Electret microphone and microphone amplifier with a bipolar transistor
I need to calculate IC,VCE of polarization in the transistor Q1...


For DC analysis all capacitors can be ignored because they are effectively open circuit, and inductors are a short circuit. So the equivalent circuit for Q1 is:-







simulate this circuit &ndash; Schematic created using CircuitLab

First calculate the bias voltage at junction of R1 and R2. If we assume that Base current is negligible then this is just a simple voltage divider whose division ratio is (R2+R1)/R1. 12v / ((22k&ohm;+2.7k&ohm;)/2.7k&ohm;) = ~1.31V. VBE is 0.6V so Ve is 1.31V-0.6V = 0.71V. The current passing through R3 must therefore be 0.71V / 220&ohm; = ~3.23mA.

IE = IB + IC. If the transistor isn't saturated then IC = IB * 500 and IC is almost equal to IE. The voltage across R4 is then ~3.23mA * 2.2K&ohm; = ~7.1V. 12V - 7.1V = 4.9V between Collector and Ground, and VCE = 4.9V - 0.71V = 4.19V. This is safely above the saturation voltage, confirming that the transistor is not saturated and has the specified current gain.


  ...and the DC voltages of the entire circuit.


The only other DC voltage that might need calculating is between the electret microphone and R6. If we assume that 20k&ohm; is the FET's DC resistance then you simply have a voltage divider with 2.2k and 20k.