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Distortion In LM386 Amplifier

Discussion in 'Electronic Basics' started by Dave.H, Aug 18, 2008.

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  1. Dave.H

    Dave.H Guest

    I have an amplifier in my workshop, for listening to tunes from my
    iPod, but if I turn it up louder then whisper level, it distorts,
    pretty bad. I've been going nuts trying to figure it out, even tried
    many different speakers, from 1/2 watt to 20 watt ratings, and swapped
    out the LM386 chip. I have another one of these kits, used for an iPod
    amp around the house played through a 1 watt 2 inch speaker, plays
    fine, with little or no distortion at normal listening levels. This
    amp is run off 4 AA batteries, while the distorting one is run of a 9
    volt battery.


    Schematic:
    (Look at the amplifier section)

    http://www.siliconchip.com.au/cms/gallery/article.html?slideshow=0&a=101845&i=3
     
  2. I got a 404 error.

    It may be oscillating. The datasheets usually show a resistor and
    capacitor in series, connected from the 386 output to ground. This is
    to deal with oscillation, and if it's missing there may be problems.

    Likewise, if the input gets too close to the output, it may go into
    oscillation.

    Those things are decades old, and really there isn't much that can
    go wrong. So unless the specific IC is somehow bad, it can supply
    decent albeit small amounts of sound. It is possible to overload it,
    but since you should have a volume control acting as a variable
    voltage divider at the input, that's not going to be a problem.

    Layout may also be an issue. If there's not good wiring to the power
    supply, the resistance of the wires may become a factor and that can
    start causing problems.

    Michael
     
  3. Dave.H

    Dave.H Guest

    No, I'm only using the amplifier, I linked to that page, as I've lost
    the schematic that came with the set. Ignore the rest of the circuitry

    Dave
    Australia
     
  4. Dave.H

    Dave.H Guest

    I've tried the amp on 3 AA batteries, and tidied the wiring to the
    battery, no success, I have yet to try the capacitor, but I don't
    think it's anything to do with the battery supply. Maybe the 220 uF
    cap on the output has gone? I haven't had much experience
    troubleshooting electronics
    Dave
    Australia
     
  5. Eeyore

    Eeyore Guest

    The fact that it's a crappy amp chip about 35+ yrs old probably has a LOT to do
    with it.

    The best thing National could do is accidentally destroy all the masks for it.

    Graham
     
  6. Dave.H

    Dave.H Guest

    Yeah, replaced that cap, sound is undistorted at normal listening
    levels now through a 4 inch, 1 watt 8 ohm speaker ripped out of a
    1980's radio cassette, I was going to replace that cap before I posted
    the original message, but thought I'd get the advice from more advance
    hobbyists first.

    Dave
    Australia.
     
  7. Dave.H

    Dave.H Guest

    Another thing I've noticed with this amp, and the iPod amp I built for
    my father (different amplifier circuit) is that every now and then I
    hear a buzz through the speaker, This can get annoying when using the
    amp for a long period. I assume it's some kind of interference, what
    could be causing this? It happens every 2-5 minutes.

    Dave
    Australia
     
  8. Guest

    Cell phone? More likely if it is a modern digital one.
     
  9. Eeyore

    Eeyore Guest

    Maybe so but I shudder whenever I see yet another audio project based
    around one.

    They are notoriously useless.

    Graham
     
  10. Yes, and they are used where they fit. A small bit of amplification in
    a small package. Nice and useful. I can remember from before it
    was released, and you were stuck with a bulkier package, and move
    back a bit in time and you needed a lot more external components, and
    move a bit further back in time, and you needed all kinds of discrete
    components because there were no IC audio amplifiers.

    The fact that some use it where it's inappropriate, trying to get
    more power than it can offer or demanding something else from it
    that it can't supply, is not the fault of the IC. A lot of those
    uses, they'd likely be junk even if some other audio amplifier
    IC was used.

    Michael
     
  11. Dave.H

    Dave.H Guest

    Quite likely. Although I don't use one, several members of the
    household leave theirs one day & night, and they are all modern
    digital phones.

    Dave
    Australia
     
  12. Jasen Betts

    Jasen Betts Guest

    your mobile phone.

    Bye.
    Jasen
     
  13. Jasen Betts

    Jasen Betts Guest

    possible, but the range of the interferance isn't very great though,
    unless your circuit is spread out enough to act as an antenna.


    Bye.
    Jasen
     
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