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McIntosh MC205 hum

My McIntosh MC205 hums. It is set up with all the proper interconnects and I use a Krell HT Standard as the processor. It hums and is a bit annoying. Is this natural? I went back to my dealer and they said I had improper grounding. It is plugged into a surge protector which goes into a 3 prong wall outlet. The surge protector indicated protected but not grounded. I have an old house. There are walls that I've opened elsewhere in the house and there ground wires running from the box. So I bought a green ground wire and grounded the wall outlet to the box. Surge protector still did not show grounded.

However, I did go to my dealer, put my ear up to their MC205 and their's hums too.

So is this something natural for an $8000 amp? Any feedback is appreciated.
128x128tobaccoleafpie
face
516 posts
 
My MC-126 used to hum though the speakers also. It appears the non-autoformer models are all prone to some sort of hum.
scanido
2 posts
 
I can confirm, my 3yr old MC205 emits this hum as well. I just recently noticed it as I got a newer amp and moved the MC205 in a cabinet. The new placement excaberated the hum. I don't mind it as it's in a closed cabinet and not really audible on any type of decent listening anyways.

Seems like this is inherent in the design of these amps.
bugxo
1 posts
 
I have new MC205 and I noticed humm in channel 2,4,5. The humm was present only when unbalanced RCA cables was connected to AV receiver MX121. I disconnected cables one by one and the humm disappeared from the channel when the corresponding cable was disconnected. I sent the Amp to RMA. They said there was cold joint on ground and repaired it. Now the humm is present only in right channel (no. 5). It is ground loop. But why only 5th channel is humming? I call technicians from company that sold me the Amp to my home. They bring another MC205, the humm was present only in channel 5 too, but a little lower. So I take a ohm meter and measure resistance from Mains PE(protective earth) to ground of RCA inputs. All channels have about 3ohms, only channel 5 has less than 0.5ohms. So I think there is design problem, and the channel 5 is grounded directly to Amp ground, not through the inverting input of amplifier. So I will use Balanced cables and will hope it will solve my problem. Can somebody measure resistance on the amp? Or have somebody disassembled the amp to check this problem?
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