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BOSS SD-1 Super Distortion

Boss SD-1

General information:

The Boss Super Overdrive SD-1 has been sold from 1981 until now. The production was started in Japan and continued there until about 1990, when Boss moved their production line to Taiwan in order to increase productivity.

This pedal has found its way to the favour of many guitar players, propably due to its excellent price-quality ratio - the sturdy and durable iron cast shell combined with excellent sound at a very affordable price is a very welcome packet to many musicians. During its history countless famous artist have used and endorsed this pedal, among them Eddie Van Halen, Jimmy Page, Zakk Wylde, John 5 (Marilyn Manson), Jonny Greenwood (Radiohead) and Adrian Vandenberg (Whitesnake) just to mention a few.

The Super Overdrive SD-1 is, as already its name indicates, an overdrive pedal that is designed to ”overdrive” the signal resulting in moderate, soft clipping of the signal and moderate distortion - it is not suited for over-the-top hi-gain death metal type distortions. The controls are simple and straightforward - Volume, Drive and Tone. The Drive control range is nevertheless rather large and enables a large soundscale from mild clean boosting to quite raw distorted rock sounds. Even with the drive control at its maximum the sound remains compact, crisp and distinguishable, with plenty of sustain and attack. The noise remains moderate but starts to grow at larger Drive settings. The pedal is at its best at moderate gains - it serves excellently as a booster and helps to push a fairly driven tube amplifier into smooth sustain and ovedrive. For a metal freak this pedal will not offer compact and tight enough sounds as such, but in combination with another distortion pedal this pedal can offer excellent added drive for solos or punchlines.



Many times you hear rumours about how the older Japanese versions of the effects pedals are superior in sound compared to their newer, Taiwanese counterpart. In my comparison I also opened the boxes the compare the circuit boards and components with each other to see if there are any differences which might explain differences in sound - if there are any. So here's my conclusions:

On the outside the pedals are almost identical. The differences between the Japan and Taiwan versions are practically only on the label on the bottom. A peek inside the pedal reveals that the electronics and the circuit boards are very similar, but not identical. The used operational amplifier JRC4558DD is the same in both pedals, and is actually quite similar (only slightly larger gain) to the opamp used in the famous and sought after TS-808 Tube Screamers.
A closer inspection nevertheless reveals some differences. The circuit boards are made of different material, the older one being dark brown, whereas the never ones are significantly lighter. Many capacitors are completely different and from different manufacturers, some of the transistors are from different manufacturers and are of different type and the resistors in Japanese version are larger than in the Taiwanese version. The components used in the Japanese version seem to be high quality components and thier assembly is accurate and clean, whereas in the Taiwanese version the legs of the components are bent unevenly and the solderings are less consistent, maybe due to cost savings in the mass production lines. It is impossible to tell how much these differences affect the sound of the unit, but it is obvious that there are many differences inside the pedal that could potentially make a difference also soundwise.
  Boss SD-1 Japan Boss SD-1 Japan Boss SD-1 Japan Boss SD-1 Japan Circuit Board Boss SD-1 Japan Circuit Board  
  Boss SD-1 Taiwan Boss SD-1 Taiwan Boss SD-1 Taiwan Boss SD-1 Taiwan Boss SD-1 Taiwan Circuit Board  


Due to it's affordable price, robust and durable enclosure, simple schematic and clean and neat circuit board layout, the SD-1 is an ideal playground for both beginners and experts in electronics to unleash their creativity and play around with the multitude of soundscapes achievable by simply exchanging opamps, clipping schemes and various component values on the circuit board. This has also been unitilized by many professional companies offering various modifications to enhance the sound and add versatily to a factory born SD-1 unit. Most of the modified units contain an added switch to choose between different clipping methods like symmetric/asymmetric clipping, different diodes (germanium, silicon), leds, etc...

Here's just a tiny glimpse at some modified versions readily availiable.


The Monte Allums modification takes the SD-1 soundwise towards the sound of the original Ibanez TS808 Tubescreamers by replacing the opamp with a JRC4558D chip similar to the ones used in most of the late seventies/early eighties Tubescreamers). Also the clipping section has been modified with a toggle switch to choose between asymmetric (as in the stock SD-1) and symmetric clipping (as in the Tubescreamer). The clipping diodes have been replaced with 1N4002 rectifier diodes and many component values have been changed to similar values used in the TS808. The LED has been exchanged with a very bright blue one.
  Boss SD1 Monte Allums mod BBoss SD1 Monte Allums mod Boss SD1 Monte Allums mod Boss SD1 Monte Allums mod  

KEELEY 5-STAR MOD (Stacked mod)

The Robert Keeley version of the SD-1 has several modifications, the opamp has been replaced with two TI RC455P ICs in parallel (stacked) for clarity and noise reduction. A mini-toggle switch is added to choose between different clipping diodes - germanium diodes for a more compressed and distorted sound or a LED for a more open and dynamic sound. The clipping is asymmetric in both modes, which resembles a more tube-like clipping. Switching between the two clipping modes has a noticeable change in volume level, which can be easily compensated with the Level setting. The bypass circuitry has been improved to minimize signal bleed through in the off position, the led has been replaced with a blue one and many components have been replaced.
Soundwise this mod offers a tight and punchy sound with added dynamics and clarity.
  Boss SD1 Keeley mod Boss SD1 Keeley mod Boss SD1 Keeley mod Boss SD1 Keeley mod  


Uraltone is a rather small company located in Finland, and has amongst many other services also offered modifications for some standard effects pedals. The Uraltone SD-1 modification has an added toggle switch, which lets you chose between asymmetric clipping (two diodes one way, one diode the other) or symmetric clipping (one diode in each direction). The symmetric/asymmetric clipping affects the amound of even add odd harmonics created in the distortion, thus greatly affect the overall tone and construction of the sound. In the Uraltone modification one of the clipping diodes has been exchanged into a LED, which also affects the sound achieved.
In addition to the modification of the clipping section, the Uraltone modification has also many other changes in component values and quality. The frequency response of the pedal has been altered to boost certain frequencies (especially low frequencies) and the Tone- and Drive- control ranges have been increased to achieve very strong distortions, but at the expense of increased noise.
  Boss SD1 Uraltone mod BBoss SD1 Uraltone mod Boss SD1 Uraltone mod Boss SD1 Uraltone mod  

  Mild overdrive
Effect settings: Output 5 Drive 3 Tone 5
Medium overdrive
Effect settings: Output 5 Drive 5 Tone 5
Heavy overdrive
Effect settings: Output 5 Drive 9 Tone 6
Clean Samples Sample #1 (Overdrive off) Sample #2 (Overdrive off) Sample #3 (Overdrive off)
SD-1 Japan Sample #1 Sample #2 Sample #3
SD-1 Taiwan Sample #1 Sample #2 Sample #3
SD-1 Keeley Stacked mod (LED clipping) Sample #1 Sample #2 Sample #3
SD-1 Keeley Stacked mod (Germanium diode) Sample #1 Sample #2 Sample #3
SD-1 Monte Allums (switch left) Sample #1 Sample #2 Sample #3
SD-1 Monte Allums (switch right) Sample #1 Sample #2 Sample #3


All the tested units are good and useable units, although they will most likely not as such fulfill the overdrive/distortion needs for most guitar players. It serves very well as a booster or a slight overdrive to enrich the sound or to cut through the mix during a guitar solo, and considering its price it has an excellent price-quality ratio.
Of course there are plenty of other modifications out there too, and the SD-1 also serves as an excellent and affordable playground to make your own tweaks and modifications as well.

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