap amp??