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miniature audio amplifier circuit schematic

Miniature Audio Amplifier Circuit

This miniature audio amplifier delivers up to 250mW and can be used like a final stage audio amplifier for radio sets. The schematic is very simple: one BC547 transistor controls a balanced power amplifier built with BC337 and BC327. The total amplification is around 15x and is determined by R1, R3 and P1. The input sensitivity is 95mV and the total current consumption is 180mA.

Small audio amplifier circuit diagram

miniature audio amplifier circuit schematic

9 Comments

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  • hegefer

    THX for this gem of good old times of discrete components’ design era. Simple to build and it’s more than convenient for lab purposes (testing, etc.)I have build it and works good. Potentiometer (P1) shouldn’t have been a logarithmic(LOG)one?

  • Chanchal Halder

    If possible please explain the working principle of the circuit.

  • GERHARDUS JOHANNES STROEBEL

    Increaase the output capacitor to 1000uf and get good bass for this size amp

  • GERHARDUS JOHANNES STROEBEL

    This circuit bring back memories of the beginning of OTL amps in the sixties I built it with Germanium transistors AC127 npn AC128 pnp output was then 1,5 watts as the saturation of those germaniums were only 0,1 volt versus 0,65 volt for silicones are Germanium still manufactured? I am just wondering

    • Jim Keith

      Manufacturing of germanium transistors is extinct, but devices remain available on ebay–sold a few in the past few years

    • P. Marian

      From wikipedia: “The major end uses for germanium in 2007, worldwide, were estimated to be: 35% for fiber-optic systems, 30% infrared optics, 15% for polymerization catalysts, and 15% for electronics and solar electric applications. The remaining 5% went into other uses such as phosphors, metallurgy, and chemotherapy.”

  • w_dm

    good effect. P1,C3 not connected,the current is 25 mA, total current consumption is 200mA when signal input, If the supply over 15V,the transistor T2 burn at once.

  • rafal

    nice! design was published in polish edition of Practical Electronic (Elektronika Praktyczna), I assembled it once, it got low harmonically distortions under 0,1%.

  • toko elektronik

    Thank’s for information in web

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