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KitGuru has reviewed both the AX1200 and AX850 power supplies and our testing has confirmed that this new range from Corsair is setting new standards in their respective classes.
Today we look at their AX750, a 750 watt unit targeting a wide audience with a reasonable asking price of £135 inc vat.
Like the other supplies in this range, the AX750 is 80 Plus Gold certified meaning it has to comply with very high standards of efficiency.
The Corsair AX750 is a fully modular design, meaning all cables detach from the main unit, ensuring you can only install what you need for your specific system build.
As with all the other units in the AX range, Corsair are offering an industry leading 7 year warranty for ultimate peace of mind.
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 Corsair AX750 arrives in an identically designed box as the AX850 and AX1200 units, featuring a very serious looking close up of the modular ports.
Inside the box the PSU is heavily protected between two thick pieces of foam. The unit itself is wrapped inside a felt bag to offer additional protection against scuffing. Corsair supply a well written manual offering support and information.
Extras include a power lead, mounting screws and cable tidies to help enhance your system build. Corsair also supply a little badge to proudly display on your case.
There is a bag containing all the cables, which can also be used for storage purposes as well. The cables are of high quality, some of which are sleeved/braided.
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MODEL
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CMPSU-750AX
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AC Input Rating
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AC INPUT
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90-264V
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INPUT CURRENCY
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12A
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FREQUENCY
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50/60Hz
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DC OUTPUT RATING
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MAX LOAD
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MAX OUTPUT
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+3.3V
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25A
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125W
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+5V
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25A
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+12V
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62A
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744W
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-12V
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0.5A
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6W
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+5VSB
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3.0A
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15W
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TOTAL POWER
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750W @ 50c Ambient Temperature
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Along the rear are all the ports for the modular cables, while these aren't colour coded it shouldn't cause confusion as it is pretty obvious how they should be connected. The 24 pin power feed is directed into two feeds which are shown furthest left, top row and bottom row. The PCIe feeds take up the remaining three slots at the bottom. Sata and Molex power is fed from the five 6-pin power connectors top right.
The unit looks identical to the AX850 we reviewed last month, simple, clean and following a design ethic to suit the ‘Professional' moniker. A large 120mm fan takes centerstage at the top of the supply and the rear is vented to allow for maximum heat removal. There is a power switch and connector here.
The fan inside the unit is a San Ace 120 – Model 9S1212F404. This is a 120mm unit (140mm fan in the AX1200) and it is a 7 blade design rated at 12v/0.19A. This fan normally spins in the 1200rpm zone, but has a maximum rating of 2,400 rpm creating 40dBa – we will look at this later. If you are interested in the full range of Sanyo Denki fans then check out this page.
Corsair are keen to extoll the virtues of their Hybrid Silent fan control system – it offers 3 modes of cooling which is dependant on the current status of power load. up to 20% load for instance the fan is disabled which generates no noise and then between 20% and 50% load it spins into low fan mode. Above this it then turns into performance mode for demanding load requirements.
Sanyo Denki are well known to make some of the best fans in the business, but they are noticeably more expensive than many others. It is good to see Corsair not cutting a corner here with a cheap fan.
Inside, as expected the design is very clean and while we have less physical room when compared with the higher end AX1200 unit there is good attention to detail and no build issues we can note. Wiring is noticeably tight which ensures the best possible connection quality. Soldering quality is just as high as the AX850 unit we reviewed last month.
The Corsair AX750 uses a design which places the 3.3V and 5V DC outputs on an independent DC output connector board.
The connector board features an integrated voltage regulation module (VRM) which produces the 3.3V and 5V output directly from a low current 12V DC input. This is a similar principle to the AX1200 we reviewed and it results in a much higher efficiency rating compared to traditional designs that place all the DC output connectors on the same board. Additionally the high current 12V DC outputs are directly soldered to the main circuit board. This helps to ensure low heat generation and resistance levels.
The capacitors used for the PFC stage are 390uF rated to 105C. This Corsair unit boosts efficiency by minimising the loss in the PFC stage by switching the primary power on and off when the cycle is at 0 voltage and 0 current.
The Corsair AX750 uses a high quality double sided PCB design which offers advantages when compared against standard PCB layouts. The primary point to note is that this specific design doubles the amount of copper used for traces and return planes and it also increases the efficiency as a result of lower resistive losses which helps to improve cooling characteristics. The AX750 also incorporates ‘through-hole’ soldering which means higher levels of reliability.
As we would expect there is over current and under voltage protection and the PSU conforms to all required international safety standards. Over current protection (OCP) for example is present on all rails, including the single +12V rail (which can deliver 62 Amps). Over Temperature Protection (OTP) and Short Circuit Protection (SCP) are also included.
Additional technical assistance: Peter McFarland and Jeremy Price.
Correctly testing power supplies is a complex procedure and KitGuru have configured a test bench which can deliver up to a 2,000 watt DC load. Due to public requests we have changed our temperature settings recently – previously we rated with ambient temperatures at 25C, we have increased ambient temperatures by 10c (to 35c) in our environment to greater reflect warmer internal chassis conditions.
We use combinations of the following hardware:
• SunMoon SM-268
• CSI3710A Programmable DC load (+3.3V and +5V outputs)
• CSI3711A Programmable DC load (+12V1, +12V2, +12V3, and +12V4)
• Extech Power Analyzer
• Extech MultiMaster MM570 digital multimeter
• SkyTronic DSL 2 Digital Sound Level Meter (6-130dBa)
• Digital oscilloscope (20M S/s with 12 Bit ADC)
• Variable Autotransformer, 1.4 KVA
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DC Output Load Regulation
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Combined DC Load |
+3.3V
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+5V
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+12V
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+5VSB
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-12V | |||||
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A
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V
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A
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V
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A
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V
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A
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V
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A | V | |
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155W
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1.5
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3.34
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1.5
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5.04
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11
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12.15
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0.50
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5.03
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0.20
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-12.13
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300W
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3
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3.34
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3
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5.04
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22
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12.13
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1.00
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5.02
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0.30
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-12.12
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445W
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4
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3.33
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4
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5.03
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33
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12.12
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1.50
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5.01
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0.50
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-12.11
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| 605W |
5.5
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3.33
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5.5
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5.02
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45
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12.11
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2.00
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5.01
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0.60
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-12.10
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751W
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7
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3.32
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7
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5.00
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56
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12.08
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3.00
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5.00
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0.80
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-12.09
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These results are excllent with primary and secondary outputs all remaining with 1% of their target values.
| Corsair AX750W | Maximum Load |
| 892W |
We managed to get 892W out of the unit before it shut down. As with the other AX power supplies we experienced absolutely no issues with the overcircuit protection circuity.
Next we want to try Cross Loading. This basically means loads which are not balanced. If a PC for instance needs 500W on the +12V outputs but something like 30W via the combined 3.3V and +5V outputs then the voltage regulation can fluctuate badly.
| Cross Load Testing | +3.3V | +5V | +12V | -12V | +5VSB | |||||
| A | V | A | V | A | V | A | V | A | V | |
| 733W | 1.0 | 3.33 | 1.0 | 5.02 | 60.0 | 12.04 | 0.2 | -12.09 | 0.50 | 5.03 |
| 153W | 15.0 | 3.32 | 15.0 | 5.01 | 2.0 | 12.01 | 0.2 | -12.12 | 0.50 | 5.01 |
The Corsair AX750 experienced no issues with our crossloading tests and even with a 60A load on the 12V output it kept everything close to a reference set of parameters.
We then used an oscilloscope to measure AC ripple and noise present on the DC outputs. We set the oscilloscope time base to check for AC ripple at both high and low ends of the spectrum. ATX12V V2.2 specification for DC output ripple and noise is defined in the ATX 12V power supply design guide.
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ATX12V Ver 2.2 Noise/Ripple Tolerance
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Output
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Ripple (mV p-p)
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+3.3V
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50
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+5V
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50
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+12V1
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120
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+12V2
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120
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-12V
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120
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+5VSB
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50
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Obviously when measuring AC noise and ripple on the DC outputs the cleaner (less recorded) means we have a better end result. We measured this AC signal amplitude to see how closely the Corsair unit complied with the ATX standard.
| AC Ripple (mV p-p) | ||||
| DC Load | +3.3V | +5V | +12V | 5VSB |
| 155W | 5 | 5 | 10 | 5 |
| 300W | 5 | 5 | 10 | 5 |
| 445W | 5 | 10 | 15 | 10 |
| 605W | 10 | 15 | 15 | 10 |
| 751W | 10 | 15 | 20 | 15 |
The AX750 ripple results are class leading and are just as impressive as the AX850 unit.
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Efficiency (%)
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155W
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90.08
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300W
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90.41
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445W
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92.32
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605W
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91.55
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751W
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90.21
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Efficiency, as we had hoped, is stellar, reading over 90% throughout the range, peaking at over 92% between 360-450W. This makes the 750W our new class leader in this category and certainly into the upper echelons of efficiency performance on the market. Gold Certification requires 87% efficiency rating at 100% load … the AX750 rates over 3% higher with our equipment.
We take the issue of noise very seriously at KitGuru and this is why we have built a special home brew system as a reference point when we test noise levels of various components. Why do this? Well this means we can eliminate secondary noise pollution in the test room and concentrate on components we are testing. It also brings us slightly closer to industry standards, such as DIN 45635.
Today to test the Power Supply we have taken it into our acoustics room environment and have set our SkyTronic DSL 2 Digital Sound Level Meter (6-130dBa) one meter away from the unit. We have no other fans running so we can effectively measure just the noise from the unit itself.
As this can be a little confusing for people, here are various dBa ratings in with real world situations to help describe the various levels.
KitGuru noise guide
10dBA – Normal Breathing/Rustling Leaves
20-25dBA – Whisper
30dBA – High Quality Computer fan
40dBA – A Bubbling Brook, or a Refridgerator
50dBA – Normal Conversation
60dBA – Laughter
70dBA – Vacuum Cleaner or Hairdryer
80dBA – City Traffic or a Garbage Disposal
90dBA – Motorcycle or Lawnmower
100dBA – MP3 Player at maximum output
110dBA – Orchestra
120dBA – Front row rock concert/Jet Engine
130dBA – Threshold of Pain
140dBA – Military Jet takeoff/Gunshot (close range)
160dBA – Instant Perforation of eardrum
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Noise (dBA)
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155W
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/
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300W
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17.8
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445W
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23.5
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605W
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30.3
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| 751W | 37.9 |
A fantastic set of results, and it is only when around 90% load that the PSU fan becomes noticeably audible. A normal system running with a few case fans will mask this noise. The San Ace 120 is a great fan and the noise with this testing is comparible to the AX850 unit. We changed our meter for this review (we used the Digital Sound Level Noise Decibel Meter Style 2 before) so results are much in line.
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Temperature (c)
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Intake
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Exhaust
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155W
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35
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37
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300W
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35
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38
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445W
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40
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44
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605W
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43
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49
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751W
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45
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52
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The 120mm San Ace fan ensures the internal temperatures are relatively low, with the unit peaking at 7c + over ambient at full load.
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Maximum load
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Efficiency
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892W
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86.0
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For those interested, we measured efficiency when stressing the unit to breaking point. 86% efficiency at almost 900W is a very good result indeed.
The AX750 is the third Corsair AX power supply we have reviewed and it has reaffirmed our opinion that the Professional Series Gold power supplies are the finest on the market, bar none.
The 750 model is finished to the same exacting standards as the AX850 and AX1200 and we love the understated design and simple aesthetic appeal. This PSU will look great in any system, regardless of lighting or internal structure.
Inside, the components used in the product composition are as good as you will find … independent DC output boards, double sided PCB and zero voltage switching to help raise efficiency and improve overall thermal performance. These claims are not just PR fluff as our testing shows how good the thermal performance and efficiency are – the unit manages to maintain over 90% efficiency throughout the full range which is not an easy goal to achieve.
In regards to acoustics the unit is fantastic with a hybrid fan design which means under very low load it switches off, therefore emiting no noise at all. This would make an ideal power supply for a high quality media center, with the user safe in the knowledge that this will not only handle potential upgrades, but it comes with a full 7 year warranty.
In the real world we tested this PSU with an Intel Core i7 970 at 4.5ghz with two 5870s in Crossfire X and experienced a fully stable system, even when running Furmark under dual GPU mode with Prime 95 in the background.
Pricing in the UK is reasonably competitive as it is selling for £135 inc vat, however the biggest competition actually comes from the AX850 which is only £15 more. If the difference was £30 or more then the AX750 would be a more viable option, but the AX850 seems better value to us at the current pricing. All being said however the AX750 is the finest 750watt PSU we have reviewed to date.
KitGuru says: Another extremely high quality product from Corsair which is helping to ensure the AX name is a class leader.
