Aaron:

     I guess Bruce Collin's threads on NFB mods have scrolled off the board, but you might try adding a 100k pot (wired as a variable resistor) in series with the existing 100k resistor and see how it sounds at different settings. If there is a particularly "sweet spot" that you like you could hard wire in the total resistance measured through the pot and existing 100k resistor. Or if you like being able to adjust it you could just mount the pot somewhere on the chassis. I started off with a 1M pot to really open up the NFB loop, but preferred the lower settings and ended up using a 250k audio pot so I could fine tune the lower settings between say 100k and 175k, and get some bigger changes at the extreme end of the pot. (That was on a Peavy Classic 30 amp that used a stock 100k resistor.)

     For cleaner rhythm sounds, the stock 100k resistance will give you a nice tight sound, but at 150k to 200k the sound will really open up for OD leads. I haven't seen the Blues Jr. schematic so I'm not sure how they wire in the NFB loop on your amp but I'd try a 100kB or 250kA pot to see how it sounds at different settings.

Steve Ahola