Power Supply Unit Voltmodding Guide

There are two systems components that traditionally undergo volt-modding: mainboard and graphics card. Besides these two, you can also volt-mod the Power Supply Unit (PSU) of your computer. A simple modification allows controlling the basic voltages of a majority of existing PSUs. Read our Guide for more details about this procedure.

by Kirill
09/17/2004 | 01:42 AM

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.

PSU Working Principles

Yes, the power supply unit has nothing in common with the graphics card or mainboard, but the volt-mod concept remains the same anyway.

The power scheme includes the so-called feedback circuit, which informs the generator element about the real voltage level on the powered device. If the voltage in this feedback circuit is somehow below the required level, the PSU (or the power circuit on a PCB) automatically returns it back to the norm. Volt-modding decreases the voltage in the feedback circuit by attaching an additional resistance (the feedback circuit is connected to the “ground” though a resistor). The PSU increases the feedback voltage to the necessary value, increasing the real voltages in the main circuits on the way.

Graphics cards and mainboards have chips that control the voltages and each chip has a separate feedback contact. The so-called sense wire serves the same purpose in PSUs. Sense wires are additional wires that go to some contacts of the 20-pin ATX connector. They transmit the same voltage as the main wires, but the PSU uses only the sense wires to keep track of the voltages. Sometimes the modification I propose is called Vsense mod, but I think “sense wire mod” sounds better and more logically.

Disclaimer

This guide is a description of hardware modifications successfully made to the construction of the device by the team of ModLabs.net. We tested each mod for operability and found it valuable. However, we cannot promise you that you will be as successful. We don’t accept any claims concerning damage to your device after the modification – such problems imply your own mistakes in the modification process. The author and ModLabs.net are not responsible for any damage inflicted by repeating of what this guide describes.

Warning! Volt-modding, if recognized, makes all warranty obligations void. So you should do everything neatly to be able to unsolder all back again in case of the device’s death.

You should take up volt-modding if all of the following is true:

Tools and Components

To do the mod, I need:

As mentioned above, the mandatory requirement says the PSU must have sense wires. Alas, if you’ve got a very cheap or two-or-three-years-old unit, you have a big chance of finding no feedback circuits at all. For example, the above-mentioned Codegens (at least, the three samples I use as stands for my bookshelf) have no sense wires, and thus cannot be modded. This is the worst case.

The best case is when you have three independent sense wires for all the three power rails. If your PSU cost you less than $80-100, there’s a little chance for that. I can only think of Antec, who equips its TruePower series cases with such a feedback circuitry. Brands like PC Power & Cooling and OCZ Technology can afford such solutions, too, since quality is more important for them than manufacturing costs. I also saw such a scheme in PSUs from Sweex (Gold Series 650W) and Antec’s OEM units under the CWT brand (the 550W model, to be exact).

PSUs from Sirtec that are selling under a score of different brands including Thermaltake and Chieftec, have one sense wire on the +3.3v circuit and control the circuits independently. That is, making the proposed modification you can only control the +3.3v rail, while the other two rails will be working independently, without any control on your side.

Some manufacturers use a scheme with two sense wires, one of which is responsible for +3.3v, while the other controls the two remaining circuits at once. That is, increasing the voltage on the +5v rail will result in a similar increase on the +12v rail.

Lastly, there is a scheme with one +3.3v sense wire that is used to control all the three circuits at once. This is the most inconvenient, but the cheapest solution from the ease-of-realization point of view. That’s why you are most likely to see it in cheap PSUs. Well, that’s anyway better than nothing!

Modification

The illustrations refer to the TrueControl 550 unit, which has all the three wires (the “best” case). I didn’t do mods for the +5v and +12v rails since the regular voltage ranges permitted setting them to +5.35v and +12.42v, which was enough for me. I found the maximum of +3.42v on the +3.3v rail rather insufficient, though. So, I will perform this mod as an example. Everything is going to be exactly the same with any other PSU.

I hope you are experienced enough for the following warning to be unnecessary, but anyway: before following any of the instructions below, detach the PSU from all the devices (mainboard, graphics card, drives and so on) as well as from the power source (by physically removing its plug from the wall outlet).

Let’s start by seeking out the sense wire. It’s simple. The necessary wires are at the sides of the ATX connector: the +3.3v orange wire on one side, and the red and yellow (+5v and +12v) wires on the other side. As you see, not only thick power wires come out of the ATX connector, but also thin wires of the same color. We need these thin wires. The thin orange wire is the sense wire for the +3.3v power rail.

You choose a location of the cut that’s convenient to you. I, personally, preferred making it inside the PSU case, outputting the resistor through the hole for the wires. I think this is the most esthetic and ergonomic design.

So, I disassemble the PSU and find the necessary wire in the heap (and make myself absolutely sure it is the correct wire!) Then I make a cut in it.

To do the mod, I need a 50Ohm fixed resistor and a 10,000Ohm variable resistor, desirably with many revolutions for a smoother control. The proposed scheme is not the only one. There are several other combinations of these elements possible, and some guides contain their combinations for 3.3v, 5v and 12v circuits. All these schemes do work. The advantage of my version is its universality (the same components for all the three circuits) and the maximum availability of the components – I use the most simple and widespread nominal values.

So, I solder a 50Ohm fixed resistor into the cut in the wire. Then, after this resistor, towards the PSU (not towards the ATX connector!), I hang one output of a 10,000Ohm variable resistor. The second output goes to the ground, which can be found in the PSU itself.

All the three modifications are performed identically (for +3.3v, +5v and +12v rails), only on different wires: you need to repeat the above-described steps for the red and yellow sense wires. If your PSU doesn’t have three independent sense wires, you’ll have to be content with one or two modifications.

Attention! I want to remind you that the resistance of the variable resistor must be initially set to the maximum, i.e. 10,000 Ohms. Make sure about that before taking up the soldering iron! After soldering, isolate carefully all the bared spots. Neglecting these requirements may leave you with a dead PSU and other hardware.

Practical Tests

After performing the mod, don’t be hasty in attaching everything back. Try the PSU alone first. Plug the PSU to the wall outlet and connect contacts 4 and 6 (or 3 and 4, as in the picture below) in the ATX connector with a twisted paper-clip:

Measure the voltage in the +3.3v circuit with a multimeter and rotate the variable resistor to reduce its resistance. You should have patience if the resistor has many revolutions – you’ve got to do a lot of turning. Anyway, the voltage will start to grow sooner or later. Rotate it to the desired level, and then return to the norm. Install the PSU into the system case, repeat the procedure in a “live” computer using the BIOS data or the multimeter for orientation (after a small additional mod, see below). That’s all, the mod is over.

Your courage alone determines the voltages you set. The limiting voltages of the standard control module in the Antec TrueControl 550 PSU may be considered as safe (this is an off-the-shelf product, which should have undergone strict factory tests). These are about +3.45v, +5.4v and +12.5v.

I heard reports from users who had been running systems with about +3.6v, +5.5v, and +12.9v for months. This is a sensible limit for everyday use, I guess.

As for breaking any records – “sky is the limit!” I know cases when the +3.3v rail was outputting +4.1v, but no one will ever warrant you the safety of your particular hardware at so super-high voltages… Do it at your own risk!

Easy +3.3v Monitoring

The mainboard’s BIOS is known to report imprecise voltage values, so the best way to measure the real voltage is a multimeter attached to the Molex connector. However, this can give you the values of +5v and +12v voltages only, which are present in the 4-pin connector. While the +5VSB, -5v and -12v are not critical for the user, knowing the real voltage on the +3.3v rail is important.

This voltage is only supplied to the mainboard through the 20-pin ATX connector, but why can’t we make yet another slight adjustment to the construction of the PSU, now that we’ve got started?

Let’s return to the place where the 50Ohm resistor is soldered into the sense wire. Towards the PSU, there’s also a variable resistor, after which there goes a reduced voltage. But before the fixed resistor, the voltage in the sense wire equals the voltage the mainboard receives!

So, I solder an additional wire into the sense wire, before the fixed resistor. You may want to use a wire with a well-isolated plug on the end.

I take this wire out of the PSU, attach a multimeter and enjoy a true voltage monitoring on the +3.3v power rail.

Conclusion

I hope the described modification will open new opportunities for devotees of extreme overclocking, while the owners of low-power or low-quality PSUs may be able to avoid an upgrade by adjusting the voltages manually.

So, good luck with your modding experiments!