I had a similar hum problem on a D-150A-II amplifier. Turned out to be the high voltage (70VDC) power supply capacitors. This uses one of the AC windings and a voltage doubler. It is drawn in above the +60V supply rail on the amplifier schematic. The two caps are both 10uF but NOT equal in voltage. I replaced them both and the hum went away completely. C4 and C5 on the main board.
I recall seeing that same amp on fleabay and figured it would be a simple fix, but I didn't need yet another DC-300A amp.
kcboobooMember Since 18 Nov 2009
Offline Last Active May 05 2016 07:05 AM
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