Speaker Hum

I have a very loud hum emitting from my speakers when only my power amp is on, however with the preamp switched on the hum reduces greatly although still audible. Any suggestions as to why the problem exists and possible solutions would be greatly appreciated.
My system:
Adcom GFA555
BK Pro5 Preamp
Sony X111ES
Nakamichi CR2A
Parasound DQ 1600
Klipsch Forte
Audioquest Topaz interconnects
Saxton 12 GA. copper stranded speaker wire