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electret microphone amplifier circuit

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mdanh2002

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Does anyone know of a good amplifier circuit using an electret condenser microphone as input? The output should be loud enough to feed into an earphone. I try this **broken link removed** which works but the output volume is very soft. I need to tap on the microphone or blow into it in order to hear the noises in the headset. I remember I came across a similar amplifier circuit that uses 3-4 transistors which was very sensitive. I built it and could hear every single noise inside my room. But I can't seem to find it now.

I adjusted the value of R2 and R3 in the existing circuit and could see some improvements, but the output volume is still not loud enough. I also tried to add one more amplifier stage using another transistor but the result is a high pitch tone in the output (some unstable oscillation I guess).

Thanks for any advice.
 
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Does anyone know of a good amplifier circuit using an electret condenser microphone as input? The output should be loud enough to feed into an earphone. I try this **broken link removed** which works but the output volume is very soft. I need to tap on the microphone or blow into it in order to hear the noises in the headset. I remember I came across a similar amplifier circuit that uses 3-4 transistors which was very sensitive. I built it and could hear every single noise inside my room. But I can't seem to find it now.

I adjusted the value of R2 and R3 in the existing circuit and could see some improvements, but the output volume is still not loud enough. I also tried to add one more amplifier stage using another transistor but the result is a high pitch tone in the output (some unstable oscillation I guess).

Thanks for any advice.

hi,
Look thru these links.

electret microphone amplifier circuit - Google Search

Have you considered using a LM358 or another OPA as a preamp, followed by transistor.??
 
Don't use an LM358 dual opamp because it has crossover distortion, lots of noise (hiss) and cannot drive the low impedance of an earphone.

A mic preamp is designed to drive the high input impedance of a power amplifier. The power amplifier has enough output current to drive an earphone.

Your preamp didn't work becase the earphone loaded down its output almost like a dead short. Adding another amplifier resulted in the mic hearing the earphone which produced acoustic feedback howling because the sound went around and around.

Here is a pretty good electret mic preamp. It can drive a little LM386 power amplifier IC.
 

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