So I just finished building a 20watt amp, and it's decided it doesn't want to be a amplifier. I Have the preamp running into the Amp, and it's grounded and everything. i plugged my mp3 player into it to test, and it works for that, but when I go to plug in the bass, it doesn't make any sound but a buzz (which is always present). What did I do wrong? I know that the mp3 player has it's own preamp already, so is it the preamp that's not working? Or is it something else? The guitar is all wired up correctly, and has a fresh new battery (it's an active bass). Any help would be great.