Get amplification with electret microphone

I have a microphone of knowles (EK one) with internal FET.
I want to use its FET to amp. it.
The problem is that I need to connect it to 600Ω load .
I try to reduce its Rs res. or get Rl higher , with no help. Without load it is o.k but the load want make me do so.
Is there any solution without adding an amp?

i think u must pass ur output signal through a capacitor. also amplification with transistors is useless. LM386 is a cheap power amp and easy to use try it and ull see.

hi,

barbar, the FET inside the electret insert is probably already amplifying the signal. These capsules are small capacitor mics (also called condensor) which use a permenantly charged plate, along with another plate acting as the diaphragm. The output from these two plates is terribly small and has a ludicrous output impedence (100MΩ?), so the internal FET is used as a sort of 'preamp' to get it to 'normal' mic levels (10-100mv) and to give a lower output impedence (≈2kΩ).

What is your application? Voice, sound sensor, recording birds??

I assume its a 2-terminal capsule, and that you have configured it as knowles have in their datasheets (with a resistor and cap). If you simply need to change impedence, and possibly a little gain (0-5) you will probably need an amp, for low gains, a single transistor would do.

There is some information about a mod for these capsules called the 'linkwitz mod', (search google) which will give you access to both the source and the drain of the internal FET, so you configure as you wish, changing its output impedence with resistors...but....its output will be much lower, and willl probably need an amplifier.

So, in answer to your question: No, I think you will need at least some external circuitry, but nothing major, a single transistor amp will do, I built one a while back on a board the same size as the capsule (11mm diameter).

Hope this helps...

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