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lm317 audio amplifier

LM317 Audio Amplifier

You probably know that LM317 IC is used as an adjustable voltage regulator, but did you know it can be used as an audio amplifier? This is a class A audio amplifier built with LM317 that delivers a maximum 1W audio power.

Use a good heatsink for the LM317 IC and adjust the 5K variable resistor so that you have 4.5V on 10Ω resistor (or LM317 pin 2, Vout).

LM317 amplifier schematic

lm317 audio amplifier

Source: BackyardAmusement’s Youtube Channel

Video explanation of the working principle

39 Comments

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  • venkatesh

    is it compatible to mobile or only for mp3 player

  • J.K. Niazi

    It is a beautiful awesome simple circuit.

  • bazerkobob

    I’m looking for a simple audio amplifier circuit and this seems to be perfect. I’m a software guy with enough electronic knowledge to be dangerous. Will this work with a 3.3v PWM from a microprocessor? Will it work with a DAC output? What should the input voltage to the amplifier be (output from DAC)? Can I use 3.3v or 5v instead of 9v by changing the values of resistors, etc.? What values would work?

  • JK

    Yes this is really amazing and simple circuit. I am thank full to the designer and as well as up loader because this is a gentle
    help with the students and engineers…………
    Once again thank you ……………

  • Frederico

    Congratulations. It’s very nice to see something out of conventional. Intelligent.

  • denmarklora

    any one can help me to my project?? we need to make audio amplifier using transistor 40 watts output. this my email denmarklora@gmail.com

    • mozikluv

      do you have enough knowledge on how to build the circuit diagram? on how to make the circuit board? or maybe able to arrive at the voltage reading of various points in the circuit? it would be easier to make if you use a power audio IC. but making a 40w power amp from discretes is entirely different matter…..

    • mozikluv

      have you search the net? there are oodles of that in the net. just a word of caution, some posted circuits are not tested or actually built. some poster do not entertain questions. i do high end power amps but i won’t post those circuits for commercial reason….

  • Greg Gallacci

    Hi!
    Wow, nostalgia time….
    Used a similar circuit, but used an LM7805 instead.

    The principle is the same: the constant 1.25 Vref on the Adj pin is used with resistors and the like to render an ‘op-amp’ kind of circuit.
    Recall that in the Op-Amp, all currents in = all currents out.
    So, play around with the resistors, apply Ohms law, and a small change in current in one part of the circuit becomes large change in voltage in another part of the circuit.
    Resistance ratios determine the gain.
    Since the Regulator has a fixed reference voltage, the ‘gain’ of the Amplifier becomes the output voltage. Vin * Gain = Vout.

    Actually, this illustrates how an Amplifier has been used as a Regulator all this time……

  • mozikluv

    LM12 regulator can also be used as an audio Amplifier. it would rated at 80w. although the device has been deemed obsolete, there would still be plenty out there in the market. if ever you find 1 i suggest buy 2 as a reserve part.

  • dennis

    hello,ive not yet build the lm338k version due to my work sched,but is the passive components the sama as the lm317t version???only the 10ohms is change to 10W,thanks that a great project this holiday season

    • Rudie

      With 16V suply, The caps need to be 25V rated, the rest of the passive components are used as is. The 470uF 16V cap could be changed to 1000uF 25V or even 4700uF 25V for better bass.

  • caks

    Please,can someone help me with how LM317 does the amplification,aside it being used as an voltage regulator?
    Thanks

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