BOSS SD-1 Mod

[dimitarmk]

First let me say hello to everybody 

I want to mod my Boss SD-1 pedal and I thought I should share the mod I'm going to do on my pedal, so I could get your suggestions and thoughts on this mod
And, would the SPDT switch work that way?



Thanks!   

[BAARON]

C2: YES.  Definitely.
C3: This will increase bass response, but because you also plan to reduce R7, it actually just compensates for the bass loss you'll have for doing that.  (See below.)
C8: you won't hear a difference changing this cap.  The bass rolloff is already well below the guitar's range (7Hz, to be specific).
C7, C10: if you believe there's a tonal difference between electrolytic and film caps in the audio range, you might hear an improvement, but I thought that electrolytic performance mostly starts to break down in the 100mHz+ range (well beyond human hearing) and they only add about 0.001%THD (again, well below the human threshold for detection).  In my opinion, it's probably not worth doing.
R2: Go bigger than 620k, because that's barely a change at all.  You should go all the way to 1M or 2M2 if you want to seriously improve the input impedance.  While you're at it, make R1 something smaller, like 2k2.
R6: decreasing this will increase gain, yes, but remember that it will also reduce bass content a bit.  Increasing C3 at the same time (as you already plan to do) will help to compensate.
D4: the existing diodes are already silicon.  Replacing them with another silicon diode (1N4002) won't change the sound on anything but the most extremely subtle level.  However, if your SPDT switch were to select between a silicon diode and an LED (which clips at about ~1.8v instead of ~0.6v), you'd hear a definite difference in the clipping.

Something else you might consider changing is the gain pot.  Try an AUDIO taper pot (1M) instead of the standard linear taper.  It gives you much more control over the low gain range of the pedal, and doesn't reduce the maximum gain level at all.

And finally, you'll probably want to add this.  It's important, because the bypass circuit on the SD-1 isn't very good.
http://www.indyguitarist.com/temp/sd1-bypass-fix-406.gif

[oldrocker]

Another way to tame some harshness is replace the 4558 with a TL072.

[TELEFUNKON]

Another way to tame some harshness is replace the 4558 with a TL072.

or have a look at the TLC series.

[dimitarmk]

Thanks BAARON 

Anyway, now I'm looking to the Monte Allums Stock SD-1 Mod. The kit:



I don't live in a paypal supported country so I can't buy the kit . From looking in the kit, the 2k2 resistor is probably for the 2X Gain mod, but I don't know for what are the other 9 capacitors. This mod sounds awesome from what can I hear from the sound clips and I want to do this mod on my pedal 

[BAARON]

Another way to tame some harshness is replace the 4558 with a TL072.

or have a look at the TLC series.

I like to use the TLC2262 in mine.  The OPA2134 is really great if you have a diode-lift switch because its voltage rail clipping is very nice, but I don't think you'll be doing that so it might be overkill.