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

[Magnus Danielson]

On 06/09/11 22:47, dan snazelle wrote:
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> On Sep 6, 2011, at 2:58 PM, Ingo Debus wrote:
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>> Am 06.09.2011 um 17:15 schrieb dan snazelle:
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>>> 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.
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>>> However, with these microphone elements, things are all weird.
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>>> 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.
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>> So you connected the mic through a 0.1 uF cap to a preamp with an input impedance of 1k? The cap is way too low then, try 10 uF.
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>> Ingo
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> SUCESS
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> switching the cap to a 10uf as Ingo suggested, and using an  inverting instead of non-inverting  amplifier made a WORLD of difference.
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> I can now get giant gains with just one opamp.
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> Can anyone explain this difference?  Does it have something to do with an impedance mis-match? Or too little/too much filtering?
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> I am going to get out my Walter Jung books and read up on mic preamps
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> thanks for everyones advice!
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> it all helped
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> now I just need to understand why it is working.

I hate to point out the obvious... the 10 uF cap has more magic smoke in it.

But seriously... Consider the high-pass filter frequency of 100 nF and 1 
kHz... it's 1,59 kHz. For the 10 uF cap you get 15,9 Hz. Should be a 
good starter, don't you say?

Cheers,
Magnus