SD-1 uses 3 silicon diodes for gain,has a different tone stack(Mids are different)...The SD-1 is more aggressive,crunchy,and not sweet like the Tube Screamer....They are circuit close,but they don't sound or act the same stock....
The TS has less gain,is warmer and sweeter sounding,not as bright,not tight and crunchy like the SD-1 and the TS almost compresses when you dial the drive knob up...
John