Pre-amplifier circuit

bloguetronica

Joined Apr 27, 2007
1,359
Now that you mention that, I might have a pre-amplifier project for that kind of mic. That came in a magazine, but it is not copyrighted material (none of the materials inside that magazine are). I will OCR it as soon as I can.
 

Audioguru

Joined Dec 20, 2007
11,251
The preamp for an electret mic is simple:
1) Use a low noise wideband opamp like a TL071.
2) Bias the input of the opamp to half the supply voltage.
3) Have atrimpot to adjust the voltage gain to 22 times.
 

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bertus

Joined Apr 5, 2008
20,055
Hi Bertus,

thanks for the reply but when i try to use the simple circuit to pre-amp the signal, the output is still range between uv to mv which i found it quite strange becoz the gain of my circuit is 100. So, when 200mv is pumped in the o/p should be around volt range.

Regards,

apple
Hello,

here is a simple schematic.

http://www.mitedu.freeserve.co.uk/Circuits/Audio/ecmmic.html

As you see there is a resistor from the mic to plus.
Did you use this also? if you forget this your signal will be very low.

Greetings,
Bertus
 

Thread Starter

finding_apple

Joined May 28, 2008
6
Hi i decided not to use preamp in my circuit. now i try to create a DC offset value of 2.5V at the o/p by biasing it with resistors 200k and 100 ohm with the gain of the op-amp=1001. But why the o/p nearly 0v, why the amplification is not done?
 

Thread Starter

finding_apple

Joined May 28, 2008
6
Hi bertus,

The biasing of the electret is done internally. the circuit start from the mic(+pin) to a 2.2k resisitor then to a capasitor the to resistors 200k and 100 acts as a voltage divider to supply 2.5mv to the op-amp then with gain of 1001 , i hope to amplfy the CD o/p to 2.5v . But why the o/p nearly 0v, why the amplification is not done?

Regards,

apple
 

Thread Starter

finding_apple

Joined May 28, 2008
6
Hi bertus,

The biasing of the electret is done internally. the circuit start from the mic(+pin) to a 2.2k resisitor then to a capasitor the to resistors 200k and 100 acts as a voltage divider to supply 2.5mv to the op-amp then with gain of 1001 , i hope to amplfy the DC o/p to 2.5v . But why the o/p nearly 0v, why the amplification is not done?

Regards,

apple
 
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