Re: capsule suggestion needed for loud environment recording
On Wed, Mar 19, 2025 at 09:19 AM, Jules Ryckebusch wrote:
If you go straight to a condenser without built in FET you can pad it with a capacitor. I¡¯ve used the 2555B with a 220pF capacitor as a drum mic.
Hello, Jules Ryckebusch.
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I have a question about this part.
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16mm ECM with no built-in Fet, as you said
If you reinforce the capacitor, can you withstand high SPL?
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How should I search for a connection method or related knowledge?
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Please give me some advice.
Thank you.
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Kandoit7.
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Re: Noisy Schoeps CMC6 body
I've seen several requests online for the CMC6 schematic over the years.. but never seen one posted?
However, I have seen a couple of forum comments that suggest that the CMC6 schematic is almost identical to the CMC5 with the exception of a different LF roll off, and the addition of a voltage regulator. The CMC5 schematic is widely available online.
The block diagram on Page 8 of tends to suggest that maybe true? If so, it maybe possible to check that the voltages around the two output transistors are similar, to help eliminate those from your investigations? ....??
Although there are 6v2 zener ptortection diodes across the C-E junctions of the output transistors, I'm not sure they would necessarily protect the B-E junctions of those same transitors, in a 'hot plug' situation?
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Would that be the perfect choice in a Schoeps circuit with such low Ciss?
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Re: Troubleshooting OPA142 circuit for noise-cancelling aviation mic
Question: why are you getting the ground for the preamp circuit from the headphone output? My instinct would be to pick up the preamp ground from the following mic input, and to keep the headphone feed completely isolated from the preamp. In other words, i would have no connection from J2 pin 3 to the preamp's ground.
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Also, just wondering why you'd choose FETless electrets for a tough environment like aircraft. Seems to me that capsules with FETs would just be easier to work with: lower power voltage, no 1G resistors, possibly less sensitivity to RF interference.
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Thx.
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Hello!
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I have the Schoeps CMC6 body (with MK4 capsule) that¡¯s much noisier (15-20 db more noise) than others.?
I¡¯ve checked and it¡¯s not the capsule, cabling, preamps etc. ?I¡¯m dead sure it¡¯s the body itself.?
Has anyone got a schematic for those? Or any hints as to what to look for? I suspect the input transistor might have gotten damaged by hot plugging? Or maybe it¡¯s a protection diode leaking? Any thoughts?
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Thanks!
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Re: Troubleshooting OPA142 circuit for noise-cancelling aviation mic
On Mon, Apr 21, 2025 at 08:18 PM, <michaeljtbrooks@...> wrote:
How would I make the input stage flat?
Making it flat is not too difficult, but making it both differential and flat is probably impossible.You need two preamps connected to a differential amp. That would require two dual opamps (4 stages in total).
I'm limited to about 12mA before the comm radio bias starts to sag. In an ideal world I'd like this to cope with 8V-20V bias because that's the range we see with the various comm radios.
12mA should be enough for 4 stages, but I'm afraid the voltage would drop too much in extreme conditions.
Would (8V variant) work,
It should. Caveat: I have no hands-on experience of this particular item.
perhaps with a 15V zener protecting its input?
It may not be necessary, but it's safe practice.
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Re: Troubleshooting OPA142 circuit for noise-cancelling aviation mic
Thanks Jerry,
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I wanted some gentle bass roll-off,? to try to trim any low-frequency engine noise. However it does (did!) sound more tinny than ideal.
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On reflection bass roll-off will probably happen naturally anyway because both capsules are cardioid, only about 3cm apart, thus I'd expect their response to be more omni towards the bass thus less differential signal at lower frequencies.?
How would I make the input stage flat?
I'm limited to about 12mA before the comm radio bias starts to sag. In an ideal world I'd like this to cope with 8V-20V bias because that's the range we see with the various comm radios. Would (8V variant) work, perhaps with a 15V zener protecting its input?
?
?
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Re: Troubleshooting OPA142 circuit for noise-cancelling aviation mic
Sounds like motor-boating, a relaxation oscillation that happens at low frequency.
I guess one of the reasons is that the supply voltage is not regulated enough. With 12V incoming voltage, the voltage at the zener is about 2V below the zener voltage. It may help prevent surges but does not regulate at all.
I would install a proper regulator there. There are now very low current 3-pin regulators.
BTW, the response of the input stage is not linear; it's a 6dB/octave slope. Is it what you want?
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Re: Troubleshooting OPA142 circuit for noise-cancelling aviation mic
I've added a link to imgur. Right click and open the image in a new tab to see full size.
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I've also added it as an attachment rather than an inline here.
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Re: Troubleshooting OPA142 circuit for noise-cancelling aviation mic
Can you provide a more legible?schematic?
On Mon, Apr 21, 2025 at 9:40?AM michaeljtbrooks via <michaeljtbrooks= [email protected]> wrote: Hi All,
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Can you help me troubleshoot the cause of failure of this OPA1642 based circuit?
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The design intentions:
- Bias power is tapped from the comm radio (8-15v), which comes from the comm radio's mic input (J3)
- This is smoothed and limited to 12V with a Zener (Z1), which is then sent to supply the mic board
- The mic board has potential divider to produce the virtual ground (R3+R4)
- Two FET-less electrets (MK1, MK2) provide the source and reference audio signals, feeding one of the OPA1642 op-amps (U1A) in a differential manner
- The second OPA1642 op-amp (U1B) is a unity buffer
- The output from the second OPA1642 op-amp goes to a DC blocking cap (C3) on the control board
- The audio passes through a 10k pot (RV1) to allow the output volume to be adjusted for different comm radio input gain settings
- Another DC blocking cap then blocks the bias voltage from reaching the pot (C4)
- The headphones audio out from the comm radio stays pretty much separate. There's a little bridge on the board for connection convenience so different headphones can be used while only having one physical cable tethering the pilot to the plane.
?
?
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To test it, I built the power injector circuit to supply the bias voltage. The 1k resistor (Rt1) prevents the power supply's output smoothing caps from filtering the signal to GND.
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This worked absolutely fine on the test bench without the mixer attached. The oscilloscope placed at J3 pin 2 showed waveforms when I spoke into one of the mics.?
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When I connected the test circuit audio output (far right, Jt1) to a standard audio mixer mic-level input, I got the expected mic audio through, no problems. If I monitored with a separate set of headphones plugged into the mixer phones output, I could hear the mic audio fine. I had been worried about the shared bias / mic line causing feedback to the op-amp via its power line but the caps C7 and C8 seemed to have dealt with this fine.
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Strange things happened when I connected the mixer headphones output (Jm2) to the circuits headphones audio-in (J2), with headphones plugged into J4. I suddenly started getting bursts on the VU meter every 500ms lasting for maybe 250ms. However these burst weren't actually audible, so I suspect these were infrasonic.
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After about 15s of bursts like this, the circuit then stopped outputting mic noise. Probing the circuit, it appears as though the OPA1642 is dead.?
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I've checked the layout on the board and am happy that it's all connected correctly and every thing is mounted with the intended polarity. I'd actually encased the PCBs in glue once it had tested fine on the oscilloscope. It tested fine after encasing too. So I'm pretty confident that there are no unintended shorts.
The only clue I can think of is when the headphones audio was connected to J2, the DC blocking cap on the GND line might have been bypassed, assuming the mixer ties the input GND to headphones GND (magenta wire on the far right). (The mixer does not output phantom power). The 12V power injector supply and the mixer's power supply comes off the same mains gang.?
The 12V power injector was a reasonable fixed voltage switched mode power supply with very little ripple when measured with a resistive load.
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I've built a similar circuit before which I've flown with a few times, but it suffered from some feedback from the RF (aviation comms are amplitude modulated) when transmitting. So this version is a redesign to fit into a better, larger, screened 3D printed enclosure.
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1) Any ideas what fried the OPA1642?
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2) Any ideas what the bursts of infrasonic were? Were they the cause of the OPA failure, or a symptom of it?
?
3) Are there any glaring unrelated errors in the circuit design?
?
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Many Thanks,
Mike
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-- Best Regards,
Jules Ryckebusch
214 399 0931
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Troubleshooting OPA142 circuit for noise-cancelling aviation mic
Hi All,
?
Can you help me troubleshoot the cause of failure of this OPA1642 based circuit?
?
The design intentions:
- Bias power is tapped from the comm radio (8-15v), which comes from the comm radio's mic input (J3)
- This is smoothed and limited to 12V with a Zener (Z1), which is then sent to supply the mic board
- The mic board has potential divider to produce the virtual ground (R3+R4)
- Two FET-less electrets (MK1, MK2) provide the source and reference audio signals, feeding one of the OPA1642 op-amps (U1A) in a differential manner
- The second OPA1642 op-amp (U1B) is a unity buffer
- The output from the second OPA1642 op-amp goes to a DC blocking cap (C3) on the control board
- The audio passes through a 10k pot (RV1) to allow the output volume to be adjusted for different comm radio input gain settings
- Another DC blocking cap then blocks the bias voltage from reaching the pot (C4)
- The headphones audio out from the comm radio stays pretty much separate. There's a little bridge on the board for connection convenience so different headphones can be used while only having one physical cable tethering the pilot to the plane.
?
?
High res:
?
?
To test it, I built the power injector circuit to supply the bias voltage. The 1k resistor (Rt1) prevents the power supply's output smoothing caps from filtering the signal to GND.
?
This worked absolutely fine on the test bench without the mixer attached. The oscilloscope placed at J3 pin 2 showed waveforms when I spoke into one of the mics.?
?
When I connected the test circuit audio output (far right, Jt1) to a standard audio mixer mic-level input, I got the expected mic audio through, no problems. If I monitored with a separate set of headphones plugged into the mixer phones output, I could hear the mic audio fine. I had been worried about the shared bias / mic line causing feedback to the op-amp via its power line but the caps C7 and C8 seemed to have dealt with this fine.
?
Strange things happened when I connected the mixer headphones output (Jm2) to the circuits headphones audio-in (J2), with headphones plugged into J4. I suddenly started getting bursts on the VU meter every 500ms lasting for maybe 250ms. However these burst weren't actually audible, so I suspect these were infrasonic.
?
After about 15s of bursts like this, the circuit then stopped outputting mic noise. Probing the circuit, it appears as though the OPA1642 is dead.?
?
I've checked the layout on the board and am happy that it's all connected correctly and every thing is mounted with the intended polarity. I'd actually encased the PCBs in glue once it had tested fine on the oscilloscope. It tested fine after encasing too. So I'm pretty confident that there are no unintended shorts.
The only clue I can think of is when the headphones audio was connected to J2, the DC blocking cap on the GND line might have been bypassed, assuming the mixer ties the input GND to headphones GND (magenta wire on the far right). (The mixer does not output phantom power). The 12V power injector supply and the mixer's power supply comes off the same mains gang.?
The 12V power injector was a reasonable fixed voltage switched mode power supply with very little ripple when measured with a resistive load.
?
I've built a similar circuit before which I've flown with a few times, but it suffered from some feedback from the RF (aviation comms are amplitude modulated) when transmitting. So this version is a redesign to fit into a better, larger, screened 3D printed enclosure.
?
1) Any ideas what fried the OPA1642?
?
2) Any ideas what the bursts of infrasonic were? Were they the cause of the OPA failure, or a symptom of it?
?
3) Are there any glaring unrelated errors in the circuit design?
?
?
Many Thanks,
Mike
?
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What are you actually trying to achieve?
There's lots of pitfalls in my suggested circuit. It isn't a
tried and tested project, and will almost certainly require
revision and troubleshooting. I wouldn't recommend it for a
beginner.
Looking at it now it seems overcomplex. If you add a third mic
each side it gets even more complex, how would you balance them?
I'm already not that happy with my arrangement of balance pots (R2
R25) and level pots (R3 R15).
If you only want to amplify one side of the accordion then you
could use essentially half the circuit, and use a single opamp
instead of a dual - so simpler.
A version which didn't stack the power supplies would also be
simpler to get right, at the expense of more current draw.
On 12/04/2025 20:19, jc.selles via
groups.io wrote:
toggle quoted message
Show quoted text
Hello
Yes I meant this circuit. I a near future I will try to built
it more or less as you sudgested it : a single opamp but with
three capsules for each sides.?
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What do you mean by a simpler circuit?
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I would like to have a way to control the volume on this
preamp but I am starting to feel that's too complex for me.
?
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Anyway thanks a lot. This is a beautiful collaborative
thread.?
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Hello
Yes I meant this circuit. I a near future I will try to built it more or less as you sudgested it : a single opamp but with three capsules for each sides.?
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What do you mean by a simpler circuit?
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I would like to have a way to control the volume on this preamp but I am starting to feel that's too complex for me.
?
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Anyway thanks a lot. This is a beautiful collaborative thread.?
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I take it you mean this?
I'd completely forgotten I did that!
It was never built, whoever was asking for it never got back to
me I think.
If you disconnect one XLR you halve the power available so not
good. The unused side of the opamp will still draw power, but both
sides will be powered from a single XLR.
However if you only wanted a single XLR version for one side of
the accordion, then you could use a much simpler circuit overall.
Or you could make it with two 1641 opamps instead of a single
1642, and separate the power for each, that would essentially be
two totally separate but identical circuits, and would be robust
for using just one. It's more parts overall though.
On 11/04/2025 20:57, jc.selles via
groups.io wrote:
toggle quoted message
Show quoted text
Hello, sorry for the topic revival
As an accordion player I am really interested in this
project.
I was wondering what would happen if only one of the two XLR
is connected?
thank you.
This is a really interesting discussion.
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Hello, sorry for the topic revival
As an accordion player I am really interested in this project.
I was wondering what would happen if only one of the two XLR is connected?
thank you.
This is a really interesting discussion.
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Re: phantom powered fet preamp question
If you have a look at Siegfried Linkwitz's site, there is an alternative method of using that microphone here?
Craig
------ Original Message ------
Date 11/04/2025 14:17:12
Subject Re: [MicBuilders] phantom powered fet preamp question
Thank you
I forgot to mention that I want to put it inside an instrument. That's why I would like to have control of the volume.
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Re: phantom powered fet preamp question
Thank you
I forgot to mention that I want to put it inside an instrument. That's why I would like to have control of the volume.
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Re: phantom powered fet preamp question
This is basically unity gain and going into a mic preamp. That¡¯s the best place to adjust the gain Best Regards,
Jules Ryckebusch?
toggle quoted message
Show quoted text
On Apr 11, 2025, at 06:39, jc.selles via groups.io <jc.selles@...> wrote:
? Hello,
?
I build this preamp and I was wondering if there is a way to control the audio volume?
My best guess so far would be to add two capacitors beside C3 and C6 and wire a dual pot. But it seems very ugly.
<ECMMicPhantomPoweredNew.jpg-nggid03671-ngg0dyn-480x0x100-00f0w010c010r110f110r010t010.jpg> Thanks a lot and have a nice day.
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Phantom Power Condenser Microphone ¨C Mute & Power Control Circuit
Hi everyone,
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I'm working on a circuit to control the power supply and mute function of a phantom-powered condenser microphone.
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The general concept is mostly in place, and I¡¯d love to get your feedback, especially if you have ideas for improvements or alternative approaches.
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I've attached the schematic for reference.
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Here's a quick rundown of how it works:
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-An NE555 timer is used to generate a trigger pulse when a pushbutton is pressed once.
-This trigger drives an 817 optocoupler to toggle the power (ON/OFF).
-The optocoupler, in turn, controls the 24V supply¡ªregulated through a Zener diode¡ªwhich powers both the condenser mic and an LED via three FETs.
-While the supply is nominally 24V, due to component losses, the actual output voltage is around 16V.
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I¡¯m also considering replacing the current switching mechanism with a latching circuit for more reliable control.
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Any input, suggestions, or shared experiences would be greatly appreciated. I'm especially curious if anyone has tackled a similar design.
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Thanks in advance!
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phantom powered fet preamp question
Hello,
?
I build this preamp and I was wondering if there is a way to control the audio volume?
My best guess so far would be to add two capacitors beside C3 and C6 and wire a dual pot. But it seems very ugly.
Thanks a lot and have a nice day.
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