相关元件pdf下载：bc413b 
the sound card f a pc generally has a microphone input, speaker output sometimes line inputs outputs. the mic input is designed f 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 transists. 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 circuit battery will be some distance from the sound card, the low output impedance of the circuit screened cable ensuring a clean signal with minimum noise pickup.
