Boss SD-1 Overdrive mods

Boss SD-1 Japan MadeI’ve got this old made in Japan Boss SD-1  on eBay.

Boss SD-1 Japan Made 2Boss SD-1 Overdrive made in japan mod 3Classic japanese JRC4558DD and green capacitors :

Boss SD-1 Overdrive made in japan mod 4

So, how does this stock pedal sound like  ?

The SD-1 schematic is close to Ibanez TS808′s one. But close does not mean “identical” ​​… some components differ in values, and the clipping is asymmetric on the SD-1 : 2 diodes in series on the one hand, a diode on the other, these two sets mounted in the opamp feedback loop. The pedal sounds a little more “harsh” than the TS808, more “marshally”… The drive at its minimum, there is less gain than with a TS808. In think it is mainly due to the 33k resistor (instead of 51k in TS808) in series with drive pot.

This drive potentiometer is 1MOhm, where it is 500k for a TS808. The result is that you can push a lot more gain on SD-1 on a TS808 (and then, imho, its “marshall side”).

Here is the Boss SD-1 schematic (to be compared with TS808 schematic) :

Boss SD-1 overdrive mods 5

What mods for this pedal?

I will simply change the resistors in the signal path to add a max of mojo (no need to insult me : it’s all in the head that mojo happens) and capacitors in the signal path with Panasonic metal film (ECQ-V) …

I begin by replacing R1 and C1 :

Boss SD1 SD-1 overdrive mods 6Boss SD1 SD-1 overdrive mods 7Boss SD1 SD-1 overdrive mods 8(Note : components are “glued” on the circuit board but it quite easy to remove them …)

Then, I replace C8 and C9 (0.047uF) with Panasonic :

Boss SD1 SD-1 overdrive mods 9

Caution : tweak of the death ;-)
I don’t have any Panasonic 0.018 uF to replace C2. Therefore, I simply remove it (and I also remove the bias resistor R4) and I shunt between the output of the transistor Q5 and the input of the opamp clipping stage. C2 usually “cuts” the DC (bias). Here, the polarization is almost equivalent (3V output transistor, 2V input of the opamp. Seeing the schematic, I would have bet on 4.5V, but hey ! we are here to rock ‘n’ roll, after all) :

Boss sd1 sd-1 overdrive mods 10Then, I replace R7 and C7 (same values, but carbon and Panasonic) :

Boss sd1 sd-1 overdrive mods 11

Then, replacement of R16 and C10 (carbon and Panasonic capacitor). C10 has a value of 1uF. For those who have always been amazed with the value of (awful) electrochimic 10uF at the TS808 output, it seems that Boss did not see why a value as important) :
Boss sd1 sd-1 overdrive mods 12

Shut the box !

Boss sd1 sd-1 overdrive mods 13

In conclusion : it sounds good, without disfiguring the pedal, and as usual, I’ll have to wait several days to try again and see if there is some “magic spot” in this pedal or not …

I think it goes well with the Les Paul (unlike the TS808 which I find muddy with HB’s) : firstly there is less gain at minimum drive level, on the other hand this pedal is a bit more aggressive than TS and that seems well suited to Gibson guitars.

Placed in front of a TS808 to emphasize a solo is also a good solution because it gives bite to the sound !

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4 Responses to Boss SD-1 Overdrive mods

  1. Jose says:

    After many attempts to make this pedal sound big and clear with a warm distortion I discover a tweak maybe you can find useful, the electrolytic capacitor C11 with the value 47uf 10v, replace it with an 47uf 100v electrolytic capacitor, it makes a huge difference in the overall sound the distortion will sound big, clear, defined, warm, I think I’m the only guy who did this, try using a quality capacitor for better results.

    • t-geek says:

      Ok, thanks Jose. Maybe it is because you swapped it with a better quality cap and not the fact to replace a 10V by a 100V ?
      Anyway, thank you for your comment !

  2. Jose says:

    Well, for my second SD 1 mod, I did the same mods and I didn’t had a Nichikon cap so I used a Jamicon 47uf in the same 100v with the same good results, so, I think is true that is about values no much quality of the components.

    • t-geek says:

      Thanks, Jose.
      First : the right value at the right place.
      Second : better quality component may (or may not) improve sound. Not always true, but often.

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