It is a bit frustrating when the tools do not do what they are suppose to do… In an earlier post, I mentioned that TINA-TI could not even perform a transient analysis on a simple amplifier, well it happened again when I tried to run some simulations of the Baby Huey design found at diyaudio. Numerous circuit examples were simmed over the years, none ever complained that they had any issue with convergence.
But true to form, when I tried to run the simulation, TINA failed immediately, and changing the parameters did not help, so that’s out – it is really a basket case. Next up, SpiceOpus, it kinda worked but the responses were somewhat puzzling, it appeared that the circuit was either un-stable (with many warning messages) or it was not quite happy with the transient analysis parameters, with a text-only interface, it was hard to tell just what was happening, so it will require some sleuthing is needed to find out why…
Ok, this one is easy, I re-ran the sim on SpiceOpus, with longer time periods, as shown in the picture below, the cause of the in-stability was due to fact that the circuit did not reach steady-state, a common problem. Adjusting the period also gave different read outs for the THD, so the output needs to be completely stable before the Fourier analysis can be run.
Output voltage rises with time – steady state not reached until the end of the period
Never say die! I next I tried Micro-Cap, which did better but only after I turned off the Period-Steady-State feature which was suppose to improve transient analysis convergence, instead it had exactly the opposite effect, hummm… yet another puzzle to solve.
I hate to say it, but perhaps there is a good reason for the popularity of LTSpice – it could just be its ability to converge. In any case, I still have no interest of using it, given the poor UI and awkward file management system. May be it will be upgraded soon, then I will give it a try.