op-amp problem

Discussion in 'The Projects Forum' started by Blackbull, Aug 24, 2008.

  1. Blackbull

    Thread Starter Well-Known Member

    Jul 26, 2008
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  2. hgmjr

    Moderator

    Jan 28, 2005
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    I don't see anything wrong with the amplifier.

    What are you concerned about?

    hgmjr
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    I don't see anything wrong with it either. It's a pretty standard inverting amplifier with a gain of 100.

    The "C" version of the LT1007 has more loose specifications than the "A" version. The input offset voltage will be amplified along with the input signal. You can zero that out by changing the reference voltage on the + input while keeping the input to R1 grounded (between the two connected battery terminals, or "artificial ground".)
     
  4. Blackbull

    Thread Starter Well-Known Member

    Jul 26, 2008
    70
    6
    Thanks for the replies. It was the polarity of the input that concerned me and also the grounding of the 9V supplies. The circuit was worked out mainly from SgtWookie's advice to bobk. That was in the absence of a ''monkey see monkey see monkey do'' circuit. The supply is normally omited from the circuits I have seen and the grounding seems to end in space. Will null the offset. Thanks again.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Ahh, OK.
    The 0V reference point is where the batteries are tied together; which is also connected to the noninverting input (+) of the opamp.

    Getting the offset nulled will be somewhat of a challenge. Just a very small change in voltage on the input will give large swings on the output, due to the 100x amplification.
     
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