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I work for a small radio station that recently acquired a refurbished Dell PowerEdge 1950 server. After placing it in the server room along with several other servers and sound processing hardware (including a sound mixer), we noticed that the headphones and monitor speakers in our radio studios (which are connected by XLR cable to the mixer in the server room) suddenly started making a low but high-pitched and very noticable sound at all times while the server is powered on.

Immediately, I suspected that some kind of electromagnetic interference generated by the new server was causing this sound, but I don't understand why this server would cause interference while the four other servers in the same room do not. Also, the sound does not seem to get lower in volume when the server is moved further away from the mixer or XLR cables.

Has anyone encountered something similar? Is it electromagnetic interference or some other phenomena? How do I reduce it?

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Maybe the folks over at electronics.stackexchange.com could be of more assistance here? –  Martin Oct 10 '13 at 11:10
    
Is everything grounded properly? From rack to ground plus ground power? –  pauska Oct 10 '13 at 11:50
    
@Martin EE.SE is more for people designing electronics, I'm pretty sure troubleshooting stuff you've bought is OT. –  Ward Oct 10 '13 at 16:15

2 Answers 2

up vote 6 down vote accepted

I've been a systems administrator for a TV+radio station a few years ago, and I also had lots and lots of analogue broadcasting units in my server room.

What I did was to make sure that every single piece of broadcasting equipment was properly grounded. I got an electrician to run a new, isolated ground feed to the server room, which I then terminated at the overhead cable guides (metal). I then ran ground cables from the cable guide down to each rack cabinet. I also had a online UPS which filtered any kind of voltage jumps.

It's also important to make sure that the equipment in the other end is grounded.

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It does seem like it is EMI. Your use case is quite unusual so it's unlikely many people will have encountered it.

As you have determined that it is the new server that is causing the problem by the simple expedient of turning it of and on then (I'm guessing you have no support) you're going to have to diagnose the hardware yourself.

If you have other 1950's you could try swaping modules from one to the other. Failing that you're kind of stuck.

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One possible option would be to use fibre connections for as much as possible. There are commercial products available for EMI shielding of these type of things. hollandshielding.com/?p=Nieuws&id=109&Lang=2 and so on. –  Tom O'Connor Oct 10 '13 at 11:11
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If turning it off works - my second "easy-fix" step would be to see if it still does it with all of the cables removed. And then, if applicable, test each PSU separately too –  Dan Oct 10 '13 at 11:12
    
I've tested each of the two PSUs seperately, but I don't see how I could test it with all cables removed. As for EMI shielding, it seems like it would be more expensive than replacing this server with one that doesn't cause these problems. Are there any components other than the PSU that could be causing EMI? –  Aqwis Oct 10 '13 at 11:36
    
@Aqwis: pretty much anything electronic in the box could cause the problem. –  Iain Oct 10 '13 at 11:43
    
I guess I meant to ask what could likely cause the problem other than the PSU. For instance, it seems unlikely to me that the RAM would be a problem, but the hard drives would be more likely. (However, I'm using the same hard drives in another server.) –  Aqwis Oct 10 '13 at 12:19

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