How to determine the polarity of an electret microphone

How to determine the polarity of an electret microphone

The electret microphone is small in size, simple in structure, good in electroacoustic performance, low in price, and widely used. The internal structure of the electret microphone is shown in the figure. It consists of two parts: the sound-to-electric conversion system and the field effect tube. There are two ways to connect its circuit: source output and drain output. The source output has three lead wires, the drain D is connected to the positive pole of the power supply, the source S is grounded through a resistor, and then a capacitor is used for signal output; the drain output has two lead wires, the drain D is connected to the positive pole



of the power supply through a resistor, and then a capacitor is used for signal output, and the source S is directly grounded. Therefore, before using the electret microphone, its polarity must be determined first. From the basic structure shown in the figure, it can be seen that a diode is connected between the gate and source of the field effect tube, so the forward and reverse resistance characteristics of the diode can be used to determine the drain D and source S of the electret microphone.
Set the multimeter to the R×1kΩ position, connect the black probe to one pole, and the red probe to the other pole. Swap the two test leads again and compare the two measurement results. When the resistance value is smaller, the black test lead is connected to the source and the red test lead is connected to the drain.