ELECTRET MICROPHONE

Thread Starter

boggydew

Joined Apr 29, 2017
13
Hi, I'm wondering how this circuit works. I understand that this is an electret microphone and the electret capsule (think J-fet) is what is amplifying the signal. What I don't understand is why there is a 0.1uF cap between the drain of the j-fet (or MC1) and the source ...or MICE (MICrophone Earth...I'm guessing....which is the LNA ground....I think). Wouldn't this provide a very low impedance to ground, filtering out the very signal we are trying to generate??? See PDF attached.

Cheers.
 

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Thread Starter

boggydew

Joined Apr 29, 2017
13
Hi ci139. Thanks for your reply. I'm interesetd in the role of C10 0.1uF. It's the same value as the dc blocking capacitor of the MIC signal C3. So C10 is by-passing the generated audio signal straight to ground (MICE being the ground of the pre-amp). When you say linearizer/ integrator what do you mean? Couldn't integrate my way out of a wet paper bag in high school. To me it seems to attenuate the signal in a big way. Why would we want to do that??

I got to wonder if the value for C3 (0.1uF) is correct. It makes a high pass filter with R4 (2K2) with a cut off frequency of 750Hz. That seems to be too high for voice. ? Perhaps Its a typo and is actually 1uF??
 
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AnalogKid

Joined Aug 1, 2013
8,439
I got to wonder if the value for C3 (0.1uF) is correct. It makes a high pass filter with R4 (2K2) with a cut off frequency of 750Hz. That seems to be too high for voice. ? Perhaps Its a typo and is actually 1uF??
Wrong direction. As the shunt element of a filter, a smaller capacitor will extend the audio passband to lower frequencies. 0.1 nF makes more sense.

ak
 

ci139

Joined Jul 11, 2016
1,443
When you say linearizer/ integrator what do you mean?
the integrator for this particular case means that it acts as "integrating op amp" -or- the testPoint in an " InputSignal--R--TestPoint--C--GND "
/// the integral is defined as a sum ← of differential values -- if you see ← this as an ongoing process in time .. and the electrons as the "values" then the "SUM" -- a charge at C -- is added up/down by in coming / out going electrons . . . about Section 4.6 Numerical Integration The Trapezoidal Rule @ www.yumpu.com

the linearizer means that fast spikes and transitions get somewhat shunted+smoothed -- so the "fractal"/"rough" signal gets more linear/continuous
 
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