Re: Suppressing RF noise - ambient mics into CODEC (on headphones)
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.
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Re: Microtech Gefell MV203 Circuit/Repair
Disconnect the tantalum cap and check voltages. You could then
check it for leakage.
If it's not the culprit, I would think it could be a micro crack
in the PCB.
Le 22/01/2024 ¨¤ 23:21, Jwaters18 via
groups.io a ¨¦crit?:
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Hello,
A while back I purchased a used MTG MV203 measurement mic to use
as comparison/testing for any of my future projects. After
researching the MTG documentation I built a rack-mounted power
supply/preamp to go with the mic. Everything was working fine (PSU
functioned nicely & super clean/healthy output from the mic).
I moved the PSU into a new enclosure to make things more portable
and started having issues with the mic. Sometimes I would get no
output, sometimes very distorted, sometimes functioning perfectly.
After thoroughly troubleshooting my PSU I found no issues with it
at all, which led me down the harrowing road of cracking the mic
body open and prodding around with my DMM.
Here are pictures of the internals and my best shot at the
schematic. Output was disconnected to verify the cable was not
causing issues. Had to replace a 6k8 resistor that took flight
when I was desoldering the adjacent mystery component.?
 
I used the component codes, DMM, and educated guesses to determine
most of the components and I plan on measuring the unlabeled caps.
I'm fairly confident the High Z section under the resin is two 10G
resistors in series and a 0.2 pF cap (input impedance is specified
at 20G and 0.2 pF). However, I am not sure what the black mystery
components are. Intuition tells me they are resistors, but they
must be on the order of >>10M because my DMM cannot read
them. I will have to carefully remove them and employ something
like to measure them on a separate board.?
Luckily I had also taken a look inside while it was working. I
know from my first measurements that, when functioning, the output
sits at around 65V DC offset. It now sits around 40V DC (sometimes
as low as 24V) and I measure no signal regardless of sound
source.?
Prime suspect is the 1uF tantalum cap as I understand they are
prone to damage and considered somewhat unreliable. The dual
diodes, MOSFET body diodes (not sure I understand why they are
used here), and Both BJTs measure ok with the DMM diode mode.
I'm posting this here mostly for general interest, but if anyone
has suggestions on troubleshooting the circuit I would greatly
appreciate any insight.?
? ?
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Re: Microtech Gefell MV203 Circuit/Repair
MV 203 is the preamplifier. What kind of capsule is it??Maybe you can get information from Microtech Gefell or Josephson (US Distributor)?
?
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Re: Suppressing RF noise - ambient mics into CODEC (on headphones)
When you say; ¡° It has a low-pass filtering at 33KHz, and so that includes some 47nF caps to GND already.¡± I¡¯m looking at the schematic as well, where do those 47nF caps tie to ground? Is there a Star ground setup? RF into low noise analog is a challenge ?especially with Cell and WiFi stuff in the gigahertz range. Evan a short wire becomes an antenna ?5Gig is about 6cm wavelength so 1/4wavelength antenna is less than an inch. ?
Best Regards,
Jules Ryckebusch?
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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.
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Re: Suppressing RF noise - ambient mics into CODEC (on headphones)
Hey Jerry,
Have you tried adding a capacitor between input and ground?
I would try with anything between 1nF and 4.7nF.
You may also want to add a ferrite bead in series.
Thanks for the suggestions. I have not yet tried either a cap to GND or a ferrite bead. I'm assuming the cap from signal to GND would be best placed as close as possible to the input pin on the CODEC. Is this correct? Also, the ferrite bead would be in series with the signal, also as close as possible to the input pin on the CODEC? Thanks! PS one other thing, I actually forgot to mention earlier that I put some filtering on the inputs of the?. It has a low-pass filtering at 33KHz, and so that includes some 47nF caps to GND already. Would you recommend trying additional caps to ground somewhere else on the circuit?? [schematic highlight image link]
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Re: Suppressing RF noise - ambient mics into CODEC (on headphones)
Hi Pete,
Yes, as a group member you can put files into a folder of your own and then link to it.
Thanks,
-Scott
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On 1/22/24 22:07, Pete Lewis wrote: 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?
--
---- Scott Helmke ---- scott@... ---- (734) 604-9340 ----
"I have ceased distinguishing between the religious and the secular,
for everything is holy" - Joe Henry
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Re: Suppressing RF noise - ambient mics into CODEC (on headphones)
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?
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Re: Suppressing RF noise - ambient mics into CODEC (on headphones)
Have you tried adding a capacitor between input and ground?
I would try with anything between 1nF and 4.7nF.
You may also want to add a ferrite bead in series.
Le 23/01/2024 ¨¤ 04:55, Pete Lewis a
¨¦crit?:
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Here's a slightly better quality attachment of my mic wiring
diagram. (sorry for the pixelation).
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Re: Suppressing RF noise - ambient mics into CODEC (on headphones)
Here's a slightly better quality attachment of my mic wiring diagram. (sorry for the pixelation).
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Re: Suppressing RF noise - ambient mics into CODEC (on headphones)
Hi Jerry, Thanks for responding! The mics signals are connected to the inverting inputs of the PGAs on each channel on the CODEC. Non-inverting inputs of PGAs are set to connect internally to VMID. They also have the necessary passives in-between the actual mic pads and the codec inputs. Power is coming from the output of a dedicated 3.3V LDO voltage regulator on the WM8960 breakout (AVDD pin), which in my setup is getting powered upstream by 3 AAA NiMH batteries at the VIN pin on the breakout.  Thanks again! Pete
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Re: Suppressing RF noise - ambient mics into CODEC (on headphones)
Hi Pete,
Welcome to the group!? Looks like a very cool project.
If I could make one suggestion with respect to using this group, it would be to take care not to send huge attachments out to the group.? We have plenty of file space for sharing such things.
Thanks,
-Scott
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On 1/22/24 20:49, Pete Lewis wrote: 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:
--
---- Scott Helmke ---- scott@... ---- (734) 604-9340 ----
"I have ceased distinguishing between the religious and the secular,
for everything is holy" - Joe Henry
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Re: Suppressing RF noise - ambient mics into CODEC (on headphones)
sounds like maybe cell phone close by?
Ferrite beads.?
Ferrite Clamshell EMI Filter?
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On Monday, January 22, 2024 at 10:22:33 PM EST, Jerry Lee Marcel <jerryleemarcel@...> wrote: Le 23/01/2024 ¨¤ 03:49, Pete Lewis a ¨¦crit?: 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! You don't say how they are connected to the CODEC. How are they powered, is there an active circuit?
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Re: Suppressing RF noise - ambient mics into CODEC (on headphones)
Le 23/01/2024 ¨¤ 03:49, Pete Lewis a ¨¦crit?: 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! You don't say how they are connected to the CODEC. How are they powered, is there an active circuit?
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Suppressing RF noise - ambient mics into CODEC (on headphones)
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 . In my basement, and around my house, I experience superb sound quality with no RF interference. But at my favorite drum rehearsal spot (), 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 , 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:   
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Microtech Gefell MV203 Circuit/Repair
Hello, A while back I purchased a used MTG MV203 measurement mic to use as comparison/testing for any of my future projects. After researching the MTG documentation I built a rack-mounted power supply/preamp to go with the mic. Everything was working fine (PSU functioned nicely & super clean/healthy output from the mic). I moved the PSU into a new enclosure to make things more portable and started having issues with the mic. Sometimes I would get no output, sometimes very distorted, sometimes functioning perfectly. After thoroughly troubleshooting my PSU I found no issues with it at all, which led me down the harrowing road of cracking the mic body open and prodding around with my DMM. Here are pictures of the internals and my best shot at the schematic. Output was disconnected to verify the cable was not causing issues. Had to replace a 6k8 resistor that took flight when I was desoldering the adjacent mystery component.?   I used the component codes, DMM, and educated guesses to determine most of the components and I plan on measuring the unlabeled caps.  I'm fairly confident the High Z section under the resin is two 10G resistors in series and a 0.2 pF cap (input impedance is specified at 20G and 0.2 pF). However, I am not sure what the black mystery components are. Intuition tells me they are resistors, but they must be on the order of >>10M because my DMM cannot read them. I will have to carefully remove them and employ something like to measure them on a separate board.? Luckily I had also taken a look inside while it was working. I know from my first measurements that, when functioning, the output sits at around 65V DC offset. It now sits around 40V DC (sometimes as low as 24V) and I measure no signal regardless of sound source.? Prime suspect is the 1uF tantalum cap as I understand they are prone to damage and considered somewhat unreliable. The dual diodes, MOSFET body diodes (not sure I understand why they are used here), and Both BJTs measure ok with the DMM diode mode. I'm posting this here mostly for general interest, but if anyone has suggestions on troubleshooting the circuit I would greatly appreciate any insight.? ? ?
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Re: Bamboo housing for nature recordings
That?2549?will work just fine
Hi Jules
Interestingly, only two balanced microphone cables are available on the Japanese Mogami website. The one that comes close to your recommended wire (Mogami W2697) at ?has the item description Mogami Part No.2549. The specifications are slightly different and can be found at (contains English descriptions...). I'll order this one.
Heinz
-- Best Regards,
Jules Ryckebusch
214 399 0931
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Re: Bamboo housing for nature recordings
Thank you, Sey. It seems our emails just crossed. :-)
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Re: Bamboo housing for nature recordings
Hi Jules
Interestingly, only two balanced microphone cables are available on the Japanese Mogami website. The one that comes close to your recommended wire (Mogami W2697) at ?has the item description Mogami Part No.2549. The specifications are slightly different and can be found at (contains English descriptions...). I'll order this one.
Heinz
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Re: Bamboo housing for nature recordings
Take a look at the official stores that distribute Mogami:
Also this:
And this
Good luck!
Yep! It's funny sometimes. It may be that the item name is slightly different here. It wouldn't be the first time. I'll find it out or find a similiar one. :-)?
The electronic shops in Akihabara are interesting, I've been there once in 2016. But because it's so famous and a tourist attraction, it's way too expensive, which is a bit of a shame. Historically and from an electronic perspective it is definitely an interesting place.
Heinz
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Re: Bamboo housing for nature recordings
Yep! It's funny sometimes. It may be that the item name is slightly different here. It wouldn't be the first time. I'll find it out or find a similiar one. :-)?
The electronic shops in Akihabara are interesting, I've been there once in 2016. But because it's so famous and a tourist attraction, it's way too expensive, which is a bit of a shame. Historically and from an electronic perspective it is definitely an interesting place.
Heinz
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Pete Lewis
Roger Gustavsson
Sey