Hi Chuck, greetings from Korea. Apology for my poor English in advance..
Thanks to you, I can explore the depths of pedals. Your work always inspire me!
I recently built BD-2 from scratch on perfboard,
Basically stock version
+ your Tight/Fat switch
+ JFET biasing with J201 (10K trimpot)
+ Dual A100K used
+ modded input impedance. (R2:220K->2M)
Your solution for dual pot is such a savior! (I wanted to build it in 1590A, but mini dual A250K is just impossible to get)
And Tight/Fat switches working great! The pedal is much useful with the mods.
However, with stock mode, the sound is somewhat harsh/fizzy than I expected. Not that extreme, but it’s enough to ruin most of sweet spot. Something like teeny-weeny splinter on fingers.
After some debugging, I finally suspected the input impedance thing, so changed back the resistor to stock value (2M -> 220K)
And it worked out! More creamy and smooth, But now the low input impedance is problem
I tried compare passive guitar direct / putting buffer (bypassed Klon) in front of BD-2.
Obviously, there’s definate difference in articulation and dynamics with buffer.
That creamy and smooth feeling is intact, and even more enhanced balance.
So I put buffer circuit from original Boss unit in, including 10K input resistor, 100n input cap(47n original. just..no-brainer), and modified for true bypassing (added 2M pulldown resistor, changed gate resistor 1M to 2M)
Now with zero gain/noon-ish volume makes unity clean, just like original BD-2.
It was much higher signal level with 2M gate resistor version without buffer.
I think Q1 is not just input, it has own role for limiting some signal into 1st stage.. like reducing input gain.
So putting ‘complete’ signal with ‘proper’ impedance makes it too hot, I guess?
p.s.
Before I change the input impedance thing, I swapped transitors BC560C-> 2N3906.. to match hfe range of original TRs.(250~500, aiming 300~400)
After swapping, the JFET bias have shifted, so I reset it.
Though 3906 has inferior S/N, it was not noticeable, and the tone balance became more stable.. I think. The drive tone is from TR, so I guess hfe is pretty influential..
p.s.2
I breadboarded OCD recently, and tried same thing with input impedance. (320K -> 1M)
And there was simillar result. not that much like BD-2 though, the high-end became messy and fizzy.