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Old 23rd September 2012, 02:01 PM   #1
emosms is offline emosms  Bulgaria
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Default electret mic preamp gain

Hi,
how to control the gain/sensitivity in the following schematic?
http://www.hobbykit.eu/sch/s1035.gif
I thought it is R2 (1M) but it is biasing resistor, not a feedback like in opamp.
So, is it the R1 (4k7), load resistor for the fet transistor inside the electret mic capsule?
Best Regards
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Old 23rd September 2012, 03:02 PM   #2
DUG is offline DUG  Canada
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Location: mississauga ontario canada
One way would be to replace R3 with a pot and connect C3 to the wiper

Generally if the mic is a two wire then R1 is external, three wire then internal.

Find the data sheet for your particular mic...or get one that you can find a data sheet for. (IMO)

Not all piezo mics have the same supply and load resistance requirements.
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Old 23rd September 2012, 06:53 PM   #3
emosms is offline emosms  Bulgaria
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Join Date: Sep 2010
the electret capsule is 2 wire, I played with R1 - put a 10k pot.
At 10k goes up, at 0k goes away... just some unpleasant hum
but around 1k or 510 it has a low sensitivity and still clean signal - needed to pick a loud source like drums
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