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Corsair Obsidian 750D Case: Well Built For Water Cooling
Date: Oct 11, 2013
Author: Joel Hruska
Introduction, Features

Over the past few years, Corsair has steadily ramped up the number and types of computer chassis it manufacturers. The high-end 700D and 800D have been followed by a number of midrange products and one uber-expensive deluxe model, the massive 900D. The case we're reviewing today, the 750D, is meant to drop into the sub-$200 price bracket, where it faces competition from Corsair's own 650D mid-tower as well as a number of other chassis from manufacturers.

Despite the name, the 750D is actually somewhat smaller than the original 700D/800D family. Those chassis were 24 inches long, 24 inches tall, and 9 inches wide, while the 750D is 21.5 inches long, 22.1 inches tall, and 9.3 inches wide.

The other major difference between the Corsair 700D / 800D and the new 750D is the weight. The 2010-era chassis came in at roughly 35 lbs empty, while the 750D is just 21 lbs. As someone who uses an 800D for his own case, whacking 14 lbs off the base weight makes an enormous difference.

Corsair Obsidian 750D
Specifications & Features

Supports 1x 360mm radiator (top)
1x 280mm radiator (front)
1x 140mm radiator (rear).

Up to eight fans inside chassis (3x included, two front, 1 rear).
Up to 9x expansion slots
Up to 10 3.5" HDDs via mounted, removable drive bays.
Compatible with micro-ATX, ATX, EATX, and XL-ATX.

Radiator support is front and center for this case design. The 750D is designed to support up to a 360mm radiator at the top of the case, which should give you some idea what kind of buyer this case is aimed at. The vast majority of radiators on the market, including all the mass market liquid-cooling solutions, are 240mm solutions. There are a handful of 360mm radiators available, but these are designed for hardcore water-cooling enthusiasts who build their own loops, not the typical high-end PC market.

Corsair's Reviewer's Guide for the 750D promises that the chassis "dispenses with the arbitrary plastic add-ons in exchange for the beauty of brushed aluminum and steel." That's ironic, because substantial portions of this case are actually made of plastic. The brushed aluminum front panels that you can see above are actually 3mm aluminum sheets glued to a plastic frame.

We're not criticizing Corsair for using plastic, particularly when the smart use of plastic and cast aluminum together is part of why this chassis weighs 21lbs compared to the 800D's 35lbs. But it's silly to market the chassis as "dispensing with arbitrary plastic add-ins", when in actuality plenty of plastic is used in its design.
Working Inside the 750D

Installing a motherboard is easy in the Corsair 750D. The cable cutouts are well-placed and the now-standard rear cutaway makes it easy to change out a CPU cooler that bolts to the back of the motherboard, even if the motherboard is already mounted. The case uses raised mounting buttons instead of screwed-in standoffs, and there's a stud, rather than a standoff, in the center of the case, which helps hold the motherboard steady for easier mounting. The tool-less drive bays themselves are flexible without feeling flimsy and they lock solidly into place once snapped around a drive.

The 750D also includes four 2.5" drive bays behind the chassis, for installing SSDs. This is fairly useful if you need to keep the front of the case clear (and you may) and four drive bays is enough for even the most ardent SSD RAID enthusiast. Realistically, it's probably overkill -- you'd likely see better performance from buying into PCI-Express-based storage rather than RAIDing four SATA 6G SSDs into a single array. Alternately, if you have a 2.5" drive from a laptop banging around, this gives you a handy way to install it without reaching for a converter kit.

As configured, the Corsair 750D is a positive pressure case, with two intake fans in front and a single exhaust fan in the rear. If you configure it as suggested by Corsair's Reviewer's Guide, however, it's going to turn into a negative pressure design. The difference between the two is captured by this diagram from Silverstone:

A positive pressure case is a case where the internal air pressure inside the chassis is higher than outside, thus helping to prevent dust buildup. A negative pressure case is a chassis where air pressure is higher outside the case than inside, which typically adds to dust formation as air is pulled through the myriad tiny gaps in any chassis. This is unavoidable. Which kind of configuration cools better depends partly on your components, but negative pressure cases require more dusting than positive pressure and are sometimes seen as less desirable for this reason.
The 750D's Tradeoffs

There are some caveats to be aware of in the 750D as compared to some of Corsair's other product lines. Specifically, the Corsair 750D lacks the Corsair 650D's fan controller, top-mounted slot for a 3.5" HDD, or the sound-deadening foam built into the Corsair 550D.

The case, with drives in default position and stacked. Note that the longer AX1200i is running cabling through the large cutout that's otherwise blocked by the third drive bay.

Then again, the 750D is also about $30 cheaper than the 650D, and the included fans -- Corsair's AF140 series -- are extremely quiet. Which you prefer here is a toss-up. We do wish that the drive chassis were easier to stack and it seems that Corsair gave up some of the 650D's best features to hit this price point. Losing the latches on the side of the mid-range C70 is also a downside, in our opinion -- they make the case extremely easy to open.

How much you like the case may also depend on your PSU. The shorter and more modular the unit, the better chance you'll be able to take full advantage of the available internal space and routing points. A 750W PC Power & Cooling unit can only use one of the two cut-outs, and has to run a significant amount of cable through the far right-hand space. Users with different power supplies won't have an issue, however, even if the unit is longer but uses modular cabling. Also note that drive cages can stack from the bottom (you can put the third unit on top of the second), but not from the top. Neither drive cage will attach to the bottom of the 5.25-inch bays.

What Corsair has done is prioritize radiator space above virtually any other features. If you're a serious enthusiast, and you wanted a case that encompasses some of the features on the 900D but at a much lower price point, than the 750D is going to make you a very happy camper. Customers who want something with broader appeal beyond monstrous water-cooling setups, however, may want to look elsewhere.
Addendum: Corsair's new RM Power Supplies

Corsair is also launched a new line of power supplies alongside the 750D, the RM family. Why RM? Not sure. Near as we can tell, it doesn't stand for anything in particular.

The new supplies are completely modular and very compact, they fit the 750D ideally and allow you to use both of the routing channels. They're also capable of keeping the fan off at low load, which will help keep system noise down. It should be noted, however, that all PSUs produce at least a faint hum -- even a power supply with no fans at all will have a characteristic sound depending on the frequency your mains power uses.

Like Corsair's other high-end PSUs, the Corsair RM650 retains the flat-pack cabling option.

So what do these new power supplies offer over other Corsair power supplies? Since Corsair's advertising and product webpage are short in details, I pulled together a full shot-by-shot comparison to show you the RM650 against the high-end HX650.

Here's the quick version:

  • The RM650 is fully modular, the HX650 isn't.
  • The RM650 has basic support for Corsair's enthusiast "Link" light/cooling management system, the HX650 doesn't.
  • The RM650 can supply up to 130W across the 3.3V and 5.5V rails compared to 100W for the HX650.
  • The HX650 uses a different type of bearing in its fans.
  • The HX650 spins up its fan at 20% load, the RM650 spins up at 40%.
  • The HX650 has a maximum fan RPM of 2200 vs 1,050.
  • The HX650 will output 46.9 db(A) at full load, versus 24.8db(A) for the RM650. That means the RM650 is much, much, quieter.

There's a final set of differences not listed above -- the RM650 has significantly longer PCIe cables, at 750mm, up from 600mm. Unfortunately, the main power and ATX12V cables, which often could really be useful if they were longer, remain the same length on both units.

So far, all these changes favor the RM650 over the HX650. The final caveat, however, is that the warranty period on the HX is 7 years, while the RM is just five. Most people probably don't cash in the warranty on their power supplies, since it's a unit you tend to need immediately. If you like the increased tolerance and quieter fans, the RM650 is worth considering.

Test Results, Conclusion
Our testbed hardware for the Corsair Obsidian 750D was a Core i7-2600K on an Intel DP67BG2 motherboard with 8GB of RAM and an AMD Radeon HD 6870. Systems were benchmarked by waiting 15 minutes after boot to record idle temps and after 30 minutes of running Prime 95 in stress test mode. All of the cases were tested using their default fan configurations.

The 750D cools more effectively than any of the mid-towers we examined under identical conditions. The differences, using a stock Intel cooler, isn't very high, but this chassis isn't really designed for stock cooling -- Corsair's documentation puts repeated emphasis on the radiator. Fan noise is excellent, but below the measurable level of our decibel meter, unfortunately.

The Corsair 750D is a great case for hardcore enthusiasts that love the look of the 900D and want something that replicates it without breaking bank accounts or backs. The AF140 fans included with the case are top notch. And we've got no complaints about the cooling performance or the general build quality, though the front mounted fan cover is a bit loose for our liking.

But for all that, the Corsair 750D is  probably not the ideal case to choose unless you want to custom design a water-cooling setup. For practical, day-to-day use, we think fan controllers, built-in external drive bays, and sound proofing are more useful than 360mm radiator options. The truth is, increasing the size of the radiator block without increasing the size of the CPU or improving the thermal transfer material is only going to get you so far, and over half of the total heat resistance that builds up between a CPU and its cooling solution happens before the heat even migrates out to the external heat spreader. There's a diminishing marginal return to ramping up radiator size, in other words. The chassis may support up to four radiators, but practically mounting them into the case would be a nightmare of tubing.

But if you're in the mood for a crazy cooling project, and you want a positive-pressure chassis that allows for this sort of insanity, give the 750D a solid look. If you want something with more practical features, other manufacturers, or Corsair's own 650D, may be better bets.

  • 900D styling in a smaller case
  • Positive pressure as configured
  • 360mm radiator support
  • None of the insulation or external drive bays that make some of Corsair's other offerings stand out.

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