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Author Topic: KM184's receiving electromagnetic interference  (Read 5011 times)

bjorn400

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Re: KM184's receiving electromagnetic interference
« Reply #15 on: April 21, 2006, 12:56:37 am »

I just tried the grounding of the female xlr to the chassis, and it didn't help.

I also hooked up the mics into an mbox hooked up to an ibook running off the battery.  I still got the EMI, so that proves that its not coming from my electrical outlets.  

bjorn
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Rick Sutton

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Re: KM184's receiving electromagnetic interference
« Reply #16 on: April 21, 2006, 01:33:49 am »

Bjorn, Ouch! I feel your pain. nothing like a massive industrial machine outside your recording environment spewing ugly crap into the air.
Here's my "stupid pet trick" that I'd try. Don't laugh, I'd do it just to see if it affected anything.
I'd take the mike and the cable that has ground attached to the shell and put it in the worst spot you got. With headphones on I'd take a 3/4" steel pipe about 8" long and clip lead the pipe to the xlr shell at the back of the mic (shell must be grounded). Listening to the interference in the phones I'd slowly insert the mic into the steel pipe and see if the pipe lowered the noise and where and how much of the mic had to be inserted. Might not do anything. Might do something. I'd just want to know if that pipe shield would help. If it does then I'd look at ways to use the mics (for the time being) with some kind of shield that didn't look like a plumber built it.
Also, I know that you don't have ths problem with other mics on the same cables, but it is possible that it is a mic/cable combination that is setting up an antannae effect. I believe that it is on klause's forum that interference problems have been discussed that have been solved with certain cables.

Have you been on the Neumann forum? Seems as though they would have suggestions.
Just some thoughts.
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Shawn Lindell

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Re: KM184's receiving electromagnetic interference
« Reply #17 on: May 22, 2006, 05:24:14 am »

I have been having similar problems with a matched pair Km184s.  The only difference that its only in the second mic in the pair when using both mics.  I am running them through a Neve 3108.  I have also been having the same problem with a TLM103s which are also a matched pair.  I figure its some weird grounding issue in the console, because it doesnt happen when i use external pre's.  Any one have any ideas?
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Bob DeMaa

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Re: KM184's receiving electromagnetic interference
« Reply #18 on: May 22, 2006, 03:11:44 pm »

When you plug the mics in, is the Phantom power already on, or are you turning the phantom power on after the mic is plugged in. I was using a Pair of Nuemann TLM 103's a few months back or maybe it was the AKG 460's, I can't recall, either way they were plugged into my Great River while I had left Phantom Power On. I don't have the manual in front of me, But it stated something the the effect of don't plug the mics into the pre with phantom power on because it may "magnetically charge" the capsule ot something similar. (I'm sure it didn't say Magnetically charge, that's just my mental picture book explanation) When I disengaged the phantom, waited a few seconds, and re-engaged, I never heard the noise again. (The Noise was the Strange random clicking, which actually varied depending on how much moving around the performer was doing.)

One of the posted mentioned the strange clicking noises, and it reminded of this.

Bob
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bjorn400

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Re: KM184's receiving electromagnetic interference
« Reply #19 on: July 03, 2006, 11:20:34 am »

I had a thought recently that maybe the problem isn't the frieght elevator nearby(the landlord says the power transformer is in the basement and I am on the 4th floor), but it may be due to the fact that my apartment is on a hill facing all of manhattan without obstruction of any sort.  Nice view, but I imagine there are a great deal of different frequencies and garbage with a straight shot to my studio.  
Just a little tin foil wrapped around the base of the mic solves the problem 100 percent though. So I'm less frustrated at this point.
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Johnny B

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Re: KM184's receiving electromagnetic interference
« Reply #20 on: July 03, 2006, 06:48:09 pm »

Did anyone mention the use of ferris metals?
(i.e. a metal that can be picked up off the ground with a magnet,)

Good old fashioned "steel" is often used as a shield because, unlike aluminum or copper, which, are weak shields in comparison to good old fashined steel, steel can shield out Both EMI and RFI. Thus, steel shielding kills the two birds, EMI AND RFI,  with a single stone.

Lead, although toxic in high doses to humans,  and more expensive than plain old steel, can sometimwes work wonders too depending upon the application.

Professional products will also shield out both RFI and EMI, these are available from:

http://www.magnetic-shield.com

http://www.magnetic-shield.com/faq/pma.html

http://www.magnetic-shield.com/newsletter/vol1-3/p1.html

http://www.magnetic-shield.com/shielding/material.html


Hope this helps.   Smile


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"As far as the laws of mathematics refer to reality,
they are not certain; as far as they are certain,
they do not refer to reality."
---Albert Einstein---

I'm also uncertain about everything.

bjorn400

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Re: KM184's receiving electromagnetic interference
« Reply #21 on: April 18, 2007, 10:56:24 am »

fyi...i no longer get the interference from my mics(at least not today).  Yay.  Whatever it was has been fixed or stopped. Don't know when that happened because I have been wrapping them in tin foil ever since the first problem.
thanks for the help
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