@tomic601 the idea of the feedback switch on the RM-9 was not about adjustable feedback, it was about adjustable gain (Nelson Pass talks about the feedback/gain relationship in the article as well), which is why it is referenced as a gain switch. Roger wanted users to have a means to use both passive and active preamps with the RM-9, so he put that feature in to allow the gain to be adjusted accordingly. However, after more questions from users about which position sounded better than he wanted to deal with (Roger's stock answer was, "whatever position sounds best to you") he removed the switch and the feedback/gain was factory set. The RM-10, while not having a switch, has instructions and a chart in the manual for adjusting the gain by swapping out some resistors and capacitors.
Here is another little snippet from Roger. This time on IMD which he felt was very important to limit in circuit designs:
"I
intend to write a paper on the more complete story of 2nd harmonic
distortion theory. I will say here that it must be minimized (but not at
the expense of adding other distortions). What listeners don't seem to
realize is that large amounts of 2nd is fine for a single note but not
for a full orchestra. As I like to say "Please tell me what is the
second harmonic of Beethoven's 9th? The amplifier is having a little
trouble figuring it out". Once music becomes a complex signal, the
second harmonic argument goes right out the window. The amplifier can
only act upon the instantaneous voltage it is given and has no idea what
notes are being played. At that point, it's Intermodulation Distortion
we had better be taking care of. How many of us have heard our
single-ended amps make a mess of a symphony yet play a solo voice
beautifully?"
