How to slow down the CPU fan?

[Dida]

I have an old machine that I would like to use as a server + video clip player. The only problem is that this old thing is extremely noisy. I counted 6 fans inside the case, they are:
- 2 fans in the power supply
- 2 case fans
- 1 cpu fan
- 1 video card fan

I plan to do the following to quiet down this machine:
- unplug both case fans
- set video card fan to 25% and downclock video card appropriately
- downclock CPU by about 40%, and slow down the CPU fan

Now I noticed that the CPU fan is connected to a +12v line (red), and has 3 pins, so fan speed cannot be adjusted. I think I should either cut the 12v and ground wire and connect them to a 5v source, this should slow it down considerably. Or, I can purchase a quieter/slower fan. What size fan should I get? Both heatsink/fan on the CPU now are stock AMD Athlon64. I think the appropriate fan would be 80mm? Can I fit a bigger fan on the stock heatsink?

A search on newegg only turned up 1 CPU fan (with no heatsink), but there are lots of standalone case fans. Are they basically the same?

 

[Genocidicbunny]

You can put a resistor in the line to the cpu fan. This will lower the supply voltage to the fan slowing it down. If you have any soldering skills you can probably make yourself a nice DIY cable for cheap.

Now, whether or not you can use a regular fan depends on the mounting mechanism. Pretty much all modern heatsinks worth any consideration have a way to attach plain old case fans. It might be through a fan clip or through screw holes for the fan. You need to check how the current one is connected and go accordingly.

Lastly, make sure your cpu wont mind the decrease in airflow. If your temps are in the high 60's at load, a decrease in the fan speed may push the temps to above 80C which is a very bad idea.

 

[Dida]

I have done it! I cut the wires to the CPU fan and hooked them up to the 5v rail instead of 12v, now it goes at about half the speed. The computer is substantially quieter now, although I can still hear the PSU fans. I guess there is not much I can do about those. Maybe I can disable 1 of the 2 fans by sticking a pencil in there to prevent it from moving.
CPU temp is good. It used to be 40degree idle, now it's about 48 idle, I bet it will be in the 60s under load. Which is hot, but probably not enough to cause damage.
The real concern is with the video card. With the fan turned down to 25%, its running at 60 degree idle. I will try to downclock it a bit more and up the fan speed slightly.

 

[Genocidicbunny]

60C idle for a video card isnt too bad. Id be more concerned if the load temps were in the high 90's.

As for the PSU fans, dont touch them. The PSU has those fans for a reason. You stop one of them and the PSU may get damaged by the heat produced.

 

[Turner]

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