Question about microphone

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
R8 works with C6 to filter the power supply for the microphone stage (so that it doesn't get messed up by fluctuations in the battery voltage when the other stage(s)' current varies). That's also known as "power supply decoupling", and the resistor and large capacitor allow the decoupling to be effective to lower frequencies.

R6 is the bias feed resistor for the FET in the electret microphone capsule. An electret capsule contains an internal FET, and that FET's current varies with the sound the capsule picks up. Since all the current to the FET comes through R6, then the varying current results in a varying voltage (V=I*R) that gets fed through C4 to drive Q2's input.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.