Switching the power on and switching between sources on the amp sends a nasty 'crack/thud' sound through the speakers. Any idea what's causing this and how it can be rectified?

Sean Davey, May 2008

Try flushing the switch contacts with contact cleaner. Sometimes switch contacts get mucky and the resistance of the switch changes causing an imballance in the pre-amps. Mucky switches may not contact perfectly causing a "breakover" spark, heard as a click. You will need to take the lid off to get at these so only for the competent...

Wid, June 2008