Pass X2 and negative feedback

By my reckoning, the letter X only requires one keystroke, whereas Su-Sy takes five.
Ma pore widdle fingers can't take all tha' extra poundin'...


(Still doesn't excuse me for being mentally sloppy. Seems I'm missing a lot of details this week. I'll try to get some sleep and be back on track tomorrow...or the next day...or the next...)
Good and bad feedback

There is no such thing as good and bad feedback.

The X-circuits in the big power amps (which only licensees of Nelson Pass can use provided patent holds and no workaround can be found) employ local feedback to around a single voltage gain stage. This is very similar to basic op-amp theory (but most op-amps have multiple internal stages, and feedback around these have become universally detested in audio).

Feedback is a method to reduce noise etc. Degeneration is generally considered the "least harmful". The next level, I will call feedback around single loop for lack of a better name, and this is the method used in the X-series power amps.

Feedback free amplifiers are like Yeti's -- many have seen them, but nobody can produce one.