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persistent 60 cycle hum only on tube gear

I know this topic has been addressed in the past but I'm hoping for the "latest tech" answer.

I have a persistent 60 cycle hum in my ARC tube gear. Not in my Bryston power amps or preamps- just the ARC tube pre and power amps. All XLR. 

I have installed an isolated, dedicated ground system (8' copper rod driven into moist earth) , a Ground Master unit between the chassis and the ground line, I  clipped the ground wire from my 20a 120v dedicated circuit, pretended to ignore the hum (that didn't work well).  I even replaced the tube sets with ARC OEM tubes in the pre and power amps (sonic improvement but no hum cure) .  Still the confounded hum.

Before I spend more money and failing I'd like your personal experience opinion on what worked for you. 

Thanks!

 

yesiam_a_pirate
retiredaudioguy
290 posts
 

I wondered and googled

"why is an isolated ground is prohibited by the electrical code?"  The result is to long to paste here. 

There is a rather exhaustive explanation of why it might be a bad idea.

 

skids's avatar
skids
120 posts
 

Remove the groundmaster/separate ground, and try different xlr's.. I guess ground loop or bad cable/s.

langla4
67 posts
 

If all else fails, I’d check the transformers.  Some are just noisy but it is inaudible when playing. My tube gear uses all Hashimoto transfers and we needed ‘pots” to drop the hum.

yoyoyaya's avatar
yoyoyaya
1,065 posts
 

@OP As above, you don't want your amplifiers grounded separately to the rest of the system. Apart from that, does your ARC pre mum when connected to the Bryston power amps. If not, there is always the possibility of bad filter caps in the ARC power amps. But ground loops still remain the main suspect.

jasonbourne71's avatar
jasonbourne71
1,842 posts
 

The power supply caps on either or both of your ARC gear may be dying. Since everything thing else is working fine that is what I would check.

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