3A is crazy for a VR..even 1A is tough for cheap transistor circuits, even then they need heatsinks  Look in your PSU if you don't believe me-those are costly, EFFICIENT transistors-power MOSFETs to be precise, and they still need heatsinks (though they handle like 20x more current than the cheap transistors we get at the electronics shop).

Most resistors can handle 1W output across the resistor, VRs are notably lower. Quick estimate calulation-5V on fan means 7V taken over on resistor..whole circuit probably pulls 0.5A when fan is spinning slowly at 5V..comes to about 3-4W on the VR-sizzle  .... VRs probably only suitable for fans drawing well below 1A when at full speed, at 5V probably only 0.1W so VR can probably take it. No way to know till try it out..guess have to redouble efforts to design & build transistor (<1A) or PWM switching (1-3A) controllers..sigh..thought it would work..didn't have time to do the calulations earlier..forgot that most of the noisy fans needing fan controllers pull 1A++..

edit:
Oh btw, I've heard that fans can still not spin if PWM is set to too low a speed. Fan just vibrates in place...pulse not long enough to give power to turn..

No le...just happen to be studying electronics as part of my physics course..also like to mess around. Anyway I'll try building it first, then I'll get back and give my results..dunno where to find time to do it also..exams coming soon  . Basically need an adjustable timing circuit (can rig a 555 circuit 4 a few ringgit) to give pulses to switching MOSFET or JFET which will act as an electrially controlled power switch turing on and off hundreds/thousands of times per second (FET-field effect transistors, sounds cool, but they're still just basic transistors, not some fancy energy thingy). The longer the switch is closed compared to when its open, the faster the fan will spin. Have parts for the timing circuit already, will try these few days when free, but need to do research on FETs (gotta dig up them datasheets-sigh, easy to find low Amp mosfet, but tough to pick good ones) before I rig one to the timing circuit.

agreed...

too technical already.... halfway thru ur paragraph i got so blur i could barely see the words

anyway...concentrate on ur exams first... then later screw around with the controller. all the best with exams dude

I'll give it a shot, probably this weekend I'll get back to you, hopefully end of this month I can figure out how to make enough to sell  . Should be quite cheap, probably way below RM100 for a multi fan control. Thinking of a way to make system monitors also (rpm, temp, voltage), already know how to make the circuit, just a matter of trying out & improving the circuit for better accuracy.

lowenhi, i just did some calculations.found out that connecting the potentiometer in parallel with the load cant do the job..any other wat to do a fan controller which maintains the voltage but varies the current w/o using PWM?

forget what i posted earlier shawty..i had a little misunderstanding of the concept..

hey..how about my CM XDream III???
any idea how to increase the speed from 2k to 6k???
i dont care the noise anymore..
my case is sound proof

Got all the stuff to built the PWM controller..hehe..stay tuned..also some stuff to build a PSU tester/loader..

Sorry it took a while, and sorry for such a short post (may consider I'm spamming, but in a hurry-PC down, so have to go CC)

hehe thanks..
b4 tht i tot everything is safe and easy to handle.. becoz just a small smaal fan.. runing 12V DC also (i think its little). Haha proof tht i was wrong  lolz

better just leave it.. dont play too much with it, as long as it can run then ok ledi...

use the power from ur molex as usual from the +12v (yellow wire) line..

as for the fan's ground...take the ground from ur 20/24 pin cable on ur PSU.

use any of the "-" line as ground...just choose which one u want...

eg.

+12v & -3.3V will give u 15.3V.
+12v & -5V will give u 17V.
+12v & -12V will give u 24V.

take note that ur fans WILL die sooner.

salute to me for wat??? salute to shah81 la....

he mentioned it before here...its just that i remembered what he said

I need to do some correction for you, there is NO -3.3v line, only a +3.3v line..
Might as well I give the full list

one thing i not so clear, how we estimate the fan speed after undervolting it at 7v or 5v... sry for noob question, kinda lack of knowledge bout this....  

may i know where can i get this item?

i think change the transistor in the fan's electronis board....then the fan will spin very fast