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I have built the following unity-gain inverting amplifier with an LM358 op-amp. I expect 3 volts at the output which the simulation confirms. However, when I build the circuit in real life, my noninverting input is at ground (expected), my inverting input is at -0.7 volts and my output is at -0.6 volts. I've verified my input is at about -3V and my supply rail is sitting at 11.9 volts.

The frustrating thing is, I swear it was working yesterday. I swapped out the op amp for a different one and get the same problem.

schematic

circuit in real life

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    \$\begingroup\$ Your schematic does not show a connection between your 12V power supply and ground. Is the 12V power supply connected to the same ground as your -3V power supply on your breadboard? Your image does not show that detail. \$\endgroup\$ Jul 26, 2023 at 11:06
  • \$\begingroup\$ what is the op-amp's negative supply voltage? \$\endgroup\$
    – user253751
    Jul 26, 2023 at 11:08
  • \$\begingroup\$ Ah yeah, sorry I messed up the schematic. The 12V supply and -3V supply are connected to the same ground. i.e. the op amp negative supply pin is grounded. \$\endgroup\$
    – xormapmap
    Jul 26, 2023 at 11:09
  • \$\begingroup\$ Your 12V supply seems to "float" with respect to ground. You could change that by using two 6V supplies in series and connect their mid-point to ground. Besides, it is a good idea to use e.g. 100nF caps between Vcc+ and GND and Vcc- and GND, close to the op amp pins. \$\endgroup\$
    – Hyp
    Jul 26, 2023 at 11:13
  • \$\begingroup\$ Are you sure protoboard matches schematic? 5 wires on schematic vs what looks like 4 on protoboard. \$\endgroup\$ Jul 26, 2023 at 11:44

1 Answer 1

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You need a ground on the power supply. For example, +/-6V.

If you ground the (-) side of the 12V supply you may experience phase reversal unless you add a Schottky diode from the inverting input to ground.

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