Corsair AX750

With sales of around 150,000 PSUs a month, Corsair is one of the largest vendors for retail power supplies. Corsair got in earlier than most other lateral entrants like GeIL or A-DATA, and their time in the market has enabled them to gather a lot of experience even if they don't have their own factory. In recent times they've used CWT, Seasonic and Flextronics as their PSU ODMs.

A few weeks ago Corsair presented their newest PSUs, the AX series. The goal is to provide performance, quality and high efficiency, this is apparently the best power supply Corsair can offer at the moment. Today we'll look at the AX750; is the 80Plus Gold certificate justified? And what other useful features does it provide?

The AX750 and 850W models are based on a Seasonic design (X-400FL and/or X-760) with some modifications in the details. For example Corsair uses flat peripheral cables and offers a 7-year warranty. They don't have the PWM fan from the original (it's an Antec patent), but they use the same kind of fan regulation; we will see that later in our test. Interesting features include the fully modular cable management and a silent, semi-passive fan control. Here's a complete rundown of the features (and marketing material).

Corsair Professional Series Gold AX750 features:

• Supports the latest ATX12V v2.31 and EPS 2.92 standards and is backward compatible with ATX12V 2.2 and ATX12V 2.01 systems
• An ultra-quiet 120mm double ball-bearing fan delivers excellent airflow at an exceptionally low noise level by varying fan speed in response to temperature
• 80 Plus Gold certified to deliver at least 90% efficiency at 50% load
• Active Power Factor Correction (PFC) with PF value of 0.99
• Universal AC input from 90~264V
  • No more hassle of flipping that tiny red switch to select the voltage input!
• A dedicated single +12V rail offers maximum compatibility with the latest components
• Over-voltage and over-current protection, under-voltage protection, and short circuit protection provide maximum safety to your critical system components
• High-quality Japanese capacitors provide uncompromised performance and reliability
• Completely modular cable system allows you to use only the cables you need
  • Power supply upgrade and replacement is easy, as the cables only need to be disconnected at the power supply
• Low-profile, flat cable design reduces air friction and helps maximize airflow through your computer's chassis
• A seven year warranty and lifetime access to Corsair's legendary technical support and customer service
• Dimensions: 150mm(W) x 86mm(H) x 160mm(L)
• MTBF: 100,000 hours
• Safety Approvals: UL, CUL, CE, CB, FCC Class B, TÜV, CCC, C-tick

The 750W version is currently on sale for $150 online, with an additional $20 mail-in rebate. That's not too shabby, considering the older Seasonic X-750 still costs $170. However, we'll need to see if the quality of the AX750 matches the X-750 before we can determine if the reduced price makes this a better buy.

Package Contents and Power Rating

There are a few extras in the package, which is typical of high-end PSUs. Included are several cable ties, mounting screws, the power cable, and a users manual, plus a couple of cloth bags that can be reused. On the package we can see that the AX750 is EuP-ready (low power loss in standby mode) and is a compact design measuring 160mm including the modular connection panel. Their reviewer's guide suggested we look at efficiency at 50% load, where the AX750 will be at the maximum 90% or greater level, but we'll also look at how it handles lower and higher loads.

Here we have an external impression of the Corsair model. The Case has a black, scratch-resistant surface with a Corsair logo on both sides. It has honeycombed ventilation holes and a small power switch near the AC plug. It's a very well-made product, with our only complaint being that the fan grille protrudes a little.

Corsair uses a single +12V rail that nearly delivers the full rated power. The AX has DC-to-DC for the smaller rails, so +12V feeds +3.3V/+5V and you can't use the whole 62A there. Even so, Corsair wants to supply modern components with plenty of juice, and 744W minus (up to) 125W is still a good rating. As you can see on the label, 100-240VAC and 50-60Hz are no problem for this PSU. The Corsair AX has active PFC, and we've tested the efficiency and PFC on both power grids.

Cables and Connectors

As already mentioned, the flat peripheral cables are a distinctive feature to Seasonic made PSUs. For the CPU and GPU connectors Corsair uses the usual cables and sleeving, and every surface and single connector are classical black.

Cable lengths are reasonably long and the AX750 should work well in most cases, including full towers with bottom-mounted PSUs. The main 24-pin, 4+4 ATX12V/EPS12V, and PCIe harnesses all measure 60cm. There are two Molex/PATA and SATA harnesses with four plugs each, and two additional SATA harnesses with two connectors each. The longer harnesses are 85cm total while the two shorter SATA harnesses measure 60cm. With modern systems, Molex connectors are primarily used for fans and other peripherals, while SATA powers the HDDs/SSDs and optical drives.

The only potential issue is if you want to load up all the SATA connectors with a bottom-mounted PSU; the distance from the PSU to the first connector is only 45cm (give or take), with a fairly large 12-13cm gap between the connectors, so you'd want the HDD bays to be relatively close to the PSU rather than in the top portion of the case.

Internals

Opening the casing reveals a clean design with a good layout. The phase and neutral conductors as well as the transformer look undersized at first, but the new resonant topology and more active controlled parts allow the manufacturer to use smaller components. Like Seasonic, this PSU has ZVS (Zero Voltage Switiching) that reduces power loss. Moreover, the soft switching is better for EMI.

All capacitors come from Nippon Chemi-Con and there are some all solid ones in the secondary circuit, but the KMR models are a usual choice for high-end PSUs. It would be nice to see some other brands or types; however, all parts are high-quality. There is a line filtering stage in the entrance and many SMDs at the backside of the PCB. The champion IC is on a sister-PCB up top. The overall design definelty looks like an X-460FL with more caps. The only point of criticism is that the fan connector could be glued down, but that's a minor issue at best.

Noise Levels

Ah! Even though Corsair doesn't use a PWM-controlled fan, they do have a nice Sanyo Denki fan. The 9S1212F404 has ball-bearings and 7 well-processed fan blades.

There is no noise at low load (or idle), and it's only when we approach 50% load that the fan begins to spin. With a 750W rating, that means you need to draw at least 375W before you get any noise from the PSU, and even a draw of 600W (80%) results in just 25dB(A)--hardly anything to worry about. Overall the cooling concept is nearly the same as the Seasonic X-series. Of course, it could be quieter at 110% overload, but you normally don't reach this level (or want to!); it's just nice to see that there is an output reserve available.

Just what sort of components would even require 600W of power? Short of running 10+ HDDs, an overclocked i7-920 (essentially i7-965 at 3.33GHz) and two GTX 580 GPUs in SLI with a single SSD maxed out at a punishing 777W... but that's wall power. Even at 90% efficiency you'd still only pull 700W from the PSU, and that's with our worst-case Furmark load. In other words, short of tri-SLI, insane overclocking, and/or tons of HDDs the AX750 should be able to handle anything you throw at it.

Voltage Regulation and Quality

The +12V voltage regulation is tight, while the weaker +3.3V and +5V drop to 3.6-3.8% below the optimal level. Nevertheless, all voltages are within the ATX specification. +5VSB starts with 5.10V and drops to 4.90V.

Ripple and Noise

There is hardly any ripple on the rails. They're always under 20mV and there are no remarkable spikes/transients.  Definitely some nice work here and worthy of praise!

Efficiency and PFC

With 80 Plus Gold certification, we expect high efficiency and the AX750 delivers. It doesn't matter whether you live in the USA or Europe; the efficiency is always high and 80 Plus Gold is no problem for the design. Maximum efficiency comes at 50% load as expected, but even on 115VAC the efficiency is always at 88% or higher provided the load is at least 150W. Worst-case efficiency at a low load of just 75W is still 82%, so we really can't complain--at such a low load, the difference between 82% and 90% efficiency amounts to only 8W. Besides, as we pointed out on the noise tests, the hardware required to even push a 750W PSU to the limits is such that you're likely to idle closer to 150W (or higher).

The power factor is also good,, staying above .90 on 230VAC as long as load is above 20%. That drops to just above 0.800 at 10% load, but any high-end system requiring the AX750 is going to be higher than that.

Conclusion

The Corsair AX750 is the best PSU Corsair sells at the moment, and it shows. It has no problems reaching 80 Plus Gold levels, and with 230VAC it even exceeds Gold requirements. 91% at 50% load is not too shabby.

When you open the Corsair PSU you can see a clean Seasonic design with all solid capacitors from Nippon Chemi-Con, a well chosen line filtering stage in the entrance (Delta), and many surface mounted devices on the PCB. A modern Champion IC in combination with an Infineon switcher are a very common picture for high-end PSUs and deliver a proven quality. ZVS and DC-to-DC are the reason for the high efficiency. Corsair is using the best modern technology, and the AX750 delivers.

Throughout the review, we could only come up with a few minor points of criticism. First, the fan connector could be glued down. Second, the fan grille on the nice black case protrudes a little. About the only real potential concern is trying to utilize all of the Molex and SATA connectors in larger tower cases; you'll want to check the case layout before going that route, although that's definitely a niche market. When that's the worst we can come up with, there's obviously very little wrong with the AX750.

At 10% load Corsair reached 82% efficiency, which is nice to see. Similarly, there is almost no ripple or noise on the rails--+3.3V for example is always under 13mV. The other rails have slightly higher results, but in all cases they're under 20mV. The voltage regulation for +3.3V and +5V could be a little bit better, as both rails drop below 3.60%, but realistically the 12V rail is the important criterion and +12V is just 0.25% under the optimal value.

The delivery contents include 12 SATA connectors on four cables (more than the older Seasonic X-750) and four 6/8-pin PCIe connectors with a black sleeving. The 60cm primary cables are sufficient for most cases, you get two floppy-adapters (just in case), a bunch of cable ties to help you clean up the installation, and flat peripheral cables.

As already mentioned in the introduction, you have to pay more for the older Seasonic X-750 than for the new Corsair AX750. Corsair offers the same quality with flat cables for a lower price. The OCZ Z-Series 80Plus Gold OCZZ850M is no match for Corsair as well, because the efficiency is lower and the soldering quality worse. One potential contender we see is the upcoming HCP series from Antec, which will start at 750W. Otherwise we have to wait for the Seasonic X-760, which should be available shortly.

What we can tell you is that right now, the Corsair AX750 provides a great set of features in a stylish package for a very good price. Yes, you can find less expensive options, and if you get a good sale price you can even get a quality PSU for under $80. However, realistically you're looking at spending over $100 if you want 80 Plus Gold, and not all Gold PSUs are created equal. Silence, performance, quality, and an attractive price make the AX750 very difficult to beat. This is easily one of the best power supplies on the market right now, and for that we're presenting Corsair with our Gold Editors' Choice award. You can get similar performance and quality, but the pricing is usually higher and unless you like waiting to see what the competition can bring to bear, this is a great high-end PSU.