The Flyleaf is based on the vintage EHX Zipper™ Envelope Follower that debuted
in 1977. It has been adapted to use true bypass switching and includes an in-
ternal trimpot for adjusting the effect for bypass unity via an onboard clean
boost. This boost is based on the LPB-1.
Although the original circuit used 2N4302 jfets, we’ve found 2N5485 to be an
ideal substitute, although others such as 2N5952 may also work adequately.