In great condition, still inside the original box, the Proton is considered the best bass envelope filter you can get these days. Handmade By Spencer Doren, Founder of 3Leaf Audio, the Proton is an optically controlled analog envelope filter. The circuit has been completely redesigned to offer better tone and a more musical response. It has a new detector circuit based on the one in the Chromatron, and the familiar control layout has a greatly expanded range that can get the classic 1970s filter sounds and well beyond. The new range switch allows for much deeper filter sweeps, and the reworked tone knob covers every soundscape from cocked wah to laser beams.