Pre-amplifier circuit

bloguetronica

Joined Apr 27, 2007
1,541
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
11,248
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.
 

Attachments

bertus

Joined Apr 5, 2008
22,270
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
 
Top