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I made this scheme:

schematic

simulate this circuit – Schematic created using CircuitLab

Gain of this differential amplifier is constant and equal to 2. I would like to have possibility to substract variable voltage but this doesn't work. Is it any easy way to make this scheme work?

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  • \$\begingroup\$ Are you using a single ended power supply (0V and Vcc)? \$\endgroup\$ – Chu Aug 11 '17 at 15:18
  • \$\begingroup\$ Yes, I'm powering this opamp from 3.3V. Used opamp is BD1321G. \$\endgroup\$ – Piotr Aug 11 '17 at 15:26
  • \$\begingroup\$ And what magnitudes are the signal and typical direct voltage at the input of R4? \$\endgroup\$ – Chu Aug 11 '17 at 15:30
  • \$\begingroup\$ Ranges of magnitudes on signal are from 1.65V to 3.3V. Voltage on R4 should be 1.65V (thanks to this on output will be signal with range from 0V to 3.3V) but it is hard to set this potentiometer to this voltage. Even if it succed current consumption rises by about 25mA which is way too much. \$\endgroup\$ – Piotr Aug 11 '17 at 15:39
  • \$\begingroup\$ But the gain is 2, so the output is trying to go twice as big as this. The op amp Output can only be between the rail voltages: 0 and 3.3V \$\endgroup\$ – Chu Aug 11 '17 at 15:43

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