Tweaking an older build of mine and have been messing around with an NFB setup. I have added a 3-way NFB switch with high/none/low. I like how the NFB quiets extraneous noise and how it cleans things up a bit (this one breaks up early and I like cleans as well as dirts). Thing is, with either of the NFB options engaged, I lose quite a bit of upper frequency clarity. Not wanting to add another knob, I got to thinking about presence circuits and wondering if the circuit could be added with a fixed resistor rather than a pot. I could use my resistance decade box to determine the desired value. Has anyone done this sort of craziness?