Here's a clean octave up effect from Tim Escobedo. The Bias control offer subtle changes, which is why I have it as an external pot. He mentioned it might need a booster in front of it, just FYI.
This is a library of perfboard and single-sided PCB effect layouts for guitar and bass. I'm not an electrical engineer by any stretch of the imagination, just a DIY'er who likes drawing layouts. It is meant for the hobbyist (so commercial use of any of these layout is not allowed without permission) and as a way to give back to the online DIY community.