Hi,
Looks like a k67/87 chinese copy. 6 or 9 micron mylar very probably.
Bias around 60v on tube mics. 40v is usuallly ok on transistor mics.
Have you connected capsule rim to ground? ( it is usually done through one of the screws fixed to the mounting or a dedicated one on capsule rim/body).
Electret are a kind of capsule, large membrane capacitor another kind even if they share some of their design requirements are differents.
Looks like a k67/87 chinese copy. 6 or 9 micron mylar very probably.
Bias around 60v on tube mics. 40v is usuallly ok on transistor mics.
Have you connected capsule rim to ground? ( it is usually done through one of the screws fixed to the mounting or a dedicated one on capsule rim/body).
Electret are a kind of capsule, large membrane capacitor another kind even if they share some of their design requirements are differents.
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Assuming krivium is right and it is a real condensor microphone capsule, it should work with the original, unmodified circuit, provided the connections from the capsule to the PCB are short.
If XLR pin 1 is not connected to the circuit ground, as simon7000 suspects, then you will get silence because the circuit can't draw any current from the phantom supply and can't work at all.
If the rim of the capsule is open, like krivium suspects, then the capsule won't do anything but act as an antenna for electric hum fields.
If everything is connected properly but the PCB has flux residues in the high impedance sections, then the circuit should work in a very dry environment, but might fail when the air humidity is high.
Is any of this applicable?
If XLR pin 1 is not connected to the circuit ground, as simon7000 suspects, then you will get silence because the circuit can't draw any current from the phantom supply and can't work at all.
If the rim of the capsule is open, like krivium suspects, then the capsule won't do anything but act as an antenna for electric hum fields.
If everything is connected properly but the PCB has flux residues in the high impedance sections, then the circuit should work in a very dry environment, but might fail when the air humidity is high.
Is any of this applicable?
If none of it is applicable, then the logical next step would be to check the bias points, keeping in mind that you can't measure anything useful in the 1 Gohm parts of the circuit with an ordinary multimeter. You could check the voltages across C7 and C2 and the source and drain voltages of J1, for a start.
By the way, what type of capacitor is C1?
By the way, what type of capacitor is C1?
That looks very much like a capsule without FET. If so, then your circuit is of the right type for that capsule.
EDIT: Sorry, some of the posts above did not appear when I posted the above.
EDIT: Sorry, some of the posts above did not appear when I posted the above.
According to https://microphone-parts.com/products/rk87-microphone-capsule it has two diaphragms and two backplates, and which you have to connect depends on the directional pattern that you want. It is a true condensor microphone capsule without built-in FET, so it should be able to work with the circuit of post #1.
WHO can give us a capsule datasheet? (hint: YOU)
You ask but do not supply ESSENTIAL data, how are we supposed to know.
By the way, where did you get the original schematic from?
Please link to original circuit/datasheet/page here.
Hi,
I think it's a variant around the typical Schoeps circuit but i'm not 100% sure. Edit: yes it is .
It could work with a k87 capsule but it'll be bright sounding ( there is no compensation for the hf boost the capsule will bring).
Depending on the headbasket shape ( diameter, height, kind of grill used) and used in close micing for voice ( playing with proximity effect) it could be close to the rendering of a C-800.
One thing that could be done once the circuit is working is to try to put membrane to ground and enter c1 from the capsule rim.
By doing so, the diaphragm is at ground reference and so should attract less dust and other nastys floating in the air.
https://images.app.goo.gl/BEN5Z56aCs9sm79t9
https://images.app.goo.gl/BoX7QLSjsSY67P9H7
I think it's a variant around the typical Schoeps circuit but i'm not 100% sure. Edit: yes it is .
It could work with a k87 capsule but it'll be bright sounding ( there is no compensation for the hf boost the capsule will bring).
Depending on the headbasket shape ( diameter, height, kind of grill used) and used in close micing for voice ( playing with proximity effect) it could be close to the rendering of a C-800.
One thing that could be done once the circuit is working is to try to put membrane to ground and enter c1 from the capsule rim.
By doing so, the diaphragm is at ground reference and so should attract less dust and other nastys floating in the air.
https://images.app.goo.gl/BEN5Z56aCs9sm79t9
https://images.app.goo.gl/BoX7QLSjsSY67P9H7
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You are most welcome.
Let's keep trying solve the issues with your circuit, when working ( which i'm sure it'll happen soon given the members giving help to you) it'll be a great reward!
Let's keep trying solve the issues with your circuit, when working ( which i'm sure it'll happen soon given the members giving help to you) it'll be a great reward!
Sorry, I want to ask a question again.
Where is the connection of point a in the figure?
What is the switch at B for
B is a pad attenuating the capsule output level before reaching the Fet.
A is OSC but i'm not sure it could be a ground connection, wait for the others to validate i've not studyed the schem ( and i'm way behind the level of other members answering you here...). Edit: could be only a test point, with no connection. It doesn't exist in the cmc5 schematic.
I did not post this schem to confuse you, just to validate it is based on the Schoeps circuit. 😉
This one is a variant too. If you want 'real' schem check the other link.
Edit: both schematic linked comes from here:
https://aeseaes.com/michael/
A is OSC but i'm not sure it could be a ground connection, wait for the others to validate i've not studyed the schem ( and i'm way behind the level of other members answering you here...). Edit: could be only a test point, with no connection. It doesn't exist in the cmc5 schematic.
I did not post this schem to confuse you, just to validate it is based on the Schoeps circuit. 😉
This one is a variant too. If you want 'real' schem check the other link.
Edit: both schematic linked comes from here:
https://aeseaes.com/michael/
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OK, friend, I'll take your advice and test my PCB tomorrow
OK, friend, I'll take your advice and test my PCB tomorrow
the schoeps has a dcdc converter (osc) that supplies the bias to the back to the capsule. the older neumanns had an oscillator around 40khz, with the risk of the osccilator residuals folding into the audio band when A/D converters were used. I did one with near 1 Mhz that generated a controlled bias voltage. I do not like the PAD method by switching a capacitor in paralell. that increases the noise floor. better to reduce the bias voltage to reduce sensitivity..
that switcheable bias system keeps the switch away from the audio path..
that switcheable bias system keeps the switch away from the audio path..