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Electret microphones can be set up using the following circuit:
The resistor should be around 1k and the capacitor around 4.7nF (if I remember correctly). Hopefully someone can verify--I don't think the capacitance value is critical, the main purpose is to block the DC from V+ from being passed into the filter. We only want the signal from the mic.
The opamp circuit shown in the first post here is not an amplifier because its gain is only 1 at low frequencies and it has a loss for frequencies higher than about 73Hz. An electret mic needs a gain of about 100 to 400 times.
The lowpass filter is very simple (only one RC) so its cut of high frequencies is very gradual. 364Hz is reduced a little. 3640Hz is reduced more. 36,400Hz is reduced much more but is still there.
An electret microphone has a Jfet inside that uses only 0.4mA. Its resistor to the positive supply should be 10k if the supply is 8V (9V that is filtered). A lower resistor value will load down the signal level because the output impedance of the Jfet is about 3.3k ohms.
Thank you all for your help. My purpose is to build a glass-break detector that want to put the voltage after the filter in A2D input of a microcontroller.
I doubt if I need to add something else to the circuit after the filter.
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