1. We will be in Read Only mode (no new threads, replies, registration) for several hours as we migrate the forums to upgraded software.

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

    Expert

    Dec 20, 2007
    11,251
    1,350
    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
    15,808
    295
Loading...