RF Frequencies in Mics

If it's not there on playback it's something in the monitor path.

hey John - before you get deep into disecting your mic - check this out, It was an annoying problem until I properly grounded my Gefell's. Could be something similar in the Upton. All it requires is a cable change / fix at the mic end. Might be complicated a touch due to it being a tube mic, but worth checking out. Get the ground on Pin 1 (not sure where ground is on the tube circuit) tied down to the Chassis of the plug. Simple, 100% effective, cheap.

www.gearslutz.com/board/high-end/111893-gefell-owners-users-what-you-need-know.html

Some good comments there too...

Think Faraday Tape could help? I actually bought the RFID fabric to try to put over the PS to see if it would work. I THOUGHT it did...but now I'm getting 99.7 pretty good again lol. Will this even work if I found the culprit? drbill I'm afraid that pin stuff is too smarts for me. Plus, I guess it could actually be the proprietary cable from the mic to the PS...

www.amazon.com/TitanRF-Faraday-Tape-High-Shielding-Conductive/dp/B07DXDSCTF

Ohhh I’m gonna kiss you if this works!

Since RF is what I do..

First, a faraday cage is simply a grounded metal mesh that's smaller than the fractional wavelengths of the signals you want to reject. The metal chassis, the metal screen over the capsule, etc are all faraday cages.

Secondly, you need a nonlinear junction (diode) and a large amount of amplification to demodulate radio down to audio. This means that somehow the RF is getting into the amplifiers in the mic.

Third, ferrites act as high impedance for higher frequencies, similar to how inductors work, but generally without coils.

4th, ferrites shouldn't be needed at all if the faraday system is working.


So all this together sounds like the ground in your mic is not working right. I'd bet the cable between the power supply and the mic has either the shield or the power wires unhooked or something, or the XLR shells are not grounded.

Does the radio bleed change if you touch the mic?




But then again, anything that you can hear through headphones should be on the recording. You're also saying that you're hearing radio but it's not actually being recorded? Or are you saying that you just have your headphones turned up so much you hear the radio through the mic but in the mix the radio is too low to matter?

Thanks man!! I might have said before that it wasn’t in the recording but I was wrong. It’s there.

Check back to my previous post, and to the thread it references.  Sometimes (don't know why) with certain mics, the XLR plug is not grounded to the chassis of the mic.  Instead it's grounded to the audio of the mic thru pin 1 of the plug which (may) be isolated from the chassis.  That sometimes seems to be problematic and not effective in certain RF high locations.  For me it was intermittent, and it can even depend on the ANGLE of the mic or the placement of a mic in the room.  Crazy times.  I had all kinds of crazies with my Gefell's until I sorted it out with the pigtail cables I talked about in that thread.

All this is really simple if you know how to solder and have had any experience making XLR cables.  What gets dicey is that now you're dealing with a 7 pin tube mic cable that's carrying high voltages - and on those cables, I'm not sure which pin is ground.    I'm sure this would be childs play for Dave, but before taking it to him, you might try getting one of those alligator clip leads and try grounding the XLR or PS to the body of the mic to see if that makes any difference.

In the Gefell mics, the magic fix was when the CHASSIS of the XLR became grounded to the CHASSIS of the mic.  Why?  I'm not the right guy to ask, but it brought such joy into my life when I finally got it sorted - AND - it was super easy - and cost nothing other than the time, research and aggravation.  Give Dave a call and see if he can experiment with taking the audio ground of the tube mic cable at the mic end, removing it from the audio ground and locating it to the chassis of the XLR on the mic end.  Or maybe it will need to go both places - audio ground and chassis ground.  For me, it was removing from audio ground, and attaching to chassis ground on the XLR plug.

Good luck!!!

Yes, that's exactly it.  Remove the ground from pin 1 and attach to the shell of the XLR.  Easy to do on Switchcraft style XLR's.

I don’t have anything to add other than that on Monday I start “Fields and Waves” and though I am not relishing having to dust off that many multivariable calc brain cells, I’m really excited to learn more about this stuff.

And I’d be lying if I said I wasn’t a tad bit excited about all the MV calculus. It’s pretty inherently amazing and useful stuff.

But JK, if you just do what svart and EmRR tell you I’m sure you’ll get it squared away.

drbill...I might kiss you. I opened the mic and saw where it was grounded and pushed that around a little bit to make sure it wasn't touching anything else...and that seems to have worked. Gonna check it later too. Thanks!!

SOCIAL DISTANCING, bros. The jubilant embrace will have to wait.

Grounding is good.
For microphones and sometimes Teenagers!
Chris