I've been experiencing some RF interference on some PUI AOM 5035L mics
into a WM8960 CODEC. Any advice on how to mitigate this would be much
appreciated!

Hi There folks!
I've been experiencing some RF interference on some PUI AOM 5035L mics into a WM8960 CODEC. Any advice on how to mitigate this would be much appreciated!

Sorry for the long message, but here it goes...

I like these mics for my application (loud drums) because of their really high AOP (135dB) and big SNR (75dB). For the most part, I've been pretty happy with my project <>. In my basement, and around my house, I experience superb sound quality with no RF interference. But at my favorite drum rehearsal spot (drumbox in Lafayette <>), I am experiencing RF noise. I will attach a recording I made of the sound, if your curious or might be able to help identify the kind and/or source.

I've tried many things, including the following:

1) Turning off all bluetooth and I2S communications on my microcontroller. It is simply controlling the PGA gains on the mic inputs and passing that through the CODEC in the analog bypass paths. This is less likely to be the culprit, because in my basement I don't experience the RF interference (even with BT/I2S running).

2) Upgrading all audio and data cables to shieled (Mogami W2697).

3) Wrapping a GND wire around the small connection from CODEC to MIC (which includes it's required pull-down resistor and in-series cap mini-PCB).

4) Putting my entire "right ear" electronics inside a box that I covered with copper tape (two layers). FWW, this stops any RF noise introduced by when I hold my RC airplane transmitter nearby. But doesn't stop the drumbox RF noise. Which I'm guessing is a stronger RF signal (?).

5) Putting a separate CODEC in the left ear, in hopes that the shorter distance of the left mic and left CODEC would help. But still no luck. I later found out that the RF noise can also enter my right ear signal - depending on the rotational position of my head (while wearing the headphones).

None of my efforts have seems to stop or reduce the RF interference into my system at the drumbox. The owner has let me know that they wirelessly beam their Wifi from the main building out to the rehearsal room (across the parking lot). So my guess is that this might be the cause.

Any thoughts would be greatly appreciated and thanks in advance!

Cheers,
Pete

PS there is much more info on my tutorial <>, but these two diagrams show the bulk of the project:





And here are my attempts at protecting with copper tapped box and wrapped GND wires:

Here's a slightly better quality attachment of my mic wiring diagram. (sorry for the pixelation).

Hey Scott,
Thanks! Sorry for the large attachment WAV file. Won't do that again.

We have plenty of file space for sharing such things.

Do you mean the files tab on the left? Should I use this first to upload, and then link to the file in the comment?

On Jan 22, 2024, at 22:56, Pete Lewis <petelewis228@...> wrote:

It has a low-pass filtering at 33KHz, and so that includes some 47nF caps to GND already.

On Jan 23, 2024, at 09:02, Pete Lewis <petelewis228@...> wrote:

?Hmm... I had a couple thoughts in the middle of the night.

(1) I'm wondering if my output could be causing the issue. The wires to my headphone driver speakers are currently just two wires without any shielding.

(2) I'm using capless headphone mode on the WM8960, which utilized VMID as the source for a buffered GND for the headphones. VMID is also used as the non-inverting input on the PGA (my mic input gain stage), so maybe the speaker wires are acting like an antennae and it's making it's way into the OUT3 pin (the buffered VMID).

As it is an output, I wasn't looking at the speaker wires (or mode) previously, but I'll give shielding the speaker cables a shot, and also I could try switching away from capless headphone mode and avoid any connection from the speaker wires to VMID.