LM386 Circuit Nightmares!

Discussion in 'General Electronics Chat' started by daroc26, Jun 7, 2009.

  1. daroc26

    Thread Starter Active Member

    Apr 4, 2009
    30
    0
    Hi All!

    I've been having a VERY difficult time with the LM386. I have the Electronics For Dummies book and I am using their schematic for the amplifier circuit. I haven't had any success.

    Most of my parts are scavenged from various appliances. I found two old portable phones and retrieved the microphone, speaker, and larger caps.

    The only part that isn't the same as the schematic is C3.

    Could you please review the attachments, my breadboard and the schematic.

    Any support of suggestions would be appreciated.

    Thank you!

    circuitnewb.blogspot.com
     
    Last edited: Jun 7, 2009
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The schematic will work fine when the circuit is built compactly on a pcb.
    C3 is important and is a standard value. Your capacitor is 10 times the wrong value.

    You used an electret microphone and it needs to be powered properly through a series resistor then coupled to the LM386 through a capacitor. You have the input of the LM386 shorted to the positive wire of the battery.
     
  3. daroc26

    Thread Starter Active Member

    Apr 4, 2009
    30
    0
    "You used an electret microphone and it needs to be powered properly through a series resistor then coupled to the LM386 through a capacitor. You have the input of the LM386 shorted to the positive wire of the battery."

    AG, thanks for your reply. I'll head to Radio Shack and pick up the correct value for C3.

    What values would recommend for the resistor and capacitor for the microphone?

    Could you explain the last sentence, shorted to the positive wire of the battery?

    Thank you!
     
  4. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,534
    Do you know how a protoboard is laid out? Row 12, F,G,H,I,J are all the same wire. You have pin 3 of the IC (D,17) jumpered to I,12. J,12 is going to the positive power strip.

    Have you seen these?

    Bill's Index

    The 555 Projects
     
  5. daroc26

    Thread Starter Active Member

    Apr 4, 2009
    30
    0
    Hi Bill,

    Thanks for posting your links, I've seen those blog posts in the past but will review again.

    If I understand, then the microphone should not be connected to V+ and V-? AG suggested a resistor and coupling capacitor, could you recommend any values?

    Also, do you know any easy circuit to test a microphone? Since it was salvaged and I soldered the leads, I want to make sure it wasn't damaged.

    Thanks again!


     
  6. daroc26

    Thread Starter Active Member

    Apr 4, 2009
    30
    0
    Hi All,

    I was finally able to breadboard the 555 timer with the LM386 to amplify the frequency generated by the 555 timer.

    I also noticed how it helps to have shorter jumper wires, it looks much more organized and I am more likely to reproduce it and troubleshoot.

    Thanks for the help!
     
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