Cleaning up a ToneBender II

[jim68000]

Hi

I've built two ToneBenders - a 1.5 and a 2. The 1.5 is a pair of OC76s at about 70 & 80Hfe, the II is three OC81Ds at 60, 70 & 110 Hfe. All transistors are original, with the OC76s and the first two OC81Ds being Mullards. Not sure what the last OC81D is. It's in a metal can rather than glass, about the size of an original AC128.

The 1.5 cleans up beautifully with a reduction in input, and the full fuzz is good if not great. The MkII is amazing at full chat, lots of harmonics and gain, but it won't clean up. It will unfuzz a little bit if you roll off the volume, and a bit more if you reduce the attack, although this makes the full volume setting a bit lifeless.

Both circuits are stock, except for the 8k2 resistor in the MkII, which I've replaced for a 12K because that sounded better with the 3rd transistor - it's quite leaky at 0.5mA.

Is the lack of clean up normal in a MkII or have I missed something?

[Electric Warrior]

They tend to clean up well at low temperatures and lose that ability when it's hot. But it all depends on your transistor selection.
Try to swap them around, that might fix it.

[jim68000]

That implies it's the leakage at Q3 that's at fault. I'll try dropping a lower leakage AC125 of similar gain in and see if that does the trick.

Ta

[Electric Warrior]

Not at all. 0.5mA should be no problem. The key is getting Q2 right, but that's always in relation to the other two transistors.

[polifemo]

What's the voltage on Q3? (Should be around -7v, right?)

Maybe a slightly higher voltage would help the cleanup a bit?

[Electric Warrior]

That would mostly make it thicker sounding and louder.

[polifemo]

OK, sorry 

I did this to my MkII and found the cleanup to be a bit better, but I bow to your deeper understanding about all this!
I'm fairly new to Fuzzes, having mostly done amps before.

[Electric Warrior]

Everything interacts, but the one that really makes a difference for the clean up is Q2. That's why some people substitute its collector resistor with a trim pot (only recommended if swapping transistors around doesn't yield the desired result - you shouldn't need a trim pot to make this work with OC81Ds, but then again the number of transistors you have is rather limited). You can make it go from hissy and cleaning up well to quiet and gating just by touching Q2.
I wasn't aware of this when I built my clone and ended up with a trim pot on Q3's collector, which is rather useless imo. I really should have known better as I had trim pots on every collector (hint: don't bother trying that. it's too many options. I only ended up making it sound worse than it did with stock values) 

[jim68000]

Reversing Q1 and Q2 didn't work for me, sadly. I just ended up with a honky gated sound. I think what I'll do is pull the trannies out and try and rebias them.

I did realise that I'd actually been testing the pedal with a buffered wah in front of it. I took that out of the chain and it does now clean up a bit better: if I play very gently at the lowest possible volume setting on the guitar I get clean, but it gets fuzzy at anything above that. Rolling the attack control off helps but it makes the fullfat fuzz less thrilling. It's not sparkly like a fuzzface, which I presume is possible. Unfortunately for me I have no experience of the real thing, so I'm going from my assumptions about how it should work.

My assumption is that, even with attack set to full, rolling off the input volume on a ToneBender II should give you a clean, but sparkly sound that goes to fuzz when the strimngs are hit harder (eg, touch sensitive). Is that correct?

[Electric Warrior]

No, they don't really get sparkly in my experience (though I never built an OC81D MKII; they're supposed to clean up a little better than OC75s). Germanium Fuzz Faces rarely get sparkly either. You need low leakage germaniums for that in a Fuzz Face from what I've gathered. Or silicon transistors.
Don't stop at swapping Q1 and Q2. You might as well swap Q3 and Q2. Try every possible combination of the three, so you can find the one that works best for you.

Some MKIIs don't clean up at all. You want to avoid that to make it work in a wide range of temperatures. At room temperature it should clean up reasonably well without being hissy.

[jim68000]

I tried Q3 in the Q2 position. It sounded like someone trying to be sick. I've done half of the permutations:

ABC
BAC
ACB

My hunch is that BCA, CAB & CBA won't yield any improvement but I may as well try them out. I also have another couple of OC81Ds that I rejected as too low gain, so I'll try those as well to see if it makes a difference. I breadboarded a version with GTE535s in Q1 and Q2 and that was much more transparent, as they're much lower gain.

If the TBII design never goes all the way to clean, though, I might just keep what I have and switch to the 1.5 for rhythm and chording, as that does better. It just doesn't do meltface at full fuzz.

Thanks

[Electric Warrior]

They do go all the way clean, but they usually don't do the sparkle thing a Fuzz Face can do.

You should be able to make it clean up a bit better than this one I guess:

In my experience hfe range doesn't matter all that much as long as there is enough leakage. OC75s in the 70 to 90 hfe range are great, but so are the ones over 150. I haven't tried any low gain transistors, though.
Transistors with too little leakage clean up really well for me, but they were always on the hissy side and gating didn't sound any good with them. I tried 2sb175s as an OC75 replacement and they just wouldn't do the trick. With OC75s the gating sounds nice, so it's possible to dial in a sweet spot between hiss and gating.

You should try BCA, CAB and CBA and choose the sequence that works best for you. If you're still not happy with the clean up then, a trim pot on Q2's collector resistor sure is in order...

[LucifersTrip]

a couple notes to the OP.

Firstly, use a battery or a 100ohm coming in on the + supply. 90% of the ones I've built had a "degenerated" sound with a walwart until I used the 100ohm, at which point they're the same.

Secondly, don't get too caught up in trying to exactly duplicate sounds in videos, since you rarely will use the exact guitar/pickups/amps with the exact settings.
For example, the killer tones from that video above sounds like they were achieved  through a very small amp.

[Electric Warrior]

Small amp indeed, it's a ZT Lunchbox.

[jim68000]

Hail Lucifer!

No wallwart involved. I even went to Poundland and bought a stack of Zinc Chloride batteries. Also, I'm not too hung up on making it sound exactly right: it's more the range of tones I can get out of it.

Jim

[LucifersTrip]

Hail Lucifer!

No wallwart involved. I even went to Poundland and bought a stack of Zinc Chloride batteries. Also, I'm not too hung up on making it sound exactly right: it's more the range of tones I can get out of it.

Jim

That's cool.

Everyone has their own way of tweaking these things. I usually swap transistors until I like the sound & get 7.5 - 8.5V on Q3C. When I use a trim, I sub one (200K) for the B to ground resistor on Q1 to set the overall gain. I turn the attack to zero and set that trim where it just has enough gain to sound cool at that lowest setting so I know it's good thru the whole sweep. That's just one more reason the MKII blows away a Fuzz Face. The attack is useable for the full range, while the fuzz control on a Fuzz Face is mainly usable dimed.

I've only gotten close to that "sparkly" tone when the attack is at zero and I don't use the optional .01uF from input to ground. My favorite "mod" is actually to put that .01 on a switch. It's a big difference for me...

[jim68000]

Ah, I think that's the missing bit of info. With the attack all the way down I get exactly what I want. My question was what should it do with the attack full on. I'm guessing the answer is "be fuzzy".

I recorded a small demo here:

https://soundcloud.com/jim68000/raw-meat-tonebender-ii-clone


It's into a fake amp (Line 6 clean Plexi) as it's late here and everyone's in bed, but it's representative of how it behaves with a real amp.

Thank you all. I declare this pedal done.