According with instructions provided here https://www.youtube.com/watch?v=dBY1k5qK2w4 (in Spanish), I tried to simulate an inverting opamp configuration, but I couldn't figure out the right vout behavior, as reported in the second graph of the following figure.

QUCS screenshot

Output results with a high DC term which is not supposed to be in the YouTube video, nor in the well known theory. Furthermore I expect an out of phase behavior of the output signal, as compared to the input one.

Is there anyone who could find out what's wrong here?

I did a second attempt . By the way, changing the opamp I've got this

enter image description here

That could mean the 741-opamp (TI) simulation software is not properly working on my QUCS.

With this other opamp the simulator seems to work reasonably well, but still there is an issue: I don't understand why there is a downward saturation on the output signal.

  • \$\begingroup\$ Why do so many people insist on using the horrible, outdated uA741? Anyway, I'm not familiar with QUCS but does it support having a negative value for a voltage source? (as opposed to turning it around, which is how I would do that) \$\endgroup\$
    – Hearth
    Jan 3, 2021 at 19:19
  • \$\begingroup\$ I inverted the second opamp voltage supplier, but still it does the some job! \$\endgroup\$ Jan 3, 2021 at 19:23
  • 1
    \$\begingroup\$ actually hang on, your output is kilovolts? that shouldn't be possible; i get the impression your simulator is ignoring some of the physical limitations here. It shouldn't be possible to go beyond the voltage rails. \$\endgroup\$
    – Hearth
    Jan 3, 2021 at 19:25
  • \$\begingroup\$ Negative voltage supply has wrong polarity. \$\endgroup\$
    – user173271
    Jan 3, 2021 at 20:51

1 Answer 1


On your images, there are tiny red circles between GND and op amp power pins. I think you did not connect it. I would also suggest using LTspice.


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