Technics SU-A600mk3 amp sound problem?

It is most likely the amp. The crackling sound is often because dirt has gotten into the potentiometer (pot) that the volume control knob turns. The tip off is the crackling sound as you rotate the control. This can be fix by spraying electronic cleaner into the small openings on the pot. Any repir place should be able to do this in ten minutes - if that is the problem.
If your volume control is electronic, i.e. push buttons up/down, this answer does not apply and you probably have a problem in the amp circuitry.

Doc
May 2007