help with external bias?

[tacobender]

Hello, ive just completed my first tone bender build (mk2) and im looking to build another with an external bias control. I was wondering if anyone can break this down for me. I have limited knowledge about building pedals, im kind of fumbling in the dark with this stuff. Im using vero for this build, if anyone can give me some ideas how to go about this i would greatly appreciate it!

[FUZZZZzzzz]

http://www.diystompboxes.com/smfforum/index.php?topic=71945.0