Lm 386 problem..........

Discussion in 'The Projects Forum' started by Bob T., Oct 23, 2012.

Lm 386 PCB problem?

Poll closed Oct 28, 2012.
  1. My lm 386 circuit is producing wierd sound.

    100.0%
  2. LM 386 is niosy.

    0 vote(s)
    0.0%
Multiple votes are allowed.
  1. Bob T.

    Thread Starter Member

    Oct 22, 2012
    35
    0
    Hello and piece........:)
    [​IMG]
    I foud this circuit on the internet and acording to my experience in electronics i see that i must work, so i transferred this to EAGLE and made a PCB for it, but when i connect a 9V (not from batt.) it started to produce weird sounds like a 555 time connected to a speaker and when i change the volume (potentiometer) the frequncy of the pulses changerd like 555 timer, but i barely could hear my vioce amplified.
    What i sould to to fix my PCB?
    Pleaze help!!!........:(

    If anybody wants the EAGLE file i am ready to send, but give me your mail.
    Thank you all................;)
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    I see no decoupling capacitors in the given circuit.
    Decoupling or Bypass Capacitors, Why?
    You could try an capacitor of 10 - 100 μF and a 0.1 μF parallel on the pins 4 and 6 of the LM386.

    Bertus
     
    Bob T. likes this.
  3. absf

    Senior Member

    Dec 29, 2010
    1,493
    373
    As you said you didnt use battery, did you try putting a 220uF across pin 4 & 6 of the LM386?

    Allen
     
    Bob T. likes this.
  4. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,652
    767
    Why a poll? It makes no sense.
     
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  5. Bob T.

    Thread Starter Member

    Oct 22, 2012
    35
    0
    Tank you.
    This is the first time to me and I don't know what are polls....
    I will try the decoupling cap, should use bypass caps?

    Shall I use a battery?
     
    Last edited by a moderator: Nov 14, 2012
  6. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,871
    1,394
    I would try a battery first to ensure that the problem is because of the power supply. Then, I would condition the output from the power supply and use it.
     
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  7. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    If the micriphone can hear the speaker then it will produce acoustical feedback howling as a sound goes around and around. When the volume control is turned down then the feedback howling will stop.

    Try it with the speaker in another room with the door shut.
     
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  8. Bob T.

    Thread Starter Member

    Oct 22, 2012
    35
    0
    I Hello, thanks to all.
    I added some decoupling capacitors every thing worker fine and clear.But when
    i boxed it in a project box is stopped producing any sounds , not even nois.
    And when i shorted pin 5 and 6 together i amplified sounds but the ic became hot
    and the sound was unclear, so whats the problem and can i fix it?
    Thanks.....
     
  9. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The datasheet shows that pin6 is the positive power supply pin and pin 5 is the output pin.
    You should NEVER short the output of a power amplifier to its power supply.
    You probably destroyed the IC.
     
  10. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    Why would you short pins 5 and 6 together? :confused:
     
  11. Bob T.

    Thread Starter Member

    Oct 22, 2012
    35
    0
    It was working good when i shorted 6 and 5, but became hot.

    i just heared sound when i shorted them?!.....
     
    Last edited by a moderator: Nov 14, 2012
  12. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,652
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    Was it The swang song?
     
  13. Bob T.

    Thread Starter Member

    Oct 22, 2012
    35
    0
    I shorted it but not damage it, i still works.....
    Thanks
     
  14. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    does the LM386 work properly when it is connected properly?
     
  15. Bob T.

    Thread Starter Member

    Oct 22, 2012
    35
    0
    It is highly related to the passive components out.....and connections......

    Can any body Help me please i still don't know what to do......

    i think it is from a capacitor
     
    Last edited by a moderator: Nov 14, 2012
  16. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    You shorted the output to the positive power supply so the LM386 is probably blown up.
    Simply fix the wiring and replace the LM386 IC.
     
  17. Bob T.

    Thread Starter Member

    Oct 22, 2012
    35
    0
    I just wanted to see what will hapen..........I need any body to help me pleaze...I dont know waht the hell is happening in this circuit, it is just like....dead....Thank you.
     
  18. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,159
    How did you reach that conclusion? What tests have you done to confirm the LM386 is ok?

    How did you reach that conclusion? What tests have you done to confirm the the passive components caused the problem?

    And what did you conclude after you shorted those terminals?
     
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