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Help with LM386 Amp Circuit

Discussion in 'General Electronics Discussion' started by McDroogie, Jan 12, 2013.

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  1. McDroogie

    McDroogie

    37
    0
    Dec 25, 2012
    I am trying to amplify my MP3 with the schematic pictured below. Can anyone tell me there are any errors? Except I've removed R3.
     

    Attached Files:

  2. davenn

    davenn Moderator

    13,726
    1,914
    Sep 5, 2009
    hi there :)

    yup you have a few errors in your wiring up
    now I can give you the answers directly or I can give you hints to help you fault find
    and that would be a much better learning lesson ;)

    1) follow you power supply from the + line on the proto board and through R1
    what then can you see wrong with the capacitor C1, compared to the circuit diag.?
    2) another capacitor wiring error .... look at the IC output on pin 6 going to the speaker
    you have the capacitor there not wired to the way the circuit diag shows ... can you see the error

    not to put too much on you at once ... lets sort those 2 things out for a start then we can look at the rest :)

    Dave
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,451
    2,809
    Jan 21, 2010
    One major issue is that your speaker is connected directly from the output to ground.

    Note that in the circuit, the capacitor connects between the output and the speaker (in series). You seem to have connected them in parallel.

    I suspect doing this is enough to prevent the circuit from working at all.

    That is just the first thing I noticed. There may be other errors.

    You need to be very careful in wiring to make sure that things are connected up the same way (unless you are skilled enough to know when it can be done differently).

    Also, you'll find it easier if you place the positive rail at the top of the breadboard, and the negative at the bottom. This is the normal way a breadboard is used and it mimics somewhat how circuit diagrams are drawn. It also helps prevent problems caused by connecting things up to the wrong power supply rail.

    I did notice that your soldering is a bit messy on the 3.5mm socket. Just be careful you haven't shorted anything out.

    Don't take these criticisms too harshly, it looks like you're gaining the skills needed to breadboard circuits. Nobody is an expert overnight.
     
  4. McDroogie

    McDroogie

    37
    0
    Dec 25, 2012
    Thanks. I had trouble desoldering the wires from that jack, so I tried my best and just did what I could and added another few coats of solder.
     
  5. McDroogie

    McDroogie

    37
    0
    Dec 25, 2012
    So connect the C1's lead to ground, make sure its positive lead is the in same row as R1 and connect it to pin 6?
     
  6. davenn

    davenn Moderator

    13,726
    1,914
    Sep 5, 2009
    Steve .... grrrr

    I was trying to get him to see that fault, mate ;) so he could learn to fault find :)

    Dave
     
  7. davenn

    davenn Moderator

    13,726
    1,914
    Sep 5, 2009
    yes, positive of C1 and one side of R1 go to pin 6, the other side of R1 goes to + supply

    now how about point 2, can you see what you have done wrong there ?


    Dave
     
    Last edited: Jan 13, 2013
  8. McDroogie

    McDroogie

    37
    0
    Dec 25, 2012
    I'm confused. It should the the negative lead going to ground right? I have posted some pictures of my attempts.
     

    Attached Files:

  9. McDroogie

    McDroogie

    37
    0
    Dec 25, 2012
    Here is a quick revision...
     

    Attached Files:

  10. davenn

    davenn Moderator

    13,726
    1,914
    Sep 5, 2009
    Thats much better :)

    you also figured out what you did wrong with that output capacitor and fixed it
    ie.... its supposed to be in line with the output and the speaker Well Done!! :)

    now one thing to do and this is just for ease of layout....

    put the positive supply on the other side of the board ie. keep the negative down the side where it is and move the positive to the other side. That is something that is common practice on breadboards and even on final PCB designs Keep + and -
    as far apart as possible
    THEN you can move R1 so it has a short hop from pin 6 to the + rail insteading of stretching the component legs way over the chip etc

    it just makes it tidier and easier to follow :)

    Dave
     
    Last edited: Jan 13, 2013
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