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Homework Help: Operational amplifier

  1. Jun 13, 2010 #1
    why is an inverting amplifier and not a non-inverting amplifier used as a summing amplifier ?

    Why must the input voltages be inverted in a summing amplifier ?

    I am told that a summing amplifier is used as mixer in concerts where different music produced by different instruments go through this summing amplifier before being amplified to the audience. Shouldn't the input by different instruments be the same as the output ?
  2. jcsd
  3. Jun 15, 2010 #2
    anyone ?
  4. Jun 15, 2010 #3
    A summing amplifier adds voltages weighed by their respective (inverse) input resistance (or impedance) with repect to ground.

    We can see that this can work when the positive input is grounded and the output is the negative of the weighted sum.

    Now try the same thing with the input resistors feeding the positive input. What do you get?
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