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lm386 and electret microphone problem

Stratos

Aug 23, 2015
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Aug 23, 2015
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Hello,
I have completed an amplifier circuit using the lm386 and an electret microphone as shown in the following link: *How to Build a Microphone Amplifier Circuit

When I blow onto the electret microphone, I can hear the sound of it. However if I start talking onto the microphone, no sound is coming out of the speaker.

I have tested the electret microphone on my pc and works fine as I can record myself talking and then hear it back.

What am I doing wrong?
Thank you very much for your time.

Regards,
Stratos
 

davenn

Moderator
Sep 5, 2009
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hi there
welcome

lets see a pic or 2 of your construction, maybe some one will see a wiring error you have made


Dave
 

Martaine2005

May 12, 2015
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Hi Stratos,
I think your amp is really a pre-amp. Which is why it works fine with your computer soundcard.
If you want to hear your voice through a speaker, you need a power amp too.
Those terms are used loosely as in a pre-amp to another amp to amplify the output signal, which is your mic.

Martin
 

AnalogKid

Jun 10, 2015
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There are a lot of low cost modules from china based on the 386 as a mic preamp. Low parts count and indestructable, but not enough gain, high distortion and noise, and not enough gain to go from mic level to 8-ohm speaker drive. Did I mention the gain?

ak
 

BobK

Jan 5, 2010
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I agree, it is not enough to drive anywhere near max output. A 1 transistor preamp (gain 10) would do it.

Typically, the electret mic will have a sensitivity of -46dB at 94dBA in. The gain is 46dB (200) so you would get 1V out at that level. A normal voice at 1 ft is 70dBA, at 3in it would be 82dbA which is -12db from 94, so you would get 1/4V out. You should hear something if you placed the speaker against your ear.

Bob
 

Stratos

Aug 23, 2015
2
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Aug 23, 2015
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Thank you all for your replies.
As far as I understood I need a preamp for the electret mic to work with lm386 as expected.
Thus I would like to make my own preamp. I have seen that a NPN transistor is needed for this.
Can I use any NPN transistor, because I have got BC547 (50V 100mA)?
In such a case what values for transistors and capacitors will I need?
Cheers
 
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