Summing Amplifier

Discussion in 'Homework Help' started by Hurt_it_Circuit, Nov 5, 2012.

  1. Hurt_it_Circuit

    Thread Starter Member

    Oct 2, 2012
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    How do you create an inverting summing amplifier on a breadboard? I have all of my connections to the om amp correct. I am unsure of where I connect my 2 power sources, my + input source, and my two - input sources with two batteries. I have tried numerous combinations and nothing has worked please help
     
  2. t06afre

    AAC Fanatic!

    May 11, 2009
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    Can you post your schematic
     
  3. Hurt_it_Circuit

    Thread Starter Member

    Oct 2, 2012
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    here you go ... The resitors are in series to give an Req o 40k Ohms on top and 25k Ohms on the bottom

    the gray wire in the bottom right corner is my V out
     
    Last edited by a moderator: Nov 5, 2012
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    What you have posted is a wiring diagram.
    A schematic was asked for.
    Can you post the schematicof the circuit?

    Have a look at this page of the eBook for some ideas:
    Averager and summer circuits

    Bertus
     
  5. t06afre

    AAC Fanatic!

    May 11, 2009
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    Here is an example. Remember GND, +9 volt and -9 volt. Should be connected to your breadboard
    [​IMG]
     
  6. Hurt_it_Circuit

    Thread Starter Member

    Oct 2, 2012
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    I calculated Vout to be -2.85V ... But I am having difficulty assembling this one my breadboard. I have 9V sources for the power but I do not want to waste the battery which is why they were not in the picture

    sorry here is actual drawing

    I have the power connected like that and I am assuming that the positive input also connects to the ground ... but what about the sources ?
     
    Last edited by a moderator: Nov 5, 2012
  7. bertus

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    Hello,

    The - side of the sources should go to ground, when the source is positive.

    Bertus
     
  8. Hurt_it_Circuit

    Thread Starter Member

    Oct 2, 2012
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    so you are saying to connect everything to ground when the sources are generating a positive current? But doesn't this short circuit the system cause I am getting a value of zero when i do that
     
  9. Audioguru

    New Member

    Dec 20, 2007
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    You did not post a schematic, instead you posted a fuzzy photo of a breadboard circuit.
    We do not know if you are using an opamp since it does not have a part number, it might be an LM386 power amplifier IC and its pin numbers are different to the pin numbers of an opamp.

    I am attaching a real schematic of an audio mixer circuit. It can drive a load not less than 22k ohms (the 330nF output capacitor C3 has a cutoff frequency of 22Hz with a load of 22k).
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    I see that you are summing DC voltages, not audio. Your answer is correct.
    Here is the schematic of your circuit (but it is missing the power supply):
     
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  11. Hurt_it_Circuit

    Thread Starter Member

    Oct 2, 2012
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    It seems to be working when I measure. I connected all the terminals to the negative. The only issue I have is that my measured values or off by a tens place. Everything else is correct my sign and the numbers ...

    Nevermind made a dumb mistake was using wrong resistor value
     
    Last edited: Nov 5, 2012
  12. Audioguru

    New Member

    Dec 20, 2007
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    What are "the terminals"? The inputs?
    What is "the negative"? The negative 9V supply?

    What is "or off"? Do you mean are off?
     
  13. Hurt_it_Circuit

    Thread Starter Member

    Oct 2, 2012
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    made a silly mistake in circuit diagram measured values are equal to calculated values now
     
  14. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    It is common practice with opamps to identify inverting and non inverting inputs. No matter what you asume.
     
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