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This simple, one-transistor amplifier provides a voltage gain over 1000 (60 dB) for driving a high impedance ceramic (crystal) earphone. The high gain is achieved by replacing the traditional collector resistor with an unusual constant-current diode that supplies 1/2 mA yet exhibits a very high resistance to the audio. This amplifier will give excellent battery life, drawing only 500 uA.

schematic

Below is a typical application using it with the first crystal radio circuit. The amplifier provides good volume with a modest antenna. You may want a volume control as with the TL431 project!

schematic

Or use the Crystal Radio RF Amplifier directly above for even more sensitivity with less than 2 mA current drain.

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