I've had this amp for over a year and I'm pretty much happy with it. But I have experienced now 2 times that while playing, the amp just stops working. The lights are on and the fan is running but there's no sound comming out. The input was not clipping and the master volume was never higher than 10 o'clock. I've had the amp checked by the shop after the first time, but they couldn't find anything wrong with it. 1st time I was playing quiet jazz with a passive 6-string bass on a 1x12 cab (8ohm). The amp had been running for aprox. 1 hour. Suddenly the sound stops comming out and it doesn't return. The next day the amp is back to normal. The 2nd time I was playing an active 5-string on a 4x10 cab (4ohm). The amp had been running for maybe 6 hours and the sound starts to go on and off. The two incidents are roughly 7 months apart. Does anybody know what is causing this ?