A local DIY Pedal supplier, Moody Sounds have in cooperation with Björn Juhl released a DIY project based on his Bone Bender which is based on Tonebender Mk.1.
HERE is a schematic and a writeup by Björn himself.
I must say it sounds pretty darn good once you have some leaky NPN germs. I tried several transistors, AC187, AC127, AC176 and 2SB72 sounded pretty good but these big russian GT404B's sounded fantastic in there.
Low leakage MP38A's worked too but it sounded more like a muddy overdrive than a fuzz.
This is the first project released by BJFE/Moody Sounds and it's supposed to release a few more in a few months.
Now that I'm revisiting some old fuzzes I've made over the past few years I've been far more curious as to how they actually work, from a circuit design perspective. The explanation by Björn is super interesting and insightful.
built this one yesterday with a 2n5457 because i have a bunch and 2 tungsgram ac176's and it sounds pretty damn good. i have a "faithful reproduction" clone of it and comparing the two they sound very very similar. this one has more top end but it still has a very sweet sound to it.
i'd say skip the "use the stock resistors and test hundreds of transistors until it works" mindset and make this if you want an mk 1 type fuzz.
a note...i did need to add a 10n cap from the circuit's input to ground to tame the oscillation (like every other time i've tried to clone an mk 1) which did not affect the fuzz at all. also shielded circuit in and out wires to make this thing dead silent.
I just built one of these with your fab layout Anders - what a cool pedal! I used a pair of AC127s with the J113 and it works a treat. I have trouble with Tonebenders in general and previously my only real success was with a Marshall SupaFuzz which is a cracker. But this one sounds excellent.
Any idea what the voltages should be set to with the trimmers? I just fiddled to get rid of some gating and get a big full tone and I have no idea of where the trimmers are set but it sounds great.
Thanks Anders - good stuff!
Oh, and I got rid of the slight oscillation issue I had with gain on full by tweaking the trimmers. It actually helped get me a fatter tone too. But I don't think I will ever use it with gain on full - I seem to like it with gain on minimum.
Aha - I just read the article by Bjorn so used his suggestions as a starting point for bias. I just built a second one of these and it's equally good. I would recommend this to anyone who wants a great Tonebender as it is a cool circuit and easier to get a great result from than a regular TB circuit.