Uberfuzz Octave Control Mod???

[andrew]

As soon as it's off waitlist, I'm going to be building an uberfuzz for my buddy.

We were talking about potential mods and the idea of an external octave control pot came up. To my beginner mind, this mod is as simple as wiring a regular pot to the PCB in place of the trim pot, just a straight point-by-point replacement. Given the relative rarity of the mod (I've been searching for it and have found precious few examples), I can only assume its not as simple as I think it is.

Can anybody weigh in on this?

 

[phi1]

Yeah the mod would be as simple as you think. I will say in my experience the ‘octave’ effect is pretty subtle. Just a slight bit on single notes in the upper range of the neck. The trimpot helps you dial in the most prominent spot for the octave effect, so could be cool to have on the outside for tweaking, just be aware of what to expect.

 

[andrew]

just be aware of what to expect.

Thanks, we'll keep that in mind! The subtlety makes sense. I know there's other things I could do to emphasize the octave effect — I think I read that omitting one of the transistors will? — but I'm not sure I'm at that level yet.

 

[Chuck D. Bones]

That trimmer is gonna be touchy. I recommended building it stock first and see for yourself whether the trimmer is something you want to put on the front panel. If you're looking for a stronger octave effect, check out the Octameyer.

 

[andrew]

That trimmer is gonna be touchy.

Touchy in what way? Subtle like phi1 said, or something else? Also yes, I plan on breadboarding it first to see how it all goes. Finally, the octave is less the point and more of a "sure, why not" thing. Otherwise we'd for sure be looking at more specialized effects.

 

[zgrav]

You may find there is only one small sweet spot on the trimmer, so there would not be much point in making it an adjustable pot on the outside of the case.

 

[Chuck D. Bones]

Yeah, that's what I meant. The spot where the octave is the strongest will be small. Every place else will sound about the same. The Parenthesis has an octave with a blend pot. You might try breadboarding that to see if you like it.

 

[andrew]

The spot where the octave is the strongest will be small.

Understood.

As a thought experiment... Presumably there is a hunk of this circuit that's responsible for generating the octave effect. Looking at the schematic, the trimmer is located right with Q4 and Q5, so it seems like not too much of a stretch to assume that its something around there. Maybe the Qs themselves, I know that transistors can be used for clipping like diodes are.

Speaking in broad stroke generalizations, could I not go in — replace a component here or there, add a this or a that — create a stronger octave effect, and then control *that* with a trimmer-turned-external-pot?

 

[zgrav]

If you're up for breadboarding it to see what happens, why not? I probably would not try subbing a bunch of parts on a PCB just because the traces may give out from multiple swaps. Doing circuit simulations on SPICE might be easier if that is in your wheelhouse.

 

[andrew]

I haven't used it yet, but this seems like as good a place to start as any

 

[Chuck D. Bones]

Understood.

As a thought experiment... Presumably there is a hunk of this circuit that's responsible for generating the octave effect. Looking at the schematic, the trimmer is located right with Q4 and Q5, so it seems like not too much of a stretch to assume that its something around there. Maybe the Qs themselves, I know that transistors can be used for clipping like diodes are.

Speaking in broad stroke generalizations, could I not go in — replace a component here or there, add a this or a that — create a stronger octave effect, and then control *that* with a trimmer-turned-external-pot?

No. The UberFuzz design produces the strongest octave effect when the trimmer is set to balance the transistors. The only thing you can do beyond that to make the octave effect stronger would be to filter the signal going into the octave generator. Even then, the difference will be subtle. There are basically three analog octave generator circuit topologies in common use:
1. The differential transistor circuit used in the UberFuzz.
2. The diode circuit used in the Squidward.
3. The transformer & diode circuit used in the Octanaut.

They all have their advantages & disadvantages. I prefer the Squidward style diode circuit because it is simple, has no dead zone and is inherently balanced. That's my opinion, other people will have their preferences.