Parts List

All the parts needed can be bought from Maplins, and should also be easily available outside the UK. You will need:

10k Linear Potentiometer Maplin order code JM71N cost 49p

LM317T Adjustable Voltage Regulator. Maplin order code UF27E cost 49p

1k Resistor Maplin order code G1K cost 1p

4.7k Miniature Preset Potentiometer Maplin order code UH02C cost 19p,

A heatsink: either your own, or a "Universal Vaned Heatsink" from Maplin, order code RN73Q cost 99p

An M3 Nut and Bolt

Some Heat Transfer Compound

A few bits of wire and connectors of your choice. Screw block terminals are Maplin order code FE78K

Wiring Diagram

This isn't a proper wiring diagram, but is meant to be as easy to follow as possible. The chip is shown with the heatspreader side down, and the big potentiometer is shown from the back, and the small one from the front. Wiring them up this way round will mean that turning clockwise will turn them up, and anticlockwise turns them down. The cyan rectangle represents the 1k resistor. Connect your fans up with the green wire taking the place of the normal 12 volt yellow wire.

Yellow wire = 12v input from PSU Green wire = Regulated output Black wire = Common Ground Orange wire = Adjustment voltage wire

Construction

Follow the wiring diagram carefully, and make sure nothing is shorting out on anything else. You will want to put a Molex connector on the input wires, and some sort of connector on the output wires, I suggest a screw block terminal for the output, and pinching a female Molex connector from one of your fans that wont be needing it anymore. Bolt on the heatsink, with a bit of goop between sink and chip. The goop does give a very noticeable improvement. You don't have to buy a heatsink, you can scavenge one from an old power supply, or even stick on a ram sink with some Arctic silver epoxy. But be warned, the metal part of the chip is actually connected to the output leg, so you cant let the heatsink short out against anything, or touch your case chassis.

How you mount the circuit inside your case is entirely up to you, You could glue the whole thing onto the back of a CDROM bay blanking plate, or mount it in a separate box, or make use of a dead CDROM drive. Just remember a sealed box isn't so good for cooling, and with 18 watts of fans, it can dissipate up to 12watts of heat. The suggested Maplins heatsink is fine for the job, if it is open to the air inside the case.

Adjusting the lowest voltage preset is simple. Turn the preset all the way down, and the main potentiometer all the way down as well. The fans should stall when you do this, as they are only being supplied with about 3 volts. Slowly turn the preset up until the fans start up again. This will make sure your fans never stall, and have enough voltage to start up again if they get jammed.

Mounting the potentiometer where ever you want it to go is simple. Just drill a 7mm hole, and use a knife to gouge out a hole for the little locating tab on the body of the pot. Maplins sell knobs to go on these pots, or you can buy ones intended for guitars, and some overclocking websites sell knobs intended for the purpose. I would recommend taking the potentiometer with you when you go shopping for a knob, to make sure it fits properly.

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