First, I have to apologize to both Nvidia and Sapphire. On one hand, I'm about to build something from Nvidia that doesn't exist yet (and might not any time soon, according to the board partners). On the other, I'm going to sacrifice one of Sapphire's cards to get the spare parts I need for the project. But resistance is futile. I have a 60 W GPU in-hand. I have to see if it'll operate stably without active cooling.
The foundation I'm starting with is Nvidia's reference GeForce GTX 750 Ti. In the event you missed our launch coverage, check out GeForce GTX 750 Ti Review: Maxwell Adds Performance Using Less Power.
In the end, we're going to be talking about the reference board with a passive heat sink, the kind you typically see on Radeon HD 7750 and R7 250s.
On paper, the match-up should be pretty close; those cards are fairly similar in their power consumption. But will our contraption work? There are more variables than just power to consider. For example, the Maxwell GPU has a smaller surface area than AMD's Cape Verde. Furthermore, Nvidia ensured that none of the current thermal solutions fit by changing the distance between the screw holes. Mainstream GeForce PCBs typically measure 53.2 x 53.2 mm or 58.4 x 58.4 mm, while Radeon cards are either 53.2 x 53.2 mm or 43 x 43 mm. It only follows, then, that the 44 x 44 mm GeForce GTX 750 Ti would be incompatible with today's most common cooling solutions
As a result, none of the board partners were able to launch using existing heat sinks. Instead, there will need to be new designs specific to GeForce GTX 750 Ti.
We figured out how to make this work though, and we're going to show you how on the next few pages. Just be forewarned: we're really tinkering here. Be careful with your own card so as not to render it worthless.
Pillaging A Sapphire Radeon HD 7750 Ultimate
We weren't able to find any older passively-cooled Nvidia cards that'd work, so we made a Radeon HD 7750 from Sapphire suffer. Why Sapphire? That's just the first board I grabbed when I came up with this idea. It could have just as easily been a HIS card. I remember that the iSilence Cooler does its job really well, going nearly unchanged since the days of AMD's Radeon HD 6670.
Within minutes, I had the sink removed and cleaned off, and the same for Nvidia's sample.
So what now? We're off by just one millimeter in length and width. In the end, I had to get crafty and enlarge the holes to make the PCB fit under Sapphire's sink.

You can do this with something like a good pair of scissors. Just be careful and trim the enlarged holes.


Of course, you need to keep a sharp eye on thermals the first time you fire up the modified card. Then, carefully re-tighten the screws after an hour of burn-in.
Why not use an Arctic Accelero S1 Plus?
Sure, that might have worked. In some situations, it could have even been better. But the Arctic cooler doesn't solve the PCB fitment issues. In fact, its bundled screws are even thicker up top to ensure the cooler doesn't go anywhere after installation. Also, the S1 Plus is extremely large, which means you need 16 cm above the upper card slot edge, and there was no way to get that into the case we're using.

No matter what you do, there's no way to avoid enlarging the screw holes. The safest way to do it is up to you. With a little skill and a little courage, you can use this cooler or try another one, so long as it's not too heavy for Nvidia's little PCB.
The installation dimensions of our little experiment don't match those of Sapphire's Radeon HD 7750 Ultimate card, although the cooler is the same size. Why? Because the GPU isn't in the same place on the physical board. So, we took our own measurements matching the distances in the diagram above.
| Technical Data | |
|---|---|
| Foundation | Reference GeForce GTX 750 Ti |
| Dimensions | Length L = 190 mm Height H = 134 mm Depth D1 = 38 mm Depth D2 = 14 mm |
| Weight | 425 g |
| Pros | + Silent + Fast + Affordable |
| Cons | - You have to cut your own mounting holes - There's only one cooler with 43 mm spacing for AMD cards - Very tall - Very deep (it could run into your CPU's sink) |
Temperature in a Closed Case
This heat sink's fin alignment is optimized for vertical operation, and it benefits from cases with some airflow. My idea here was to go completely noiseless. I wanted to test a true passive solution. So, we're once again using our Enermax Fulmo ST, testing in a closed case.

It takes just 20 minutes for the Maxwell-based GM107 to hit an 80 °C ceiling. Then, the chip gets some help from Nvidia's GPU Boost technology and its ability to back off clock rate to duck under certain power and thermal situations. Even the voltage regulators continue working within their specifications. Their roughly 93 degrees after an hour of work still falls within the safe zone.
Clock Rate And Throttling
Nvidia might not have been considering passive operation when it designed this card, but what we see from it (including GPU Boost performance) is still impressive.
What follows is a 40-minute loop of Metro: Last Light. Boost clocks do drop, but they also stabilize after the card hits its thermal target zone.

In the end, GPU Boost to around 1136 MHz, though as a percentage, performance drops more noticeably. Remember, the actively-cooled card reached a GPU Boost clock rate of 1162 MHz, occasionally dropping to 1150 MHz.
The base frequency of these cards doesn't change. You're guaranteed at least 1020 MHz, regardless of your cooling solution.

Our passively-cooled GeForce GTX 750 Ti loses about two percent of its performance compared to the reference model. To better hammer that point home, the aggressively cooled and factory-overclocked Gigabyte GTX 750 Ti Windforce OC achieved 1.3 percent-higher performance than the reference card. In the end, we're talking about about a three-percent performance loss in the quest for passive cooling.
This is for Cautious People
If you're not willing to trust Nvidia's 80 °C temperature target (the company says 95 degrees is the GPU's thermal threshold), you can of course set a lower target of, say, 70 °C. That's going to give up a lot of performance though, and we're not sure such a compromise makes sense. At that point, you might as well buy a Radeon R7 250, which you don't have to build yourself. They already ship passively-cooled.
For some reason, naked cards make me want to customize. If you can get motivated to enlarge this board's screw holes on your own (really, it's not a difficult task), then you're able to attach any heat sink with a hole distance of 43 mm. In essence, that's coolers compatible with AMD's Radeon HD 7700 family.
You might not think that this project is worthwhile to you, since existing partner cards run cool and quiet already. That's fair enough. But this is about cooling GM107 with no moving parts.
We can only concede that GPU Boost and its associated mechanisms are great for controlling the thermals on passively-cooled cards, even if that's not what it's meant for.
The technology works almost perfectly though, without much performance hit. It's also better about preventing the panic attacks triggered by passively-cooled Radeon cards in fanless cases. We've seen those boards crest 100 degrees, which is very dangerous.
Wrapping Up
We plan to continue tinkering, ensuring that any heat sink we experiment with has to at least be rated for 60 W and support a 43 mm screw pattern. If you're willing to follow in our footsteps, you'll end up with a nice, silent, and most important, fairly high-performance card. The GeForce GTX 750 Ti is typically a little slower than AMD's Radeon HD 7850. But that Pitcairn-based board can't be cooled passively.













