2. amps-preamps
  3. 1176092929

Massive buzz when using CJ PV10A with NAD C372

I think I have a ground loop problem, but the magnitude of it is so off the scale I am not sure where to start. Help, please.

I have an NAD C372, Magnepan MG1.6, and a Vandersteen 2Wq sub. A friend loaned me his Conrad Johnson PV10A for the next month. I am very eager to hear what a good tube pre-amp stage will do.

The NAD pre-amp stage was completely disengaged. The Vandersteen sub was also removed from the configuration. The CJ's main outs are tied into the main in's of the NAD. CJ is turned on first and then the NAD.

When the NAD powers up, I get a massive buzz. I am talking about a cover-your-ears, jump-out-of-bed loud buzz.

I re-configured the system to use the NAD pre-amp stage with the CJ signal on the AUX input. I can now at least control the volume and hear the hum safely. It most definately sounds like a the buzz from a ground loop problem and it is independent of CJ level setting.

When I gradually increase the NAD volume level I notice a change in humm character as I get into the low-mid range. If I crank it a bit more and/or leave it on at that moderate level, the NAD detects something is not right and shuts down.

I've heard ground loops before, but this one is so dibilitating that I wonder if there is a fault in the CJ unit.

Any ideas? Thanks.
sonicrealism
aball
2,016 posts
 
Yeah, sounds like there is something wrong with the CJ. That it too bad but Lew Johnson is a swell guy and he can get it fixed, no problem.

Arthur
sonicrealism OP
6 posts
 
Perhaps I spoke too soon.

Do these preamps require 20 seconds or so to warm up before processing a source signal? The painful loudness of my first experience hooking this up has caused a hypersensitivity to having it on if something seems wrong. I quickly turn it off if I don't hear what I think I should hear. I have since found if I leave it on for 20+ seconds I get a signal processed through the preamp.

I have also discovered that tying the ground post on the CJ to the negative of one of the main out RCA removes a component of the hum but not all of it. There is a lower frequency component that remains. I am not sure, but it is almost sounds like I remove a harmonic.

In case anyone wondered, I have also pulled the surge protected powerstrip out of the equation and instead used an unprotected connection back to house power. Having it in or out of the configuration makes no difference.

So, I'm back to having a signal but noise that I cannot remove by any means I know of. This time I am truly out of ideas. I sent an e-mail to Conrad Johnson last night and referenced this tread. Hopefully someone there will have some ideas.

Thanks for the help.
sonicrealism OP
6 posts
 
I had the CJ looked at. Lot's of DC noise present. It needs repair. I need to talk with my friend who loaned me the unit before doing anything else.

Thanks for the help.
akpt
1 posts
 
Sonic, if you happen to still signin could you share what the issues was and how it worked out?  
Thanks 
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