[sdiy] trying to understand amplification of an electret mic element

[Ian Smith]

I'm not entirely sure if this will help, but I did a quick Google-fu and found this link: 
http://www.minidisc.org/mic_preamp/Simple%20Stereo%20Electret%20Mic%20Preamp.htm
-Ian

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> From: subjectivity at hotmail.com
> Date: Tue, 6 Sep 2011 11:15:00 -0400
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] trying to understand amplification of an electret mic element
>
> normally when I want to add a lot of gain to something quickly, I grab a TL072 and use a resistor combination of say 1k to 1M.
>
> However, with these microphone elements, things are all weird.
>
> I started off as I understand you are supposed to by connecting the element to a 9v source through a 1k resistor. i tied the other end to ground. I took the signal out through a .1uf cap.
>
> well, with the opamp as above, I got very little gain.
>
> So I tried with a single transistor. (220k from collector to base, emitter to ground, 22k to +v and a .1uf cap out from the collector)
>
> It was much better. But still not enough. ( i want it to be enough gain to pick up background noise, not noise directly at the element)
> So I tried putting THAT signal through an opamp.
>
> I got weird offset issues EVEN with a blocking cap. And it still didn't add much gain!
>
> What is going on? I have plenty of experience working with REAL mic pre-amps but I have never made one from scratch before for an electret element.
>
> its interesting and somewhat of a challenge because all other inputs I have tried (synth, line level stuff, guitar) all was very easy to add gain to.
>
>
> thanks for ANY help.
>
>
>
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