Death by Audio Total Sonic Annihilation 2

 Schematic is avaiable HERE.

Schumann F Loop

 Here is a an old, rare and weird one traced by Deadend Fx.

It is a feedback looper that includes both modulation and an active filter sections. If you you don't like the hassle with the offboard wiring this layout requires, Deadend Fx has nifty PCBs for sale.

Schematic and more info HERE.