How to clone 'Damage' function of the Ibanez FZ7 Fuzz

[guile]

A while ago I heard an Ibanez FZ7 Fuzz pedal. It has this great function on it called 'Damage'. This simulates a broken speaker.
You can hear it a little in ZZtop's 'Alley Gator' (2:10): http://www.youtube.com/watch?v=BzDTOjjMNVg

Does anyone know how this works and how it could be installed on other pedals?

[kothoma]

http://elektrotanya.com/PREVIEWS/63463243/23432455/ibanez/ibanez_fz7.pdf_1.png

Looks like different bias settings for the second op amp.

[guile]

Would love to know how to make it work.