The sound of the vacuum tube amplifier is determined by its damping factor!!

[Cbdb2]

IIRC this is not true except under quite overdriven conditions. Who listens to hifi amplifiers in this manner? There's no question that going from 0db to 20db negative feedback progressively lowers distortion. There isn't an area where it gets worse then better as you approach this 20db magic number. The people pushing this nonsense are voodoo hifi designers selling a story to justify the existence objectively incompetent amplifiers.

So you dont agree with B Putzeys? Is the math wrong? Where do you get the "except under overdriven conditions"? The distortion in fig 15 is inside the feedback loop and not from overdriving. If you actually read the paper it was written to debunk the "negative feedback is bad" mantra. The reentrant distortion was first MEASURED and than used to support that mantra by Baxandall in 1978 and people are still using that flawed paper to back the no feedback bs.

Edit: right from the paper about fig 14

"This mathematically derived graph predicts exactly what experimenters found: if you start with a de-
cently sounding zero feedback amplifier and you add some feedback, it sounds somewhat opener
in the bottom end but otherwise more unpleasant. The trend continues at least for the first 10dB to
20dB so one finds oneself compromising between musicality and something we’ll call “accuracy” for
want of a better term."

 

[pma]

There's no question that going from 0db to 20db negative feedback progressively lowers distortion. There isn't an area where it gets worse then better as you approach this 20db magic number. The people pushing this nonsense are voodoo hifi designers selling a story to justify the existence objectively incompetent amplifiers.

No. Not that simple.