What is the signal level (either input or output)? Distortion in a common-source JFET or triode is normally very sensitive to level. The 2nd harmonic at 46dB roughly (0.5%) below the 1KHz signal and 3rd harmonic roughly 30dB lower looks like a pretty good tube or JFET as it approaches saturation. This should sound pleasant. I would expect distortion to drop significantly at lower levels, and 3rd harmonic to rise rapidly above this level.
The OPA Alice is remarkably clean, as expected. (Yay Jules!)
A K596 or other JFET with diode input has additional distortion mechanisms which make it unsuited for this circuit. It will have too much 3rd harmonic. It is possible to get similar percentages of distortion using different circuitry, though. Whether it sounds like a triode is a matter of opinion. Some will maintain you need a real vacuum state amplifier and transformer for a true triode sound. Which triode? Any tube guy will tell you they sound different. Others will say as long as the harmonic structure is the same, it makes no difference what's inside the mic. Build 'em and see if you can hear the difference. If I take 2 of my mics with the same capsules and transistors, one with a clean Schoeps circuit, and one with a Transformer-Less Charge amp which has around 0.5% 2nd harmonic, they sound ALMOST identical. The Schoeps will have more fine inner detail. The TL/C will have more "body" or "richness" or "warmth". Without doing an A-B comparison though, I wouldn't hear enough difference to choose one over the other.
