Tone Bender MkII question

[LJN]

Hi, all. I have a question (actually a few questions) about the Tone Bender MkII. I have a clone that I built using 3 AC128 transistors (all with hfe in the 60s and fairly low leakage) . At first, it sounded very gated and Farty, but on Q2 collector I placed a 47k and a 100k resistor in parallel and that made it sound better. There's plenty of gain available and it has plenty of what I like to call the "Tone Bender buzz". My first question is this: Shouldn't the MkII clean up when the guitar volume is rolled back? Mine won't clean up much with my Epi LP, but it will with my Kay LP copy. My second question is : shouldn't the attack control have a wider range? The way mine is, there's a subtle increase in gain from the minimum setting up to a bit past noon, then the most change comes in the last bit of rotation. Is that normal? My clone's attack pot is a 1k linear taper. I'm sure I have other questions, but I can't think of them at the moment because I'm getting tired. Thanks in advance for any help in figuring out if I actually have this even close to working properly.

[akosbev7757]

I don't know which layout you are using, but the gains on your transistors are too low for a MKII. Q1-74-80, Q2-85-95 and Q3-100 and up. That is a pretty standard rule for a MKII. Let me know if you need a set of transistors and I can steer you to some. You can email me direct at akosbev@gmail.com. Thanks , Chris

[Radiotron]

Not a big fan of the 100k/100k (Q2C/Q1B) configuration myself, prefer the 47k/10k as it to offers better range on the attach pot and the fuzz isn’t as balls out, it’s a little trickier to set up though.

One of my favorite transistors for the MK-II actually is the cv5712 with gains in the 40’s, does not sound gated at all, so I’d say you’re good with those AC128’s gain wise.

I’ve seen those values (70/80/100) posted and reposted all over the place but the Mk-II circuit is pretty forgiving with the transistor selection, although some really do work better than others. I remember seeing some reading of an original Mk-II with Q1-2 somewhere in the 30’s and Q3 all the way up in the 300’s.

Try a bunch of different transistors, see what you like best, fuck the 'rules' just my 2 cents

Have fun and good luck

[Electric Warrior]

The 100k/100k will work better with lower leakage transistors.
IIRC LJN used 10k/47k and his voltages weren't all that far off...

[akosbev7757]

I have built MKII's with all different gain buckets in different positions and they have sounded great, but as a rule the 70',80,100 does work and I have sold over 285 MKII's, and about 1,000 transistor sets with these same gain buckets. If you are going to use low gain then by all means use the two 100K to bias up Q2, but your attack knob will be pretty much useless, and you will still need a higher gain for Q3 to bias up and sound good. But yes, I built a MKII that sounded great with 120,90,110 and every other combination you can imagine, but never had any come out right without any transistors with a gain under 90. Hope that didn't come off as rude, was not my intention.

[SonicVI]

I always used 20K in my MK2's. The 100K was always too much and the 10K not enough. 18-22K always seemed to hit the right amount of gain for me.

[LJN]

Wow! Thanks for all of the replies! Okay, so I've ordered a matched set from Chris and I'm sure they'll sound great. I mean, his MkI set sounds KILLER ! Electric Warrior , I remember posting about this on FSB and you were very helpful. If it hadn't been for your replies there, I would've given up on this one. Thank you. Sonic IV, I get what you're saying and I have tried at least two different sets of those AC128 transistors in it with very little (if any) difference. I'm using a SS amplifier and I guess it's a bit more difficult to make a fuzz sound good with that amplifier. It's not a modern one, but a Kasino from the early 70s. The reason I mention the amp is that I've been told that these circuits sound their best with a tube amp. Thank you all for the replies.

[LJN]

I don't know which layout you are using, but the gains on your transistors are too low for a MKII. Q1-74-80, Q2-85-95 and Q3-100 and up. That is a pretty standard rule for a MKII. Let me know if you need a set of transistors and I can steer you to some. You can email me direct at akosbev@gmail.com. Thanks , Chris

I'm not really using any particular layout. I just sort of have it wired point to point on a pad per hole perf board. I know the originals were built on strip board, but I've never used that before and it seems a bit confusing. My components are all kind of sitting parallel to each other with the exception of the electrolytic cap on the attack control, which I literally soldered right onto the lugs of the attack pot. It's not pretty, but it works and has not really given me any problems other than the lack of clean up with my Epi LP. I'm just uncertain if I have it working properly. I'll try to find a proper layout and start over on this one when the transistors arrive. Thanks, Chris.

[akosbev7757]

Just email me direct and I will send you a layout. I have pretty much all the classic germanium fuzz layouts.

[Electric Warrior]

Thank you. Sonic IV, I get what you're saying and I have tried at least two different sets of those AC128 transistors in it with very little (if any) difference.

You mean complete sets of pre-selected transistors? You need to swap them one by one, to see what difference more or less leakage and higher or lower hfe make in each spot for tone and voltage.