Lazar Pancic - Yugoslavia
This circuit was submitted by Lazar Pancic from Yugoslavia. The sound
card for a PC generally has a microphone input, speaker output and sometimes
line inputs and outputs. The mic input is designed for dynamic microphones
only in impedance range of 200 to 600 ohms. Lazar has adapted
the sound card to use a common electret microphone using this circuit.
He has made a composite amplifier using two transistors. The BC413B operates
in common emitter to give a slight boost to the mic signal. This is followed
by an emitter follower stage using the BC547C. This is necessary as the
mic and circuit and battery will be some distance from the sound card,
the low output impedance of the circuit and screened cable ensuring a clean
signal with minimum noise pickup.