2SJ28 Vfet SE Amplifier

[mos57]

My point of view is quite different: in SE circuit we can better evaluate the intrinsic component's character. In PP there are partially cancellations for some aspects or superimposition for others.

Is SE is easy to view with a scope the lower distortion of IRF 530 against IRF540 or 240: so why we not choice always the 530 i.e or better L-Mos or V-fet?
Because, on the other hand, for musical pleasure is not only important distortion but also other things as low output impedance for example, and in this way IRF540/240 are better than 530.
Whith its higher trasconductance/lower output impedance IRF540/240 are capable of better bass quality with better damping factor (read faster bass) than IRF530. Then, if not need high power it isn't need excessive voltage swing, the bigger IRF240/540 can become the first choice for the following: the difference in distortion becomes also little meanwhile the bass response remain much better than 530.
So the advantage of use IRF540/240 is to have bass much impressive and controlled and a sound more warm (ZEN amp).

But what about the high ends and details? Pheraps the little devices are better? SURE.

But more bigger devices are better always? No.
When devices is capable to manage very high current, then it become linear at very high quiescent current, value impossible in the field of linear amplification (10-20A). In the same time the parasitic capacitors (especially the input cap) becomes very relevant and tend to close the bandwith without high freq. tones.

So at the end not exist one components better for all.
I tend to have a compromise for these opposite necessity: from my experience in audio world, i prefer unipolar devices with Id from 7 to 15 A and low/medium Gm, low Rout.

Francesco.