LanceB

I have the KA-1000-THX Amp that just started to buzz, even with the input disconnected. The buzz is not too loud, so I am thinking a capacitor went bad somewhere in the unit. The buzz gets louder when the THX switch is turned off. I open the unit, disconnected the preamp connector from the main amp board, and the buzz stopped, so it looks like either the preamp or the power supply is creating the buzz. Any thoughts? Are schematics available? Are parts available?