3 transistor mini amplifier for 9 Volt only suitable to amplify beep signals demo and schematic

Описание: Please read the description first, for the best and most complete information.

A 3 transistor audio amplifier, only suitable to amplify “beeps” or “clicks”, when they are in the order of 1 Hertz up to (say) 5 KC (perhaps even higher).

Not usable to amplify pur audio or music. Too much distortion will be heard in that case.

Thus it is a “bare” Opamp-like 3 transistor schematic and everything is told in the video.

Feel, of course, free to elaborate more on this circuit. I am sure you can get it working as a properly working (very small output) audio Amp. This is not the aim here, like I tell in the video: there are many properly working audio amplifiers (1-15 Watt, with schematics and their tests) on my YouTube Channel.

The output electrolytic capacitor was in this case 220 uF/16 Volt, but 100 uF or a smaller value also works.

With the switch (blue dot in the drawing) in the emitter lead of one of the end-transistors, the sound gets more fierce, but of course the current taken out of the 9 Volt battery goes (somewhat) up when a signal is amplified, thus a somewhat shorter lifetime of the 9 Volt battery, when in use.

The idea was to make this amplifier in such a way that the 9 Volt battery can last for a long time, by using the class B type of amplifier to amplify the clicks/oscillations of the metal detector oscillator coil/2 transistor schematic.

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Upload 4 February 2026.