Microphone uses 'phantom power'

摘要

The electret microphone capsule is similar to those commonly used in telephones, cassette recorders, and computers. The element functions as a capacitor with a fixed trapped charge. Sound pressure moves a diaphragm, producing variations in the capacitance. This action produces an ac-output voltage with an extremely high source impedance. A FET inside the capsule uses an external-resistor drain load (Figure 1). R_1 and R_2 provide an appropriate load impedance and voltage from the 10V supply. The basic performance of this simple capsule is excellent, but it requires further signal processing to conform to professional phantom-powered-microphone standards.