Newb with a lm386 audio amplifier issue.

Discussion in 'The Projects Forum' started by AntiMS, Dec 27, 2014.

  1. AntiMS

    Thread Starter New Member

    Dec 27, 2014
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    Hi, folks. Newb here. I'm trying to build a simple lm386-based audio amplifier circuit. I've attached a schematic of what I've got.

    I've got a simple pair of earbuds plugged into the audio output end, and an FM radio plugged into the input end for testing purposes. I'm powering it off of a 9V battery.

    What I hear through the earbuds is a "click" at regular intervals. Listening closely, I can tell the "click" is actually a very short snippet of audio from the FM radio. (Just a single note or even less.)

    Again, I'm pretty new to this. Please don't hesitate to point out anything bone-headed I'm doing. All help is greatly appreciated!

    Thanks, folks.
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Your amp configuration has a gain of 200, which is likely too much.
    Try removing the cap between pins 1 and 8, which will give a gain of 20.
     
  3. #12

    Expert

    Nov 30, 2010
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    Your 10k resistor is way off the recommended size.
     
  4. AntiMS

    Thread Starter New Member

    Dec 27, 2014
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    Tried that. Same result (except that I get slightly more background noise.)
     
  5. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    If the amp were to work, it would overpower the earbuds. Replace them with a speaker.
     
  6. AntiMS

    Thread Starter New Member

    Dec 27, 2014
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    Ah. Good call. I just mislabeled the diagram I posted. That's actually a 10 ohm resister in my circuit. Sorry about that. Thanks for pointing that out, though.
     
  7. #12

    Expert

    Nov 30, 2010
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    I can't imagine that the 386 is reaching into your FM radio and snatching pieces of audio. Try a different input source and see if that makes a difference.
     
  8. AntiMS

    Thread Starter New Member

    Dec 27, 2014
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    Gotcha. Thanks. Tried a pair of speakers and got the same result, but it didn't sound like you thought that would solve the issue.
     
  9. AntiMS

    Thread Starter New Member

    Dec 27, 2014
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    Hmm. Well, trying a *different* FM radio gave me *different* results, but not necessarily *better* results.

    The other FM radio, when plugged directly into ear buds plays music just fine, but when plugged into my circuit, produces a god-awful screeching sound. (Not a very loud one.) I turned off the lights just to make sure it wasn't the flourescant lights or anything, and still had the same result.
     
  10. tracecom

    AAC Fanatic!

    Apr 16, 2010
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  11. #12

    Expert

    Nov 30, 2010
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    I already stole your circuit and placed it in post #3 :p
     
    tracecom likes this.
  12. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    The key is adding some 1k resistors to the input from the left and right channels (as Tracecom had done). Your input signal is too stron for a 20x amplification without the resistors.

    You could also use a double-ganged potentiometer from the headphone to ground and use the wiper of the pots as inputs. That way you have some control. A 50k to 100k log (audio) pot will work best.
     
  13. AntiMS

    Thread Starter New Member

    Dec 27, 2014
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    Ah. Yeah. I noticed those. I'll try that out (probably won't get to it until tomorrow, thgough.)

    I also found that one of my wires might be causing the intermittent playing thing. I'll try getting those two things fixed and report my findings (positive or negative) tomorrow. Thanks, all!
     
  14. AntiMS

    Thread Starter New Member

    Dec 27, 2014
    7
    0
    Great success! Adding those resistors and fixing the input wire short fixed everything.

    I started this project just to get a feel for how the lm386 works before starting on a laser audio transmission project. I'll start another thread if I have trouble.

    Thanks, folks! You've been a great help!
     
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