I have a mesa boogie m-pulse venture 2x10 combo. Ive been having an odd problem. When at my bands practice space, i can practice with it on for up to 4 hours straight with no problems. Whenever it comes time for a gig, the sound will cut in and out. Ive tried various basses, the problem is def. the amp. The amp itself stays on but just no sound. i dont do anything special to make it cut back in. it doesnt feel as if its over heating. Any ideas?