BOSS SD-2 "Yellow mode"

teleholic · January 11, 2015, 05:33:07 PM

Hi guys, discovered this the other day on my newly acquired SD-2..i hooked a patch cable from the remote input to a pot and was able to get red, green and a 'secret' yellow mode..basically as you can guess it combines both modes, loses some volume but all pots work in adjusting tone, makes it sound like a tube-y heavy od which i really dig! So my question for the experts here is, is there a way i can switch between the 3 modes in a more elegant manner, preferably stomp switches? Also, is there a way to solve the volume drop in 'mix' mode? Not sure what causes the volume drop, i would guess some parallel thing...

Also lastly, there were two versions of this pedal, an earlier 'darker' version and a later brighter one, the only diff i can see is the C100 capacitor..is it as simple as removing C100 to convert it to the older spec? Thanks!

teleholic · January 12, 2015, 03:26:06 AM

Here's a schematic if it helps: http://aronnelson.com/gallery/KHE/Boss_SD2_schematic?full=1

duck_arse · January 12, 2015, 10:11:54 AM

Quote from: teleholic on January 12, 2015, 03:26:06 AM
Here's a schematic if it helps: http://aronnelson.com/gallery/KHE/Boss_SD2_schematic?full=1

also quote: "404
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The resource requested could not be found on this server!"

Quackzed · January 12, 2015, 10:28:37 AM

http://www.synthdiy.com/show/?id=2268

i'd guess that the pot is 'blending' between 2 channels? and the yellow mode is the 'mix' of the 2? if so you should be able to find an on off on type switch to switch between the 2 channels , and then use 2 resistors to replace the pot (measure each side of the pot to the middle) and put those resistors on the outside lugs of the switch, so in the middle 'off' position it looks like the pot. not sure if you were using the pot as a variable reesistor,2 lugs, or as a potentiometer, 3 lugs... if 2 then same but just one side of the switch to replicate the 1 side of the pot you're using...
smaller value pot might give you more volume, well, less volume drop...

duck_arse · January 12, 2015, 10:34:42 AM

"C100 capacitor" ? 404, not found!

teleholic · January 12, 2015, 12:18:56 PM

sorry guys..here's a photobucket link with two schematics of the SD-2: http://s642.photobucket.com/user/kupervaser/media/Boss%20SD-2/Boss_SD2_schematic.jpg.html

Also here's a link to a stompboxzone thread showing the pcb: http://www.stompboxzone.com/forum/viewtopic.php?f=11&t=30&start=420#p27233

Hey Quackzed, thanks for the help! I hooked up a 250k pot and just alligator clipped the tip and sleeve of a patch cable to the outside and center lugs..when i turn the pot, i go from red to yellow to green..sound wise there's no blending though, it acts like a switch..so the change from red to yellow to green is abrupt and no blending of tones occur.. would i be able to get a stomp switch (on off only i assume) to work somehow? Thanks!

Quackzed · January 12, 2015, 01:08:58 PM

ok, i get it... so with an on/off/on type spdt switch you can have 1 of the remote leads go to the middle 'off' lug of the switch (lug2), the other remote lead to lug 1. then a 250k resistor from switch lug 1 to sw lug 3, and another 250k resistor from sw lug 1 to sw lug 2.
so when switch is in the middle, the only path is through the 250k resistor from lug 1 to 2. 250k resistance/green? i think
when switched down, lug 1 and 2 are connected for 0 resistance/red i think
when switched up lugs 2 and 3 connected, the path goes through BOTH resistors in parallel for resistance of 125k ,hopefully yellow.
you might need to play with the resistor values a bit if the switching is bunched up on either side of the pot you're using, but if one side of the pot is red and the other is green and yellow is in the middle ,these values should be good...

Quackzed · January 12, 2015, 01:18:39 PM

...you could 'test' it out by connecting the remote leads together, see if you get red... then with a 250k in between the leads see if you get green, then 2 250k resistors in parallel (for a 125k resistance) between the remote leads and see if you get yellow, thats all the switch is doing...

teleholic · January 12, 2015, 02:42:29 PM

Wow thanks for the help Quackzed! I think i understand what you've described so far ( i'm far from an expert on electronics)..i take it there's no way for a stomp switch solution?

Quackzed · January 12, 2015, 07:14:50 PM

yeah, you can make it remote... only restriction is you'd need 2 stomps to get to all 3 'channels'.
as is , the remote switch switches btween crunch / lead, but you could rig it just as easily to go between any 2 channels... crunch/yellow or lead/yellow
its because a stomp has only 2 states. stomp(on)1 and stomp(off)2 stomp(on again) ...off again etc... on or off.
doing 3 channels with one switchr gets pretty complicated for a mod... more like a separate circuit...
using a separate switch could do it though...

teleholic · January 13, 2015, 03:29:03 AM

I see.. i might opt for red/yellow then as i still don't really like the green channel.. one more question if you don't mind, if the only difference between the earlier dark version and the later bright version is the C100 cap and a resistor on the back of the pcb (which you can see in that second link i posted on page 1), would removing c100 and adding that resistor effectively convert it to the earlier spec? Thanks!

Quackzed · January 13, 2015, 11:07:00 AM

IF its the only difference, then yeah, but I couldn't find any c100 on the schematic... so not sure wheather you'd need to just remove it, replace it with a different value or jumper it...same for the R...
if theres an older and newer schematic you can compare them and see...

teleholic · January 13, 2015, 12:19:17 PM

I see..what's the difference between removing a cap and removing and jumpering the points?

Quackzed · January 13, 2015, 05:02:27 PM

if the cap is in the signal line, then removing it will stop the signal getting through the circuit, if its between the signal line and ground you can remove it and the signal will still get through... so in the first case you'd need to replace the cap with a jumper, in the second case you could just remove it and be ok... depends what the cap is doing...

teleholic · January 13, 2015, 05:15:41 PM

THanks, you're a real wealth of knowledge...time to get to modding...

Voltron · November 24, 2015, 12:31:59 AM

Hi, I've been studying the SD-2 recently. Old thread but I might be able to answer some abandon questions here.

There is no "blending" on the "yellow channel". The channel switching uses a gate logic chip. The remote switch just connects a ground direct ground line. A resistor should make the red channel gate open so you have both channels on (and both led lights on, hence the yellowish color).

Regarding different versions:

According to info on other threads the extra, solder-side, resistor should be 1M and connected parallel to the 250k log GAIN pot (IF pot values remain the same for both versions). As far as I know, 1M + 250k in parallel = 200k.

The C100, I saw the board pictures but cant figure out exactly how its connected. My guess is: parallel cap to C10 or parallel to C19. Basically both mods would be just a slight alteration on the gain stage over gain and freq range.

Would be great if we can trace all the changes and document them, so people would have version accurate schematic.

Althou this pedal was never popular some people like it and seems like has resale value. The production ran for a short time so no many units around (compared to other production runs), used market price may go up in future.

Voltron · December 15, 2015, 10:33:41 PM

Quote from: Voltron on November 24, 2015, 12:31:59 AM
There is no "blending" on the "yellow channel".

There is not "EDIT POST" on this forum.

With "blending" I was refering to conecting an expression/volume pedal to the remote jack. There is no gradual change when rocking the expresion pedal. But you can still use the volume controls to balance the sound.

Also, Im not sure for this one but I think the 1M resistor paraleled to the 250k gain pot might alter the range excursion as a super log pot?

lethargytartare · December 15, 2015, 11:26:27 PM

Quote from: teleholic on January 13, 2015, 03:29:03 AM
I see.. i might opt for red/yellow then as i still don't really like the green channel.. one more question if you don't mind, if the only difference between the earlier dark version and the later bright version is the C100 cap and a resistor on the back of the pcb (which you can see in that second link i posted on page 1), would removing c100 and adding that resistor effectively convert it to the earlier spec? Thanks!

Or you could opt for two switches so you can get all three channels, but make one of the two switches a smaller toggle -- that way you can have it set to stomp=red/yellow most of the time, but flip the toggle for those odd occasions you want to access the green channel (like toggle up would introduce a second resistor and give you yellow/green, but toggle down leaves the stomp red/yellow). I get greedy and can't stand burying a feature if I can keep it accessible.

bluebunny · December 16, 2015, 03:20:14 AM

Quote from: Voltron on December 15, 2015, 10:33:41 PM
There is not "EDIT POST" on this forum.

There is if you come back quick enough ("Modify").

November to December isn't quick enough.

I think there's a 24 hour window, or something similar. Keeps us from rewriting history and making confusing reading for someone trying to read the whole thread later on.

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BOSS SD-2 "Yellow mode"