by Oleg Golubovich
10/04/2006 | 12:04 PM
The clock is ticking its seconds, minutes and hours that amount to days and weeks and months… Perhaps time is the only thing in this world that everyone has, but you can’t control or halt it no matter what you try.
It seems it was just yesterday that I was shopping for the newest GeForce 6600 series cards, but now they are a thing of the past. Their place is occupied and their glory of being the best buy in the mainstream sector is taken over by Nvidia’s 7600 series products, 7600 GS and 7600 GT. It is actually the same story told anew: the same graphics chip, but different memory. The different frequencies provide different performance and, as a consequence, determine the market positioning of the products.
A year ago the core of the ordinary 6600 could be overclocked to the level of the senior model or even higher, but what do we have today? The reviewers are all talking about poor overclockability of the 7600 GS series and do not recommend it to overclockers, but few of them point at the reason for such a dissimilar behavior of absolutely identical chips on different cards – a greatly reduced voltage.
But what if this voltage is increased? Let’s try it out? We’ve got an EVGA GeForce 7600 GS card for this test. It’s time to check it out in action.
In this review I will volt-mod the EVGA card and compare its performance with that of a 7600 GT made by XFX. We’ll see if the junior model can beat the senior one. Let’s first take a look at the XFX which is an interesting product in itself.
The EVGA card is based on the reference design (Nvidia PCB P345)…
…and has 400/400MHz frequencies by default. This graphics card is equipped with 256MB of 2ns DDR2 memory from Infineon.
Its heart is a G73 revision A2 chip.
Without any modifications this graphics card could be overclocked to 507/493MHz (GPU/memory). It’s a gain of about 25% in both frequencies. It may be good, but not for enthusiasts who just can’t brook a low frame rate in their favorite games.
Next goes our disclaimer, just to get rid of the weakest link (those who won’t follow us to the end) and move on to the point.
The modifications described in this article have been successfully made in practice. Each mod was tested by us and helped achieve the desired result. We don’t accept any claims concerning damage to your graphics card or any other PC component after the modification because such problems imply your own mistakes. The author and X-bit Labs are not responsible for any damage inflicted by repeating anything of what is described in this article. We also cannot promise you that your final result will be as good as ours due to the variation in the potential of particular samples of graphics cards.
Warning! Volt-modding, if recognized, makes all warranty obligations void.
You should take up volt-modding if all the following items are true:
Before doing any volt-modding, make sure the graphics card is properly cooled (sometimes the standard cooler may be insufficient even for ordinary overclocking).
So, you’ve made up your mind? Let’s move on then. In order to experiment with a 7600 GS that has the reference PCB design, you need:
The regulators we are interested in are located on the reverse side of the PCB:
The core voltage is the main problem because it is a mere 1.1V by default in 3D mode on each GeForce 7600 GS regardless of the manufacturer, as opposed to the GeForce 7600 GT’s 1.35V. It is due to this difference rather than to the lower clock rate that the GPU on GeForce 7600 GS cards generates so little heat that some models even come with passive GPU coolers. The GPU and memory voltages are regulated by two identical linear regulators from Intersil, ISL6549. To increase the voltage, you should solder one lead of a 10,000Ohm variable resistor to leg 4 of the chip marked in the picture and the other lead to the common wire (make sure the resistor is set at its maximum resistance before doing that!):
I used the point in the bottom corner of the PCB:
Now you can reduce the resistance to increase the core voltage (if you set the variable resistor at a resistance of 3,200Ohm, the core voltage would grow to 1.7V).
Use the capacitors marked in the picture below to monitor the voltage:
Warning! Some resources recommend using 50,000Ohm resistors to perform the above-described modification. The outcome won’t change for that, but I must warn you that the core (and memory) voltage begins to grow up rapidly after a certain threshold which is about 4,000Ohms. So, if you use variable or trim resistors with a bigger rating than mentioned above, you make it harder for yourself to accurately set up the necessary voltage. Be careful as an extra turn or even half a turn of the resistor may send your graphics card to its ancestors!
As I wrote above, the regulator of the memory voltage is identical to the GPU voltage regulator, so it can be modded in the same way: connect a 20,000Ohm resistor to leg 4 of the regulator with one lead and to the ground with the other lead (you can use the leg of the neighboring capacitor for that):
The memory voltage can be read from that capacitor:
DDR2 memory works at 1.8V by default.
To check out the result of the modifications described in the previous sections, I used an open testbed configured like follows:
The CPU was clocked at 2800MHz (350x8) and worked at 1.6V voltage. The memory worked as DDR-133 at a clock rate of 233MHz with 2-2-2-5-1T timings and a voltage of 3.4V.
The testbed ran Windows XP SP1. I overclocked the graphics card by means of RivaTuner 2.0 RC16.
The graphics card driver was ForceWare 91.31. I left the default performance/quality ratio and didn’t use anisotropic filtering or FSAA.
The following benchmarks were used:
For a more illustrative performance analysis we would like to also provide the results obtained from the GeForce 7600 GT from XFX. But before we move on to the benhcmarks let me say a few words about the XFX solution.
The XFX GeForce 7600 GT graphics card, the opponent to the volt-modded EVGA GeForce 7600 GS, comes in a green-colored box with a picture of a very stylish doggy:
The box contains:
I took the card out of its box and… could I have seen that all before? It reminded me of the EVGA e-GeForce 7600 GT CO, but on a closer inspection I could only mark the same color and overall design of the PCB, and a similar-looking cooler. There are some exciting things in the GeForce 7600 GT 256MB I haven’t seen on other cards. First of all, it uses a non-standard PCB:
The power section has moved away from the connectors to the far edge of the PCB, but the core and memory regulator circuit hasn’t been changed.
It means the card can be volt-modded in the standard way. The XFX card is equipped with two DVI outputs. There is a special ledge on the card’s mounting bracket a sticker with the serial number is attached to:
I don’t quite grasp the purpose of the metal cloth between the bracket and the TV output:
I doubt it helps suppress interference in the signal sent to the TV-set.
An aluminum bar with the manufacturer’s logo goes along the edge of the card to prevent the PCB from bending. XFX seems to suggest that the user installs a heavier cooler and overclocks the card!
The card carries four 1.4ns memory chips from Samsung for a total of 256MB.
The GPU is cooled by a copper cooler (thin copper ribs are soldered to the copper base). The noise, or rather the howl, the fan emits at the maximum speed is rather irritating. You will certainly want to replace it with something more efficient and quiet if you value your acoustic comfort.
The default frequencies of this GeForce 7600 GT are slightly higher than those of the reference card: 570/725 (1450) MHz. I reached 680/850 (1700) MHz when I overclocked the card with its native cooler and without any modifications.
Now let's move on to the actual performance tests of our modified solution and compare the results against those of the GeForce 7600 GT.
The voltage on the GeForce 7600 GS chip was increased to 1.72V which helped achieve an impressive frequency of 765MHz. This is 89% above the default frequency! The chip was cooled by a water cooling system that consisted of a Revoltec water-block (it is a CPU water-block but I had remade it so that it could be installed on GPUs), an external 600lph Eheim pump, and an Airplex EVO 360 radiator with three low-speed Aerocool Turbine 3000 fans. The liquid cooling system worked only for the graphics card during the test.
To generally improve the thermal conditions of the card, a 120mm fan was set to blow at the reverse side of its PCB.
The GPU worked at frequencies higher than 765MHz, but with image artifacts. It seemed that a minor voltage increase would solve the issue, but I had those artifacts even at 765MHz after I had increased the core voltage to 1.8V and then to 1.85V. So, the chip on my sample of the graphics card reached its frequency limit under the given conditions. I could also try to increase the frequency of some of the GPU subunits by reducing the frequency of the geometric subunit, but that would have been beyond the scope of this review. By the way, the maximum GPU frequency at which the card could work, although with image artifacts, was 798MHz!
The memory wasn’t near that good: a frequency growth of only 10MHz after a voltage increase from 1.8V to 1.95V. All further attempts led to visual artifacts. On the other hand, 1GHz is good enough for Infineon’s DDR2 memory which has never been really good for overclocking.
The XFX GeForce 7600 GT was benchmarked at the default frequencies only as a reference point for the modded 7600 GS.
The performance of the GeForce 7600 GS card grows up along with its frequency in this popular synthetic benchmark. It is important that the GPU and memory frequencies grow up together: a 100MHz increase in both frequencies provides a considerable performance boost whereas the tremendous GPU frequency leap, by 250MHz more, yields a smaller performance gain.
Another version of Futuremark’s benchmark produces the same picture as the previous test. The graphics card lacks memory bandwidth to transform the colossal overclocking potential of the G73 chip into an appropriate performance boost.
As you can see, the real gaming applications agree with the results of the synthetic benchmarks. I didn’t reach the level of the full-featured GeForce 7600 GT as I had anticipated before the tests. I had been even sure that a volt-modded and well-overclocked GeForce 7600 GS would deliver more performance than the senior model. But it turns out that you can’t get far with DDR2 memory – it provides too low a bandwidth for the graphics chip to show its best.
Frankly speaking, I had hoped for a somewhat bigger performance growth from the volt-modded EVGA GeForce 7600 GS 256MB. It was the graphics memory that turned to be the bottleneck because its frequency is much lower than that of 7600 GT cards. The core voltage increase, however, helped overclock the GPU to the same frequency as that of the senior model. Taking the frequency of the 7600 GS as the reference point, there is an almost 100% frequency gain! Few chips are capable of such achievements and such graphics cards are sure to become popular and demanded in their price category.
As for the market perspectives and shopping choices, you can note that we’ve seen all that before: a junior model, a senior model, and, later on, a third model that becomes the golden mean in terms of price/performance. That was the case with the GeForce 6600 with DDR2 memory which, however, was not widespread and only hit the market in limited quantities, and now the GeForce 7600 GS with GDDR3 memory is about to arrive. Fortunately, Nvidia didn’t wait till the end of the lifecycle of the 7600 series and released the in-between product in proper time.
Basing on the results of today’s tests I can tell you one thing. If you don’t have the money to buy a more expensive graphics card, take a GeForce 7600 GS with DDR2 memory and overclock it, if you want, but despite the sky-high core frequency, the memory frequency will be the bottleneck. And no volt-modding can help here.
But if you’ve got $15-20 more in your wallet, look for the “right” GeForce 7600 GS with normal memory (I mean GDDR3, of course). It won’t disappoint you!