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Question about hum from speakers

I know there's at least one amp engineer here... I'd like some help.  I bought a used solid-state amp from ebay; the ad read " McCORMACK POWER DRIVE DNA-.5 Deluxe REV B POWER AMPLIFIER - EXCELLENT CONDITION!"
Well, I swapped it in, replacing a Dynaco Stereo 120, and there's a hum from both speakers.  I have to believe that the seller was well aware of the hum.  What I'm wondering is, is the hum a result of some electronic component(s) in the amp failing (or having failed), such that it's salvageable by replacing the bad component(s)?  Or would that be hoping too much?
bhakti-rider
erik_squires
16,349 posts
 
Disconnect all inputs. If it is still occurring chances are you have a failing power supply component. Not rocket science to identify and replace

If it does not, you have a ground loop. That's very system dependent.
stringreen's avatar
stringreen
6,483 posts
 
Try running a wire( any kind) from amp to the screw of the wall plug faceplate
millercarbon's avatar
millercarbon
12,531 posts
 
Either way you got one of the finest power amps on the market regardless of price. I know, I had one. Very hard to beat. Worth the work if it even needs it.
yogiboy's avatar
yogiboy
5,746 posts
 
"I have to believe that the seller was well aware of the hum. "

If that’s the case you should return it and get your money back! Why would you keep a defective amp?
deepee99's avatar
deepee99
86 posts
 
Your power supply cap(s) are shot. Easy to replace if you’ve any skill with a screwdriver and a soldering iron.Likely you had one bad cap, and nobody noticed. When the second one failed, that’s when the AC hum started. And in defense of the seller, these literally can fail overnight.I doubt if it's a ground-loop all of a sudden. That hum would have occurred  with your original amp.

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