[HOW] to diode-clip in opamp FB loop 50 years ago:

[A.S.P.]

(click smiley)

[wampcat1]

you mean to tell me someone cloned the tubescreamer circuit that long ago?

[Paul Perry (Frostwave)]

I doubt that is the first time anyone put a diode in a feedback loop.
If you read the "claims" (the last para) it looks like what they are doing, is converting a sine wave into a square wave (or at least something with a sharp rising edge) with minimal phase difference between the zero crossover of the sine input and the edge of the square output.