Kiwi Quiet P4 Cooling

Do-It-Yourself Systems
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December 20, 2004 by Peter Scott

Peter Scott is a computer consultant who works with computers much of the day in a quiet home office environment, an eco-inspired earth house with amazing acoustics. He writes from Auckland, New Zealand about his efforts to quiet a noisy P4 2.66A box. His article is another saga of experimentation and inventiveness that seem to be requisite for a successful PC silencing project. Peter also shows us yet another variant of the HDD anti-vibration decoupling suspension technique we espouse; he would probably say it's part and parcel of Kiwi make-do ingenuity. It's also reminiscent of the first year of SPCR when DIY project article submissions were the norm, not the exception. I expect this article will inspire those who live in places where the latest "silent" gear is not available.

Mike Chin, Editor / Publisher of SPCR

I approached the task of quieting this noisy office PC by tackling each of the four noise sources in turn. It turned into quite an incremental approach, chipping a bit of noise off here and bit there, until no one source really stood out and the overall noise level was very tame. It took several weeks, surprisingly.

Firstly I ordered an all copper heatsink, the Thermaltake Golf 325, which was available locally for a reasonable price. My criteria for the CPU cooler were:

  • must be able to fit 80mm fan,
  • no more than NZ$50 and
  • be efficient enough to run on a slow fan.
  • It's shown below complete with some homemade rubber fan mounts.

I ditched the supplied Thermaltake Smartfan because it has a real growl of a rumble at any speed. I guess its strength would be in overclocking, etc., as it spins up to 4500 rpm. I couldn't locate any NZ sources of either Papst or Panaflo L1 fans, but did track down a supply of 80mm SilenX thermistor controlled fans. These are quiet, and seem to have good build quality, but more about these later.

So with the parts arrived, I gutted the box, and set about improving the ventilation into this particular case. Something you might know about NZers is that we do things on a shoestring, using bits of whatever we have around. The case has survived a number of upgrades, and, due to its vintage, was in serious need for some more air flow. I enlarged the lower front air holes, and created air holes at the upper rear where none previously existed. In hindsight I should have cut these out completely and used wire grids, but I was being cautious about RF pollution. Note the soft silicone rubber mounts, and sundry other case holes taped over to preserve the thermal chimney effect.

As for the PSU, I couldn't locate a NZ source of Seasonic or Nexus gear, and thought I'd have a go at modifying the existing PSU. After taking the top off the PSU and fitting one of the SilenX fans using the supplied silicone mounts, I figured the thermistor should go near the heatsinks but out of the main airflow. After firing the modified PSU up, initially it ran quietly but the new fan quickly rev'd up due to the inherently warm environment of a 65% (in)efficient switching PSU. 

For all the manufacturers raves about silence, the SilenX fan certainly didn't sound too silent to me. It was only after reading some more that it dawned upon me that so called silent fans aren't really that much more quiet for a given airflow, they just tend to run slower and hence more quietly. (See graph at  www.cpemma.co.uk) The SilenX 80mm starts off at about 1400 rpm and tops out at around 2400 rpm. So I sorted through my old fan collection (which comprised mostly of a bunch of plain old garden variety case fans) and basically tested each one for a) starting reliably at 5v, b) absence of vibration and "rumble", and c) decent airflow at 12V.

After concluding that the SilenX themistor wasn't really much use, with a quick snip it was lopped off. I determined with a multimeter that it has about 11K ohms resistance when cold, and about 1K when hot. So I soldered on a 10K resistor and — lo! — a permanently silent, albeit low airflow fan.

Unsatisfied by this lack of control, I found a simple fan controller circuit on the web (www.cpemma.co.uk/ef.html) which has only 5 parts. I threw that little circuit together, and mounted it on an empty PCI slot hatch. Our local electronic parts retailer had these rows of header pins which when you snip a pair off and solder them onto the circuit board, fit most fan socket connectors quite nicely. Here's the finished result.

The fan voltage varies between 5V and 11.3V, and it will cope with 40W of fans! The cable pair at left is the incoming 12V power which comes from a Molex adapter.



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