MXR Distortion III Mods
When I got this pedal, I was unimpressed with how it coloured my tone. It removed a lot of bass and treble. So, I looked at the schematic:
The main bass removal comes from the capacitor marked C2 in the schematic. Treble rolloff comes from C12, C5, and C4. Looking on forums, removing C4, or replacing it with a lower value cap, was a common mod to increase treble response. I tried it, and it worked very well, but there was still the problem of the lack of bass. So, I bridged C2. This did increase bass response, although it increased gain, and the upper third of the gain control is now gated. That problem could probably be fixed by replacing it with a higher value cap connected from the 2M2 resistor to ground. Anyway, I'm happy with it.
To mod your Distortion III like this, remove C4 as marked on the PCB, and bridge the 0.1u cap underneath the distortion pot.
Wanting even more bass, I replaced the 0.1u cap with a 0.47u cap. This is more a matter of personal preference, but it matches bass a lot better with the bypassed signal.