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Strange Grounding Problem?

I have a unique grounding problem unlike any in my past experience.

I'm using a pair of the latest NuForce Reference 9 amplifiers and a dbx 14/10 equalizer that has a two prong AC plug with a floating ground. The NuForce amps and preamp use 3-prong grounded AC plugs.

I have a kind of low-level spitty high-frequency noise in the left speaker when using the dbx. It is audible a few feet from the speaker if you listen on axis. It can't be heard at the listening position and doesn't affect the sound quality, but I'm a nit-picky kind of guy.

If I turn the left monoblock on first, there is no noise, but when I turn the right amp on, the spitty hissy noise appears in the left channel as soon as the relay kicks in. There is no hum, so that's not an issue. Even more oddly, if I turn the power off on the EQ the noise gets louder and can be heard in the right channel as well. If I unplug the dbx the noise diminishes. If I bypass the dbx EQ and hook my solid-state preamp directly to the amps, both channels are stone dead silent. Problem is, I have a broad bass peak in my room at 125Hz and I need the EQ for the system to sound natural.

I was thinking of buying a Behringer EQ, which should be more quiet, but I'm not convinced it would sound as transparent as the dbx. I was just wondering if anyone has experienced this type of odd problem and if it could be easily resolved.

I switched the amps from left to right and that did nothing. I also tried grounding the dbx chassis and that did nothing. I use a PS Audio UPC-200 power conditioner and my AC power is relatively clean. I must be missing something, but I'm not sure where to look at this point. The only thing I'm fairly sure of is that the problem is somehow centered on the dbx. The negative sides of the input/output jacks are linked to the chassis by small capacitors for RFI rejection, but I don't think that's the problem. Any help or insight would be appreciated.
plato
plato OP
1,543 posts
 
Hi Jea48,

That's interesting, but actually, I did reverse the plug polarity, but there was no change in the noise.

Maybe reversing the plug and then grounding the chassis to the preamp would work, but it seems like a long shot.

I'm still waiting for a call back from NuForce, so I'll see what they have to offer, if anything.

Best regards,
Frank
plato OP
1,543 posts
 
Just to follow up, Jason at NuForce did offer to check over my equalizer if I send it to them. However, since I can only hear the hiss up close to the speaker and don't particularly want to take my chances with shipping right now, I think I'm going to leave well enough alone.

Thanks to all who replied and Happy Holidays!
beno1967
1 posts
 
I had a similar problem using nuforce ref 9 monoblocks with inputs (single ended) from my Apogee DAX crossover to the ref 9 monoblocks. When my apogee minigrand speakers were run directly from the ref 9's there was a barely audible tweeter hiss - more on the left than right. When a active crossover was introduced (first the Apogee DAX then a Hsu high end crossover) the hiss became a blaring wall of white noise before the amps cut out (scaring the daylights out of me).

I have since tried using balanced interconnects between the Apogee DAX the Nuforce ref 9's. This seems to have removed the hiss altogether.

I'm certain the source of the hiss was the Nuforce monoblocks. When I replaced them temporarily with my old Audiolab power amp connected to the crossovers with single ended interconnects no hiss was heard.
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