My hartke 3500 amp is sick. it sounds like the input jack is barely making contact, there is a little bit of sound coming out of the amp, and it fluxuates, it will be louder then go back to being quiet. The sound is also very fuzzy. I've checked all my cables and my bass, and my cab, and it is the amp. So my question is, is this going to be a costly repair? Could it just be a bad solder? Thanks for your help in advance.