The mods I did are in 3 places.
1. Keeley clipping mod. Replace one of the clipping diodes (D4 or D5) with a red LED.
2. Tone mod. Replace C11 (22nF) with 47nF. Replace R16 (6.8K) with 3.9K. This gets rid of the dreaded mid notch.
3. CB voice mod. I've seen other people mess with the gain and biasing of Q2, the gain stage in front of the opamp, but no one made Q2's gain or freq response switchable. Until now. Replace R9 (22Ω) with 470Ω. Add a SPDT on/off/on toggle switch and wire it so that it adds either a 22uF or a 2.2uF (or neither) in parallel with R9. With 22uF in parallel with R9, you get the same gain as the stock pedal. With 2.2uF, you get a tighter bottom end. With the switch in the center position, you get less gain and very little, if any, distortion in Q2.
Almost forgot: I increased C2 from 470nF to 2.2μF and C3 from 47nF to 1μF. Fattens up the bottom end. I used tantalum for C2 & film for C3.
The other thing people like to do is reduce R13 and increase C8 for more gain when DISTORTION is dimed. I didn't bother with that mod because I think the DS-1 has plenty of gain already.
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