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. We can use any NPN transistors such as BC […]

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Electronic Ear

Circuit below is a very sensitive 3-transistor amplifier using a speaker transformer. This can be wound on a short length of ferrite rod as show above or 150 turns on a 10mH choke. The biasing of the middle transistor is set for 3 V supply. During idle conditions and the quiescent current is just 5mA, the second and third transistors […]

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