What is the Circuit Etymology of This Schematic?

[Cybercow]

The Kokko Distortion pedal, by many, is claimed to be a Tube Screamer. However, after doing some rudimentary tracing and web searching, I found this schematic that nails the actual Kokko Distortion pedal. The Kokko Distortion is NOT a TS circuit with soft clipping. Rather, it appears to be closer to a modified Rat layout with hard clipping. The dual-ganged "Gain" control is interesting too.



So, my question is: Does anyone know what typical pedal circuit this Kokko Distortion circuit comes closest to?

My curio stems from discovering that this specific pedal circuit creates a monster combo when placed in front of an OCD. I've tried a few other old favorites, (Rat, BMP, TS, SD-1, etc) in place of the Kokko Distortion, but nothing comes close to the it.

 

[manfesto]

Kokko Distortion as in this?



Where'd the schematic come from?

If it's accurate, I'd be pretty surprised that a $30 pedal has a custom dual-gang gain pot with two different tapers, that'd be weirdly cool.

If so, yeah looks to maybe started as a heavily modded Turbo Rat (LED hard clipping, LPF tone control, and they moved the buffer after the volume control instead of before) and added a second op-amp gain stage before the tone control with a different taper to the gain control, interesting

 

[manfesto]

Wait, and am I reading it right that the gain controls are wired opposite one-another, so as the gain on the first stage (that gets clipped) goes up, the gain on the second stage (no clipping, so I guess gain recovery/clean boost?) goes down and vice versa? Interesting!

 

[andrewsrea]

It looks like many distortion circuits which employ one dual op amp. Looks a lot like an OCD with buffers and LEDs for clippers. The first stage is pushing the mid-range somewhat like a TS but centered on 965hz frequency instead of 723hz (TS).

It also looks like its low range of gain starts way beyond what folks would consider 'overdrive.' It starts deep into distortion.

 

[andrewsrea]

Wait, and am I reading it right that the gain controls are wired opposite one-another, so as the gain on the first stage (that gets clipped) goes up, the gain on the second stage (no clipping, so I guess gain recovery/clean boost?) goes down and vice versa? Interesting!

Interesting indeed. That design looked like they were originally aiming at a two-control pedal in using the concentric pot to reduce the 2nd stage recovery when the 1st stage is pushed.

 

[Cybercow]

Kokko Distortion as in this?

View attachment 88638

Where'd the schematic come from?

If it's accurate, I'd be pretty surprised that a $30 pedal has a custom dual-gang gain pot with two different tapers, that'd be weirdly cool.

If so, yeah looks to maybe started as a heavily modded Turbo Rat (LED hard clipping, LPF tone control, and they moved the buffer after the volume control instead of before) and added a second op-amp gain stage before the tone control with a different taper to the gain control, interesting

Yeah, that's the exact pedal. I found the schematic thru a simple Google search at Imagur and it came right up in Images when searching on: "Kokko Distortion schematic". And yes, the Gain pot actually is a dual-gang 100K pot.

And yes, it kinda looks like a Rat, but uses both parts of a TL072 instead of a single LM308. Still, a curious build.

 

[Cybercow]

Wait, and am I reading it right that the gain controls are wired opposite one-another, so as the gain on the first stage (that gets clipped) goes up, the gain on the second stage (no clipping, so I guess gain recovery/clean boost?) goes down and vice versa? Interesting!

Yes, you read the schematic correctly. And good eye too. I missed that aspect of the 2nd gang of the Gain pot. I've corrected it so it reads correctly. I dbl-checked the orientation & sweep of the clockwise motion and both gangs rise in resistance as the control is turned up. So the schematic is now corrected. Thanks for the head's-up.

 

[Cybercow]

Interesting indeed. That design looked like they were originally aiming at a two-control pedal in using the concentric pot to reduce the 2nd stage recovery when the 1st stage is pushed.

The schematic is now corrected after I dbl-checked the PCB traces, pot lugs and clockwise rotational sweep. So, both stages increase in gain as that control is increased.

 

[andrewsrea]

The schematic is now corrected after I dbl-checked the PCB traces, pot lugs and clockwise rotational sweep. So, both stages increase in gain as that control is increased.

I misread it the first time and it behaves like I thought. When Gain A goes hotter, the Gain B for the post-clipping recovery takes some of the loudness out (moves toward being a buffer).

 

[Robert]

I misread it the first time and it behaves like I thought. When Gain A goes hotter, the Gain B for the post-clipping recovery takes some of the loudness out (moves toward being a buffer).

The Keeley Fuzz Bender does similar when adjusting the bias.