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Is this circuit diagram correct?

Discussion in 'General Electronics Discussion' started by That one guy, Dec 25, 2016.

  1. That one guy

    That one guy

    17
    1
    Dec 23, 2016
    Hi guys, i need to follow this circuit diagram to make a speaker-mic-amplifier circuit but i have my suspicions that the the diagram is incorrect. Could you please let me know what you think
     

    Attached Files:

  2. davenn

    davenn Moderator

    13,244
    1,744
    Sep 5, 2009

    at first glance I don't see anything obviously wrong
    what did you think was wrong with it ?

    You can google the datasheet for the LM386 and confirm that part of the circuit
    the transistor is just a pre-amp for the electret condenser mic



    Dave
     
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  3. OBW0549

    OBW0549

    159
    118
    Jul 5, 2016
    Looks OK to me, too. Depending on which electret mic you are using, it's possible you may need to use a different resistance value for R1; but other than that it should work.
     
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  4. Audioguru

    Audioguru

    2,549
    574
    Sep 24, 2016
    1) The Jfet in an electret mic draws 0.5mA so the value of R1should be reduced to about 10k to prevent the Jfet from saturating.
    2) The transistor has a high input impedance then the high 10μF value of C1 passes low earthquake frequencies so its value should be reduced to about 0.22μF and it should be a non-polarized film type.
    3) The 2N3904 has an hFE of about 200 so the value of R2 should be increased to about 1M or 1.5M ohms.
    4) The low value of the volume control is killing the signal level from the preamp so it should be increased to about 100k ohms.
    5) The high 0.1uF value of C3 is killing all medium and high audio frequencies. Remove C3.

    Hey, the transistor has a voltage gain of only 10 so it is not needed and a 10μF capacitor can be connected between pin 1 and pin 8 of the LM386 to give it 10 times more gain.
     

    Attached Files:

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  5. That one guy

    That one guy

    17
    1
    Dec 23, 2016
    There were comments on the website that i got this from that it wasn't working so i wanted to ask you guys.
    Thanks for all the suggestions davenn, OBW0549 and Audioguru. They helped alot.
     
    davenn likes this.
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