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Author Topic: KM184's receiving electromagnetic interference  (Read 5012 times)

bjorn400

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KM184's receiving electromagnetic interference
« on: April 15, 2006, 11:11:16 am »

Hi,
I just got a pair of lightly used KM184's(their bodies are in perfect condition, no wear at all, in box, with all clips and screens). I plugged them into my system, and I find that they are receiving EMI(electromagnetic interference), like the way a single coil pickup buzzes when you are facing a specific direction(or 180 degrees opposite that direction.)

None of my other mics are humming this way(studio projects c1, sm 58, Microtech Gefell M930), and both of these pair are being affected in the same way. I have tried many a cable, so thats not the problem.

Only when I clutch the mic body in my hand does the buzzing go away totally no matter which direction it is pointing.

What is causing this? Why are the km184's experiencing this and no other mic. Are they bum? Is there something special about their construction that makes them susceptible to EMI? They do sound great when the buzzing isn't there, but that only happens when I'm holding it. Is it a grounding problem in my building?

Are there any suggestions for how I can stop this?

thanks
Bjorn Quenemoen
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Rob Darling

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Re: KM184's receiving electromagnetic interference
« Reply #1 on: April 16, 2006, 01:42:09 pm »

Bjorn- what kind of sound is it?  I've seen something strange with three clients recently, all in different parts of the city, with two different Neumann mics- 2 with u-87's and one with a tlm 103- and all at about the same time, just around this past Thanksgiving- developing a problem they never had before.  

It is like a cyclical clicking, like the sound of a motor.  It is related to 60 cycles but isn't any normal ground hum at all.  It is different from straight rf- no voices, no sweeping or phasiness in the sound, no shift by moving it around- and it is different from basic ground hum in that there are almost no higher frequencies in it and there is a definite switching of on and off to the sound, rather then a constant hum.  And it is pretty low in level- it is only on quieter performances requiring, say, 42db of gain- where you start to hear it.  Very strange. And yes, grabbing the mic and grounding to it seems to make it go away.

Is this similar to what you've had?
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OOF!

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Re: KM184's receiving electromagnetic interference
« Reply #2 on: April 17, 2006, 01:21:00 am »

i have the same thing with my 184s, which is one reason i hardly ever use them anymore. grab them and the problem goes away. i thought it was just living in midtown manhattan.  sometimes, and only sometimes mine make a very high pitch sound that goes on and off.  like dog whistle freq.  i took them in to joe leyung years ago and he "put them in the bomb"- this hilarious bomb-like contraption- to fully isolate them from the real world, and measured no noise.  so it's definitely picking up something in the air.  poorly built surface mount neumann crap.
never found a solution other than using m300s instead. (huge sonic improvement as well)
good luck and let us know if you find a remedy,
david lawrence
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Rob Darling

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Re: KM184's receiving electromagnetic interference
« Reply #3 on: April 17, 2006, 09:18:42 am »

I definitely think "surface mount Neumann crap" applies here- no other mics have this issue- but what is interesting is that the noises have kind of come from nowhere after functioning for a long time.  Also interesting is that it is a noise I've actually never heard before.

r.

ps- does the pitch start high and then descend, and then the mic is gone, only to come back later?  I think it's a phantom power thing.  
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Dominick

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Re: KM184's receiving electromagnetic interference
« Reply #4 on: April 17, 2006, 11:41:02 am »

[quote title=bjorn400 wrote on Sat, 15 April 2006 11:11]Hi,
Only when I clutch the mic body in my hand does the buzzing go away totally no matter which direction it is pointing.

Make sure the cable you are using is properly constructed. The shield must be connected to both pin 1 and the case of the XLR female that plugs into the mic.
Neumann relies on the female XLR plugged into the mic to supply ground reference to the microphone case. If the case of the XLR is not connected to the cable shield (ground) the mic case floats from ground.
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Dominick Costanzo

Fig

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Re: KM184's receiving electromagnetic interference
« Reply #5 on: April 17, 2006, 05:01:32 pm »

I have found, for whatever reason, the quad cables work best for this brand's microphones - old and new.  My $0.02.

As with every grounding scheme, your results may vary - but touching the body is a dead giveaway.

Good luck,

Fig
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theo mack

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Re: KM184's receiving electromagnetic interference
« Reply #6 on: April 17, 2006, 09:52:18 pm »

[quote title=Dominick wrote on Mon, 17 April 2006 08:41]
bjorn400 wrote on Sat, 15 April 2006 11:11

Hi,
Only when I clutch the mic body in my hand does the buzzing go away totally no matter which direction it is pointing.

Make sure the cable you are using is properly constructed. The shield must be connected to both pin 1 and the case of the XLR female that plugs into the mic.
Neumann relies on the female XLR plugged into the mic to supply ground reference to the microphone case. If the case of the XLR is not connected to the cable shield (ground) the mic case floats from ground.



keep in mind this is not the standard for xlr wire termination.
You should make sure to keep these cables with the pin one tied to chassis clearly labeled. and only use them on the mics that need them.

Wired with chassis tied to ground xlr cables can cause many problems. and in some cases be dangerous.

I'm sure this type of cable will solve your issue with the neumans. Just dont make it the standard for all your xlr.
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Rob Darling

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Re: KM184's receiving electromagnetic interference
« Reply #7 on: April 17, 2006, 10:57:08 pm »

Hey Dominick,

Nice to see you around here.  I'll try that with these mics.

best,

r.
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Ronny

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Re: KM184's receiving electromagnetic interference
« Reply #8 on: April 18, 2006, 06:23:26 am »

[quote title=Dominick wrote on Mon, 17 April 2006 11:41]
bjorn400 wrote on Sat, 15 April 2006 11:11

Hi,
Only when I clutch the mic body in my hand does the buzzing go away totally no matter which direction it is pointing.

Make sure the cable you are using is properly constructed. The shield must be connected to both pin 1 and the case of the XLR female that plugs into the mic.
Neumann relies on the female XLR plugged into the mic to supply ground reference to the microphone case. If the case of the XLR is not connected to the cable shield (ground) the mic case floats from ground.



Exactly. Touching the mic and hearing the buzz attenuate is an indication that he's lost balancing. It's likely that he's floating the cold leg, so no reverse phase and therefore no CMR. Having a cable with hot and cold reversed on the pins will do the same thing, you lose balance and -6dB gain, but you still get signal. When you touch the case of the mic and the buzz attenuates, it's because your body is acting as the ground.

On the guitar, getting less buzz from single coil pups when the guitar neck is perpendicular to the amp. The reason for this is that the strings act as strong antennae. When the strings are parallel with the lines of electro-magnetic flux, there is less interference. When the strings are perpendicular to the field, your buzz increases to maximum. This is because the electro-magnetic field that the amp is exhibiting has a flux line pattern that looks much like when you took a magnet back in science class in middle school and poured iron filings on top of it, the field is not round but eliptical. You have a broader EMI field running perpendicular to the lines of flux. Closer to the amp you get the louder the buzz gets and the more you angle the guitar strings perpendicular to the field, the more buzz you'll get. Dual coils or humbuckers negate most of this by reversing phase on the second coil. Basically it's the same principle used when balancing a mic signal with the cold reverse phase and 3 conductor XLR cable, which these days is typically  going pin 1 ground, pin 2 hot, pin 3 cold. Some of the older European model mics and some of the EV's sold in the US in the 60's had pin 2 cold, pin 3 hot. If the input device has hot 2, cold 3, you lose the balance as you are floating the cold leg "when it's not connected on both sides of the sending and receiving units". I've bought XLR cables that had the pins reversed on one end, best to check continuity with a multi-tester when you first use a new cable, to make sure that pin 2 on FXLR side is going to pin 2 on MXLR side.
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Rick Sutton

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Re: KM184's receiving electromagnetic interference
« Reply #9 on: April 18, 2006, 11:56:46 am »

Ronny wrote on Tue, 18 April 2006 03:23


Exactly. Touching the mic and hearing the buzz attenuate is an indication that he's lost balancing. It's likely that he's floating the cold leg, so no reverse phase and therefore no CMR. Having a cable with hot and cold reversed on the pins will do the same thing, you lose balance and -6dB gain, but you still get signal.  


Maybe you're talking line levels here Ronny 'cause in microphones I've never seen anybody floating a leg of the balanced signal. Mics run all three connections all the time that i'm aware of. And it shouldn't matter if it is accidentally phase reversed for this kind of problem.
The "floater" is the case of the microphone.
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Ronny

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Re: KM184's receiving electromagnetic interference
« Reply #10 on: April 18, 2006, 02:17:42 pm »

Rick Sutton wrote on Tue, 18 April 2006 11:56

Ronny wrote on Tue, 18 April 2006 03:23


Exactly. Touching the mic and hearing the buzz attenuate is an indication that he's lost balancing. It's likely that he's floating the cold leg, so no reverse phase and therefore no CMR. Having a cable with hot and cold reversed on the pins will do the same thing, you lose balance and -6dB gain, but you still get signal.  


Maybe you're talking line levels here Ronny 'cause in microphones I've never seen anybody floating a leg of the balanced signal. Mics run all three connections all the time that i'm aware of. And it shouldn't matter if it is accidentally phase reversed for this kind of problem.
The "floater" is the case of the microphone.




If you reverse hot and cold "on the cable on one end", you lose balance. The case is acting as ground in this case, the cold is floating if it's not connected to the differntial amplifier on the receiving device.
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Rick Sutton

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Re: KM184's receiving electromagnetic interference
« Reply #11 on: April 18, 2006, 03:08:45 pm »

Ronny wrote on Tue, 18 April 2006 11:17




If you reverse hot and cold "on the cable on one end", you lose balance. The case is acting as ground in this case, the cold is floating if it's not connected to the differntial amplifier on the receiving device.


Well, I gotta admit that you got me confused. When I'm talking about a balanced line I refer to the signals as plus/minus/shield or ground......   or......   hot/cold/shield or ground.
Are you referring to cold as a shield/ground? That's the only thing I can figure as reversing hot and cold (in my terminology) just means polarity reversal which should have nothing to do with the issue at hand.
Also, I think that the problem the original poster (and others) is having is specific to this mic model and the cables they are using are wired correctly for 99.9% of the mics out there. The mic circuitry is balanced and getting ground, it's the case around the mic circuitry that is not properly connected to the internal mic circuitry ground. I've seen this with an early AKG C412, exhibiting the same problem, that had a ground wire get loose between the internal mic ground and the wire screen around the capsule.
Also, I hope that the original poster would be so kind as to fill us in when he tries the shield to connector shell mod on the mic cable.
Inquiring minds want to know the results.

Yours truly,
Confused in California
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Ronny

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Re: KM184's receiving electromagnetic interference
« Reply #12 on: April 18, 2006, 04:25:37 pm »



You are probably correct about the mic casing with regard to the grounding problem. I'm talking reversed pins on hot and cold from a store bought XLR cable causing a problem, which I've encounted on more than one occasion, but yes it would reverse the polarity on the mic and float the cold on some devices that need it connected on the receiving end.  
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Rick Sutton

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Re: KM184's receiving electromagnetic interference
« Reply #13 on: April 18, 2006, 04:51:01 pm »

Ronny,
Thanks for the clarification. I agree that a "polarity challenged" cable is a potential nightmare, especially in a situation where you are going between balanced and unbalanced gear. All kinds of ugly things can happen and will surface at the worst possible time.
Cheers, Rick
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bjorn400

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Re: KM184's receiving electromagnetic interference
« Reply #14 on: April 21, 2006, 12:04:38 am »

Hey, thanks for the replies.  I didn't know people were replying.  I also posted this on tapeop forum and I have been following that more closely.  
I do have a bunch of updates for you all though.  If you want to see the tapeop thread, here it is:
 http://messageboard.tapeop.com/viewtopic.php?t=33624&sid =281de4be956c156222c5b2c7e6db8418

A brief catchup.   These mics seem to operate correctly almost everywhere but my apartment(Ridgewood NY, on the queens and brooklyn border).  They even work almost without flaw just a short way down the hall from me.  And they work perfectly in an apartment on the other end of the building.

It seems to me that it is related to the freight elevator across the hall from me.  It gets really loud in places near that.  It really depends on what point in space its in, not what direction I'm facing.  It has a low ground buzz in one place, take one step forward and it reduces in volume a lot. Also, when pointed staight up, a high rf buzz is heard.

I have checked all the pins, and everything is hooked up properly, no shorts.

Grounding the XLR ground to the chassis is something I will try this weekend.  Thanks for the tip.

So is this something you think nuemann can fix?  Or should I just sell these and buy different mics, or keep them until I move?

Bjorn

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