I have inherited a circuit from a colleague using a MAX4063 pre-amplifier and an electret microphone. It's almost identical to figure 4 from the preamp datasheet:
But where that circuit has 2× 1 kΩ resistors in series, I have just one. I'm not happy with the overall volume and noisiness of the audio, and I'm starting to wonder whether the 1k resistors are too small, as they're smaller than the 2.2k output impedance of the microphone.
How, in general, should I select the bias resistor for an electret in this situation? What's the relevant theory?
Edit: While all the answers so far have been useful, I'm still interested in having an analytic understanding of why the bias resistor should have a particular value; I've seen other electrect circuits on the internet with values up to 10k, which must make some difference to something?
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