Troubleshooting Op-Amp Circuit in LTspice – Common Issues

1. TL072/74 is a good op amp with low offsets in case you want to increase your time constants with high value resistors.

2. It will integrate on the high side of the cutoff frequency.

3. If you need high Z or high CMRR then an instrumentation amp will be better but I do not think that is an issue.

4. you have quite a bit of gain from your Proportional (50) and the last stage (20) plus you have the gain in your integrator too. Have you looked at the step response? I am not sure how to do that with LTSPICE. You can also balance or tune things by incr.decr R12, R13 and R16.

I am playing around with a similar circuit for a temp controller too. THanks for the look.

You specified a linear frequency sweep, with 50 points from 1 Hz to 120 MHz. That means the simulation is run at 1 Hz, 2.400001 MHz, 4.80001 MHz, etc., up to 120 MHz.

Most importantly, it means that the part of the output curve between 1 Hz and 2.4 MHz is generated by interpolation rather than by doing any simulations at the intermediate points. Apparently it did a linear interpolation on a linear scale, which translated to a curve when you changed your plotting axes to be logarithmic.

I'd recommend to switch to a log sweep, which is called either "decade" or "octave" sweep in LTSpice, depending whether you want to specify the number of points per decade or per octave.