This microphone preamplifier circuit can be built with any basic single supple op-amp (eg. MC33171, LM358). The circuit will amplify a small signal produced by a dynamic or electric micorphone to a level that can be read by a stereo or mono input.

 The following component values should be used:

    

Component	Value
R1*	4K7
R2	1K
R3	100K
R4	100K
R5**	100K- 1M
C1	0.1uF
C2	0.1uF

 *R1 is only used with an Electret microphone. R1 will provide a 1 mA bias current to the Electret microphone.
 If a dynamic microphone is used, R1 should not be connected.

**R5 is adjusted to provide the appropriate gain using the formula:
Gain = R5/ R2

Note:
This circuit can be run at higher supply voltage. Although make sure your output signal voltage does not exceed the maximum voltage on the stereo input A/D.

Submitted by : Clint Lozinsky, Duncan Cambell, Grant Cunnigham, Richard Shultz