To add to that, the Mxr M77 is basically an sd-1 clone with less noise and greater versatility. It has a 100Hz knob and a "bump" switch that reconfigures the eq to more of a bass and mids curve. Same asymmetrical clipping as an sd-1 though, which comes across as a little more "grindy" and aggressive than a tubescreamer. I have one of them and use it more often than my Ts-9. There's not a huge difference, but it's noticeable.