Boss SD-2 Mods

[sherminator1995]

I recently got a Boss SD-2 as n "upgrade" to my SD-1 but I'm not feeling the sound of it much. I thought it'd be like 2x SD-1's in one enclosure but there's a huge disparity in the sounds between the two channels, and it sounds really loud and rough - more like a distortion, no doubt due to the LED's I can see inside the pedal. With this, I intend to go ahead and mod it. My SD-1, which has since been sold, was quite heavily modded:

- OPA2134PA Op Amp
- 2N7000 MOSFETs instead of the silicon diodes
- Many caps replaced with Panasonic metal films
- Some cap and res values changed

I was wondering if it would be possible to do these mods again to my SD-2 to get something a bit more "boutique" like my SD-1 became (especially as I can't afford a Chase Bliss Brothers ). Either way, I think it'd be nice to have a compilation of resources in case someone like me wants to mod their SD-2 in the future!

First, a picture of the innards (PCB) of my particular SD-2, and the schematic:





My research found me the following mods:

• Increase the value of R36 for more gain on the Green Channel. Suggested values are 68k or 33k.
• Decrease the value of C28 to tighten up the sound. Suggested values are from .47uF to 2uF.
• Replace C34, C13, C9, C18, C43 and C22 with better quality replacements
• Tubescreamer style:
  - Remove C36, C46, C47 and R49 and replace with a 1 uF NP cap. Any indication what this actually means? Do I just, like, take these all out and replace the whole thing with one capacitor??
  - Replace D4 with a silicon diode.
  - Replace D6 + D7 with one 1N400X diode. If I'm not mistaken, this and the previous mod combined make this a symmetric clipping section. However, I prefer assymetric. Am I right in saying I could replace D4, D6 and D7 with 2N7000 mosfets?
  - Possibly also swap out D10, D11 and D16, maybe by putting sockets in and trying out different diode combinations (space looks tight though). D14 and D15 are "shunt diodes", if I'm not mistaken. Don't know what this means but I'd appreciate if someone could explain like I'm a mechanical engineer (not an electrical one ). Could I replace these with silicon diodes? I'm really not a fan of LED's: I've tried them out in my SD-1, but I don't know what the effect on this section will be. Maybe just leave it as is?
  - Replace C28 with a 220nF or 100nF cap
  - Replace R37 with a 4.7k resistor and run one end to Vref. I'm guessing this means run it to ground?
  - Replace C12 with a 1uF NP cap
• The following is an image of a "Keeley Modded" SD-2, or rather the thumbnail of it. The original page seems to not have the images any longer, but this thumb can be found on google images.
  
  - From what I can tell, the mod replaces C9, C25, C26, C27, C34, C38, C46, and C48 with posh orange capacitors.
  - Apparently one diode (looks to be D15) changed to a silicon diode.
  - Same thread also suggests increasing C10 to reduce mids in the lead channel. Suggested value somewhere from 0.22 uF to 1 uF.
  
• The op-amps (IC2, IC3, IC4) used are apparently SIP versions of the 4558. What would the SIP equivalents of other popular op-amps be? Such as, for example, TL072, TL084, OPA2134PA. ESPECIALLY OPA2134PA: I NEED MY BURR BROWNS
• Just sell the damn thing, save myself the pain and buy a Chase Bliss Brothers. Apparently livers can grow back from a small, remaining amount - I'm a healthy (ish) non-drinker so I think I can fetch a good price for a chunk of it, pay off the debt from the pedal

So, any tips, additional mods, or answers to my questions (underlined) would be very helpful.

Cheers!

Sources
http://www.diystompboxes.com/smfforum/index.php?topic=56976.0
http://www.stompboxzone.com/forum/viewtopic.php?f=5&t=91
http://www.diystompboxes.com/smfforum/index.php?topic=79897.0

[sherminator1995]

Does no one want to help? I'm going back home for a week and I'm planning to mod there - my landlord probably won't like me soldering here... I'll need to order parts ASAP so I can get modding as soon as I get home...

[JUANSNEIDER]

hi, i just have adquired a damaged sd2, all cables are solderless, do you have any diagram to reconnect all this disaster?, help please, send me some pictures!!!!!!, my email is juansneider@hotmail.com, and my ws phone is +584245060612

[Gila_Crisis]

I got an old SD2 lately, what a very cool pedal it is! Btw after playing it stock for a while I performed few small mods (a good starting point was the Wampler book):

Crunch Channel:
C36 Jumper
C47 remove
D4 2x 1N4001 in series
C24 47n
C12 470n

Lead Channel
R28 1k
C10 330n
R29 270k
D14 2x 1N4148 in series
D15 1N4001
C31 100n
C38 33n (or swamp C38 with C24, this way both channel have a better tonal balance, before crunch was way to bright and lead to dark)
C43 470n
R90 jumper