2. amps-preamps
  3. 1226436662

Ground Loop Issue 427

After talking with the manufacturer's of both the amps & preamp, I still have a 60hz hum. Here's the story:

Just changed amps to 845 SET monos, and now I hear the hum whenever the amps are on and RCA interconnects are connected to the amp inputs. Didn't have the problem with two prior pairs of amps. The pre could be turned off, and I still hear the hum. With shorting plugs in the amps, no hum.

The pre is battery powered, with no ac cable, and the trouble persists whether or not any sources are connected to the pre.

I've tried multiple types of interconnect, including the heavily-sheilded cheapos from a vcr, but no change.

One friend questions if adding a "hum potentiometer" to the amps would make sense. Others have suggested the $600 Granite Ground Zero, which is unaffordable for me.

I've already tried cheater plugs any/everywhere. I've added a grounding wire between the monoblocks metal bottom plate and floating one power cable while leaving the other grounded, all per the amp manuf's suggestion. I've tried HighWire LiveWires, which might be good sonically for RFI, but aren't helping the hum issue. This is a music only rig, no cable tv anywhere in the room. I am in a heavy RFI area, 1000ft from a radio tower, if that matters...

Anybody got any suggestions other than moving elsewhere? Thanks,

Spencer
128x128sbank

Showing 1 response by armstrod

armstrod
601 posts
 
Since you can short the amp inputs and the hum goes away, have you tried a different preamp? If the hum goes away, you know it's some sort of incompatibility between the preamp and amp. You've already tried the preamp with other amps and it was fine, so I'm guessing the hum will still be there when you switch preamps. That means your amps probably hum with everything, so either they have bad design (unlikely) or they were put together wrong, e.g. a bad solder joint, a wire misrouted, an input jack accidently shorted to chassis, something like that. Will the amp manufacturer take it back and check it out?

David
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