I have a bog standard 80mm case fan on my exhaust which has been running at full speed (don't know what speed as there is no sensor) and is dead noisy. Tried fitting a potentiometer to vary the speed but fan would no run until I got to about about 90% on the potentiometer dial, speed was very hard to judge in the remaining movement. Do I need a special type of potentiometer to control fan speed? Am I better off buying a proper control unit from somebody like CoolerMaster?