baffled by simple op amp circuit

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biff44

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Deleted

Never mind, figured it out.
 

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Your calculation is simply wrong. The 0.822 V offset adds also to the output voltage. The measured voltage is quite near to the expectable value.
 

Re: Deleted

Hi BIF44,

The voltage at the pos. terminal (0.822 volts) is multiplied by 6 (instead of 5).
 

Jeez, maybe I didn't figure it out. What about the 12 K feedback resistor and the two series 1.2K input resistors. Don't I get a gain of -5?

What I realized is that the input voltage I measured +1.336 volts DC probably had some AC riding on it, and the voltmeter was probably lying to me.
 

Hi BIF44,

-1.336*5+0.833*6=-6.68+4.998=-1.682 volts
 
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