Ideas For (Needlessly) Adding To One-Knob Fuzz?

[Ginsly]

I have a couple of these One-Knob Fuzz kits from Fuzzdog: https://shop.pedalparts.co.uk/product/okf.

I'd love to add something to one of these kits, but I'm not sure what. I like to have Transistor Bias controls, but I'm not sure which one would have the most impact - Q1 or Q2.

Some fuzzes seem to have a pot to control how much gain from the first amplifier stage is hitting the second (Clusterfuzz, maybe Hawaiian Pizza??), which can result in cool square wave sounds - would that be possible?

Just tryin to mess around. I already added stuff to the Executive and Propolis I recently built, so why not this too?

 

[finebyfine]

Going off that schematic:
- I’ve replaced R3 with a 2K pot before. The entire sweep isn’t usable but it does add some interesting (and some bad) sounds. There is some disagreement on some forums about what the exact value of R3 is on the original inspiration for the one knob fuzz (name escapes me currently) so I figured I’d try a pot.
- External bias knobs on fuzz face derivatives are usually the collector resistor on Q2 (R4)
- Some people like input attenuator / volume pots on fuzz faces. I don’t, but they’re a common mod

The PedalPCB Sandspur schematic has examples of the last two - the input attenuator on the Sandspur is an internal trimpot, and the bias control has both an external potentiometer and an internal trimpot to set the range of the external one.

 

[Ginsly]

@finebyfine Excellent!

-So how does the 2K pot in place of R3 change the sound?
-If I went the route of a transistor bias knob in place of R4, what pot value ya think? Would I still need a resistor in series with the pot?
-I'm still interested in the idea of controlling how much gain from Q1 hits Q2 (a la Clusterfuzz). Not sure how I'd do that, though.

I appreciate the input! I have two of these, I HAVE to mess one of them up...

 

[finebyfine]

So how does the 2K pot in place of R3 change the sound?

I’ll try to find the build I did that to jog my memory tomorrow. It can definitely make the fuzz “sharper” for lack of a better word.

-If I went the route of a transistor bias knob in place of R4, what pot value ya think? Would I still need a resistor in series with the pot?

I would keep a resistor in series with the pot just so you don’t have a dead side of the knob sweep. If you can rig up an internal trimpot instead of the series resistor you’ll be able to dial the outer pot in a little better (if you do this I’d do 5k internal and 5k external), but something like a 2k series resistor and a 10k pot would be alright

-I'm still interested in the idea of controlling how much gain from Q1 hits Q2 (a la Clusterfuzz). Not sure how I'd do that, though.

Doing the input attenuation mod can definitely soften up the fuzz, not familiar with the clusterfuzz, but it sounds like it could be using that.

 

[Ginsly]

Doing the input attenuation mod can definitely soften up the fuzz, not familiar with the clusterfuzz, but it sounds like it could be using that.

Thanks for all that info! Much appreciated.

As far as the Clusterfuzz goes, I think the “8-Bit” control actually goes in the opposite direction. Instead of attenuating/softening, it slams that second transistor harder, resulting in a Square Wave kinda thing.

 

[finebyfine]

Thanks for all that info! Much appreciated.

No problem! The one knob fuzz is such a fun starting point. Couldn't find my build this morning but in all honesty I don't really recommend the R3 mod it unless you're absolutely dying for another knob.

 

[Ginsly]

Haha, gotcha! I'll look at a Bias knob for Q2 I think. According to the makers of the Clusterfuzz, it's a BJT common emitter boost pushing another BJT common emitter amplifier followed by hard diode clipping. I don't know if this mode of operation is possible with the One Knob, but I'd love to try it on something...

 

[cdwillis]

Make R3 1k and replace R4 with a b10k pot for a q2 bias. It has a good useable range. I've used that setup with some Meathead and Colorsound fuzz clones several times.

 

[Ginsly]

Excellent to hear, thanks @cdwillis! Haven't jumped in yet, but I'll try that out! So no resistor needs to be in series with the b10k pot in R5, correct? You're just making sure R3 is 1k?

 

[cdwillis]

R3 is 1k. I forgot to say it has a 4.7k resistor in series with the b10k pot. Check out how I used it on this Powderkeg fuzz:

Powderkeg

This is a new fuzz circuit I've been working on lately. I haven't reinvented the wheel, but sounds pretty cool and you can coax a few different sounds out of it. Looking at the schematic you'll see it's a cool tonebender mkII/III and big muff hybrid. You have an attack control that adjusts how...

forum.pedalpcb.com

 

[Ginsly]

R3 is 1k. I forgot to say it has a 4.7k resistor in series with the b10k pot. Check out how I used it on this Powderkeg fuzz:

Powderkeg

This is a new fuzz circuit I've been working on lately. I haven't reinvented the wheel, but sounds pretty cool and you can coax a few different sounds out of it. Looking at the schematic you'll see it's a cool tonebender mkII/III and big muff hybrid. You have an attack control that adjusts how...

forum.pedalpcb.com

Ah! Ok good to know, thanks - will check out the Powderkeg too!