Archive for the Category


Crystal Radio (and other purpose) Audio Amplifier

Wednesday, July 1st, 2009
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Here is a simple audio amplifier using a TL431 shunt regulator. The amplifier will provide room-filling volume from an ordinary crystal radio outfitted with a long-wire antenna and good ground. The circuitry is similar in complexity to a simple one-transistor radio but the performance is superior (with the exception of the amazing one-transistor reflex ). [...]

Op-Amp Audio Amplifier

Monday, June 22nd, 2009
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The above circuit is a versatile audio amplifier employing a low cost LM358 op-amp. The differential inputs give the amplifier excellent immunity to common-mode signals which are a common cause of amplifier instability. The dotted ground connection represents the wiring in a typical project illustrating how the ground sensing input can be connected to the [...]

Class-A Small Audio Amplifier

Sunday, June 21st, 2009
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A class-A audio amplifier is pretty wasteful of power but when plenty of power is available the simplicity is attractive. Here is a simple darlington transistor example intended for use with a 5 volt power supply:
The 5 volts should be provided by a regulated power supply. The efficiency is below 25% and significant DC current [...]