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Quieter PSU Modification
Written by David Artschan (19/Apr/04)
Page 1 of 4

Lately, a lot of quiet power supplies have come onto the market, I assume to fill the gap in quietness that silent CPU coolers and low speed case fans left. The only way to quieten a PSU down is to modify it, which seems to scare a lot of people.

Either the existing fan can be removed and replaced for a quieter, possibly temperature controlled fan (airflow and noise vary with temperature) or the existing fan just slowed down, usually by lowering its voltage. This drop in voltage can be achieved quite simply in a number of ways.

The Methods

One way is to introduce a resistor into the fan circuit - this, as the name suggests, "resists" the flow of electrons. While not lowering the voltage strictly speaking, the combination of current flow and the resistor mean less voltage for the fan to use.

Before explaining the following method, I must explain that voltage, although usually measured with reference to ground (zero volts) does not always have to be measured in this way. Another way of describing a voltage is a potential difference between 2 points. So, if we want to reduce the voltage a fan is running at, we can either lower its "live" voltage, or increase its "ground". Both of these will effectively reduce the potential difference across the terminals of the fan.

A computer fan will usually be connected to +12v, and 0v giving a potential difference of 12v. Another voltage available inside a computer is +5v. If we take the positive (live) terminal down from +12v and put it on +5v, the fan will then only see a 5v potential difference, therefore making it spin very slowly indeed, perhaps too slow. A happy medium is to leave the positive (live) wire connected to +12v, and change the negative (ground) for 5v. This will then give a 7v potential difference, spinning the fan at just under its normal speed, making it hugely quieter at the expense of airflow.

I've done this modification to 6 or 7 power supplies now and they have all been just as simple as each other. Personally, I tend to go for 5v but this is not enough to start some fans which will lead to a rapidly overheating machine.

Step By Step Guide

As with all guides, it is highly recommended you read all the way through before attempting anything. Perhaps read through it and then print it out, so you can reference it while your computer is turned off.

Begin by switching off your machine and removing the power supply from the machine. Give it a 5-10 minutes to let the capacitors discharge or you might be in for a shock. Then remove the cover of the PSU - if the power supply has a fan on the outside of the casing, it may be easier to unscrew it first. The cover is usually held on by 4 machine screws, one in each corner. I have seen some with more screws around the base, so if the cover doesn't come off easily have a good look around for any more screws.


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