Don’t do this:
Do this (from the tech note I posted just a few posts below the bad design 
; the right opamp is unused):
This works if you have a split supply; for single supply designs you have to construct a mid-supply rail (see the tech note for how to do that).
(also, as noted elsewhere, there’s no noticeable difference between TL074 and TL084 so if you have the former, you don’t need to buy the latter. But whichever you use, don’t leave the unused opamps hanging…)