Simple 2 Transistor Audio Amplifier

This simple 2-transistor (2-stage) audio amplifier circuit with feedback is a useful preamplifier for use with microphones or in a radio circuit. It is ideal for small signal amplification and uses the 2N3904 transistor, which is cheaply and readily available from online auction shops. In this design, a 100-kΩ resistor provides feedback thereby increasing the input impedance.

This extremely simple and cheap circuit works well, and when I first made it, I was just a small whippersnapper. It is ideal for building on a strip-board or breadboard, and forms a useful amplifier block for a vast number of projects.