Help with the simulation of Phase 90 on LTSpice!!! JFET's giving 0.3 Volt sweep

[savethewhales]

Hello!

I've done some posts already regarding the construction of a phaser, for my college, based on the phase 90 by MXR. I've already studied everything and understood as much as I could.

As I am doing simulation of the circuit of the phase 90 on LTSpice, just to experiment with what I'd like to change, (circuit is shown on the figure testephaser3)

I noticed that when I'm using the 2N5486 JFET's (because Spice doesn't have 2n5952 or 2n5457), I only have room for 0.3 Volts of sweep.
What I mean by that is that, with the bias voltage at 1.1 (given that the 2N5486 is written to have -4 VGScutoff, then 1.1 minus 5.1, which is the reference voltage, equal -4 VGScutoff), I have the results shown correctly with the calculations I made (with the parallel of the resistance of the filter being 24k ohm).
Now when I change the bias voltage to 1.4 Volts, the results show what's in figure testephaser:

And when I change the bias voltage to 1.5 Volts, the results show the following in the figure testephaser2:

Which in practice shows that I would have 0.3 Volt margin to oscillate the voltage in the oscillator.

This makes absolutely no sense. Could it be that these JFET's don't work for this matter? Or am I doing something wrong?  would highly appreciate any help regarding this matter.

Greetings,

Frederico Vilar