Fuzzhugger Fx Phantom Octave
A glitchy fuzz with the ability to produce some bad tracking octave down. The key is to play with your guitar volume and tone controls.
Inverted Cross Audio Octaver
Here is a useful little circuit that can be used before or after your favorite dirtbox. It is basically a Green Ringer circuit with a buffered clean blend. Schematic is avaiable HERE.
Inverted Cross Audio Low Rider
A candidtade for the ultimate Rat for bass and down tuned guitars? Maybe. Schematic and BOM is avaiable HERE.
Walus Audio 385 Overdrive
This one has a pretty interesting backstory. It is supposed to be be based or simulate the tube section of Filmosound projector from the 1950s. After listening t o the demos it seems to be a Tweed style overdrive. Schematic is avaiable HERE.