Doubts about SPICE analysis

[RawCode]

Hello there!
I'm an electronic enginering student, and at the moment I'm attending the ECAD subject. I use Micro-Cap 12.0.2.1 Evaluation Version as a ECAD software, and at the moment I can't switch to something simpler like LTSPICE, since i have to take an exam with Micro-Cap.

First thing: what is, what is the purpose and when i should use the PSS(Periodic Steady State) analysis in the transient analysis?

I was messing around with a guitar effect, but I found something strange in the simulation.
Let's start.
First thing strange: i was studying this buffer stage, which has this spectral response:



Is that normal that i get a transient response (a sinusoidal wave @60k) of this kind? I mean, i know that there is a resonance at more or less 11kHz, but i didn't expected this behavior at the beginning, because i'm "far" from the resonance.
(Blu=input, Red= output)



Here it is another strange thing. I was analyzing the input and output impedance of this stage with the ac analysis - i'm using a what micro-cap calls "generic model" for the opamp.(blu=input, red=output)

But in the plot of the analysis, it shows something strange, like a "resonance of impedance" at more or less 12kHz of almost 1Meg, and everywhere else an impedance of 10k. For me at least this is very strange, because i expected something near zero impedance.

but if i remove the toggle to the option "operating point" i get this kind of impedance, which is more "reasonable".


What am i doing wrong? Can you help me?

[exe]

The oscillation could compensation/stability issue of the opamp. Which opamp is that? Anyway, I'd first increase the compensation cap to see if behavior changes.

[RawCode]

The oscillation could compensation/stability issue of the opamp. Which opamp is that? Anyway, I'd first increase the compensation cap to see if behavior changes.

I'm using the ne5532.

I solved the issue with the impedance though, doing the analysis of the input impedance grounding the output and vice versa. I thought that I could do the complessive impedance analysis in one shot

Inviato dal mio LG-H930 utilizzando Tapatalk

[exe]

Did you ground the output of opamp?

[RawCode]

Yes I did.
Anyway I solved this simulation issues and all my doubts.
Thanks

Inviato dal mio LG-H930 utilizzando Tapatalk

[exe]

Could you please explain why grounding is needed? I thought input impedance of opamps is generally high and not related to output anyhow (unlike a bjt amplifier). Also datasheets mention input bias current, this should sort of tell the input impedance immediatelly. Or you mean impedance of opamp input and surround circuits?