My SVT 4 pro seems to have some problems. It does not get very loud through my old fender 2x15 and the clip light comes on a lot during normal playing and slapping. I have tried a number of things such as pushing in the pad button, turning down my bass volume. But the amp usually just shuts down after about 10-20 minutes of use. It was repaired by Ampeh here in St Louis once before. I have seen similar analysis of this amp here and elsewhere and am just wondering: Is this model just a lemon?