SD-1 to OCD conversion ILLUSTRATED (pics)!

Well, I broke down and did it. It's almost midnight, and if my wife finds out she'll bury me, but there's no turning back now!

I will attempt to illustrate parts of the text only mod (http://www.tdpri.com/forum/burnt-fingers-diy-effects/156945-sd-1-ocd-cc-drive-conversion-part-ii.html) that are hard to visualize with just words.

First, the input stuff, first gain stage mods, including removal of stock diodes (which is obscured by the 220pF cap that now occupies D4's place):

Next, the removal of C4 and R7, with clipping diodes installed, 2X10K resistor pair, and jumper wire connecting the two. Note that for a completely accurate OCD, the diodes should be 2N7000 mosfets, bypassed with a .001uF cap. But these pics show whatever clippers you put in there, where they should go:

Next, rewiring the stock tone control as the OCD's 2nd gain stage. The blue heat shrink "loop" next to the chip contains the 150K resistor (it's a 100K and 47K in series). Note that "terminal 5" is now open at the top of the board. And you can barely make out the red wire jumper between "terminal 8" and "terminal 11."

Next, rewire for the new tone circuit. Note that this is slightly different from the OCD, as it's a variable low pass filter. It mainly eliminates the need for the HP/LP switch and wiring, as it covers most of the range with the sweep of the tone pot only. Notice the "new" tone cap, with a red series wire running from the "top" of R10's place on the board, and connected at the ground lug of the output jack. Also note that the brown and purple wires get connected to this junction as well. And the gray wire goes in R10's "bottom" hole.

EDIT: A series resistor with the gray wire should really be there. It both tweaks the tone sweep range, as well as keep a little load on the output of the op amp when the tone knob is at "minimum cut" (and the pot is at ~0 ohms). Typical values are like 1K to 2.2K, but 100 ohms will suffice.

Next, the output caps and resistors, for the most part. Fairly straightforward in the written instructions, but here nonetheless. C7 is actually down near the "terminals" and chip. It also gives another view of how the clipping diodes get connected in C4's "right hand" hole. And finally, a complete pic of the entire board, giving a semi clear picture of the whole shooting match.

Please note that this pedal was modded pretty quickly, and the workmanship is less than stellar. Many solder connections could have been done more cleanly, and a bit of heat shrink here and there would help to prevent any shorts when you close her up. Also note that cheapo ceramic disk and Xicon "greenie" film caps were used as opposed to fancy metal film caps. I just wanted to see if the pedal would sound good with cheapo caps, and it also illustrates that the SD-1 has ample room for some big honking components, namely the HUGE .1uF cap in C5's slot, and the monster 10uF nonpolarized baby blue electrolytics. This mod can be done with stuff from RS for the most part, including a TL082 chip, if your heart desires. The only thing that they won't have are the 2N7000 mosfets.

Hopefully, these pics will make the conversion project much much easier. That is my sincere hope! Happy modding, and enjoy the tones!

Oh god, I gotta' get this saved to my PC. This freakin' great!

By the way - what sort of genius are you, anyway?

Don't tell me, you're not an EE, but totally self-taught, right?

Don't tell me, you're not an EE, but totally self-taught, right?

Well, not really either. Lotsa science, math, electronics, and other classes/courses from grade school up thru college. I think I reverse engineered almost every electronic device that I ever received as a child. This included many audio devices - radios, tape players, walkie talkies, etc.

As a teen, I spent a lot of time building my own audio equipment, as I never had the $ to buy the nice stuff.

...But it always amused and intrigued me how with electric guitar gear that the goal was typically to introduce things to the sound that were being removed from the hi fi rigs.

Man! This is what I wanted to see when building mine. Thanks again for all the help 11Gauge you definately know your stuff! Im glad that you are so helpful with us. You know Ive always been a motorhead and never could figure out why people didnt understand things about their cars now Ive found something that some what stumps me at time and I take it as a chalenge to master it. thanks again, clint