Re: Suppressing RF noise - ambient mics into CODEC (on headphones)
Half of LNprimer.pdf in my Files is dedicated to RFI/EMI suppression.
RFI is usually due to some internal circuitry demodulating the RF.? You need to get the yucky RF that is coming in to a low enough level so demodulation doesn't happen.? But even 1" of wire or track is enough to act as an aerial ... or even a 1" slot.
The ideal is a Faraday cage (or box when we are considering UHF like cell phones).? Every line coming into or out of the box is shielded and the shields are connected DIRECTLY to the box on the OUTSIDE at RF.? This is the function of the "circumferential capacitor" on the?Neutrik EMC-XLR series connectors.
|
Re: Groups.io "reverification" is legit
Thanks Scott
Best Regards,
Jules Ryckebusch
toggle quoted message
Show quoted text
On Jan 25, 2024, at 15:25, Scott Helmke <scott@...> wrote:
?Hi folks,
Groups.io is doing a "reverification" of some (just a few, I think) members as part of keeping spam at bay. It's legit, be careful as always but this particular thing is legit.
Thanks,
-Scott
--
---- Scott Helmke ---- scott@... ---- (734) 604-9340 ----
"I have ceased distinguishing between the religious and the secular,
for everything is holy" - Joe Henry
|
Groups.io "reverification" is legit
Hi folks,
Groups.io is doing a "reverification" of some (just a few, I think) members as part of keeping spam at bay.? It's legit, be careful as always but this particular thing is legit.
Thanks,
-Scott
--
---- Scott Helmke ---- scott@... ---- (734) 604-9340 ----
"I have ceased distinguishing between the religious and the secular,
for everything is holy" - Joe Henry
|
Re: Microtech Gefell MV203 Circuit/Repair
Replaced the tantalum cap and the mic is working once again!?
|
Jules' Ambi-Alice and the Rycote BBG windshield
Hi everyone, does anyone know if the Ambi-Alice (GoPro mount version) will fit inside the
They make them to fit 20,21,22,and 25mm mic bodies. I think the GoPro mount diameter is 25mm? I can measure to make sure before I buy, but also want to make sure the basket will fit inside the windshield.
?
|
Re: Microtech Gefell MV203 Circuit/Repair
You are probably correct. I was basing the value off the input impedance specified in the data sheet.?  Measuring it on the pcb is tricky since the cap is encased in resin and I don't want to mess around with removing it. Probing my LCR meter from the capsule terminal to FET gate gives around 180 pF so 200 pF seems likely 
|
Re: Microtech Gefell MV203 Circuit/Repair
C4 is probably 200pF, not 0.2.
Le 23/01/2024 ¨¤ 20:58, Jwaters18 via
groups.io a ¨¦crit?:
toggle quoted message
Show quoted text
Just got done measuring the blank resistors. They form a simple
2x100Mohm voltage divider with 10Gohm feeding the divided voltage
to the rest of the circuit. Here is the updated schematic with all
component values.
|
Re: Microtech Gefell MV203 Circuit/Repair
Just got done measuring the blank resistors. They form a simple 2x100Mohm voltage divider with 10Gohm feeding the divided voltage to the rest of the circuit. Here is the updated schematic with all component values. 
|
Re: Microtech Gefell MV203 Circuit/Repair
Capsule is the MK221.
Removing the tantalum cap seems to have restored the correct biasing conditions (65VDC offset at the output) so I will be ordering a replacement (and maybe everything to make another board). I'm about to etch a quick pcb I can use to determine the values of the mystery resistors. I will post an updated schem with the measured values later today.
Thanks for the help!??
|
Re: Suppressing RF noise - ambient mics into CODEC (on headphones)
That is worth a shot ?for sure. RF and EMI are deceptive. Your headphones wires can easily act as antennas. ?Having one single ground point for everything helps. People normally think of ground loops happening with higher current draws but with RF a short wire has impedance properties, especially at Cell Phone and RF frequencies.?
Best Regards,
Jules Ryckebusch?
toggle quoted message
Show quoted text
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.
|
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.
|
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?:
toggle quoted message
Show quoted text
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.?
? ?
|
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)?
?
|
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?
toggle quoted message
Show quoted text
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.
|
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]
|
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
toggle quoted message
Show quoted text
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
|
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?
|
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?:
toggle quoted message
Show quoted text
Here's a slightly better quality attachment of my mic wiring
diagram. (sorry for the pixelation).
|
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).
|
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
|
Mark Day
Pete Lewis
Roger Gustavsson
