File:Dan Armstrong Green Ringer circuit - an octave-up effect with a ring-modulator touch to it - just finished building (2006-03-05 22.51.45 by germanium).jpg - Wikimedia Commons
Simple Octave Up schematic
CMOS workshop part 3 - octave down - PARASIT STUDIO
DIY Octave Pedal Demo (Part 3) - YouTube
CMOS workshop part 3 - octave down - PARASIT STUDIO
One Octave Foot Pedal Controller Schematic
Boss OC-2 Dual Octave Down Guitar Pedal Schematic Diagram