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

[dan snazelle]

On Sep 6, 2011, at 5:32 PM, Magnus Danielson wrote:

> On 06/09/11 22:47, dan snazelle wrote:
>> 
>> 
>> 
>> 
>> On Sep 6, 2011, at 2:58 PM, Ingo Debus wrote:
>> 
>>> 
>>> Am 06.09.2011 um 17:15 schrieb dan snazelle:
>>> 
>>>> 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.
>>> 
>>> 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.
>>> 
>>> Ingo
>> 
>> 
>> 
>> SUCESS
>> 
>> 
>> switching the cap to a 10uf as Ingo suggested, and using an  inverting instead of non-inverting  amplifier made a WORLD of difference.
>> 
>> I can now get giant gains with just one opamp.
>> 
>> 
>> Can anyone explain this difference?  Does it have something to do with an impedance mis-match? Or too little/too much filtering?
>> 
>> I am going to get out my Walter Jung books and read up on mic preamps
>> 
>> 
>> thanks for everyones advice!
>> 
>> 
>> it all helped
>> 
>> 
>> 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
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i am glad you pointed out the obvious....I was completely overlooking it

I made the mistake of looking at a few schematics (which showed a .1uf) and then taping on an opamp, without thinking about the ways that the caps and resistors would interact....

filters and filter theory are one of the weakest areas in my immediate knowledge of electronics...I use a lot of filter calculators or trial and error....and often when I use a cap I use values that have worked before with similar
signals,etc

anyway, thanks goes to all who helped!
I am now happily at the bench reading a filter book