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LM386 Amplifier Project

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by TheNewGuy, Aug 25, 2009.

  1. TheNewGuy

    TheNewGuy Member

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    I'm trying to use Eagle Software to draw out the schematic, and I'm thinkin' of just using paint to draw it out. :p

    I'm just using this schematic as a basis so I have an idea where things should go. I'm going to add an attentuator at the output. Which would consist of a couple of resistors, as said before? (Correct me if I'm wrong). I looked at the box for my earbuds, and they are rated at 16 Ohm.

    EDIT: I've changed my libraries from this link: here
    Much better!
     
    Last edited: Sep 3, 2009
  2. TheNewGuy

    TheNewGuy Member

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    I've gotten this far. (01.JPG).

    Now I just copy the wiring of the schematic you gave before for each LM386 IC?
     

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    Last edited: Sep 3, 2009
  3. audioguru

    audioguru Well-Known Member Most Helpful Member

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    A single resistor in series from an amplifier output to an earphone makes a voltage divider attenuator.

    EDIT:
    Don't copy my circuit that has an electret mic and a gain of 200.
    I told you what to eliminate from it so that your music player can feed it.

    The stereo amplifier needs only one supply bypass capacitor and a dual volume control.
     
    Last edited: Sep 3, 2009
  4. dave

    Dave New Member

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  5. TheNewGuy

    TheNewGuy Member

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    What to do with Pin 4 and 7?

    What I get hung up on, is knowing what you need where? Like, you do not need a Capacitor on Pin 2. (right?)
     

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  6. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Your circuit has its output capacitors with backwards polarity and is missing the pin 4 connected to ground (0V). Pin 2 does not need a capacitor since it is connected to ground.
    Your circuit is missing the very important supply bypass capacitor and the important RC network at each output.
    Each amplifier should look like this one as it is shown in the datasheet:
     

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    Last edited: Sep 3, 2009
  7. TheNewGuy

    TheNewGuy Member

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    All the GND connections just connect to the negative termial of the battery, correct?
     
    Last edited: Sep 3, 2009
  8. TheNewGuy

    TheNewGuy Member

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    Would this schematic have too much gain?
     

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    Last edited: Sep 3, 2009
  9. TheNewGuy

    TheNewGuy Member

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    Tommorrow I'll put in the attentuator.

    Tomorrow I'm going to the Shack for parts.

    What size resistor do I need for the attentuator? (16 Ohm headphones)
     

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  10. audioguru

    audioguru Well-Known Member Most Helpful Member

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    You showed the circuit from the datasheet with bass-boost. Its gain is fine and is shown on the next page of the datasheet.
    Then you show an amplifier without bass-boost and a gain of 20 but it is missing the important supply bypass capacitor.
     

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  11. TheNewGuy

    TheNewGuy Member

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    What measurement should it be? And the attentuator resistor?
     
  12. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The volume control adjusts the volume from the amplifier. When the amplifier's gain is from 10 to 20 then it will be fine.

    The attenuator resistor is selected so that the max sound from your headphones is not too loud. Each set of headphones has a different sensitivity so try a range of resistors.
     
  13. TheNewGuy

    TheNewGuy Member

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    Ok, what about the size of the bypass capacitor?

    I have to go out and buy all these things that is why I ask. =/
     
  14. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The supply bypass capacitor should be 220uf.
    If you are using a wall-wart adapter then add a 47uF capacitor to ground at pin 7 on each LM386 IC.
     
  15. TheNewGuy

    TheNewGuy Member

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    The Shack did not give me what I needed, and I spent a total of $20. I needed 0.03uF Ceramic Disk Capacitors and got only 0.022uF. I needed 0.05uF Ceramic Disk Capacitors and got only 0.047uF. These wont work will they?
     
    Last edited: Sep 5, 2009
  16. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Your circuit does not use any 0.03uF ceramic capacitors. If they are 330nF (0.33uf) input coupling capacitors then they should be film type (not ceramic) and are avaiable at every real electronic parts distributor except RadioShack.
    The 0.05uF capacitors in the output RC networks can be 0.047uf.
     
  17. TheNewGuy

    TheNewGuy Member

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    I'm not going to RadioShack anymore. It costs so much and I've never gotten what I need. Wasn't there a 0.033uF Capacitor next to the 10K Resistor, forming a loop from Pin 1 to the wire leading out of Pin 5 on the Bass Schematic?

    EDIT: Also, the 220uF bypass capacitor goes on Pin 7, correct?

    EDIT (Again): All the conections that connect to the ground, I can just connec them to the negative battery terminal right?
     

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  18. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The bass-boost circuit in the LM386 datasheet shows the "bypass" capacitor at pin 7 to ground. It is 47uF and is needed only when a cheap wall-wart adapter has hum.

    The 9V supply needs a 220uF supply bypass capacitor to keep the 9V from jumping all over the place.

    If you use 0.022uF for the 0.033uF bass-boost capacitor then the upper bass sounds will also be boosted.

    All the grounds connect together and connect to the negative terminal of the battery.
     
  19. TheNewGuy

    TheNewGuy Member

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    How do you figure out the values of the components for a circuit? Like 220uF for a 9V power supply on the Bass Boost circuit?

    Do you have to go deep into it and study it or just a simple formula?
     
  20. audioguru

    audioguru Well-Known Member Most Helpful Member

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    When a battery becomes discharged its internal resistance rises which causes its voltage to fluctuate up and down as the music changes the supply current from it. The supply bypass capacitor smooths the voltage. A good value is the same as the value of the amplifier's output capacitor since the output capacitor's value allows it to feed low frequencies to a high current speaker then the supply bypass capacitor having the same value will smooth the supply's voltage at those low frequencies and will smooth higher frequencies much better.

    The amplifier is stereo with two channels. But the fluctuating voltage on the supply voltage is double the frequencies that the amplifier plays. So you don't need a supply bypass capacitor to be double the value of one output capacitor.
     
  21. TheNewGuy

    TheNewGuy Member

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    I've run into a confusion:
    I've bought this board. One side, as seen, has copper rings and one doesn't. Which side is the component side and which side do I solder connections?
     

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