There are two systems components that traditionally undergo volt-modding: mainboard (Vcore, Vdimm, sometimes Vagp, Vdd, Vio, and certain model-specific modifications) and graphics card (Vgpu, Vmem, sometimes Vref, Vddq, OVP). Besides these two, you can also volt-mod the Power Supply Unit (PSU) of your computer. A simple modification allows controlling the basic voltages (3.3v, 5v and 12v) of a majority of existing PSUs.
Few off-the-shelf PSUs offer you such control over the voltages. I could only name certain hi-end units from Antec (like the TrueControl 550), PC Power & Cooling, OCZ Technology and SOYO. However, even such units would only become better from some additional tweaking, as their standard voltage ranges are rather narrow.
Why Would You Want to Mod Your PSU?
Some people at Internet forums wonder why PSU modification is necessary at all. What does it achieve? Here’s my answer.
As always, overclockers were the first to express the need for increased voltages. A higher voltage on the +3.3v power rail is the most useful in this respect. As you know, an overwhelming majority of modern mainboards generate the voltage for the memory slots out of the nominally closest voltage as defined by the ATX standard, i.e. 3.3v. The mainboard’s BIOS usually does not allow setting Vdimm above 2.9v; only certain overclocker-targeted models, mostly from ABIT and MSI, provide a wider range. However, after a modification of the appropriate control element (a traditional Vdimm-mod, available on all mainboards), the ceiling rises up to the level of +3.3v as actually outputted by the PSU. And if a cheap Codegen unit bottoms out to 3.0-3.1v under a small load even, you cannot get 3.3 volts on the memory slots with it. Thus, the overclockability of the memory worsens. Moreover, certain memory chips (particularly, Winbond BH-5 – and that’s already enough J) show a frequency growth proportional to the voltage without any limitations. 3.5v is normal enough for BH-5 chips, and you can get higher if going for a record result. So, a modification of the 3.3v voltage is going to amplify eventually the effect of the Vdimm mod.
The 5v power rail affects the overclockability of graphics cards that get their power from the Molex connector. You can’t expect much here, but extra 10-20MHz can sometimes be pocketed. Besides that, a low voltage on this rail negatively affects the CPU overclockability, especially with Socket A models.
As for any uses for a higher voltage on the +12v rail, I can’t think of any. The fans would rotate a little bit faster, but the HDDs would also heat up more. I don’t think you’ll notice any great difference between 11.5v and 12.5v.
On the other hand, the mainboard and the graphics card do receive electricity from these +5v and +12v lines to power a ton of components. Even if this is not obvious in terms of frequency growth, high and stable voltages have a definitely positive effect on extreme overclocking at large.
Well, not all of us take to extreme things. The other traditional overclocking ideology implies saving money by overclocking cheaper parts to the level of more expensive ones. Fortunately, no one is now buying a no-name system case with a preinstalled 250-300W PSU on the money left from the purchase of other hardware, but anyway – a PSU cheaper than $30-40 cannot be absolutely stable in a modern computer system. It’s impossible to save on components (there are Codegens that sell for less than $10!) without losing in quality. If a PSU belongs to the lo-end class and/or works at the limit of its capabilities (the system consumes almost as much power as the PSU can output), you can’t expect stable voltages. In the best case, there will be fluctuations, in the worst and widespread one – the voltages will drop down below their required nominal values under a load (in games or benchmarks). This situation can be amended with the proposed modification, too, as you can adjust the voltages to the required levels.