Overclock3D.Net :: Print Page :: Corsair HX750w (750w) ATX PSU

Introduction

It's very rare that you get the best of everything all in one package. Supercars break down more than the family estate, busty blondes are rarely as intelligent as the petite brunettes and PSU's tend to be either powerful yet noisy, efficient yet unstable or in some cases, just rubbish all together. However, A short while ago here on OC3D we checked out one of two new PSU's in Corsair's immensely popular HX line-up. The HX850w, to put it simply, was an all-round stunner. Solid rails, extremely high efficiency, virtually non-existent ripple and great looks to boot. For the first time ever, you really could have your cake and eat it while driving along in your extremely reliable Lamborghini with your big breasted blonde (who happens to have a degree in engineering) sitting beside you.

So when several weeks after the initial review Corsair dropped us an email asking if we'd like to take a look at the 750w model, naturally we agreed. Being released at the same time as the HX850w an educated guess would tell us that both PSU's are more or less identical probably barring some slightly uprated components in the 850w version. With this in mind we're going to be skipping past a lot of the usual waffle regarding the packaging and appearance of the HX750w and concentrating more on the performance of the unit and any differences that present themselves along the way. Of course, if you haven't yet already checked out our full and extremely detailed review of the HX850w, now is the time to do so!

• Guaranteed to sustain its full rated wattage at an ambient temperature of 50°C
• Up to 90% energy-efficiency under real-world load conditions
• 80PLUS Silver Certification
• Single +12V rail design providing up to 62A
• Multi-GPU ready
• 105°C solid state capacitors
• Active Power Factor Correction (PFC) with PF value of 0.99
• Supports ATX12V 2.3 and EPS12V 2.91 standards. Backwards compatible with ATX12V 2.01
• Auto switching circuitry for universal AC input from 90-264V
• Over Current/Voltage/Power Protection, Under Voltage Protection and Short Circuit Protection provide complete component safety
• Dimensions: 150mm(W) x 86mm(H) x 180mm(L)
• MTBF: 100,000 hours
• Safety Approvals: UL, CUL, CE, CB, FCC Class B, TÜV, CCC, C-tick

During our initial review of the HX850w we received word that the unit had actually met 80PLUS Gold standards. However as the unit barely scraped past the requirements for meeting this certification (>87% at all loads), Corsair took it upon themselves to downgrade both the HX750w and HX850w PSU's to Silver certification. Therefore the difference in 80PLUS ratings between our initial review and this one are merely cosmetic, and does not suggest any physical differences between the PSU's. All other specifications seem pretty much identical aside from the slightly lower power output on the 12v rail which can be seen below:

Corsair HX750w Rail Layout
DC Output	+3.3V	+5V	+12V1	+12V2	+12V3	+12V4	+12V5	+12V6	-12V	+5VSB
DC Output	25A	25A	62A	-	-	-	-	-	0.8A	3A
Max Power	150W		744W						9.6W	15W
Max Power	750W

Corsair HX850w Rail Layout
DC Output	+3.3V	+5V	+12V1	+12V2	+12V3	+12V4	+12V5	+12V6	-12V	+5VSB
DC Output	25A	25A	70A	-	-	-	-	-	0.8A	3A
Max Power	150W		744W						9.6W	15W
Max Power	750W

With an 8A difference between the +12v rail on the HX750w and HX850w, this more or less explains the 100W deficit (8A x 12v = 96W) of the HX750w, once again implying that both of the units are more than likely 'the same' with just some minor changes inside. However, let's move over to the next page and actually open up the HX750w to find out for certain.

Appearance & Internals

Starting off with the externals of the HX750w, everything looks pretty much identical to the HX850w barring the model number on the stickers. Both units have exactly the same dimensions, the same matte black powdercoat finish and the same modular connector backplane layout.

However one easily overlooked difference between the two is the number of hard-wired connectors on the unit. Whereas the HX850w has 2x PCI-E connectors along with the usual ATX and EPS12v connectors, the HX750w is void of any hard-wired PCI-E connectors.This brings the total number of hard-wired connectors down to 4 for the HX750w which is probably about right given the rated power output of the unit.

One positive way to look at the removal of these hard-wired connectors is in the name of vanity. If like me, you'd much rather see Corsair's sexy flat style modular connectors routing around your PC rather than the sleeved versions, then the HX750w would be the natural choice as you can run two high-end GPU's from the four modular PCI-E cables without needing to hide away the remaining two hard-wired cables.

Moving on to the internals, everything at first glance appears to be identical to that of the HX850w. Three rather thin heatsinks run in parallel along the length of the unit and all cables going to the modular backplane and other areas of the PSU are extremely tidy. Two DC-DC daughter boards with solid-state capacitors can be seen over on the low voltage side of the unit which, as mentioned in our previous HX850w review, are responsible for the stepping down of the PSU's primary +12v output down to +3.3v and +5v for the other rails.

Going in for a closer look, we can see that two Nippon Chemicon 420v / 330uF / 105°C capacitors and two custom-wound Viking Controls transformers have been used over on the primary (high-voltage) side along with a collection of Nippon Chemicon 16v / 2200uF / 105°C KZE capacitors over on the secondary side. This is exactly the same configuration as that of the HX850w, leaving us none the wiser as to what the physical differences between the two models are.

In a last ditch effort to try and spot any minor changes between the HX750w and HX850w units a negative image of the HX850w was placed under a 50% transparent image of the HX750w. Any differences between the two units show up in bright blue, orange or white shades. Once again there is very little to separate the two units with the only noticeable discrepancy being in the size of the inductor on the secondary side, which shouldn't really have any effect on the output power of the unit.

So with virtually no visible differences between the two PSU's other than a couple of missing PCI-E connectors, let's see if any differences present themselves during the testing over on the next page...

Simulated Load Testing

To provide accurate and consistent results in all of our PSU testing, Overclock3D uses professional grade DC electronic load equipment capable of placing a sustained load of 3690w across a total of six rails (including +5vsb and -12v) on the PSU! This is achieved by using a combination of SunMoon and Analogic electronic load equipment which allow us to adjust amperage loads in increments as small as 0.01A while also measuring voltage and wattage readings on-screen.

During today's tests, we will be placing the Corsair HX750W under 25%, 50%, 75% and 100% load levels at both room temperature and inside a hot box regulated to a temperature of around 50°C. Additional 'Cross Load' and a 'Max Load' tests will also be performed under these conditions to simulate how the PSU reacts to heavily uneven loads as well as running above its specified output.

Corsair HX750W Results @ Room Temperature
	+3.3v	+5.0v	+12v	+5vSB	-12v	AC Watts / DC Watts	Efficiency	Intake / Exhaust	Δ Temp
Test 1 (Low)	4.37A	4.37A	12.00A	0.75A	0.20A	206w / 188w	91.26%	28.6°C / 39.3°C	10.7°C
	3.32v	5.09v	12.16v	5.06v	-11.83v
Test 2 (Med)	8.75A	8.75A	24.00A	1.5A	0.40A	404w / 376w	93.06%	29.0°C / 45.0°C	16.0°C
	3.30v	5.07v	12.12v	5.02v	-11.75v
Test 3 (High)	13.12A	13.12A	36.00A	2.25A	0.60A	608w / 563w	92.59%	29.3C / 48.5°C	19.3°C
	3.27v	5.05v	12.10v	4.98v	-11.73v
Test 4 (Full)	17.50A	17.50A	48.00A	3.00A	0.80A	820w / 748w	91.21%	29.5°C / 51.8°C	22.3°C
	3.24v	5.03v	12.08v	4.93v	-11.72v
Test 5 (x-load)	17.00A	18.00A	1.00A	0.00A	0.00A	189w / 159w	84.12%	29.1°C / 35.9°C	6.8 °C
	3.29v	5.07v	12.16v	5.11v	-12.46v
Test 6 (x-load)	1.00A	1.00A	61.35A	0.00A	0.00A	808w / 750w	92.82%	29.9°C / 50.4°C	20.5°C
	3.29v	5.06v	12.10v	5.06v	-13.14v
Test 7 (MAX)	21.00A	21.00A	59.00A	4.00A	0.80A	1013w / 913w	90.12%	29.9°C / 54.5°C	24.6°C
	3.22v	5.01v	12.06v	4.87v	-11.78v

Comparing the results in tests 1-4 with those of the HX850w, there really is very little difference between the two units. The voltages show roughly the same amount of droop from 25% (Low) to 100% (Full) load and efficiency is highest in tests 2 and 3 at around 93%, while tests 1 and 4 also do extremely well at around 91% efficiency. Intake and exhaust temperatures are the only areas which show significant difference to that of the HX850w, but this is more than likely down to our recent upgrade to a Fluke 52-II digital thermometer which is hooked up to two 'K' type thermal probes for more accurate delta temperature readings.

Cross-load tests 5 & 6 tell a very similar story to that of the HX850w, with the voltages and efficiency levels once again being pretty much a mirror image. The lowest efficiency level is seen in test 5 with the unit dropping down to 84.12%, but the scenario of a PC system using over 170w on the +3.3v and +5v rails and only 12w on the +12v rail isn't something that you're ever likely to come across in the real world.

Finally in test 7 the HX750w was pushed as far as it could go without OCP (Over Current Protection) kicking in and switching the unit off. This is the one test that could actually tell us if the HX750w is simply a re-badged HX850w, or if indeed there are some minor differences inside the unit that give it its 100w lower power output. With a whopping 21A load on both the +3.3v and +5v rails and 59A on the +12v rail, the HX750w topped out at a total of 913w. This is of course WELL above its rated output, but still a little below that of the HX850w which managed an amazing 1084w before showing signs of weakness. However, even at these extremely high loads, the HX750w managed 90.12% efficiency along with some rock solid voltage outputs.

Corsair HX750W Results @ 50c
	+3.3v	+5.0v	+12v	+5vSB	-12v	AC Watts / DC Watts	Efficiency	Intake / Exhaust	Δ Temp
Test 1 (Low)	4.37A	4.37A	12.00A	0.75A	0.20A	206w / 188w	91.26%	52.9°C / 55.3°C	2.4°C
	3.33v	5.09v	12.14v	5.06v	-11.87v
Test 2 (Med)	8.75A	8.75A	24.00A	1.5A	0.40A	406w / 376w	92.61%	52.6°C / 58.7°C	6.1°C
	3.30v	5.07v	12.12v	5.02v	-11.79v
Test 3 (High)	13.12A	13.12A	36.00A	2.25A	0.60A	611w / 563w	92.14%	53.1C / 61.6°C	8.5°C
	3.27v	5.05v	12.10v	4.97v	-11.78v
Test 4 (Full)	17.50A	17.50A	48.00A	3.00A	0.80A	824w / 747w	90.65%	52.4°C / 64.8°C	12.4°C
	3.24v	5.03v	12.06v	4.92v	-11.79v
Test 5 (x-load)	17.00A	18.00A	1.00A	0.00A	0.00A	189w / 159w	84.12%	51.0°C / 55.0°C	4.0°C
	3.29v	5.07v	12.14v	5.11v	-12.46v
Test 6 (x-load)	1.00A	1.00A	61.35A	0.00A	0.00A	815w / 749w	91.90%	51.6°C / 60.8°C	9.2°C
	3.29v	5.06v	12.08v	5.06v	-13.14v
Test 7 (MAX)	21.00A	21.00A	59.00A	4.00A	0.80A	1002w / 887w	88.52%	54.3°C / 66.0°C	11.7°C
	3.21v	5.00v	12.04v	4.86v	-11.85v

Bumping up the ambient temperature to a toasty 50°C and re-running the room temperature results, hardy anything at all changed. In fact, aside from the odd +/-0.2v fluctuation on a couple of the rails and a few dips in efficiency, the only real thing worth talking about is the MAX load test which topped out at 887w - 26w lower than in the room temperature tests. This is by no means anything to get upset about as the HX750w is still operating at 137w above its rated capacity, and with 88% efficiency too.

Corsair HX750W Scope Results @ 50c
	+3.3v	+5.0v	+12v
Test 1 (Low)
Test 2 (Med)
Test 3 (High)
Test 4 (Full)
Test 5 (x-load)
Test 6 (x-load)
Test 7 (MAX)

Finishing up the testing, snapshots of the HX750w's +3.3, +5 and +12v rails were taken using a Rigol 25Mhz 400MSa/s oscilloscope while installed inside the 50°C hot box. Unfortunately there's not enough room on the page to put these side-by-side with the results from the HX850w, but if you're interested, the 850's results can be found here.

Once again the HX750w closely resembles that of the HX850w giving stunning results with the +3.3v and +5v rails staying at or below 10mV ripple in tests 1-6 and only hitting 12mV ripple in test 7 on the +5v rail. The +12v rail was also extremely clean with ripple starting at 12mV in test 1 and only increasing to 40mV by test 4. Test 7 saw the ripple hit 52mV, which is 10mV higher than that of the HX850w, but still way below the maximum of 120mV as specified by ATX standards.

Conclusion

To cut a long story short, the HX750w is every bit as good as it's bigger brother the HX850w. Throughout the testing the voltage and efficiency results were so uncannily similar that if not for the MAX load results topping out at 913w (vs 1084w on the HX850w), we would have happily put money on the HX750w simply being a HX850w with different stickers and less two of the hard-wired PCI-E connectors.

In effect, this positions the HX750w as THE BEST 750w PSU we've tested on OC3D to date. For an extremely reasonable £113 (over at Scan.co.uk) you get a 750w PSU that not only looks awesome with its smooth powdercoated finish and flat modular cables, but also performs among the best in its class. Efficiency levels rarely went below 90% even when running well above its rated output, and voltages refused to budge by any noteworthy amount no matter what kind of load we threw at it.

So, for the moment at least the choice is simple. If you're looking to power a tri-sli system and need a full six PCI-E connectors, then the HX850w is the way to go. However, if you're sitting on a small roll of £20 notes and are looking for an awesome PSU to power your single or dual GPU system, then you really should be looking no further than the HX750w.

The Good

- Extremely high efficiency at around 90-93%.

- Runs reasonably cool and quiet (from what we could tell over the din of the load tester)

- Excellent voltage regulation on all rails, even in cross load situations.

- Ripple almost non-existant on +3.3v and +5v rails. Also very low on +12v rail.

- High quality internal components.

- Great modular connector system with plenty of sexy 'flat' style cables.

- Well packaged. Hardly any chance of damage during shipping.

- Has a sustainable peak output of 887w when running at 50°C!

The Mediocre

- Would quite like for hard-wired cables to use the same 'flat' style cables as the modular connectors.

The Bad

- Nothing at all

In recognition of the HX750W's outstanding performance Overclock3D is pleased to award the unit our highly coveted Best In Class Award in the PSU class of 650-850W.

Thanks to Corsair for sending the HX750W in for review. Discuss this review in our forums.