I have a line 6 spider 4 15 watt amp that i bought from a friend of myn. When i first got it worked perfectly. afer a few weeks i noticed that the sound was dull and it was not the volume becuase i turned it up. Out of frustration i hit the top of the amp and the sound got louder nd clearer for a few seconds. Thats when i was sure that something was wrong. I can not seem to find what is the problem and i am hoping that someone here can help me. Thanks.