Boss SD-1 Bypass Mod

Discussion in 'Effects, Pedals, Strings & Things' started by critter74, May 28, 2015.

  1. critter74

    critter74 Supporting Member

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    Hey

    Is the bypass/bleed through mod/fix for the SD-1 fairly easy? What all is required to have it done?

    I do not want any of the other mods usually done to it, I just want the bleed through issue fixed. If someone can tell me or pint me to some instructions on how to do it I would appreciate it. I don't want to send it to someone just for this small (yet a little annoying) issue.
     
  2. MrKite89

    MrKite89 Member

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    Hey, same problem here! Do you found out the solution?
    Thanks...
     
  3. MIM#1

    MIM#1 Member

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    Last edited: Jan 29, 2016
  4. coltonius

    coltonius Señor Member Silver Supporting Member

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    If it ain't broke, don't fix it! The method that is.. I performed that mod just a few months ago. Still works, so why change it?
     
  5. Clark GriswoId

    Clark GriswoId Supporting Member

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    ^ that looks like an easy fix, for the added board joints do you completely remove the resistors/ capacitor legs from the existing board then solder the new wires to the legs?

    Or you just solder the new components to the board right where it shows?
     
  6. MIM#1

    MIM#1 Member

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    Well, I heard theres a much simpler,cleaner fix than adding all those offboard wires. I just cant find it!
     
  7. MIM#1

    MIM#1 Member

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    I've done it in the past,you can leave the resistors in place and tack the new wires onto their legs.
     
  8. Silvio55

    Silvio55 Member

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    I'm looking for it, but I can't find it either! The best I could find was that the mod consists in removing the input resistor R1 from the board, (probably changing the value too to 1K5???) soldering it directly to the input, and run a cable from the resistor to the board where R1 was, but it's not fully confirmed yet.
     
  9. MIM#1

    MIM#1 Member

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    Awaiting confirmation! :aok
     
  10. rck

    rck Supporting Member

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  11. MIM#1

    MIM#1 Member

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    That looks cool! But at that point I'd rather buy a pcb and build a complete DIY pedal.
    I just did the old Eternity mod to my SD-1 and it sounds great! But the 'illusive' bypass mod is still illuding me...:-D
     
  12. Silvio55

    Silvio55 Member

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    I'm pretty sure the "simplier" mod is the one I described, it may adress some layout issue that's possibly the cause of the bleeding. But I don´t have the pedal to confirm it, or somebody else that has performed the mod and checked if it works.
     
  13. snow and steel

    snow and steel Supporting Member

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    I did the c6 clip, and adjusted the bass level [so it was no longer cut but was flat]. When it came time for the true bypass and bleed fix, I had neither the time nor the patience. Member "Coltonius" did mine for me, turned it around in a week door to door and was extremely reasonably on the price.
     
  14. stinkfoot

    stinkfoot Member

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    Brace yourselves - this will be a long one... :D

    Over the years, much has been said/written about the SD-1 bypass bleed issue. At first, there was discussion if it was even a real problem - not everybody could even hear it (I didn't, at first). This was probably because the fizz was being covered up by other things (amps set slightly dirty, for instance) or simply wasn't there because the user wasn't running the pedal at high enough gain settings. And that is still true today, of course - not everybody hears it, or sets the pedal up so it can manifest itself. So if you have an SD-1 and don't know what all the fuzz is about, don't worry :cool:

    Anyway, at first glance it looked like a simple case of the JFET that mutes the output from the distortion circuit not being able to close fully. The weird thing was that it didn't seem to matter how the volume pot was set (which it should, if the mute JFET was the problem). This theory was finally debunked when someone physically removed that transistor, and found that the bleed was still there. And not only that - it was present even at the input buffer stage, pointing towards a fundamental problem with the circuit itself or the physical layout of the circuit board.

    Over time, a couple of solutions were devised, both involving adding transistors to open or close paths, and using the pedal's switching system to control them. The first was the mod linked to earlier in the thread, which basically manipulates op-amp's gain setting when the pedal is bypassed (so there isn't enough gain to create a fizz in the first place). A later mod borrowed from the DS-1, and simply muted the input to the op-amp in bypass mode (so the drive section isn't handling any signal at all). Both mods works fine, even though they're only addressing the symptoms, rather than the root cause of the problem.

    The mod suggested by @Silvio55 above seems to involve physically moving R1 (the main input resistor) to the input jack - basically from one end to the other of the input wire. Electrically speaking, that shouldn't change anything. But when looking at the board itself, I can see that R1 is located right next to D4 (one of the clipping diodes), and physically moving R1 would of course move the input signal farther from that clipping diode. Going by the description above, I'd try removing R1 and moving the brown wire from connection point 3 to where R1 was (use the hole closest to C1 - farthest away from the top end where all the wires are). Then desolder the brown wire at the input jack, solder R1 (or a fresh 10K resistor) to the end of the wire and solder the resistor to the input jack lug where the brown wire used to be. Now, I haven't tried this myself yet, so I can't say if it does the trick or not. But at least that's how I interpret what's being proposed.
     
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  15. MIM#1

    MIM#1 Member

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    I can attest that there actually is a bleed with 'some' sd-1's. Where I heard it once was through my JC120 at gig volume, and it drove me nuts until I found out what the source was. Of course this is a pristine clean platform, so I doubt that somebody with a tweed amp would hear anything at all. I did the old 'add a cap and transistor fix' and the problem was gone. This was years ago however. Now I have a different SD-1 [with eternity mod] and hear no problem through my home champion 600 amp. It will be a few months before I break out the JC120 so I dont want to try and 'fix' it if there is no bleed through.
    So I'll wait to see if anybody else can verify the fix.
    But thanks you guys for chiming in on this topic,its something that every diy modder should know how to cure!
    Stinkfoot, you are a wealth of info here,as is .011 Guage at the tdpri. We owe guys like you for sharing your knowledge and helping us all learn along the way. :beer
     
    Last edited: Feb 28, 2016
  16. stinkfoot

    stinkfoot Member

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    Reviving this thread to report (to @MIM#1 among others) that I have now tried the proposed fix (moving the input wire to a different location). I removed R1 and C1, moved the input wire to the south end (farthest from the upper edge of the board) of where R1 used to be, and wired up a joint R1/C1 series combination to fit where C1 used to be. The theory was that by doing that, the main input signal would no longer be present as close to the anode of D4 (which is part of the clipping circuit) as before, which should clear the problem. But it didn't... There may have been a slight reduction in the amount of leaking, but there was definitely still some bleeding going on.

    And looking at the way the circuit board traces are laid out, I'm not surprised. That point (solder point 3, where the main input wire enters the board) isn't the only place where the input signal is routed uncomfortably close to the clipping circuit. In fact, the trace that D4 anode connects to also runs right underneath R1 to connect to R5 and R6, and that junction is just as close to the south end of R1 (where I moved the input wire to) as the north end of R1 is to D4 anode. Also, from that junction, there's a trace that loops directly underneath C1 back to the op-amp. Basically, that whole area is littered with traces and junctions that connect to the clipping diodes, and the main input signal should never have been positioned there in the first place.

    Maybe - but just maybe - moving the whole input section (input wire, R1->C1) to the north end of R2 could yield a better result. But you'd still have the trace leading to Q5 (the input buffer transistor) passing close by other traces that are connected to the clipping section, so even that move might not be enough. It seems the best fix still is to either mute the signal going into the op-amp in the first place (like in the DS-1), or use a JFET to force the op-amp to unity gain (as suggested in the fixes posted earlier in the thread). Even though it doesn't solve the underlying problem, it definitely clears the symptoms. Installing a true bypass relay kit will of course also solve the problem (then the bypass signal doesn't even enter the main circuit board, so no leaking can occur). Or you can just use the SD-1 into a slightly dirty amp - then you won't notice the slight buzzing :)
     
    Last edited: Feb 7, 2018
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