Microphone Interference

[timtom]

A friend of mine has a strange noise problem in his studio with vintage mics (Neumann Km84, CMV563, Oktava MK-12.)
I guess it has to do with some RF Interference. Could be from the police station that is across the street.

This video shows the noise and how to stop it with some aluminium foil. Is there way to deal with this other then wrapping everything in aluminium foil?

 

[Khron]

Less than great shielding in the connector area? Questionable wiring? Good chance those old connectors weren't necessarily expected to need to block off as intense RFI as we're dealing with nowadays.

 

[Barry Hufker]

He might check this discussion…
https://repforums.prosoundweb.com/index.php/topic,37510.0.html

 

[Ike Zimbel]

There was another thread on here about this a few months ago, that I'm too lazy to search for. This is getting to be a more common problem with the buildout of the new cellular networks. Neutrik EMC XLR's, especially on the female (mic) end of the cable can help a lot.

 

[ccaudle]

Neutrik EMC XLR's, especially on the female (mic) end of the cable can help a lot

I believe that is considered the best solution if you do not want to modify any of the mic internal connections.
If you are willing to modify the microphones you can sometimes correct the problem there so that the mic will work with any cable. Basically like any other pin 1 problem, get the shield connected to the chassis as quickly as possibly (i.e. short and wide connection for lowest resistance and inductance), and connect the circuit reference node to the chassis somewhere else so that shield currents do not flow through the microphone circuit.

 

[Ike Zimbel]

I believe that is considered the best solution if you do not want to modify any of the mic internal connections.
If you are willing to modify the microphones you can sometimes correct the problem there so that the mic will work with any cable. Basically like any other pin 1 problem, get the shield connected to the chassis as quickly as possibly (i.e. short and wide connection for lowest resistance and inductance), and connect the circuit reference node to the chassis somewhere else so that shield currents do not flow through the microphone circuit.

A good point. I neglected to mention that, while I do not work on a lot of microphones, those that I do I always make sure the chassis ground connections are tight, especially since this is often made via screws and other mechanical connections. This has occasionally cured noise issues.

 

[TLRT]

Km84 hasn't got "proper" filters like the later u87 etc, you can try to add the LCR filter of the u87 by adding the LC parts into the xlr body