Post by: bjorn400 on April 15, 2006, 11:11:16 AM
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
Post by: Rob Darling on April 16, 2006, 01:42:09 PM
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?
Post by: OOF! on April 17, 2006, 01:21:00 AM
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
Post by: Rob Darling on April 17, 2006, 09:18:42 AM
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.
Post by: Dominick on April 17, 2006, 11:41:02 AM
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.
Post by: Fig on April 17, 2006, 05:01:32 PM
As with every grounding scheme, your results may vary - but touching the body is a dead giveaway.
Good luck,
Fig
Post by: theo mack on April 17, 2006, 09:52:18 PM
| 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.
Post by: Rob Darling on April 17, 2006, 10:57:08 PM
Nice to see you around here. I'll try that with these mics.
best,
r.
Post by: Ronny on April 18, 2006, 06:23:26 AM
| 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.
Post by: Rick Sutton 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.
Post by: Ronny on April 18, 2006, 02:17:42 PM
| Rick Sutton wrote on Tue, 18 April 2006 11:56 | ||
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.
Post by: Rick Sutton 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
Post by: Ronny 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.
Post by: Rick Sutton on April 18, 2006, 04:51:01 PM
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
Post by: bjorn400 on April 21, 2006, 12:04:38 AM
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
Post by: bjorn400 on April 21, 2006, 12:56:37 AM
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
Post by: Rick Sutton on April 21, 2006, 01:33:49 AM
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.
Post by: Shawn Lindell on May 22, 2006, 05:24:14 AM
Post by: Bob DeMaa on May 22, 2006, 03:11:44 PM
One of the posted mentioned the strange clicking noises, and it reminded of this.
Bob
Post by: bjorn400 on July 03, 2006, 11:20:34 AM
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.
Post by: Johnny B on July 03, 2006, 06:48:09 PM
(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.
Post by: bjorn400 on April 18, 2007, 10:56:24 AM
thanks for the help