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Noise & Hum Rating

I am having a hum issue - steady state regardless of whether the pre-amp is connected, and no change with an increase in volume - and the amp has been back to Cary where it checked out fine. At this point I've assumed it's a ground loop.

The manual for my amp, a Cary V12R, states "Noise/Hum: > 84db below rated output." Output on the amp is 50 watts triode and 100 watts UL. Does the rating suggest that there will always be some hum and that this is normal? Does anyone know how this rating works at a practical level? Cary didn't have much of an explanation except to say that yes, some hum is normal.

Thanks!
grimace
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rodman99999
6,188 posts
 
Unplug the other equipment from your AC outlets, one at a time, while still disconnected from the Cary.
grimace OP
624 posts
 
I did move the pre-amp to a different power supply, which helped, but the hum did not go away entirely. Unfortunately the cheap Monster power supply is not quite as clean sounding as PS Audio.

The hum itself is barely audible, and not at all when music is playing. I may simply be over-thinking the problem. It's certainly livable.

Would a dedicated line from the box in the basement improve this condition? It seems that if another circuit in the house is creating interference it would effect the dedicated line too, since all of the lines would originate from the same panel. Is there a way to install a sub-panel to keep EMI/RFI from traveling up the line?
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