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LM386 Coupling Capacitor

Discussion in 'Electronic Basics' started by zero, Feb 3, 2005.

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  1. zero

    zero Guest

    I'm building an audio amplifier using an LM386. According to its datasheet,
    I should connect the LM386's output through a 220uF coupling capacitor to
    the 8 ohm speaker.

    If I use a 220uF polarized electrolytic capacitor (the only kind of
    capacitor of this size at the local Radio Shack), should I connect the +
    node to the LM386 output, and the - node to the speaker so it won't explode?

    Also, will there be any problems with initially charging the capacitor when
    power is first applied?
     
  2. Lord Garth

    Lord Garth Guest

    The LM386 uses a single ended supply, +5 volts and ground for instance.
    The answer to your question is in the datasheet located here:

    http://www.national.com/ds/LM/LM386.pdf

    Look at the typical applications on page 5...
     
  3. The 386 has internal bias resistors to set the average output voltage
    at about half way between its positive and negative supply rails. If
    the speaker connects between this node and the negative rail, then the
    positive side of the capacitor goes to the amplifier.

    There will be a brief pop from he speaker as the capacitor charges to
    half the supply voltage. If this is bothersome, you can replace the
    single capacitor with two 100 uf caps in series across the supply,
    with the speaker connected between their junction and the output of
    the amplifier. This puts half the supply voltage on the speaker.
     
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