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Boss SD-1 Super Overdrive

10/29/2004 3:23 PM
Gord Boss SD-1 Super Overdrive
Does anyone here have any experience with one of these? How does it sound? How does it compare to a TS-9?  
11/1/2004 10:34 AM
Mark Hammer

As a matter of fact, there's one on my bench.  
It's a nice pedal that essentially differs from a TS-9 by one diode. The inclusion of an additional diode in the feedback loop does a couple of things.  
First, it results in more clipping for one half-cycle of the input signal than it does for the other, once you get enough drive. That latter phrase is important. For both the TS-9 and SD-1,there ought to be no audible difference if the drive is low enough, since the signal will be below the clipping threshold (roughly 500-600mv) much of the time.  
Where you notice the difference is with drive levels and input signals that exceed that clipping threshold. Pick harder or set the drive a little higher (or both) and the pedals start to pull apart. Where the TS-9 will clip BOTH halves of the input signal (positive and negative half-cycles), the SD-1 will clip one half cycle, but not clip the other unless the drive or input signal are higher.  
This results in a slightly different array of harmonics much of the time. Some describe it as asymmetrical, and while asymmetrical clipping IS more in the direction of what tubes do, I would simply suggest this is a different sort of tone rather than suggesting the SD-1 sounds more "tube-like".  
The second difference is that the SD-1 has a little more dynamic breathing space than the TS-9 *because* of the fact that one half-cycle of the input signal is hard-clipped at 500-600mv while the other half-cycle is allowed to go higher than that (twice as high, given that there are two diodes in series). So, some players wil say they find the TS-9 too compressed sounding, compared to the SD-1. The reality is that they can both sound very compressed if you push them hard enough, but the SD-1 manages to retain a little bit more capacity to let harder and softer picking be heard as louder and quieter over a broader range of drive settings and input levels.  
The third difference is that with the same amount of drive and input level, the SD-1 is capable of being a bit louder than the TS-9 over a broader portion of drive settings.  
I built myself a TS-808 clone but included a pot in series with one of the clipping diodes. As the pot resistance is increased, the clipping for one half-cycle of the input becomes relaxed and the pedal starts to resemble the SD-1 more. What you notice is more output volume and a little more dynamic sensitivity. If you are curious about these beasts, consider picking up any cheap TS clone like a TS-10, TS-5 or TS-7, and adding in a third diode. It's a very easy mod to do. For now I would recommend going to and looking at the Tube Screamer project shown there. It includes the option to configure it like an SD-1 or TS-9.
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11/4/2004 12:34 PM
Ben N

Check here for mods:  
There is also a recent LONG thread around here that is mainly about IP issues, but in which Brian of posts a mod which he claims makes the SD-1 sound like a Fulldrive II.  
Right now this is my favorite OD (this changes about 1x/month :)), because it is matching up so well with my current favorite amp, a vintage Ampeg Jet. Played an AS120 through them this mornng, and it sounded so wicked good I almost deluded myself into thinking I had gotten better. I was late for work.  
I agree with Mark that the distortion sounds a lot better than the TS, but it is still similar in that (a) it is really a lead pedal, the eq contour is not suitable for rhythm--too nasal sounding, and rolling off your guitar volume will clean it up somewhat, but the lack of bass will really be a problem, and (b) it sounds best when it is pushing the input of a tube amp that is already at its sweet spot. I also think it works better with heavier strings (I use .11s on Fender style guitars, and .10s on the AS120, which is a bassier guitar). So it is not that versatile, although used this way I think it sounds very good pretty much through the range of the distortion and tone controls. It is really a blues or alt-country (think Eagles) pedal, and if you have other distortion needs get other pedals.  
My only gripe with it is that it is somewhat noisey, which is noticeable even on moderate setting and with humbuckers when you stop playing. This should be easily improved, though, by substituting some metal film resistors and a better opamp.  
The common mods for it are to (a) change it to a TS-808 (why??? to each his own, I guess), (b) flatten the frequency response to get rid of the nasal sound (this makes it rather like a Bluesbreaker), (c) increase gain, and (d) improve noise/fidelity. None of these are terribly difficult to DIY, and are also done by the usual suspects (Keeley, AnalogMike, Brian W., et al) if you prefer to pay for it.  
These little yellow guys are pretty cheap, too.  
11/5/2004 1:17 PM
Mark Hammer

I wouldn't say it sounds better, just different. That's why I made my own TS-copy with the option to select EITHER tone. They each serve a purpose, depending on the role being filled. For instance, the TS-808 compression is helpful for keeping a more constant level for rhythm or quasi-rhythm work. Conversely, the slightly greater dynamic range of the SD-1 may be better suited to more expressive rhythm work, where your goal isn't to stay out of everyone's face.
11/6/2004 10:42 PM
Ben N

Sorry, that other thread was at diystompboxes (Aron's), not here.
11/16/2004 12:11 AM
Sean K

I'm just getting into this stuff,etched a TS-808 board this morning complete with flip flop setup,and put a space in to switch diode trains from Si to Ge and also switch symmetry for asymmetry and I'll be able to put a pot in series in there too and create a voltage divider between the diodes and the drive control,great idea Mark,but I'm wondering how the diodes actually work.Si cuts at .6 and Ge cuts at .33 or should I say drops.So two Ge's in series drops at .66 which comes out about equal'ish to Si.  
Without getting the scope out and putting the final power cord on the signal generator,which of course I should do but I'm so busy at the moment and haven't the space either,what exactly goes on as the signal goes through the diodes and how does this work at the opamp input.I've mostly got the idea of how they amplify and cut bass or treble in that more resistance in the feedback loop lowers the signal at the input by ampimg the difference and also how taking treble out in the loop amplifies that but how do the diodes work?  
With what I've already said I'm surmissing that only the peaks above the cut get through the diodes and when summed with the ingoing peaks then this is what gets taken out.Am I on the right track?
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