This is the documentation to clone the 1978 EHX Echoflanger. The Polychorus is exactly the same circuit. This is the Nirvana In utero sound and makes an excellent feedback modulator. It is by far my favourite chorus pedal.
Original Unit
I based this layout based on a photo of the original PCB provided by Stephen_Giles at Aron's forum. I know of one person who has built this unit successfully. It is hard to set up and is recommended for the experienced only. factory schematic available in the schematic section.