LM386 difficulties

Discussion in 'The Projects Forum' started by leejongfan, Nov 5, 2008.

  1. leejongfan

    Thread Starter New Member

    Nov 5, 2008
    1
    0
    I have been trying to use this LM386. Actually, when I used breadboard to build my 1st prototype, it worked fine (yeah still had noise but acceptable, at least i can understand the sound)

    But now I am doing the prototype using PCB and its performance is very bad. I cant even hear anything except noise and buzz.

    [​IMG]

    I also used decoupling cap for the power supply and an 8Ohm speaker.
     
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Hi Leejongfan,
    You have a capacitor with backwards polarity connected between pin 1 and pin 8. This capacitor increases the voltage gain 10 times.

    The capacitor from pin 5 in series with the 10 ohms resistor to ground looks like an electrolytic type instead of a 0.05uF (0.047uf) ceramic or metalized plastic film type.

    With the very high voltage gain then the input must have a shielded audio cable because ordinary wires will act like an antenna and pickup mains hum and buzzing.
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
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