BMP Reborn as Tonebender MkII (Ge Small Bear “Flat Hats”)

[Big Monk]

Been tinkering with the TB MkII circuit for a while. I moved recently and lost Q3 from my old Small Bear "Flat Hat" set. I ordered a new set not too long ago in preparation for this build.

I've gone from Ge, to hybrid Ge/Si, to full Si, and now back to Ge. Tried a bunch of mods but finally landed on the following:

1.) an "Easy Face" pre-gain
2.) Output cap switch (faux bright switch)

I had a bombed out old BMP that I tried and tried to get how I wanted without much success. So I harvested the shell and here it is:

[Steben]

Cool. Can you elaborate on the versions and why you reverted to Ge?

[Big Monk]

Cool. Can you elaborate on the versions and why you reverted to Ge?

Sure. I recently got back into the hobby with the idea that I would finally, after years of building little onesy-twosy boost and fuzz face circuits, build myself a Tonebender MkII. I purchased a set of GE "Flat Hats" from Small Bear and a Tonepad MkII PCB to get myself started. That initial build did not work on startup. I ordered a GGG MkII board (I was used to the boards from GGG) as a backup while I did my troubleshooting. I learned while wiring up the unit pictured above that, among other things such as sloppy soldering and lifted traces (I was very rusty), that I forgot to install the jumper for the ground plane!

So, I wired and installed the GGG board when it came and was off and running. I was impressed by the sustain of the pedal but it was a touch "wooly" for my tastes, I socketed the output cap and the input cap to ground. After playing with that a little bit, I kept the sockets for the output cap with the idea I would make that a switch. I liked both values of output cap (0.01 mf and 0.1 mf)  and preferred simply having the 0.01 to ground at the input so removed the sockets and installed it permenently. For this first iteration, I also tried swapping Q2 and Q3, but ended up with them back the way they were. So I played it for a bit in this largely original, 2 knob version and found myself wanting it to be a little tighter and brighter. Enter the RDV Sili-Bender.

I made a secondary circuit using the RDV schematic. I should note that the original Ge version I did had a standard 1k "Attack" pot.This worked OK but did not have as much range as I would have liked. When I ordered parts for the secondary Si circuit, I added in a 1kC pot for the attack as an additional part. I initially installed a normal 1k pot on the Si circuit. I really liked the brightness and general attack but noticed right away that while the wooliness of the Ge circuit was gone, I had also lost the wild and signature sustain as well. It would still slip easily into feedback and notes would sustain fairly well but much of the feedback "bloom" of the Ge version had disappeared. In short, it was now more of a fuzzy distortion pedal which would grind nicely rather than the saturated sustain monster one expects from a TB MkII. I played it for a while and found I liked it for crunchy rhythm tones but not as much for lead tones.

I then took the Q2 and Q3 from my Small Bear set and tried those in Q3 of the RDV Si Bender. This struck a very nice balance between the two versions, restoring some of the wild sustain from the all Ge version while keeping the crunch and grind of the all Si version. I believe I kept the Q2 "Flat Hat" in the Q3 position of the Si Bender. At this point I settled in to try it out and get a feel for what it could do. One thing that annoyed me was now the "Attack" pot was almost totally useless. There were a few things I tried to fix this:

   - Change the resistor controlling the overall output volume (R5) back to the original 1k (I had changed it thinking the TB MkII needed MORE volume!)
   - Change the resistor from Q1 base to ground (R1) to a few different values between 10k and 100k
   - Installed the 1kC pot

Around this time I found a wrecked NYC Re-issue BMP on Reverb and snatched it up. That's a whole other story but to summarize: I changed a bunch of stuff trying to remove some of the mud (diodes, caps, etc.) but while it got tighter and brighter, it lost much of its essential Big Muff Pi-ness. I quickly tired of both pedals and stuck them in my pedal toolbox. It just was not what I wanted and since I had recently purchased a new home, I had ZERO time to do anything anyway.

Fast forward a few months and after listening to music while painting, I realized that I might take another pass at the Ge TB MkII. I decided to gut the BMP and keep it's  enclosure, LED and stomp switch. I also realized that I had lost Q3 from my original "Flat Hat" set so I ordered a fresh set and a new Tonepad board. Based on how much I liked the socketed output caps, I decided to make that switchable. Also, after reading some information concerning mods to Jimmy Page's MkII, I decided that an "Easy Face" pre-gain control might help to shave off some of the "wool" inherent in the pedal and get me some more crunch while maintaining the sustain inherent in the Ge version. Also, I decided that i'd try the 1kC pot in the Ge version.

Only had a chance to take it for a short spin last night. I had mis-wired the battery and DC jack so it was only working on the DC jack and had no LED. I fixed that last night and it is working great on both battery power and DC power. Also, I had the Level control pot ground lead extending too far into solder tab and it was cutting out. Trimmed it and it was fine. Other than those 2 issues, it was a clean power up. Tone was very nice, with the "Attack" pot functioning perfectly.