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Chasing 60 hz hum

I have an MC 7150 and an MC 7104 in my system, both plugged in to the same circuit on a power strip. The problem is that McIntosh went away from two prong and moved to 3 prong grounded wiring when the 7104 came along. I also moved from a C39 to an MX119 preamp, again the change from ungrounded to grounded. Having these units together on the same circuit produces a nice fat 60 Hz hum. To cure this, I used cheaters (3 to 2 adapters) on the 3 prong devices and this works.......mostly. Then, every few months the hum comes back and I go to the strip, wiggle one of the adapters a little bit and it stops....but this is a pretty goofy way to run an otherwise nice railroad....anyone got any ideas that are not radical (such as rewire the house!)
broimp
jea48
2,944 posts
 
11-10-11: Kirkus
Actually I've experienced at least as many grounding-related problems with "double-insulated" equipment as those with safety grounds. This is because they still have leakage reactances in their power transformers, and thus AC-related currents will still flow between their chassis -- this will now be flowing wholly through the interconnect shields. And for unbalanced interconnects, the shield resistance then becomes the primary dictator of the attainable hum level.
Al,

And in how many cases can the problem be blamed on the manufacture of equipment for not checking for the proper AC orientation of the primary winding of the transformer..... .
Jim
almarg's avatar
almarg
8,673 posts
 
And in how many cases can the problem be blamed on the manufacture of equipment for not checking for the proper AC orientation of the primary winding of the transformer.....
Good question. I don't know the answer, of course, but it wouldn't surprise me if it is 50% :-)

Best regards,
-- Al
broimp OP
10 posts
 
Guess I stimulated some good discussion here. Thanks to all for chipping in.
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