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How to test preamp circuit for electret mic?

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New Member
I made this preamp circuit for the project i am doing. I am not sure about whether its working or not...Can anyone plz guide me in testing whether its working or not? How to test the preamp circuit?
My source of ciruit is this...
ECM Mic Preamplifier

Thank you


Well-Known Member
Most Helpful Member
If you can sing (or bark) then sing into the mic and hear if the output of the preamp can drive a power amplifier that drives a speaker.

This circuit shows an electret mic with 3 wires. The link shows how to connect an electret mic that has 2 wires.


New Member
Dab a wet finger on the input and listen for a buzz.

Low-end rolloff is bit low innit? With a peak next to 10 Hz as well. Must be the huge bypass capacitors that were chosen. Wader you think Audioguru?


Set the Voltmeter on a DC range that is just above the supply voltage.
Measure the DC voltage at the emitter of Q2.
Is it about half of the supply voltage?

Measure the voltage at the emitter of Q1.
Record it.
Measure the voltage at the base of Q1?
Is it about 0.6 volts higher?

Now change the voltmeter setting to the lowest AC range.
Connect it to the "Output". Tap or make a loud sound into the mic.
Does this effect the voltmeter?

One thing I would change in the circuit.
If you are using a two contact ECM change the 1k resistor that powers the mic to 10k.
Last edited:


Well-Known Member
Most Helpful Member
Yes, the frequency response is flat down to 5hz which is too low. The 10uF input capacitor should be changed to 1uF for a flat response to 50Hz.
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