Pro Sound
Little-Scale
http://little-scale.blogspot.co.uk/2008/05/prosound-gbc.html
Low Gain
http://lowgain-audio.com/GBCmod.htm
Johann Kotlinski
http://www.littlesounddj.com/lsd/prosound/
Editors note: This page needs an amalgam of all the above versions and differences where they vary.