Keeley classic mod (copied from his website a long while back):
D3 -> Change this 1SS133 to a different (1N4002) diode for asymmetrical clipping. This adds second order harmonics. This adds to the tube type sound. I like the sound of this change.
D7 and D10 -> Change these diodes from 1SS133 to 1N4002. More second order harmonic distortion. Although the change is slight, I like it.
C1, C7, C6, C12, C13, and C15 -> Change this electrolytic capacitor to a 10uF tantalum. Tantalum capacitors sound better than electrolytic capacitors. It would be best to have a non-polarized cap here. I like these anywhere there is signal coupling at this high a value. Tantalum capacitors are easy to find in this range.
C14 -> Increase input coupling capacitor value to 0.1uF for increased bass response from your guitar.
R1, R2, R18 and R19 -> Here is some magic. Change the resistors to carbon composition. These old resistors probably have some frequency dependent component, which means that there is a capacitive element to the resistor. This is because of the spacing in the material. Add these for vibe, MOJO, and magic.
C100 -> Here is where we can affect the tone control. I prefer a little more lower-midrange and bass frequencies through the tone section. You can increase the lower frequencies by increasing the capacitor value to 0.033uF.
I modded a BD-2 to these specs a long while back and it sounds great!
