Here is what echo park has to say on their F-2 Fuzz:
"Influenced by several iconic circuits made popular threw the mid 1960's..
The F2 circuit is designed to satisfy the purely devoted vintage fuzz freak and the seeker of new sonic territories alike.
We have added a second set of 'glass' clipping diodes to the unit as a second palate of textures and tones..
These Fuzz units work best as first in line or before any boosting.
The 'Level' sets the dry to affect volume of the F-2
The 'Blend' Control combines the first stage of silicon transistor 'Glass' clipping diodes (silicon transistor) into the second stage simultaneously. Creating everything from a subtle fizzle to a big fat hairy boost with harmonic flutter. Sacrificing nothing when you use the instruments volume control or adjust the pedal volume.
Hand Made in Los Angeles"