Justin Bread’s Guitar Hero Controller synthesizer is a modified Playstation 2 Guitar Hero controller:
Just about everything is left the same with only slight modifications to the actual controller. The circuit that drives the oscillator is based on the LM386 amplifier chip. Here’s the schematic. You can download the full image here.
Pretty uninspiring. He could have done something interesting, like make the buttons a binary based sum, thereby creating the ability to (technically) produce up to 32 different notes, which would be almost 3 octaves. Or even use the first four buttons as binary scales (considering you can only realistically hold down 4 buttons at once) with the 5th button being a 'shift' style button, which when combined with the other four buttons changed settings. (orange plus green and red for octave shift, orange plus yellow and blue for tone/patch change).
Oh well. It's still a nice little project regardless, i guess.