Does this circuit simulation graph make sense?

[cd]

See here:



It's an AC frequency simulation from Multisim.  I use a Frequency Generator to input a 55mV, 440Hz sine wave into the circuit, with an oscilloscope at the output.  What's the cause of that big stair step at around 3kHz, where the phase suddenly inverts from -180 to 180 degrees?  Does this mean that in effect, the lows are out of phase with the input and the highs in phase?

[Jason Stout]

0.0° is "in phase" if you post the circuit we might learn something! Is there feedback in the circuit? That may explain the phase flip at ~3kHz.

[Arno van der Heijden]

That big stair step means that the phase passes -180 degrees (instability if feedback is applied!) at that point. You have to interpret the part at the right of the stair step as if it would start at -180 degrees.

[toneman]

what's the circuit??
tb

[cd]

Circuit can be found here:

http://www1.korksoft.com/~schem/rumbleamps/jfet.pdf

Nothing special, just a vanilla JFET gain stage (similar to Orman MOSFET booster if you don't want to fire up Adobe Reader).

OK, so 0 degrees is in phase with the input, so -180 and 180 degrees is out of phase.  Alright, that makes sense to me.

[toneman]

Ahh, the circuit appears.....
from the frequency chart, the response is "flat".
looks like an allround/general purpose amp/buffer.
drawn funny IMO.
"phase changes" happen cause U got caps in there.
U don't hear them.
is the freq response graph with the "bode plotter"?
i have an old version of ElectronicWorkbench.
like the guy said, like the Orman Booster, but
the Booster is specifically 4 guitar, ? i think..?
afn
tone

[Paul Perry (Frostwave)]

I havn't used a simulator ever, but I think what happened here is that the phase at higher freq approaches -180 deg, and then just tips over to a bit more than -180, so the simulator output flips it over (note -180 deg and +180 deg are the same phase).
Eyeballing the circuit, ther cannot be a sharp phase discontinuity.

[cd]

Perfect - thanks for the help everyone!