Simple amplifier circuit

Discussion in 'The Projects Forum' started by Octember13, Dec 29, 2009.

  1. Octember13

    Thread Starter New Member

    Nov 3, 2009
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    The other day, while I was plotting brilliant ways to create brilliant works of electronics, the idea of making iPod speakers occurred to me. I found a broken pair of iPod earphones I had lying around, cut and stripped the wire, sanded of the enamel from the wires, and quickly found that speakers besides the iPod speakers worked fine, as well. After doing a quick victory dance, I found that the speakers played fairly quietly, while the iPod was at full volume. After some searching around online, I found that I would need to build a simple amplifier circuit, and that this had been done many times before.

    I bought a pair of LM386 semiconductor IC's from radioshack, plugged them, along with everything else I had salvaged from old equipment, and tested it out on a breadboard. The result was a distorted, muffled, sporadically loud amplifier. I gave up on the guide I had been using, and found this. http://josepino.com/?mini_amplifier_lm386 I would be using the "General Purpose Amplifier," the third diagram on that page.

    If I can get this to work, i'll be making using a stereo potentiometer for the volume of both the left and right speakers.

    As close as I am, a bit of that diagram confuses me to no end. At the far left, the volume control. As far as I can tell, it's a 100k potentiometer. In the diagram, two leads go in, and two come out. The third wire of the potentiometer seems to go to the capacitor, and then to pin 3 of the IC. But what about the second output? Should I attach wires from pins 2 and 4 of the IC to one of the outside wires of the potentiometer, as well as to the negative end of the battery?

    I know this is long and confusing, but i'd love any help I can get. If you have any suggestions about the project in general, they'd be greatly appreciated. Thanks in advance
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I guess you're referring to this schematic:

    [​IMG]

    You'll need two of these circuits, one per channel.

    The plug for your Ipod is probably a typical mini stereo plug; it has a tip, a ring, and the ground. The ground will be common to both channels.

    So, the lower end of each volume pot will go to ground, and to the input common ground.

    The left and right channel input goes to the left and right pot - the upper end of the pots. The wiper of each pot goes to the 0.1uF cap on the input of the two separate amplifiers.
     
  3. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The general Purpose Amplifier is missing the important RC at its output to ground and the missing supply bypass capacitor shown on the datasheet.

    Of course it needs a volume control since its gain is 20 times or 200 times.
    Since its input DC voltage is very close to 0V then the input capacitor is not needed.

    The LM386 has an output of only 0.45W with a 9V supply which is as loud as a cheap clock radio. Increasing the supply voltage hardly increases the output power, it just makes the LM386 hot.
     
  4. awwende

    Active Member

    Feb 17, 2009
    39
    0
    I would recommend using the TDA2822. http://www.st.com/stonline/products/literature/ds/1464/tda2822m.pdf

    it's not the quietest op-amp in the world but will work fine. it comes in a 8-dip which is the same size as the 386. When I was in high school I made it to fit in an altoids tin for my ipod to drown out the noise of other kids on the bus. I've used it to drive portable speakers when I'm down stairs working on my electronics and I never have to adjust the volume over 50%

    http://www.next.gr/inside-circuits/1w-stereo-headphone-amp-tda2822-l3458.html

    that's the schematic I used to design it with a 9v supply.
     
  5. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    With a 9V supply, the output of an LM386 amp at clipping into 8 ohms is 450mW.
    The output of each channel of a TDA2822M is 700mW per channel which is slightly louder. It takes 10 times the power to sound twice as loud.

    The position of a volume control shows the amplifier's sensitivity (gain) not its power.
    My 1000W amplifier has a low gain. I can turn up its volume control to maximum but its max power is only 2W when its input is at a normal level.

    My Sony Walkman radio has high gain. I can turn down its volume control to almost zero but it is still too loud at about 30mW (0.03W) per channel.
     
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