Mcintosh transformer hum

I recently acquired a Mcintosh MC 7104. It is in mint condition, and works perfect except for one annoying issue. There is a physical/mechanical hum eminating directly from the transformer. It is not loud, but is audible from a few feet away when the room is completely quiet. It is sometimes noticeable on quiet passages from my chair. About as loud as a purring cat. I haven't had this problem with any other audio equipment, but feel it might be a power issue. Could this amp be more sensitve to power conditions or could it be defective? It does sound great except for this. Any suggestions?

B&K 4090 pre
Mc 7104 (bridged to 2 ch) replaced B&K 120x2
Yamaha MX830 (for sub)
B&W 705
Peerless subwoofer 12DVC (DIY)
Dahlquist active crossover
audioquest and vampire interconnects
i would try the amp on another outlet or a cheater plug,i owned a mc7104 & it was dead quiet,if its not some problem with your power source then i'd say it needs service,there should be no noise at all from a 7104.
I'd suggest you contact the McIntosh factory for suggestions. They're quite responsive and there's an email address on their web site for this type of request.

Also, I'd suggest you post over at the Mac board at A good bunch of folks there, too.


You also might try tightening down the transformer. I had this problem a few years ago on a Parasound amp, and tightening the 4 bolts solved the problem. However, Bigjoe is right, most Mac's don't have this problem.
My Mac 162 power amp had audible transformer noise and very audible hum coming from the speakers. It was hard to take after living with Japanese high end amps which are tomb quiet. I sold it rather than going through the repair hassles.
I have never heard a McIntosh make any sound. There could be two simple problems - the transformer got loose in shipping or the grounding is bad. The latter could be a loose chassis ground or your outlet/circuit/house has a bad ground.

You could take the cover off and check these things very easily. It should be rather obvious. Also, Joe is right about trying out a cheater plug.
As stated above, you should contact McIntosh Labs with your question on the physical or mechanical hum coming from the transformer on your MC7104. If your unit does not turn on or if your situation is an emergency, do not e-mail or fax McIntosh. Phone the factory, ask for Tech Support and leave a voice message for Chuck. He will return your call promptly.
Chuck Hinton:
Hours: 9:00 am - 5:00 pm EST, M - F
Toll Free: (800) 538-6576
Phone: (607) 723-3512
Fax: (607) 724-0549
If you have a DAC or other digital equipment they could be causing this problem. Some brands will not work well with others and there is nothing you can do, because it is air borne. It could also be getting some DC voltage off the main power line from something in your house and again a good power conditioner(not all are good at removing DC or a ground loop no matter what they cost), but I have found BPT and PS Audio to be the best for these problems, but I am sure there are others too. Hopefully it is just loose.
Jesus Is The Way,