Ubu Roi (Modded KOT)

jubal81

jubal81

Well-known member
This guy is a KOT with all the controls on the top. I used a 2P4T rotary to replace the dip switches for all 4 clipping options and included a toggle for normal/HiGain modes.
I also used Rail-to-rail opamps and added another inverting stage to have more output on tap (like morning glory) and make the output phase match the input phase, which the KOT does not do.

Ubu-Roi-Face.jpg

Ubu-Roi-Guts.jpg
 
That looks great! Really nice layout, are you using an inductor or ferrite between the two jacks?
 
Thought you guys might want to see the schematic. The more I use this one, the more I love it. Really impressive how good it sounds at all the stages between clean boost and serious distortion.

The LEDs you see there is a dual unit. Looks like one LED bulb with two leads, but it's a green one in one direction and a red one in the other. They're more or less like OPAMP input protection clippers here.
Ubu Roi Schematic.png
 
jubal81 said:
Thought you guys might want to see the schematic. The more I use this one, the more I love it. Really impressive how good it sounds at all the stages between clean boost and serious distortion.

The LEDs you see there is a dual unit. Looks like one LED bulb with two leads, but it's a green one in one direction and a red one in the other. They're more or less like OPAMP input protection clippers here.
View attachment 12951
Click to expand...
That's a pretty special layout. I love the clipping arrangement.
 
'Tis a wee beast of compact beauty. I was hoping to get as much into a 1590BB and thinking it would be a cram.

That's a lotta schtuff to shrinkwrap into a 1590N1!
Great build.


Oooh! And thank you for the schematic! 🙏
 
Lots of interesting things on the schematic, awesome! Those BAV99 diodes two in one smd package, you seem to be happy with them. Are they comparable to the near extinct MA856 or so?
The power protection with PMV50, how does that work and I guess it's a better way then the 'normal' diode in line? What's the purpose of D6?
And what value of inductor do you use there? What diodes did you end up in the sockets there for D1 and D2?
Oh questions.... cheers Jason, amazing stuff!
 
cooder said:
Lots of interesting things on the schematic, awesome! Those BAV99 diodes two in one smd package, you seem to be happy with them. Are they comparable to the near extinct MA856 or so?
The power protection with PMV50, how does that work and I guess it's a better way then the 'normal' diode in line? What's the purpose of D6?
And what value of inductor do you use there? What diodes did you end up in the sockets there for D1 and D2?
Oh questions.... cheers Jason, amazing stuff!
Click to expand...
BAV99: As far as I can tell, these are pretty much identical to 1N4148/914. I'm in the camp of not being able to hear the difference between those and MA856

Polarity Protection: Here's an explanation of using a P-Mos for reverse polarity protection. It's pretty much overkill for a stomp box, but I bought a huge pile of PMOS for another project and I like being fancy.

D6: This diode provides over-voltage protection for the Vref net. I love these opamps, but they can be delicate little bitches. Gotta credit Chuck for this and a few other tips to keep them from blowing up. If he hadn't helped me out, I'd probably be in the booby hatch muttering part numbers in a straight jacket.

The inductor is 100uH and 2A, I think. Again, a fancy and much more expensive choice for a power line filter. I'm rather preoccupied with low-noise design. I really hate hiss. Another reason I use these fancy opamps. Even at higher gain levels, you can hardly tell this pedal is on if you're not playing.

The socketed diodes are 1SS133. I got them from eBay and they're in the same DO-34 package as MA856. Over the years I've been buying random diodes to play with just for shits and giggles.
 
I just realized something. Those 1SS133 look identical to MA856. Now I can't honestly say for sure I've ever had a MA856 in my hands. Not that I think it matters all that much in the sound, though.
 
jubal81 said:
I just realized something. Those 1SS133 look identical to MA856. Now I can't honestly say for sure I've ever had a MA856 in my hands. Not that I think it matters all that much in the sound, though.
Click to expand...
The only way I can tell them apart is by forward voltage and the panasonics have a little black mark on the lead at the cathode side.
 

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