turn chained effect on and off with knob

howdy there fellow midi freakz)))))

its been a while since i was last on this community ........ and since i last played with my midi toys and traktor

now i want to get back into the condition and want to do some mapping modifications to my setup.

basically the trouble is this: i want to assign a knob that when turned up to do both the effect on and the amount of effect (chained). so when i turn up the knob, the effect is on and the amount rises, when i bring the knob down to -infinite the effect turns off.

what i have succeded is to turn the effect permanently on, but how to turn it off?

i know it must be something simple but i cant figure it out, damn........ please help