Hi there,

I have three cheap PC "Soundblaster" electret microphones[0] that I
need connect to a multi-channel sound card. The problem is that the
microphones expect a +5V DC bias from their connection with the sound
card[1]. The multi-channel sound card only has line-level inputs and
doesn't provide power for electret microphones[2]. I need to build
three circuits to a) provide the necessary voltage to the microphones,
and b) amplify the microphone signal.

I have found a circuit that appears to cover both issues[3]. However,
I need some clarification on a couple of things. Firstly, I will not
need the dynamic microphone input. Can I simply remove the dynamic
mic terminals and capacitor C3 from the circuit, or is there more to
it than that?

What I'd like to do is build a single box with three circuits on a
single piece of copper-track board and have it supplied by a single
wall-wart power supply. I'm a little unsure how to adjust the circuit
to accommodate this. How can I supply three such circuits from a
single power supply? From what I recall of my physics lessons, I can
either run them in parallel or serial, the consequences of which are
either a tripling of the power supply voltage (from 9V to 18V) or a
tripling, or possibly 1/3ing of.. something else.. amps? I forget.
Any pointers would be appreciated.

Thanks,

Robert Ham


[0] http://www.ebuyer.com/product/111661
[1] http://www.hobby-hour.com/electronic...microphone.php
[2] http://www.m-audio.com/images/global...10_UG_EN01.pdf
[3] http://www.tkk.fi/Misc/Electronics/circuits/micamp.html