Oktava MK-012 high pitched tone. Need help.

[Big Valley Audio]

Generally a combination of lack of RF filtering on pin 2 and 3, and improper connection of pin 1 go case.
See a copy of "Radio Frequency Susceptibility of Capacitor Microphones" from the web site of one of the presentation authors:
http://www.audiosystemsgroup.com/AES-RFMicrophonesASGWeb.pdf

You can sometimes correct the problem by rewiring the pin 1 connection point, or use Neutrik RFI XLR connectors on the cable.
NC3FXX-EMC-B

Great post! Lots of info in one place.
We leaned on this info heavily while troubleshooting the issue over the previous couple of months and it did improve things. Unfortunately in this location the signals are so strong that even though these measures improve the noise, it’s still around 10dB above the noise floor (depending on the microphone). Fine when using one mic but not fine when recording a large group of musicians as the noise is accumulative.
and that’s with the antennas pointing at the studios turned off!
I’m not sure if I mentioned it earlier but the studio is 200 feet from the antennas

 

[ccaudle]

We leaned on this info heavily while troubleshooting the issue

Yet there still seem to be three wires from connector pins to the circuit board. Are you sure you understood the info about microphone pin 1 problems in that paper I linked?

 

[Big Valley Audio]

Yet there still seem to be three wires from connector pins to the circuit board. Are you sure you understood the info about microphone pin 1 problems in that paper I linked?

I did understand the info in the link.
In this specific case, we would like to find the best solution possible that involves reduction of RF that the studio is exposed to first.
The studio has clients from all around the world and some of them bring very expensive mics that they would be hesitant to have modified in order to work at a particular studio, so the first course of action for this client is negotiating a RF reduction with the cell phone company involved.

 

[ccaudle]

In this specific case, we would like to find the best solution possible that involves reduction of RF that the studio is exposed to first.

Sorry, I didn't realize that you had steered the topic slightly. I don't want to assume that Stason99 can (or that his neighbors would appreciate if he did) ask the local cell phone companies to turn off all their towers near him.
Since those MK-012 mics are already modified I would still recommend to stason99 cleaning up the pin 1 wiring per the linked document to make sure no RF is going to be flowing on the circuit board, and maybe move the 10nF filter caps down to the connector, connected directly from pins 2 and 3 to pin 1 at the connector instead of up on the circuit assembly if there is room (I can't quite tell from the pictures if there is actually room, and I don't have a MK-012 myself to check).

 

[Big Valley Audio]

Sorry, I didn't realize that you had steered the topic slightly. I don't want to assume that Stason99 can (or that his neighbors would appreciate if he did) ask the local cell phone companies to turn off all their towers near him.
Since those MK-012 mics are already modified I would still recommend to stason99 cleaning up the pin 1 wiring per the linked document to make sure no RF is going to be flowing on the circuit board, and maybe move the 10nF filter caps down to the connector, connected directly from pins 2 and 3 to pin 1 at the connector instead of up on the circuit assembly if there is room (I can't quite tell from the pictures if there is actually room, and I don't have a MK-012 myself to check).

Absolutely, I got a bit off track. My original response to the original post was that if he was hearing 4KHz in his microphone he should check for cell phone interference being the issue as 4 KHz is a known switching frequency for cell signals when they are AM demodulated.
Cheers