How to insert -10dB Pad circuit

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Bernhard

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Dec 9, 2017
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Hi all!

First newbie-post..
I’m planning to diy a schoeps like circuit with electret capsule I found here:
https://www.instructables.com/id/Modify-a-cheap-LDC-Condenser-microphone/

..for 2 reasons: I want some further training as it is my 2nd diy mic project and I plan to do a pair of D87 next. And also I for sure will find uses for a this cheap LDC as utility mic anyways.

As for this build I got a question:
I’ve seen microphone parts com sells it with a pad circuit. Is there any way I could implement that in my diy project. (Sure there is but could someone more experienced please tell me how to do?)

Thanks a lot and cheers,
Bernhard.
 

RuudNL

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With a 'real' condenser capsule there are two options: lower the polarisation voltage, or shunt the capacity of the microphone capsule with an extra capacitor. (To ground or as a feedback capacitor)
For 10 dB select a capacitor to ground with the double value of the capsule capacity. (That will give ~ 10 dB.)
 

Bernhard

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Dec 9, 2017
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Thanks Jakob and RuudNL for your fast responses!

I will try when I have the capsule. Still on its way..

Bernhard
 

RuudNL

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If you follow the AliceRF circuit diagram, there is no guarantee that the FET is properly biased.
I would connect a trimpot (500 K or 1 M.ohm) over the source resistor and connect the 1 G.ohm resistor to the wiper of the trimpot (instead of ground). This way you can adjust the correct bias for the FET.
 

abbey road d enfer

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RuudNL said:
If you follow the AliceRF circuit diagram, there is no guarantee that the FET is properly biased.
I would connect a trimpot (500 K or 1 M.ohm) over the source resistor and connect the 1 G.ohm resistor to the wiper of the trimpot (instead of ground). This way you can adjust the correct bias for the FET.
Actually, the circuit shown in the originallink describes that.
 

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