Courtesy of Lazzer408 from Techpowerup!!
I personally don't want to spend 20 USD on fans that include PWM and are minutely quieter. So, I just went with Koolance fans. 9 Bucks, can't beat that. I bought 10 of them. http://koolance.com/fan-120x25mm-108cfm
For this project you will need soldering iron, flux, and solder, solder wick and decent soldering skills. I recommend helping-hands and a vice, and a magnifying glass with LED lighting. (But that's overkill)
This guide will show you the simplest way to PWM control up to 10 fans safely, (or about 3 amps). 11 amps on 18 gauge wire is the recommended maximum for molex connectors. Proceed at your own risk. (Looking at you Delta Fan owners and lovers)
Here are some references before we get started:
Pin Outs and Power
Parts List and Links to Purchase
5.1v Zener Diode: http://www.mouser.com/ProductDetail/Vishay-Semiconductors/TZX5V1A-TR/?qs=sGAEpiMZZMtQ8nqTKtFS%2fC7KvLOwmmQCtCYT1%2fs1PtE%3d
10k Ohm Resistor: http://www.mouser.com/ProductDetail/Vishay-BC-Components/PR01000101002JA100/?qs=sGAEpiMZZMsPqMdJzcrNwiCREInfUjhCku0gD%2fN6gQU%3d
N Type MOSFET: https://www.radioshack.com/product/index.jsp?productId=13339909
(Best, I'd recommend a heat sink....
TO-220 heatsink for nte2985: http://www.mouser.com/ProductDetail/Wakefield/274-1AB/?qs=sGAEpiMZZMttgyDkZ5Wiuita4PD18Ap7e0ZyfdsUPiE%3d
Solder Board: http://www.amazon.com/gp/product/B0073XD90K/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
4 Pin Fan: http://www.moddiy.com/products/4%252dPin-Male-Fan-Connector-%252d-Black.html
3 Pin Fan: http://www.moddiy.com/products/3%252dPin-Male-Fan-Connector-%252d-Black.html
Molex Female: http://www.moddiy.com/products/4%252dPin-Molex-Female-Header-Socket-Connector-for-PCB-Mounting.html
When making your runs, please use 22-24 gauge wire. Solder runs are fine, but may not hold up to the amperage. Solder joints also tend to crack very easily.
So, the first thing I did was space out my components and connectors in a nice, semi-tight area. If this is your first time ever using a soldering iron, I would use the full board to get used to routing wire and give yourself some room to play. Components are cheap, buy a few of them.
The schematic is as simple as it gets. Be sure to route gate between the zener and resistor. This is for PWM.
So, all completed. If PWM IS NOT CONNECTED YOU SHOULD RUN AT FULL SPEED. (12v)