A typical electret microphone preamp circuit uses a FET in a common source configuration.  The two-terminal electret capsule contains an FET which must be externally powered by supply voltage V+.  The resistor sets the gain and output impedance.  The audio signal appears at the output, after a DC-blocking capacitor.
File:Electret condenser microphone schematic.svg by wdwd
Д.Ильин: translation, optimization