The orange Boss DS-1 distortion pedal has been around since 1978. With one tone knob, one level knob, and a distortion knob, it can produce sounds ranging from a thin, light distortion up to a heavier harsher sound.

The DS-1 was used in songs such as Nirvana's "Smells Like Teen Spirit" and by guitarists like Joe Satriani and Grunge McGurgan from Delayed Reaction, who use it mostly as a booster. The DS-1's thin distortion is not great, you will get a used DS-1 much cheaper than one of the original Ibanez Tubescreamers. However some guitarists, like Steve Vai, used a customized DS-1 with Robert Keeley's Seeing Eye or DS-ULTRA modifications.

If you want to pick up a used DS-1 and try out the Keeley DS-ULTRA mod, James Haskin has made a step-by-step guide to show you how. You will need some electronics skill as the modification process involves replacing 3 resistors, 4 capacitors, and an LED.

Link: Modifiy a Boss DS-1 using the Keelye Seeing Eye and DS-ULTRA mods