The ps3 fan runs off of a 12v line and ground but it has a third line the PWM line. This is the line to control the fan speed. 3,3v will set the fan max @ 12v. When you add a potentimeter in between the PWM line and a 3.3v line you get a fan controller of atleast a simpler version of it.
Now with that being said, you should be able to add a resistor between a 3.3v( easiest i found atleast on slims is on psu) and the PWM line of the fan to get whatever speed your looking for. now as for how to find your resistor value depends on what speed you want your fan on. The closer u are to the 3.3v the higher it will be and the lower voltage you go the lower the fan speed. just remember you are overriding the main fan controller. And curious as to why not just add a variable?
