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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
ghdprentice's avatar
ghdprentice
9,466 posts
 

The only hum I have ever had was created by having some of my system components plugged into one outlet and some plugged into another. I assume you managed to plug them all into the same outlet and the hum still exists... correct? I solved it by getting another direct line from the same breaker box (we have two).

motoraway's avatar
motoraway
68 posts
 

This may be worth a try.......I used a Rolls MB 15b ProMatch converter when I was experiencing a similar problem between amp and preamp. It eliminated the hum completely and to my ears didn't taint the signal path. It's relatively inexpensive piece of equipment. I still have the unit, but it's no longer in use since I've parted ways with that amp/preamp combination. 

 https://rolls.com/product/MB15b

zlone
1,353 posts
 

I am confused, did the problem exist before you established a second ground and/or clipped the ground wire to your breaker box? BTW, pretty sure separate grounds are frowned upon, and can pose some risks.

erik_squires
17,551 posts
 

Using an isolated ground is expressly prohibited by the National Electrical Code.  It is unsafe and may also prevent any surge protection from working correctly.  For Audio, it is also completely unnecessary.   You would have seriously created a less dangerous situation by just lifting the ground altogether, which is also a bad idea.

It’s highly likely that you have an issue with the voltage differential between your new ground and neutral, and some gear may be more sensitive to others, causing the hum. 

There is exactly 1 condition under which you can use an isolated ground, and that is when you have an isolated power generator, such as solar, or battery back up that is not otherwise bonded to the incoming grounding electrode system.  So if your only priority is to have an isolated ground, then you have to have an isolated power generation system as well.  

Of course, should something happen to you, or you sell the house, this wiring mistake will live on with no one aware.  

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