Hi,

I just built my new rig with 2 GTX580, a 2600K and all the rest. I currently use a Enermax Modu 87+ 900W. I measured the power draw while running Unigine Heaven at approx. 500W at the power socket. So 900W is kind of an overkill.

However, my main concern is noise. The Enermax doesn't get any louder when loaded, but the fan is buzzing audibly even at idle. I will exchange the unit, but just in case the replacement isn't better, I need a recommendation for another power supply in the 700W range that is as quiet as possible.

I have my eye on the Corsair AX750/850 and the Seasonic X-Series 760/850. As far as I know, there is no difference in fan size for these models, but what about the fan control characteristics and heat sink size? Again: As quiet as possible please. No whining, buzzing, humming, grinding

The cable length doesn't matter, I am using sleeved extensions anyway.

Thank you and best regards
boxleitnerb

With two GTX 580s in SLI and a 2600K (presumably not (yet) overclocked) I would say that 500w at the wall under a gaming engine load is maybe a touch on the light side. For this reason I think you should look at 1000w PSUs rather than 850w. A suitable candidate would be the Silverstone Gold 1000W SST-ST1000-G Strider model. It has a 135mm fan and should be pretty quiet at idle - probably as quiet as you're going to get.

Well, 1000W is way too much I think. If you assume 90% efficiency, the power supply has to offer 450W to the components. Add to that a comfortable 50% headroom you get 675W that the power supply has to give. I will OC the CPU and the GPUs a bit, yes. But without excessive increase in voltage.

Idle with the semi-passive Corsairs/Seasonics is no problem - the fan won't run at all. It is load that I'm concerned with. The Enermax didn't increase in noise while running some benchmarks, but the base level was just to uncomfortable for me. I want both: Silent at idle and at least very quiet at lets say 600W load at the wall.

I think it can be argued that power supplies are normally at their most efficient and quiet up to about 50% of their nominal capacity. So on that basis a real power load of 450w would certainly point to 900/1000w capacity, particularly as two GTX 580s are going to impose a significant drain on the 12v rail. The Corsair AX-850/Seasonic X-850 are the same PSU with a different cable set for the Corsair. There is the advantage with both these PSUs of the fan not being turned on at low loads, but I still think 850w is not enough, particularly if a worst case scenario could be as much as 540w actual load. Under this loading I would expect both to have some reduction in efficiency, but perhaps not that much. There would certainly be significantly elevated PSU exhaust temperatures which might be unwelcome bearing in mind how much heat the rest of the system would be producing.

If you propose a real load of less than 500W, why would I need a power supply that can provide double that amount? That makes no sense, even for power peaks. Admittedly, the peak efficiency is around 50%, but we're talking maybe 2-3% here when compared to 80% load.

At 500W load the difference in power dissipation for a 700W and a 1000W unit should be about 10W, so not that much.
I should add that I have a watercooled system and the power supply will be in a different compartment in my case. Temperatures should be no problem.

I will not buy an oversized power supply. It is a misconception that you need this much power - similar to the notion that MHz = performance for instance. No offence, but this much I know

I recommend the corsair ax850 it's more than enough and still very efficient up to high power loads. SPCR tested it to like 1000watts from the wall so it's overkill, a 750w could easily run them too.
I have a 2600k and one 580.
My AX850 is seperated from the rest of my case and under artificial load with a single 580 i get about 380w from the wall. It takes 15 minutes of this artificial load (prime 95 and furmark) for the fan to even start spinning. Even then it spins slowly and without much audible noise. My system is very quiet (accelero xtreme plus cooler and HR-02 on the 2600k) so I can safely say I basically never hear my ax850.
It might be a bit more audible under load of 2 580s but I doubt it'd break 15db if you're sitting at 500w load. Not sure if the fan would start up with 2600k and 580SLI @ idle.. I think it would depend idle would be around 200w I assume and I think the ax850 fan starts up around 150w load or temperature dependant.
The one nitpick I can say about the power supply is the cables aren't the smartest(no molex/sata combination) and the cables require quite a bit of force to secure into the power supply. The packaging is complete overkill as well.

Thank you for your input.

Yes, the cable combination is a bit odd but I think I'll manage. First I will return the Enermax, though. Noisy bugger...

I'd recommend not getting a super oversize power supply, I have a couple of i7 980x systems with dual gtx 460s, I've been folding with them 24/7 so they were using 500W+ from the wall pretty constantly, and they both have 850W PSUs, one is the Antec Signature and the other is a Corsair, I think, don't remember right off the top of my head. Haven't had any trouble from either, both are pretty quiet. A bigger supply might be slightly more efficient, but whether you want to optimize for that really depends on how much time the system will spend at peak load. If the system will idle or be under low load for any significant streches, then you'll lose a lot of efficiency at idle. With dual 580s you might have some higher load on the 12V supply, but I wouldn't worry about it too much.

I would challenge the assumption that 500 W assumption so that you do not get a PSU that falls a bit short.

First of all, there are programs that will tax the graphics card much more than Unigine: as an extreme case, in my tests, Unigine sucks around 60 Amps for my graphics card, but Furmark around 90 Amps. This translates into 50% more watts (glubs!). Granted, furmark is written so that it sucks lots of power -but maybe you'll want to test your card for stability with it or a similar program at some moment, so...

Second, if you overclock and raise voltage to do so, your graphics card will suck even more voltage. Overclocking can be done without making the system noisier, so you might be tempted to gain 20 or 30% performance. I have overclocked cards that run 25% more fps with an accelero xtreme plus cooler, and they are completely silent even at load.

As an example, at stock furmark sucks 63 Amps, and at maximum crazy overclock it sucks 106 Amps, meaning we are almost duplicating power consumption.

As additional evidence, think that at anandtech they found that two GTX580 in SLI will suck aroud 850 W for furmark, and 620 W in Crysis (http://www.anandtech.com/bench/Product/308).

You might be interested into considering all of this before committing to a certain power limit. Like you, I think most people heavily overestimates power consumption and buy oversized PSUs...but it is a pair of GTX580 you have there, really hungry beasts

Hope the Enermax guys give you back a working unit, it is a great PSU -though I had to replace an Enermax PSU fan with a BeQuiet SilentWings when it started to get noisy

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PS: having the PSU sucking air from the outside instead of the hot air in the case will make it much, much quieter, especially if you have two 580s, which will be a furnace. We are talking about 8/10 dbs here, really. But you probably already know this...

500W were no assumption, I measured it

As my cards have cost 1000 Euros, I will not risk running furmark. It makes no sense anyway because this load is unrealistic and the 580 have over current protection enabled by default which is there for a reason. I think if I test with the highest load I can possibly give under realistic circumstances (Downsampling with 2560x2048 resolution, 8xSGSSAA and for instance Unigine or Crysis or something) and add to that a buffer of 50%, I'm good.

Concerning stability, there are better tests, because every software taxes the cards differently. It can happen that your setup is furmark stable but that it crashes in a game or gives you artifacts. Furmark is just good for testing temperatures. I hit 45°C max while playing Crysis or running Unigine Heaven, so this isn't really an issue. That is, having the fans running at only 4.5V

Nevertheless I will get the AX850 as it costs just 18 Euros more than the AX750 and I don't know how much I will overclock the cards over their lifetime

Go for the AX850, but i woudlnt OC with SLI 580 with 850W, probably stock you might be fine, but OCing might push it.

Seasonic was going to release 1000W psu, but idk when they will be launching, might be wroth checking out for your setup.

Yeah, I knew. What I meant is 500 W might not be a very reliable "high watermark", but given that you are adding a 50% pad, you are taking that into account, albeit in a different way. When you asked about the subject, I did not know you were adding that amount


Of course, furmark is not realistic, but I think it definitely serves as a high watermark for power consumption and can highlight VRM refrigeration problems. I feel that, once you measure what furmark needs, you have an absolute graphics card maximum you will never surpass in real life. Add 10/15% to be on the safe side, and you are set.


In fact what I found in my case is furmark adds that 50% over Unigine -amazing. I would use a larger pad, more like 60 or 65% just to be absolutely sure. By choosing the AX850 over the AX750 you are doing that


Too true, IMHO furmark has an undeserverd reputation when it comes to stability testing. In my setup unigine finds problems much faster than furmark, and in many cases finds problems furmark never showcases. Nowadays, Furmark is only good to highlight power related problems, an interesting test when you use aftermarket coolers. I use an Accelero Xtreme Plus, so it is a concern for me.


That's a good PSU, but, as abula mentioned, I would not OC if you go for the AX850 (unless those 500W you measured are with max overclok, then everything is ok).

Just to make absolutely sure I'm not too far off, I checked current consumption under Unigine, not just furmark, which is enginereed to suck power and might bias the experiment. At stock speed, my core consumes around 36 amps and 52 at absolute max overclock (let's be safe), a whooping 44% increase. Granted, my VGA is a 5850, but... I would hate you spend so much money to find you are off by a mere 50/100 W.

Enjoy your little silent monsters

I did a fair amount of reading on this because I expected to possibly add a second 580 into my rig. There are several threads on OCN about this as well as several users of SLI 580s. At least one also has the 2600k. I really think you'll have absolutely no problems OCing your computer to basically any level. My single 580 overclocked to 910/2170 @ 1075 voltage + 2600k 4.4ghz just barely inched towards 400w from the wall.
However that could be 10% or so below where an absolute absolute max would be since the 500 series of nvidia cards have power protection that is enabled when using furmark. The maximum the ax850 will supply is 1000w from the wall (or possibly slightly more since it's likely a little overrated) so that's a lot of headroom.

Just talked to a senior mod @ OCN as a point of reference and he runs his SLI 580 @ 850 core and 2600k @ 4.5ghz day to day no problem.