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Re: Boss SD-1 Super Overdrive

11/1/2004 10:34 AM
Mark Hammer
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Re: Boss SD-1 Super Overdrive
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 www.tonepad.com and looking at the Tube Screamer project shown there. It includes the option to configure it like an SD-1 or TS-9.

 
Replies:
Ben N Check here for mods:fuzzcen... -- 11/4/2004 12:34 PM