The CHARLIE effect from Red Ant is a hybrid silicone-germanium fuzz, based on the now very rare and valued HARMONIC PERCOLATOR HP-1 made by INTERFAX. This effect was created in Milwaukee, USA in 1970 by Ed Giese.
The secret of the unique sound of the HP-1 lies primarily in its specific wiring and use of both germanium and silicon transistors. Over the years, the effect has been modified by many designers, probably the most famous is modification by Steve Albini. CHARLIE sticks more to the original, with the limiting diodes at the end of the circuit being silicone, instead of the original germanium ones.