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Basic amplifier construction

  1. Sep 22, 2013 #1
    Hi,
    I have a single 2 watt, 8 ohm speaker from an old radio that i wired directly to a headphone audio jack and tried it in my phone. as you can probably guess, my phones speakers are much louder.

    How could i make a basic transistor amplifier that could give decent volume from the speaker?

    I have seen many circuit diagrams for this but i don't know how a device would be connected to them.

    Any schematics that would suit this application would be greatly appreciated.
     
  2. jcsd
  3. Sep 22, 2013 #2

    meBigGuy

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    You can do it with opamps, or discrete transistors. I'd recommend opamps. Just look at google images for audio amplifier IC and start reading about an approach. Note that amplifiers require a power source which can be as simple as a wall wart.
    For example:
    http://www.rason.org/Projects/icamps/icamps.htm
     
  4. Sep 22, 2013 #3
    with the amp in the link, how would the input be connected to a 3.5mm auxiliary jack ?
     
  5. Sep 22, 2013 #4

    meBigGuy

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    The link shows a mono amplifier. The 3.5 jack has three rings, ground, left, and right. You would connect ground to ground and either left or right to the amp (or use a stereo IC with 2 amps). Or, you could make a resistive mixer where you connect both L and R to the input, each through, say, a 1K resistor.
     
  6. Sep 22, 2013 #5
    i have found this diagram
    :::scroll down a bit for the diagram:::
    http://sci-toys.com/scitoys/scitoys/computers/solderless/amplifier.html

    could the Darlington transistor be replaced with a "normal" transistor and also using resistors of lower value?

    Also, is the input wire connected where it crosses over in between the 2 100k resistors?
     
  7. Sep 22, 2013 #6

    meBigGuy

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    I don't think that will work for what you are doing. It requires the proper DC levels on the input, and drives a continuous DC signal through the speaker when there is no signal. It is a pretty specialized hack for his radio application.

    Look at this page --- Question 5 is probably the simplest design that will work, question 8 shows a 1 transistor approach.
    http://www.allaboutcircuits.com/worksheets/trouble_bjtamp.html

    The problem with the 1 transistor approach is that the speaker loads down the amp.
     
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