Hi.
My question is this simple one.
Is there any easy test to make sure that a dual side true condencer capsule is not burnt or shorted or faulty without using it on a mic. No data available. Cheaper- about 30 euros- Ali Express capsule.
Thank you in advance.

Here's my longer story .After experimenting a bit on electret with success using the OPA alice design (all OPA 1642 bought from Ali Express because of the know shortage from known retailers - good results). Used larger Electret capsule bought from Ali Express for 15euros, All good so far with that simple built.
Then I experimented a bit with the Hex Inverter DC - DC CMOS design and I managed to build 2 boards, One providing 65VDC and another one - 65VDC.
So now I 've decided to use a dual side true condenser capsule I've also bought from Ali Express for 30 euros for a more ambitious built,
I'm using 4 pcbs. 2 different single OPA ones for the signal (didn't have dual OPA pcbs around), and two Voltage ones for + and - polarity. For "real estate purposes" I'm using an external box for the pcbs and then leads to the mic and leads to the xlr of the pre amp.
My initial testing with it?(just cardioid, then just omni, then just fig. 8),? was quite all right. All out of the box, really noisy there is signal and appropriate behaviour in accordance to each mode, but it seems to have really low signal and after trying to change the lead and positions and using the box, with some grounding issues, I lost signal alltogether.
Firstly I'm afraid of having burnt or shorted something on the capsule and then I would like to know if this capsule is all right and whatever problem occurs hasn't got to do with it.

That's all.

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As a simple first test, measure its capacitance?

-Scott

Hi.
My question is this simple one.
Is there any easy test to make sure that a dual side true condencer capsule is not burnt or shorted or faulty without using it on a mic. No data available. Cheaper- about 30 euros- Ali Express capsule.
Thank you in advance.

Here's my longer story .After experimenting a bit on electret with success using the OPA alice design (all OPA 1642 bought from Ali Express because of the know shortage from known retailers - good results). Used larger Electret capsule bought from Ali Express for 15euros, All good so far with that simple built.
Then I experimented a bit with the Hex Inverter DC - DC CMOS design and I managed to build 2 boards, One providing 65VDC and another one - 65VDC.
So now I 've decided to use a dual side true condenser capsule I've also bought from Ali Express for 30 euros for a more ambitious built,
I'm using 4 pcbs. 2 different single OPA ones for the signal (didn't have dual OPA pcbs around), and two Voltage ones for + and - polarity. For "real estate purposes" I'm using an external box for the pcbs and then leads to the mic and leads to the xlr of the pre amp.
My initial testing with it?(just cardioid, then just omni, then just fig. 8),? was quite all right. All out of the box, really noisy there is signal and appropriate behaviour in accordance to each mode, but it seems to have really low signal and after trying to change the lead and positions and using the box, with some grounding issues, I lost signal alltogether.
Firstly I'm afraid of having burnt or shorted something on the capsule and then I would like to know if this capsule is all right and whatever problem occurs hasn't got to do with it.

That's all.

-- 
---- Scott Helmke ---- scott@... ---- (734) 604-9340 ----
"I have ceased distinguishing between the religious and the secular,
for everything is holy"  - Joe Henry

Le 09/05/2022 à 14:37, tedsorvino via groups.io a écrit?:

For "real estate purposes" I'm using an external box for the pcbs and then leads to the mic and leads to the xlr of the pre amp.

Wires between capsule and head must be kept as short as possible and must be shielded for proper operation.

However shielded cable is improper since it adds parasitic capacitance that reduces sensitivity.

Thanks Jerrt Lee Marcel.
That's a really good advice. By head I guess you mean the pcb outs (signal and voltage polarity). Am I correct?
Is there shielded wire of such small gauge (or could I create one by "knitting" 2 wires)?
In my case what would you do to achieve my goal?
I mean it's highly improbable to find a donor body capable to host all 4 pcbs. Even 3 of them (and forget about fig. 8.

As a simple first test, measure its capacitance?-Scott

Could you please be more specific,? Scott? How can I do that with a simple multimeter and a small variable DC supply up to 50V? Thanks.

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Could you please be more specific? How can I do that with a simple multimeter and a small variable DC supply up to 50V? Thanks.

You can start with checking with the mulimeter that the capsules are not shorted.

Le 09/05/2022 à 19:51, tedsorvino via groups.io a écrit?:

Thanks Jerrt Lee Marcel.
That's a really good advice. By head I guess you mean the pcb outs (signal and voltage polarity). Am I correct?

Head is the circuitry that receives the capsule and transforms the very high impedance into a more manageable impedance.

Is there shielded wire of such small gauge (or could I create one by "knitting" 2 wires)?

As I wrote earlier, using shielded wire is not adequate. You have to make sure that all the high impedance circuitry is in a shielded enclosure, which must also be acoustically transparent, such as mesh.

In my case what would you do to achieve my goal?

I would try to make a PCB that holds all the high impedance circuits for two capsules, and put the rest, included the bias generators on a separate PCB.

I would try to make a PCB that holds all the high impedance circuits for two capsules, and put the rest, included the bias generators on a separate PCB.

Thanks Jerry. Is it necessary the bias PCBs being in the same enclosure with the high impedance circuits??

As I wrote earlier, using shielded wire is not adequate. You have to make sure that all the high impedance circuitry is in a shielded enclosure, which must also be acoustically transparent, such as mesh.

True. Sorry for that. I read it later. The capsule is in a mesh - the normal faraday BM 800 microphone top . Can I use copper foil around? the mic enclosure on the inside - like I'm using on my guitars- to reduce EMI noise, or does it affect sensitivity?

You can start with checking with the mulimeter that the capsules are not shorted

Without being sure I just used the continuity mode on my DMM. No continuity between capsules and between capsules and backplate (common backplate cable).

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I would try to make a PCB that holds all the high impedance circuits for two capsules, and put the rest, included the bias generators on a separate PCB.

Thanks Jerry. Is it necessary the bias PCBs being in the same enclosure with the high impedance circuits?

No. It can be separate.

As I wrote earlier, using shielded wire is not adequate. You have to make sure that all the high impedance circuitry is in a shielded enclosure, which must also be acoustically transparent, such as mesh.

True. Sorry for that. I read it later. The capsule is in a mesh - the normal faraday BM 800 microphone top . Can I use copper foil around? the mic enclosure on the inside - like I'm using on my guitars- to reduce EMI noise, or does it affect sensitivity?

Copper foil is OK.

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You can start with checking with the mulimeter that the capsules are not shorted

Without being sure I just used the continuity mode on my DMM. No continuity between capsules and between capsules and backplate (common backplate cable).

As I suspected from the start, I believe your capsules are good and the problems you had are elsewhere.

As I suspected from the start, I believe your capsules are good and the problems you had are elsewhere.

Thanks Jerry. To start with while I was reducing cabling length I shorted either the bias IC or a cap - diode around it. When I sort that out I will try all the meters you suggested.
Just a couple of quick questions
Is it ok to leave one side of the dual capsule disconnected with it's lead on? Is it a possible cause of interference and lack of signal sensitivity?
Does it matter if I connect the center of the capsule on the bias pcb and the backplate on the high impedance one or vice versa? Does it affect the microphone output?

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As I suspected from the start, I believe your capsules are good and the problems you had are elsewhere.

Thanks Jerry. To start with while I was reducing cabling length I shorted either the bias IC or a cap - diode around it. When I sort that out I will try all the meters you suggested.
Just a couple of quick questions
Is it ok to leave one side of the dual capsule disconnected with it's lead on? Is it a possible cause of interference and lack of signal sensitivity?

It should be OK as long as the unconnected wire is properly dressed as not to pick up interference.

Does it matter if I connect the center of the capsule on the bias pcb and the backplate on the high impedance one or vice versa? Does it affect the microphone output?

Well, it does matter, since the stray capacitance of the backplate is higher than that of the center termination, so the output level and distortion may suffer a little. In addition, applying bias to the backplate makes it attract dust instead of the diaphragm.

As I said I would get back with updates. I insulated both pcbs (bias- high impedance) using tape around them and I cover all the inside of the mic body with copper tape. Good signal and healthy signal? initially with phantom. No noise.??All my testing setup is good with any other mic.?
But.... after a couple of minutes (on a shockmount) a "squeeking" pitch raising sound starts and then the sound starts coming and going.
Can't blame the OPA IC? since with the simple electret it works really well - same pcb . And the capsule seems like it's working, since initially is functioning absolutelly properly.
Maybe a problem with any of the larger electrolytic caps on the high impedance pcb or the 2 small 20nf around the xlr pin 2-3?(for noise reduction)? or maybe the 1gohm resistor (which could be sensitive since its value is huge)?
I can't blame the bias pcb since it's providing constant 65V.

--

I assume that you are constantly measuring it?

Hi Jules. I mean I was measuring the supply on its own for quite a long time several times before using it on the mic. Because it was built last (after an accident on the previous one). I will follow your guidelines carefully (most of my voltage are correct - haven't? measured around the 1gohm yet), And the SMDs can be a little bit frastruting on what is considered a good or bad solder without microscopic inspection....It's good to know that such problems have sn easy(???) fix.

?

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Also ensure you clean the PCB well especially around the 1gig?

All good. As I said before no issue with the voltage (constant 64v occasionally -50mv). Mainly housing issue. I mean very tight space for all components and interconnections. I reflowed some solder around the 1gohm and the Opa legs and all good. I put things back while I was auditioning? it loudly through headphones (I know it can be dangerous for a lot of reasons - but I 've done it before with other builds). The issue was mainly the interconnection cable of bias that was touching somewhere, and something around the xlr base (I guess all the trial - error with heat on the cheapo components of BM 800 mic body don't help a lot). Covered the exposed things, put things back carefully while listening. No external noise. Really really quiet built. Good signal to noise ratio for my liking. A bit darker sounding mic, compared to my usual ADK Vienna and also compared to the OPA based electret build.
I think it will be an ongoing project, since I have some more boards and there is another capsule side that asks to be used (and a personal ambition for a 3 mode DIY mic). But I guess I will allow myself some time with the cardioid part just to familiarize myself with the characteristics and the potential issues that may arise on these 2 newly built mics.
Thanks Jules for the excellent design and Jerry Lee for the advice and help while things were not clear.

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Congrats!