Dynamic Microphone Pre-Amplifier

Dynamic microphone uses a moving coil around magnetic field to convert mechanical movement into electrical signal. The ordinary mini speaker is turned into a very sensitive microphone.  Although it looks like misusing the speaker as a microphone, but actually a real standard dynamic microphone  uses the same principle as this speaker.

DYNAMIC MICROPHONE AMPLIFIER circuit schematic diagram

We can use any NPN transistors such as BC 547. The circuit will operate from 2v to 9 v. It’s a common-base amplifier and accepts the low impedance of the speaker to produce a gain of more than 100. The best type for the speaker is the all-range type, almost any diameter could be used. The larger the speaker diameter the more sensitive the reception.

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