Why is CircuitLab so slow to simulate this simple circuit? (Op Amp DC-coupled to BJT phase splitter.)

Question

Not sure how much is known or published about the back end of CircuitLab, but:

While simulating a different circuit, I noticed very long simulation time. I narrowed the culprit down to the below portion. With a DC sweep on V1 from 0V to 5V and a relatively large step of 0.1V it still takes several minutes:

^{simulate this circuit – Schematic created using CircuitLab}

Changing the Op Amp or BJT model didn't make a difference.

Simply replacing the BJT with a MOSFET speeds up the same simulation so that it runs in a fraction of a second.

^{simulate this circuit}

Any ideas what's tripping up CircuitLab? Is it just that the BJT model implementation is more complex than the MOSFET?

(Please no answers telling me to use different software.)

Answer 1

(CircuitLab developer here.) It's much, much faster if you use the Op-Amp model without voltage rails:

^{simulate this circuit – Schematic created using CircuitLab}

From which I get the following plot in just a few seconds:

This slowdown is noted in the CircuitLab documentation:

If the op-amp will not be asked to saturate its output at voltage rails, using the op-amp component that doesn't have the rails will lead to faster simulation, and generally "behaves better" in terms of circuit convergence.