Author Topic: Boss SD-1 mods  (Read 32942 times)


Boss SD-1 mods
« on: March 07, 2012, 02:00:02 AM »
Hi~ I started modding a stock recent made in taiwan sd-1 pedal the other day with the monte allums sd-808 mod and was successful in accomplishing the mod with noticable improvements in tone although I'm still not sure it'll stand up to my stock made in japan version from the eighties... I can't quite put my finger on how much it improved... I guess the distortion is more compressed and less crunchy... The highs aren't that clear but there is way more gain... The instructions also came with the bypass mod which I think is useless since there is still "tone-sucking".. The massive volume drop... The bypass mod involves a .1 uf cap with a j102 tranny and a diode... These parts attach to three different sites with ineffectual results...  Normally I never mod anything since I'm a vintage pedal guy who is stuck in a rut... Any ideas? Thanks!


Re: Boss SD-1 mods
« Reply #1 on: March 07, 2012, 05:44:14 AM »
I've modded afew sd1's with monte's kits and they sound pretty good but I never could get it to sound good enough for what I wanted. The so called "bypass mod" is really not a bypass mod. Its a bleed thru mod. SD1's have a really bad bleed thru when the drive is all the way up. With out it you can still hear faint distortion still coming thru your clean signal. I'd leave that mod in. It works really well. If you want it to be true bypass. I'd would just build a bypass loop. I tryed TB'ing an SD1 but it  made it sound like crap. At least with a TB loop, You can still keep everything intact and avoid the "tone sucking".


Re: Boss SD-1 mods
« Reply #2 on: March 07, 2012, 12:25:41 PM »
I like 2 LED's in the feedback loop for that sort of thing.  ;)
Stomping Out Sparks & Flames


Re: Boss SD-1 mods
« Reply #3 on: March 07, 2012, 08:33:33 PM »
I appreciate the input guys! It's a good thing I didn't desolder the bleed through mod out of the pedal only to notice the clean signal not being so clean! At a later date I may try to put in a loop if the volume drop starts to get to me... I'm not sure if I want to short the D6 to make the sd-1 more tube screamer-ish with the symmetrical clipping yet.. Thanks again!


Re: Boss SD-1 mods
« Reply #4 on: March 07, 2012, 09:21:20 PM »
read somewhere some time ago and saved...

*Clip out the C5 cap , no jumper required . ( this is to smooth out the clipping from factory , but if you add the the 1n34a germs, i feel this C5 cap is uneeded )
*Add a 1N34a Germainum diode to each of the clippers in D3 & D4 ( this will add a touch more gain , but a way warmer clipping , or more tube amp like tone etc )
*Also i would install a op amp socket & run a JRC4558D !( Classic Tube Screamer Tone , my personal fav Op amp ! )

For your Treble issue Increase the C7 cap to .47 uf . ( Note anytime you are adding Gain , you will have an added amount of noise etc . )


***** Boss SD-1 5-Star Ge Keeley Mod *****

Keeley Custom Shop designed this mod to enhance the tone and functionality of the SD-1.

Freely copy and distribute. We have the right to change our modifications at any time without notification. It is fun to watch what big name people use the mods.

* Board Number, New part, Old part, Reason

* C10 --> Metal Stack Film 1uF, remove electrolytic, increased fidelity
* C7--> Metal Stack Film 1uF, remove electrolytic, increased fidelity
* R6 --> 2.4k ohm metal film, 4.7k, increased distortion
* C3--> 0.1uf metal stack film, 0.047uf, fidelity and bass response
* C2--> 0.1uf metal stack film, 0.018 fidelity and bass response
* R2--> 620k ohm metal film, 470k ohm, increased input impedance, better bypass
* Add 47pF cap across diodes in clipping section to smooth out distortion, just like TS9

On some older units, short out D3 and the 470 ohm resistor in the power supply section to increase the voltage to the circuit. This increase the headroom and gain. Newer units have it shorted already.

Here is the tricky part of our mod, take a germanium (Ge) transistor and use the Base-Emitter junction (legs) of the device and use it in place of D6. If you use a PNP transistor, the Base will be the negative or cathode side, the Emitter will be the anode. Here is a diode drawing Cathode---|<----Anode. This increases the amount of distortion produced by the pedal, it also sound really nice. Try this! Don't leave it out! It's fun. Get your Ge transistors from Steve Daniels

If you want to drill out the LED and install a 5mm big job, change R30 to a 1.2k-3.3k ohm depending on brightness and battery drain you want, replacing the stock 3.9k ohm.

The Boss SD-1
 The Boss SD-1 Super Overdrive is one of the premier Overdrive pedals that's currently being manufactured. It's also probably one of the best overdrive pedals that's ever been manufactured by any company. (In my opinion, it's hands-down the best overdrive bang for the buck!) It's about half the price of an Ibanez TS-9, and it's also quite a bit more durable, especially the switch that controls the JFET electronic switching of the pedal. Here's the description of the SD1 from the Boss website:

 "Provides warm, smooth overdrive tones that respond to your picking style the way a tube amp does, even at low volume levels. Exclusive BOSS asymmetric overdrive circuitry delivers a genuine overdrive effect for a classic guitar sound."

 Believe it or not, the SD-1 actually lives up to the manufacturer's description, and then some! But like most mass-produced effects pedals, there's room for improvement. The manufacturers tend to use the parts that they can acquire the most of for the lowest cost, which usually means that they aren't the best sounding parts that could be used in the circuit, but they're good enough to make a lot of people happy...but we're not those people, are we? HERE is a schematic of the Boss SD1, unmodified from it's out-of-the-box condition. You'll also notice that the schematic has the component numbers that appear on the Boss circuit board...slick huh? The circuit is almost exactly the same as the TS9, with a few differences here and there that make it a little more "hairy" sounding. Also notice the difference in the clipping section of the pedal. The SD1 has asymmetrical clipping, which I believe produces a more natural sounding overdrive. The only reason Ibanez doesn't use asymmetrical clipping is because Boss/Roland holds the patent for it. The SD1 also doesn't have the 51pF capacitor across the clipping diodes, which would otherwise help to smooth out the distortion.

 Now, let's take a look at the modifications that I performed on my pair of SD1s. These mods are based on Robert Keeley's "5-Star Germanium" mods, but I made a couple of changes and omissions. HERE is a schematic that has the changed components highlighted in red. And below is a table that lists all the changes made to the circuit.

  Component Number  Original Part  New Part
  C2  18 nF  100 nF Metal Film
  C3  47 nF  100 nF Metal Film
  C7  1 F Electro.  1 F NP* Metal Film
  C8  47 nF  100 nF Metal Film
  C10  1 F Electro.  1 F NP* Metal Film
  D6  1N4148 Silicon  1N34A Germanium
  LED  3mm Red LED  3mm White Super Bright LED
  R2  470K, 5% Carbon Film  620K, 1% Metal Film
  R6  4K7, 5% Carbon Film  2K2, 1% Metal Film
  R30  3K9, 5% Carbon Film  1K, 1% Metal Film
  U1  JRC4558DD  Burr Brown OPA2134PA
  * NP = Non Polar

  These modifications add a great deal to the audio quality of the circuit. You can get a little creative when choosing a new OPAMP for your SD1. The normal choices are the original JRC4558DD, the Texas Instruments RC4558P, the Burr Brown OPA2604AP, the Burr Brown OPA2134PA, and even the Texas Instruments TLC2272ACP, which is a linear CMOS OPAMP. I chose the Burr Brown OPA2134PA because it's designed specifically for audio applications, and because it's super high quality and low noise. The Burr Browns aren't cheap though... the OPA2134 was about $2.50 for a single one and the OPA2604 is $3.50 for a single one. So here's what we're doing with the rest of the SD1's circuit:

Changing C2, C3, and C8 to 100 nF will increase bass response.
Changing C7 and C10 to 1 F NP metal film will remove some harshness from the circuit.
Changing D6 from a 1N4148 Silicon diode to a 1N34A Germanium diode will help to further increase the distortion.
Changing R2 to 620K will increase the input impedance of the input buffer resulting in more clarity when the pedal is in effect more or when it's bypassed.
Changing R6 to a 2K2 will increase the amount of avalible overdrive.
Changing R30 from 3K9 to 1K will increase the current being supplied to the LED, therefore increasing the brightness of the new LED, but it will also put more of a hurt on the battery, if you use one.
Changing the original not-so-bright 3mm red LED won't do anything for the sound, but putting that 3mm water clear super bright white LED in there will certainly make the pedal look a little more "trick."
  Some Final Points
 If you own an older SD1, there will be a diode and resistor on the circuit board, D3 and R31 (not shown on the schematics), that are connected to the negative pin of the DC power jack. I would recommend that you remove these two components from the circuit board and replace them with jumpers. Doing this will increase the power being delivered to the circuit so that it will have even more "oomph." If you own a newer SD1, then these two components are already replaced with jumpers, so you won't have to worry about them.
Done an' workin'=Too many to mention - Tube addict!


Re: Boss SD-1 mods
« Reply #5 on: March 09, 2012, 08:04:35 PM »
Thanks a bunch renegadrian for that information! Kind of makes you want to buy a bunch of sd-1's and compare the mods!   :icon_biggrin:


Re: Boss SD-1 mod gone wrong - help!
« Reply #6 on: December 21, 2013, 11:31:46 AM »
So, I did Renegadrien's first mod on my SD-1, now when I turn the volume know on my guitar it sounds like a dirty pot (scratchy) and with the volume on 10, the signal cuts out completely. I've tried 2 different guitars that work correctly on other equipment, I've tried 2 new Opamps and no change. It happens with the pedal on or off but works correctly (no scratchy pot or cut out) with a CS-3 compressor patched in front of the chain. I reverted the pedal back to stock and it was ok (I think) then re-did the mod again with the same results.

Thanks for any help u can offer!
Moncton, NB Canada


Re: Boss SD-1 mods
« Reply #7 on: December 21, 2013, 12:19:42 PM »
I still have a long way to go and a lot to learn but
last time this
"now when I turn the volume know on my guitar it sounds like a dirty pot (scratchy)"
happened to me.
RG Keen said I must have DC leakage on the output IIRC
I put a meter on it and low and behold he was right.
I'd start here and check that first. Just my two pence.
Jellybean dodging since 2012.
Smoke me a Kipper. I'll be back for breakfast.


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Re: Boss SD-1 mods
« Reply #8 on: December 22, 2013, 01:21:41 AM »
if ya get that scratchy sound, try cleaning the connections to the pots, and flow some fresh solder on there.
works a lot more than it don't. ;)
"Fuzz, distortion, and wah, are plenty abound. Mutron Flanger, not so much.  8)"


Re: Boss SD-1 mods
« Reply #9 on: July 24, 2014, 01:53:47 AM »
Howdy all. New here and I thought I'd share something. I used a number of these mods on a few SD-1's and recently, after some experimenting, I went to test a pedal, and the output was super weak and it didn't matter if the pedal was on or not. But, the the output would be normal if I ran another buffered pedal (on or off) after it. I'm not a schooled audio electronics tech but I have some electronics understanding from being a schooled auto mechanic and self-taught pedal/tube amp kit builder (full disclosure-I own a small guitar/amp shop next to my auto repair business where I build/mod/repair guitars/amps/pedals). So, having said all that, I downloaded a signal generator app for my iPhone, grabbed my automotive digital oscilloscope, opened up an unmodded SD-1 and started checking stuff out. I figured that since the pedal misbehaved when it was on or off, the problem had to be in either the input or output buffers and, since putting another buffered pedal in the chain after it brought the output up to normal, it was some kind of impedance issue. Sure enough, testing the signal after the 1uf coupling cap (C10) on the unmodded unit showed it at around 0v, where the modded pedal with C10 removed showed the signal at 4.5v. Higher signal voltage equaled lower output. Anyone have any thoughts on this? The amp being used is a Bogner Shiva.
Chris Brandt
Owner GL Garage Guitars


Re: Boss SD-1 mods
« Reply #10 on: July 24, 2014, 12:12:06 PM »
The first part of the note I read somewhere on the net and saved is not about C5 but C6. C5 - don't clip it!!!
Done an' workin'=Too many to mention - Tube addict!


Re: Boss SD-1 mods
« Reply #11 on: October 02, 2014, 09:29:08 AM »
Hi all, I'm new to the sight, but have found it informative in the past.
I had a question about sd-1 mods, one in particular, and that is switchable diode clipping.  I've done this mod on a ds-1, but I'm a little confused with the sd-1.  Would I remove both d5 and d6, and wire my diodes and LED's in series, from each side of the switch, and then run wires to the d6, or d5 slots?  Or remove d4, and wire the switch in the same fashion, with just one LED and Ge diode?
Thanks for any help.