cMP drivebay PSU - options for approaching silence?

[Letstryit]

Hi all,

(TLDR: What's the best option for getting 2x7950s in a cMP safely and with as little added noise as poss?)

I'm in the market for a cMP 2010-2012. One of the big reasons is the opportunity to put dual 7950s in it, and I don't want to risk doing it on the stock PSU so I'm going to get a secondary one for the drivebay. I'm also looking into 7970s, as in whether it's possible and worth it.

I've read some really great walkthroughs by HappyMac314 and OrangeSVTguy, and am planning to run the power rails off the stock PSU to get a neat and tidy solution.

My research has so far tended to lead me to Seasonic... anyway onto the questions!

• What PSU would you recommend, with lowest noise being the goal?
• How deep can the PSU be? The 400 and 500w Seasonic drives look long, but I've read that they run fanless until 250w.
• Does the 'Active PFC' part mean that the fans are controlled by the draw from the PSU rather than being on all the time?
• I don't use an optical drive. Is putting a 2U PSU into the cMP an option, in case I can find something quieter in that format?
• Is 250w enough for a 7950? Specs wise yes, but is it recommended I have more redundant power?
• Is it possible to run dual 7970s, one off the stock PSU and one off a secondary PSU, and if so is it worth it over the 7950?
• Do I need to use a particular model of 7950 (I'm looking at the reference cards)? If not, do I need the pair to be the same model?

Thanks in advance for any advice anyone can give - I'm really looking forward to getting set up!

 

[h9826790]

(TLDR: What's the best option for getting 2x7950s in a cMP safely and with as little added noise as poss?)

I am currently running 2x 7950 with internal power only. Only very little noise from the graphic card when under full load. And I run this for a year now. Usually stress it few hours continuously a day by gaming in crossfire (in Windows), or using FCP X to edit 4K video (not as stressful as crossfire gaming). The trick to get it work is to get a card that run at stock frequency (800/1250Mhz), and try to lower it's voltage as much as possible (from memory, the stock voltage is about 1.095V, and both of my card can be lower to about 0.9V but remain stable). Please refer to this sharing.

https://forums.macrumors.com/thread...mac-with-2-d700s.1732849/page-5#post-21722712

• Is 250w enough for a 7950? Specs wise yes, but is it recommended I have more redundant power?
• 250W is more then enough. Standard 7950 only draw ~145W under load, and ~177W in stress test (Furmark)

• Is it possible to run dual 7970s, one off the stock PSU and one off a secondary PSU, and if so is it worth it over the 7950?
• Yes, but still require some power management, AFAIK, all standard 7970 come with at least one 8pin input. And then card will draw much more then 75W under stress. So, you have to thing about how to power the 7970 with internal power safely. You can refer to this thread.

https://forums.macrumors.com/thread...ake-it-your-king-of-mac-with-2-d700s.1732849/

• Do I need to use a particular model of 7950 (I'm looking at the reference cards)? If not, do I need the pair to be the same model?
• No, technically, you can use whatever model you want. However, if you want to boot screen. It's highly recommended to get the reference card, which can be flash and still has all ports working properly. If you click the link in my signature (R9 280 / HD7950), you can see the actual cards I am now using. In fact, one of them is the R9 280, but that has exactly the same device ID as the 7950s, just rebranded by AMD.

The PSU in the cMP has juice for more than 2x7970 + 2x5690. It's rated 980W, if you are happy with DIY solution. You can actually consider this Pixlas mod.

https://forums.macrumors.com/threads/pixlas-4-1-mac-pro-mod.1859652/

 

[Letstryit]

Thanks for your reply! I had read your guide too, sorry I forgot to mention you in my original post.

My only concern with running both cards off the stock PSU, even underclocking, is that if anything goes wrong I just won't be able to afford to replace and I will be using this computer for work and plan to hold on to it for some years.

I have a long history of being the exception that proves the rule when it comes to bad luck with stuff that 'should' work fine!

It's definitely something to think about though - the performance hit seems fairly small. Is there any safeguard so that if there's a risk of something becoming damaged I can get notified and switch before the worst happens?

Thanks again,

 

[h9826790]

Thanks for your reply! I had read your guide too, sorry I forgot to mention you in my original post.

My only concern with running both cards off the stock PSU, even underclocking, is that if anything goes wrong I just won't be able to afford to replace and I will be using this computer for work and plan to hold on to it for some years.

I have a long history of being the exception that proves the rule when it comes to bad luck with stuff that 'should' work fine!

It's definitely something to think about though - the performance hit seems fairly small. Is there any safeguard so that if there's a risk of something becoming damaged I can get notified and switch before the worst happens?

Thanks again,

IMO, the best safe guard is to limit the card's power draw in the firmware. It's supper effective. once you do that, the card won't draw anything more but will reduce the performance to fit inside that power envelope (I mean the average power draw. Most of the mid - high end GPU can momentarily pull more than the cable's limit, just the average is below. It's normal).

If you want 99.99% safe (nothing can go 100%, right). I will do the following.

1) Get a 7950.

2) Only install that single 7950 in the cMP

3) Boot to Windows, and then lower the voltage as much as possible (by running any Benchmark e.g. Unigine Heaven, Furmark, or OCCT, and then lower the GPU's voltage until it crash. e.g. It crash at 0.85V, then you can try to stress your card at 0.9V. If that's stable, then I will run the card at 0.9V.

4) Make the ROM with 0.9V. Flash it to the card and then boot to OSX (I assume you work in OSX).

5) Run Furmark, and check the power draw from the PCIe slot. (e.g. 40W)

6) 40+75 = 115. Therefore, if we limit the max power draw to 115W. The card should not able to draw more than 75W from the 6pins.

7) Make another ROM with 0.9V and max draw 115W. Make it Mac EFI enabled, and then flash it to the card again.

8) Repeat this procedure with your 2nd card.

9) Now, you have 2x 7950 which each of them can only draw 75W from the 6pins. If you are running something like FCPX, this power limiter should not really limiting your GPU's performance.


For your info, I initially limit the power draw of my card to 130W (as a safety precaution). And after a year of real world usage and few more tests. I now just go back to their stock max power draw setting. I did try to push this setting to limit. For testing purpose, I intentionally push them until the machine shut down. In fact, the buffer is much higher than what I expect.

All tests are conducted with 2x7950 crossfire gaming in Windows 10 to simulate a reasonable real world max loading. The result as follow.

1) Min voltage. No matter what I do, it's cool and quiet. However, I cannot OC the card to more then 850Mhz, anything at or above 880Mhz may crash. I can run this config for 6 hours Crossfire 4k gaming, and the GPU still stay below 70C (system ambient 30C) with a manual fan profile that inaudible during gaming.

2) Stock voltage with max power draw 130W. I can set a higher frequency, but not much real world performance gain. Because the card will stop go further when it hit 130W. In fact, this is not a effective setting. Both card run warmer because higher voltage, but roughly the same performance.

3) Stock voltage with stock max power draw. I can set higher frequency (e.g. ~1050MHz), the card will run hotter and nosier, obviously can draw more then 100W from the cable, but still won't shut down the Mac Pro.

4) Increase the voltage to 1.15V with stock max power draw limitation. I can OC both cards to 1150/1500Mhz, and this eventually shut down the Mac Pro (the self protection) when running the Benchmark (after about 20-30 seconds, not instantaneously).

So, IMO, with 800/1250Mhz, ~0.9V, 130W limit. It's far far away from the Mac's real limit. Of course, it's still technically beyond the official limitation. If you are not comfortable with that, further down to 115W limitation should be extremely safe.

If you are "unluckily", by installing extra PSU can also gives you troubles (e.g. unstable power output, which kill your GPU, or even kill the PCIe slot via the card, or catch fire, or whatever possible).

 

[Letstryit]

Thanks again. I think you've pretty much convinced me. It'd be nice to have the full power of the two cards, but running 90% of the power of the cards without the hassle of the aux PSU outweighs it for me I think - especially if it's quieter.

So, you've been running your 2x7950 plus USB3 PCI card system for some years now without problems?

Also - assuming I had the space for sufficient airflow, am I correct in thinking that it's still safe to install a PCI soundcard as long as the power requirement is less than 75w (should be significantly lower) plus a USB3 card?

I really appreciate your help - I'd be really interested to hear anyone else's experience too!

 

[h9826790]

Thanks again. I think you've pretty much convinced me. It'd be nice to have the full power of the two cards, but running 90% of the power of the cards without the hassle of the aux PSU outweighs it for me I think - especially if it's quieter.

So, you've been running your 2x7950 plus USB3 PCI card system for some years now without problems?

Also - assuming I had the space for sufficient airflow, am I correct in thinking that it's still safe to install a PCI soundcard as long as the power requirement is less than 75w (should be significantly lower) plus a USB3 card?

I really appreciate your help - I'd be really interested to hear anyone else's experience too!

If you limit it to 115W. I am sure it's very easy to make a low noise fan profile even with the poor reference cooler.

By installing 2x7950, there is only one slot left, due to the slot 3 or 4 will be blocked by the 2nd 7950's heatsink no matter how you install it.

If you really want to use all 4 slots. You can either install the 2nd 7950 at slot 4, but then no HDD in bay 2 3 4, and you need to cut the case a bit. Not ideal for most user.

Or get a PCIe extension cable. However, the PCIe card then will floating around, it may be OK for PCIe SSD, but since all USB, graphic card, sound card need to access the port at the back, so not a good idea as well.

 

[SoyCapitanSoyCapitan]

Drive bay PSU is a PITA.

Search this forum for Pixlas mod.

 

[h9826790]

Drive bay PSU is a PITA.

Search this forum for Pixlas mod.

I gave him the Pixlas mod link on my 1st post already.

 

[Letstryit]

Thanks for the replies gents, underclocked and running off the stock PSU it is!

 

[h9826790]

Thanks for the replies gents, underclocked and running off the stock PSU it is!

Unless you get a OC version in order to get a better cooler. I don't think you really need to under clock the GPU. Under volt should be enough. Of course, nothing stop you to try your own comfortable setting.

In fact, I did run my cards at 1.05V 970/1375MHz for quite a period of time. It's stable, and survive from all the tests. However, the GPU with the reference cooler can go up to 77C, and I can hear the fan noise. Since I only use FCPX for fun, not really need that extra speed. And I don't want to further increase the max temperature for lowering fan noise. So I finally went back to stock frequency, and enjoy the quiet and cool GPUs.

 

[h9826790]

Not sure what do you want to do with 2x 7950. If possible, I can do the test for you. Anyway, more info for you about the power draw. So that you can understand more what will happen on different usage.

The label is wrong in Hardware Monitor. From the consumption, you can easily tell:

PCIe Slot 1 12V Line = 6pin 1
PCIe Slot 2 12V Line = 6pin 2
PCIe Slot 1 12V Boost Line = Slot 1
PCIe Slot 3 12V Line = Slot 3

1) This is the actual power consumption during FCPX rendering a 4K video (form memory, 3 layers with few filters and special effects). As you can see, the power draw actually stay at a comfortable level. This is my general real world usage.

2) This is to simulate very high real world usage by running Luxmark 3. One of my card will draw around 85W continuously from the 6pins. However, another card only draw right at 75W. So, in fact, if you get the right card, which call pull more from the PCIe slot (the blue line), and pull less from the 6pins (the orange line), you can actually run 2x7950 at stock frequency, and stay right at the 75W limit even the work load as high as running something like Luxmark. Anyway, the cMP of course can handle it without any problem.

3) This is running Unigine Valley on one card, and Unigine Heaven on another one. Should be above most real world usage can do in OSX. As you can see, the power draw is not as stable as Luxmark. Peak can go to 90W for both card. But from the graph, you can see the average is actually around 85W. That's 10W above the official max on both 6pins, however, since we know the cut off point is at about 120W. I personally very comfortable to run at this config. This should be very close to what I have during crossfire gaming. IMO, as long as you can evenly distribute the power draw, that extra 10-15W demand should not cause any big trouble.

4) The ultimate test, simultaneously running Furmark on both 7950. I don't think any "normal ops" can do anything heavier than this in real world. The power draw is fluctuating (may be limiting by the CPU single core performance, since each of the Furmark copy demanding 100% from the CPU). I am quite sure that 95W is not the real power draw. The real power draw should higher than that, but just cannot be displayed properly.

However, we can get the rough number indirectly. Total power draw 449.4W (on the menu bar). Since the CPU only using 200% during running 2x Furmark, a quick test showing that the CPU only consume about 50W in this situation. By comparing to the Luxmark (CPU + GPU test), CPU was drawing about 70W, and total 422W. A rough calculation can be done as follow.

Extra loading on the 6pins (compare to Luxmark) = 450 - 422 + 20 = ~50W

So, if all these 50W also goes into the 6pins, and I successfully evenly distribute the power draw. Each 6pin was delivering (85 + 75 + 50)/2 = 105W.

This is my personal max max power draw. I don't want to go anything beyond that (I've already done one "shut down" test by increasing both card's voltage and OC them in crossfire gaming, that's enough for me ). Anyway, the cMP can run this dual Furmark stress test without any issues. I absolute won't recommend anyone run this stress test on their machine. Not even do it at your own risk. However, I did it, and the cMP survive without any problem.

 

[ActionableMango]

Top notch post, h9826790. Thank you.

 

[Letstryit]

Wow thanks for that - and sorry I didn't reply sooner I didn't see your post until now!
I have a Mac Pro about to be delivered and just got two 7950s - I didn't get to choose the model and ended up with a sapphire with one fan and a gigabyte with three.

I'll look into this more when I get a chance this week, but just wanted to reply to say thanks for your detailed response now before I forget!

 

[Letstryit]

Right, I'm nearly ready - most of my parts have turned up!

I need to order 6-pin splitters. I just need to get female to 2x male and plug them into the male ends of the mini-normal 6-pin and then both 6-pin ports on each card, right? (https://www.amazon.co.uk/Startech-com-Express-Power-Splitter-Cable/dp/B004NNTVT6/ two of this?)

I have one more question: Rather than split the power of the 6-pin boost for both cards, would I get any benefits from getting a 2x SATA to 6-pin adaptor for one of the cards to get it more power?

Thanks!

 

[h9826790]

Right, I'm nearly ready - most of my parts have turned up!

I need to order 6-pin splitters. I just need to get female to 2x male and plug them into the male ends of the mini-normal 6-pin and then both 6-pin ports on each card, right? (https://www.amazon.co.uk/Startech-com-Express-Power-Splitter-Cable/dp/B004NNTVT6/ two of this?)

I have one more question: Rather than split the power of the 6-pin boost for both cards, would I get any benefits from getting a 2x SATA to 6-pin adaptor for one of the cards to get it more power?

Thanks!

Yes, 2x this cable should works.

Of course you can use 2x SATA to 6pin to drive one card, but I personally didn't do it.

1) All my 4 SATA ports are full of HDD / SSD.

2) Of course I don't want to burn anything. But I don't mind to risk my on board mini 6 pin (relatively), if anything goes wrong. I can still go the Pixlas mod as work around (or enhance the Mac Pro's power system). However, I don't want to risk my SATA 2 port. I didnt find any reference to make sure each SATA port in cMP can provide 55W, but from memory, so far no one reported burn the SATA port via a 2x SATA to 6pin cable.

Anyway, it can gives you one card "full power". e.g.

7950 A - mini 6pin -> 6pin + dual SATA -> 6pin (as primary card, you may even able to OC this card a bit).

7950 B - mini 6pin -> dual 6 pin (as supplementary card, highly recommend run at stock 800/1250MHz and under volt as much as possible)

 

[Letstryit]

Thanks again for your help!

I'm really keen to try asap, the magic of Amazon Prime NOW means I should receive the cables tonight!

The only important thing I'm waiting on now is the OWC SSD drive sled, which is due to arrive Thursday - annoyingly the HD that came with the Mac is failing SMART so I can't upgrade OS X and install Bootcamp Win7 even to try things. I might try temporarily tying the SSD to support it while I play around tonight.

I am really interested to see whether I can in any way fit the 2x7950, an Inatek USB card, and then somehow - via extender ribbon cable perhaps? - install a PCie SATA3 card for my SSD. Maybe that's something for another thread, though.

I'll post up my results!