2. amps-preamps
  3. 147825-119821

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
bhakti-rider OP
44 posts
 
Erik & Yogiboy:  I did disconnect the inputs, and there was no hum.  So I found a spare cheater plug and inserted that, connected the inputs again, and the hum was gone.  Thanks!
erik_squires
15,709 posts
 
Do not use the cheater plug as a long term solution. It does indicate you have a ground loop however.


It also absolves the previous owner. :)
bhakti-rider OP
44 posts
 
Erik, what is the long-term solution?  I'm using one for my PrimaLuna preamp too, and if there's a correct approach, then I need to employ that for both of these.
erik_squires
15,709 posts
 
bhakti


That is a safety ground. Lifting the ground could lead to fires and lethal voltages at the case. That's why the ground wire in your outlet is required to be the same gauge as your power line (12 or 14 gauge) : So in the event of a short to the case a breaker will trip.


The best way to fix it is to identify the root cause. Often this means making sure multiple equipment is on the same strip or outlets or adding isolators to any external coax lines (for cable/internet or outside antennas).


Unfortunately it's no one solution. 

Best,
E
Post removed 
More to discover