Amplifier circuit help (simple)

Discussion in 'General Electronics Chat' started by ol'trusty, Oct 12, 2009.

  1. ol'trusty

    Thread Starter Member

    Sep 9, 2009
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    HI guys
    I Have just made this voltage amplifier to try and learn electronics.
    It does not seem to be working for me.
    Can someone please explain to me where Vin and Vout are suppose to be exactly ? I think that is my error.
    Any other advice is very appreciated.
    Thanks
    Trusty
     
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  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Read the comment in the schematic.
     
  3. Audioguru

    New Member

    Dec 20, 2007
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    The base voltage of a transistor is low and the output voltage is supposed to be near half the supply voltage. So the base should have a voltage divider to reduce the input voltage.

    But each transistor has a different amount of current gain and a different amount of base-emitter voltage and both change with temperature. So emitter resistors are used to reduce these differences.
     
  4. ol'trusty

    Thread Starter Member

    Sep 9, 2009
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    Thank you for the responses! I didnt ask my question clearly and for that I am sorry. Where do I PLUG in the two wires for vin and vout ? Can you please show me on the schematic?
    Thanks a lot
    Trusty
     
  5. ol'trusty

    Thread Starter Member

    Sep 9, 2009
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    Here is what I mean.
     
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  6. Audioguru

    New Member

    Dec 20, 2007
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    The slider of the 10k pot is your Vin. The transistors amplify its slider voltage which should be about +0.90V.
    But the transistors are not biased correctly so they do not work properly.

    The first and third transistors will be almost saturated and the second transistor will be almost cutoff when the pot is set so it works. But I think the amplifier will oscillate at a high frequency due to phase shifts.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Like this:

    [​IMG]

    See the lines with the circles at the end? Those are connection points; terminals.

    Vin and Vout are in respect to ground.

    [eta] Audioguru beat me to it.
     
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