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  • 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

    
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    35 Responses to "LM317 Audio Amplifier"

    1. Nigreats says: on March 3, 2012 at 10:20 am

      Thanks for your contributions to the growth of electronics., have tried it and it worked

    2. wowwww
      its be simple amplifire
      thanks so much

    3. Awesome!!

    4. amazing,,, thank you very nice..

    5. if u use 8v what wil be de output?..jarulebebeh 4rom nigeria

    6. it’s very simple amplifier schematic …

    7. Farhan Khan says: on March 30, 2012 at 10:39 pm

      is the Output should have only 8ohm …?

    8. how much will be its gain?

      • WOW!!!!! I needed this Circuit About 6 years ago BIG TIME!!! Nice Design. 8 OHM SHOULD WORK. I’M guessing 5k/470. Any Lower in Ohms Might fry the chip!!! Old Design = New Design ,,,,,,And Regulator becomes Amplifier!!! Nice Design People!!!!

    9. thabiso says: on May 5, 2012 at 2:01 pm

      IM A STUNDENT AT TUT,DOING DESIGN PROJECTS.I PRESENTED ABOUT DC POWER CONTROL AND MINE WAS BASED ON POWER SUPPLIES.NOW IM STRUGGLING 2 DESIGN A PROJECT THAT RELATES 2 MY PRESENTATION.ANY SUGGESTIONS.

    10. The most amazing, an IC LM317 is used to small size power amplifier.
      Thank for very well post.

    11. the 5K variable resistor replaced with 1K. 4.0V voltage on 10Ω resistor , it is a little hot,replaced with 20Ω. The current consumption is 300-400mA,when RP=0,the amplify times is nil.when RP=1K,the R3 is very high temp.

    12. phamkhoe says: on June 6, 2012 at 5:40 pm

      very nice!thank you so much!

    13. manny6967 says: on June 17, 2012 at 3:14 pm

      nice circuit will give it a try tomorrow thanks.

    14. dpls i want to know more on the circult i like the amplifier i need the complete circult diagram of LM317 audio amplifier nd d power circult of it

    15. Dis circuits work well when hi test it thanks Plz.can u give me stereo amplifier of Lm317

      • just build two of that and you have a stereo set up, but if your asking for a preamp circuit that’s another story

    16. project has very attractive

    17. The pin outs seem wrong
      pin 1 =In
      Pin 2= adj and
      pin 3 is o/p

    18. Sorry it right i was looking at it from the schematic view rather than the component

    19. I used an LM386 chip on a 4 Ohm speaker and it sounds great. No heat sink, and perfect volume adjustment with a 20kBX2 pot. :D

    20. Kentronics says: on September 23, 2012 at 1:55 pm

      Please,explain the working principle to me.Thanks.

    21. hello out there!!can i use LM338??thanks

    22. hello out there!!can i use LM338??thanks ya all

      • Yes, the LM338 can be used..
        With the LM338 the suply voltage can be rased to 16V with the voltage on the 10ohm resistor ajusted to half the suply voltage, eg. With 16V in, Voltage on 10ohm resistor must be 8V. The 10ohm resistor must then be rated at 10Watt, and the LM338 needs a large heatsync.

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

    24. 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

      • 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.

    25. mozikluv says: on January 7, 2013 at 4:32 am

      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.

    26. Greg Gallacci says: on February 20, 2014 at 10:11 pm

      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……

    27. denmarklora says: on February 27, 2014 at 6:47 pm

      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

      • 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….

      • 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…..

    28. Frederico says: on April 29, 2014 at 6:14 pm

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

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