I am wanting to add a diode switch to the egghead, so that o would run all diodes off board, and add some different ones. Could anyone tell me how I would wire this up? Thanks
There's many ways to do this. In any case, don't populate D1 and D2 (leave open, don't jumper), and run wires from the solder pads of D3 to a switching setup of your choice. You only need to switch one side of the diodes, so you can use an SPDT to get two choices. Or you can go fancy and use a rotary like this one over here (the instruction pdf might be helpful as it explains it better than I can): http://shop.pedalparts.co.uk/Clipping_Switcher/p847124_14712436.aspx (http://shop.pedalparts.co.uk/Clipping_Switcher/p847124_14712436.aspx).
One setup I particularly like is used by Grind in several places, like this one (check out the build doc and look at the diodes): http://www.grindcustomsfx.com/product/gcfx-fengdrive-v2/ (http://www.grindcustomsfx.com/product/gcfx-fengdrive-v2/). It uses a simple SPDT center off switch to get the sound from three sets of clipping diodes. The LEDs are always in the circuit, but they have the highest clipping thresholds. This means they will only contribute to the clipping when the other diodes are not in the circuit. Nifty!