Why isn't this amplifier amplifying?

Discussion in 'General Electronics Chat' started by dsharp02, Feb 21, 2016.

  1. dsharp02

    Thread Starter New Member

    Aug 8, 2015
    17
    1
    So I was playing around with an oscillator circuit and RC filters to try and make a sine wave generator. I succeeded in getting what appears to be a pretty decent sine wave, but after filtering the amplitude has dropped from 12v peak-to-peak to 0.5 volts peak-to-peak. So tried to setup a non-inverting amplifier with a gain of 2, using an op-amp. However for some reason the output from the op-amp is a steady 11.2v.

    What am I missing here?

    Thanks,
    Dave

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  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    Upload a LTspice file.
    Notes that the voltage at non-inverting amplifier input contains some DC-offset around 6V, and this DC voltage is also amplified by your opamp. So we need to add a voltage divider and the capacitor at non-inverting input and a capacitor in series with R9.
    See the example
    58.jpg
     
    Last edited: Feb 21, 2016
  3. dsharp02

    Thread Starter New Member

    Aug 8, 2015
    17
    1
    Thanks for your reply. Your response made me realize that I just needed to attach R9 to +6v instead of ground.
     
  4. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    1,097
    Also why do you not use your op amp as a active filter?
     
  5. dsharp02

    Thread Starter New Member

    Aug 8, 2015
    17
    1
    I'm just a beginner. I haven't gotten to active filters yet.

    Thanks,
    Dave
     
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