This modification will allow you to use your footswitch to change
the boost setting on the drive channel.
Here you'll find the schematic to the Ibanez Metal Screamer MSL
and the modifications necessary to turn it into either a TS-10,
TS-9 or TS-808 tube screamer pedal.
A scan of the original FX56 schematic.
Links to other useful guitar electronics sites with schematics, etc.
