FA-1

FET Amplifier

BOSS® FA-1 FET Amplifier
Manufactured from 1980 to 1984, was an always-on effect that clipped to your belt and ran on a 9-volt battery.

It’s a solid and versatile circuit, but the non-standard implementation prevented it from getting much attention — although it was famously used by The Edge which caused vintage prices to skyrocket.

https://www.tonehome.de/boss/fa-1-fet-amp/