Schematic diagram of electret microphone working principle

The shape of the common electret microphone is divided into two types: the built-in type and the external type.

electret microphone


Machine-mounted electret microphones are suitable for installation in a variety of electronic devices. The common machine-mounted electret microphones are mostly cylindrical in shape, and their diameters are φ6mm, φ9.7mm, φ10mm, φ10.5mm, φ11.5mm, φ12mm, φ13mm, and the pin electrodes are divided into two ends.


There are two types of three-terminal type, the lead type of the lead-in type with the soft-shielded wire and the lead-type type without the lead wire which can be directly soldered on the circuit board. If classified by volume, there are two types: normal type and miniature type.


Working voltage: UDS1.5~12V, commonly used 1.5V, 3V, 4.5V three

Working current: IDS between 0.1~1mA

Output impedance: generally less than 2K (ohms)

Sensitivity: Unit: volt / Pa, domestically divided into 4 files, red dot (highest sensitivity) yellow dot, blue dot, white point (lowest sensitivity)

Frequency response: generally flat

Directivity: omnidirectional

Equivalent noise level: less than 35 decibels


normal type and miniature type


The following schematic is to use the NPN three-stage tube 9014 to make an amplifier circuit for the microphone.

Materials: Universal board / 1.5V dry battery / 1KΩ resistor * 2 / 1MΩ resistor *1 / 9014 NPN three-stage tube 1 / 10uF electrolytic capacitor 2 / mic microphone one (early used in the old recorder)


Schematic diagram of electret microphone working principle


Schematic Diagram  analysis:


The resistor R1 is responsible for supplying the working voltage to the microphone, R2 and R3 are responsible for providing the bias voltage to the tertiary tube, and the capacitor C1 is responsible for coupling the signal of the microphone to the tertiary tube 9014 for amplification, and finally the amplified signal is coupled through the capacitor C2. Returned to the positive level of the microphone line.


9014 has the following magnification levels: A=60-150 B=100-300 C=200-600

(-9014 C 998 used here) D=400-1000


After the QQ chat test, the sound quality is clear and there is no noise. And in a 13 square meter room, there is no problem talking to the microphone one meter. Most importantly, a typical seventh battery can also be powered continuously for several months. The circuit is simple and the parts are few, which provides a good method for the friends with small microphone sound. After the speech is not so tired, the other party can hear clearly.