CJOD-modded BOSS SD-1 crackles with very low signal passing

mlp-mx6 · Post by **mlp-mx6** » 08 Mar 2016, 16:47

I did this analogguru mod to my unused SD-1:
(viewtopic.php?f=11&t=3341#p24066)

1.) Remove R5 - R9, C2 - C6, D4 - D6, IC 1
2.) place a jumper wire instead of D5
3.) assemble a socket for IC1
4.) assemble R5 = 10k, R6 = 1k, R7 = 1k, R8 = 220 Ohm, R9 = 1k
5.) assemble C2 = 100n, C3 = 220n, C4 = 220n, C5 = 220n, C6 stays empty
6.) solder a 10k resistor in parallel to C4
7.) assemble the 2 red 5mm LED´s in D4 and D6
8.) take a chip of your choice (OPA2134) and plug it into the socket. (I used a NE5532)
9.) put a 47pF cap across D4

But now all I get in bypass is a crackling sound of the note, and that only when I hit it hard. When engaged it passes a small amount of signal, still with lots of crackle (like signal crossing a threshold). I've quadruple-checked my soldering, etc. Of course, I did not check if the pedal was functioning correctly before I did this - but it did work the last time I used it (several months ago).

Can anyone point me in a direction to solve this? I'm not terribly bothered, since the SD-1 was basically unused (and I think I bought it new for $25), but I would certainly prefer getting it working with this mod. I can post pics later if that will help.

Anyway, thanks.
Michael

mlp-mx6 · Post by **mlp-mx6** » 19 Mar 2016, 16:52

OK, I figured it out. The trigger was I accidentally discovered that if I turned the guitar volume pot down just a little, it started working. Then I noticed scratchiness when I turned the guitar volume, which sounded like DC on the pot. Voila! Yes, there was DC on the pot. Turned out that C1 on the SD-1 schematic (the first input cap) had failed and was passing DC onto the input. I replaced the cap and all was well.

So there you go.

mlp-mx6 · Post by **mlp-mx6** » 19 Mar 2016, 21:13

Can anyone explain why the pedal started working when I turned the guitar down?