Sola Sound - Tonebender Mark II Professional [schematic]

[Scruffie]

Lol ah cool, cheers anyway for posting it up, ah maybe I wont bother with vintage caps, probably end up being unworthy hassle, I probably wont be able to tell the tone difference, i'l just use up the carbon comps, only wanted to use the parts for recycling really.

As for those tranis I'l be socketing them anyway so I guess i'l just try them all out and see what either works or sound best, there all vintage germaniums so i'm sure i'l end up with some pretty good original mojo tone...

[Electric Warrior]

yeah, check out what works best for you..
you could socket the caps as well, to see what difference different types can make. or use a breadboard...

[Scruffie]

Me and breadboard have a troubled past lol, Something about converting layouts from schematics to vero or breadboard I just can't do, I understand the schematic, I get how the circuit works once it's layed out on vero or bread but I can never get it to do it right unless i'm building the circuit myself and follow it as I go, but if someone has a breadboard layout done would be handy, as it would be nice to check out the variables and I don't wanna ruin a piece of vero by socketing everything then wanting part stability so soldering the parts back in and ending up with an unclean board.

[yeeshkul]

In the Mk1.5/Mk2pro are 2 R (1k/8,2k) connected in series to the collector of the 2nd transistor, though some units have 470E instead of the 1K.

The 47k is connected to the collector of the 1st trannie and I recommend to subs the R with a 50k trimpot for biasing Q1.
If you set the value of the trimpot lower than 33k you have to decrease the FB-resister too or Q2 will be misbiased.

JHS

This makes me confused - are you talking about 2 or 3 tranzistor bender?

[Electric Warrior]

he's talking about both.
I have never seen one with a 1k instead of 470R. Units with OC81D transistors have 100k instad of the 47k, maybe he confused it?

The org. TB MK2Pro circuit was designed for the use of the weak OC81D (hfe max. 40, and made for the use in driver and phasesplitter stages in radios).

OC76/44 and similar trannies (hfe app. 70-80) don't match the 2pro circuit specs. as perfect as OC81D, yielding in an dist. sound even at min. gain. and an overcompressed fuzz when maxed. Sola never adapted the circuit for trannies with higher hfe but used them in the later made TBs.

JHS

early units were made with OC75s on MK 1.5 boards. (picture here: http://stompboxes.co.uk/History.html)
furthermore, scruffie just reported us that his Mullard OC81Ds are higher gain.

[Scruffie]

As for your layout electric warrior, where do I place the trimmers? Not the 8k2 as I thought?

[Electric Warrior]

8k2 is right. you can tweak the other collector resistors as well.

[Scruffie]

Oh I thought from the previous comments it Didn't really work biasing that transistor. I would bias the other transistors... but I only have 1 10k trimmer lying around lol plus with the big caps and tranis, not enough spare room really to stick in more trimmers without using a bigger board which i'd rather not do.

[Electric Warrior]

it's probably better for you to make two. one with sockets to find out what you like and a smaller one with the parts that you liked the best..

[Scruffie]

That's a good idea, i'm not actually building this for myself, a friend wants a Mk II with all mojo parts (physcological thing probably, and I can see the attraction it does look pretty in the old ones) so if I built a second one with sockets could have it for myself.

[yeeshkul]

keeping the Q2 collector resistor 47k helps a lot to the Q3 biasing. 100k is makes too strong a divider and you can have troubles with just 10k trimpot in Q3 collector.

i made a test circuit for fiddling with TB parts and found out this (applied for 80-120 Hfe trannies):
1. if i use 10k bias resistor for the Q1 base, the unit gives no more fuzz than Fuzz Face. When i push it up to 100k (= base voltage up) there is a hell lot of fuzz coming out of it in comparing to FF (easy comparison due to the FF/TB switch).
2. even a small starve/filter resistor (divider on the battery) helps with the overall volume a lot - because it works like a common collector resistor for all 3 stages.
3. using 47k resistor (instead of 100k) for Q2C helps a lot with easy biasing Q3C(!) wia 25k trimpot. Using 100k res. you can have troubles to push the bias down to 4.5V.
4. pushing bias of Q3 to 6.5-7V doesn't affect the sound as far as i can judge and helps with the overall volume.

[Electric Warrior]

I built one with OC75s.
1. It has plenty of fuzz with the 10k at Q1's base. Much more than a Fuzz Face.
2. I have no volume issues at all. It's very loud.
4. That's roughly where bias for Q3 ended up with stock values.

Scruffie has some OC81Ds, so he should definitely start out with the 100k bias resistors, imho. There must have been a reason why different values were used for these.

[yeeshkul]

"There must have been a reason why different values were used for these."

Sure! 100k = more fuzz. Weak trannies -> we need more fuzz -> we use 100k (1.)

[Electric Warrior]

I don't think they were weak compared to OC75s..

[yeeshkul]

What Hfe were your 75's? JHS mentioned that 81D's were about 40 ... that is really not much but it makes perfect sense regarding the different resistor values.

[Electric Warrior]

between 70 and 90 iirc.
Scruffie wants to use some old Mullard OC81Ds that measure 90-110 on his multimeter. If they don't leak too much they're in the same gain range as my OC75s.
The new production DSIs are supposed to be in the low thirties..

[yeeshkul]

"on his multimeter" that sounds dodgy . i suppose he knows they leak and so he can't measure them straight

[Electric Warrior]

I suspect he hasn't built the circuit to measure leakage, yet
The guys who have built pedals with Mullard OC81Ds always complain about the low gain new production ones...

[playon]

http://fuzzcentral.ssguitar.com/mkII.php

The transistor gains for the MKII should be something like 70 for Q1 and Q2 and 100 for Q3.

Thank I already tried Q1, Q2 = 70 and Q3 = 100. The sound is not so good. Someone said Q1& Q2 must have high Hfe than Q3. What's the correct statement.? I tried many hfe of OC-75 but it could not complete with AC-128.

I had the BYOC kit of the MKII... is sounded not so good with the three OC75s they included with the kit. It sounded much better when I messed around with different trannys, at the moment it has Q1 AC128 90 hfe, Q2 OC75 80, and Q3 OC81D 40 hfe. It sounds better but I'm going to keep messing with it as there is still room for improvement. I think if you are looking for info on how to build the best sounding MKII, the D.A.M. site is your best resource... Dave Mains probably knows more about these pedals than anyone, and he's shared a lot of info, you may have to search for it.

[Electric Warrior]

seconded! David knows his Tone Benders. I luv the D*A*M forum!