Here is a simple audio amplifier circuit that is easy to build and has few components. This circuit is built around the LM386 (click for datasheet) audio amplifier integrated circuit, useful when you need to power medium sized speakers from a music player that can only drive earphones.
From left to right, the first part is [...]
This project is based on ISD2560P IC which allows us to record 60 seconds voice and playback it with very high quality. As shown in the schematic, we input the voice by using an electret microphone. If a dynamic microphone is used, R2,R3,R4 resistors and C3,C5,C7 capacitors will be omitted and microphone will be connected [...]
A simple two-stage amplifier. Use any general-purpose NPN with high gain. It will drive low impedance headphones directly. A speaker will probably require further boost.
Original source:
An old HAM handbook I found in the school library many years ago.
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