Dual Graphics Cards with Riser cable?

Discussion in 'Mac Pro' started by m3rob, Apr 15, 2018.

  1. m3rob macrumors member

    Dec 28, 2010
    I have two Geforce GTX 680 Mac edition cards and would like to run them both on my 5,1 Mac Pro. I already have a way to power them both. Is it ok to use a riser cable to install the second card in Slot two and just have the card setting outside the case with the case open so that it doesn't block slot 3 or 4? Is there any reason that this wouldn't work or isn't advised?


    Here are a couple options for cables:



    Any thoughts would be greatly appreciated!
  2. h9826790 macrumors G4


    Apr 3, 2014
    Hong Kong
    As long as you have a way to secure the card at a safe location. I can't see why not.
  3. flyinmac, Apr 15, 2018
    Last edited: Apr 15, 2018

    flyinmac macrumors 68040


    Sep 2, 2006
    United States
    I would take the time to read the 1 star and 2 star reviews.

    Those match more closely with my experience in ideas like riser / extension cables.

    You’re moving a lot of data at high speeds. To pull that off successfully, you need something better than what looks to be a ribbon cable.

    As soon as you take something designed to plug straight into a circuit board and extend it on a ribbon cable, you’ve got interference and and performance issues.

    Ribbon cables were not designed to carry significant power loads. I wouldn’t push power over a ribbon cable and expect anything but a fire hazard. Think about how much power modern graphics cards use. Then think about how tiny those wires are in the ribbon cables. It’s beyond their rating. Unless they go with solid core wiring (which would still be potentially problematic).

    Then you’re extending the data bus away from the circuit board. And doing so with a flat cable. Now you’ve got shielding issues. Essentially you’re allowing a lot of interference and crosstalk... your data is going to get scrambled.

    I can tell you from experience (I was there) that this design idea was tested thoroughly in older computers running at 1 Mhz and Pushing half a watt of power through the cable many years ago. It was found unstable no matter how much shielding we threw at it.

    I certainly would not expect it to work with today’s technology. The graphics cards pull far more power today. And run at much higher frequencies of speed.

    Cards want and need to be plugged into a slot in a board inside a shielded chasis.

    If you want to try to do this, I would lean more towards an external shielded case where the card could sit in a circuit board. A bus expansion Chasis. And then have a shielded data rated cable run between that chasis and an expansion card in your computer. The data moves over the shielded cable between chasis units, and the card would be independently powered by the bus in the external expansion chasis. Significantly more expensive, but more reliable. You’re usually talking several hundred dollars for an external bus expansion chasis unless you have the ability and equipment to build your own (which it doesn’t sound like you have that laying around).

    Anything less and you’re just asking for trouble.

    Alternatively, consider an e-GPU or USB GPU option.
  4. fendersrule, Apr 15, 2018
    Last edited: Apr 15, 2018

    fendersrule macrumors 6502

    Oct 9, 2008
    flyinmac- I don't doubt your experience and i agree with most of your points. However with my experience:

    1) Vertical mounted cards I think is actually a trend that's probably here to stay with PC builds. Many people use riser cables. It's a pretty cool look when done right.

    2) I can vouch for the Thermaltake cable. Many of the one star reviews are from the initial revision of the cable which had problems. The latest revision seems to be very rock solid. I have one in my "Mac Pro" PC with an RX580 for several months now. Looks, sounds, and games lovely. The RX580 is also pretty power hungry so if that doesn't cause problems, then it's highly doubtful that a 680 will.

    What I find weird though, is you are not really using the cables for looks, but for pure function, and it's probably going to look like a frankenstein computer when you're done. I guess "it will work", maybe it's time to replace the 680s all together? Do you absolutely require a bootscreen, or just think you do? A MacOS + Windows drive needs zero boot screens; pre boot screen drive selector is actually the slowest way to switch between them. But I understand others have many other boot volumes, so yea...

    At any rate, I'd consider a GT120 for your boot screens, and move up from the GTX 680. Keplar is long dead. There's still people out there that "think" they need a GTX 680 and will gladly pay for them, so you can recoup some cost.

    Here's my PC build using almost entirely spare Mac Pro parts with a 5770 before I put in a RX580. You can see the Thermaltake Riser cable. Really cool build; it's actually faster than my pimped out 5,1 Mac Pro. You can't "feel" any difference between them though, but synthetic benchmarks show otherwise.

    W3680 @ 4GHz
    12GB DDR3 @ 1600MHz
    500GB SSD Windows 10 Pro

    Attached Files:

  5. flyinmac macrumors 68040


    Sep 2, 2006
    United States
    That is a pretty cool looking setup you have there. And I’ll accept and appreciate your experience with it.

    In your particular design, if it were me, I’d have gone with a riser card. But I understand if the variables of potential alignments with other chasis designs made it difficult to locate such a card that fit exactly with your intended setup.

    Not everyone has access to the equipment necessary to produce their own circuit boards either.

    For a hobbiest, there are options to produce one-off circuit boards at home. And I’ve done that as well in some instances where I just needed one, and didn’t desire to get crazy. Such a project can be done in about an hour, aside from the soldering time and time to drill out the holes. Which depending on experience level might take a bit for some people. A dremel works in a pinch.

    But I know most are looking for prebuilt solutions.

    A riser card / bus provides benefits of reliable long term durability. It won’t degrade, burn up, crosstalk, or act as an antenna for every frequency surrounding you. And it can handle as much power as you can throw at it (naturally within the limits of what you intend to attach to it).

    I don’t do circuit design anymore. But I could if the price was right, or if I decided I want to do something custom. I still get the equipment out periodically and build what I want when I either don’t like the available options, or when I want it today and logistics make it impossible for a premade solution to arrive in the next couple of hours.

    Had it out yesterday doing some modifications inside a PC. I wanted an internal feature that didn’t exist on the mainboard (PATA) for an old device. So I got out my probes, soldering iron and set to work integrating PATA onto the mainboard. Yeah, I know I could use an external USB adapter, but I didn’t want the drive external.

    Yes, I know about PATA to SATA adapters. But I wanted it then and now. Not to wait for shipping.

    So, I still dabble as needed. And it’s more fun to get in there and work on the circuit level like I used to. What’s the fun in just plugging things in?? :p

    But back to your project, it does look pretty cool. I like it. If I had the extra time, I’d be tempted to get with you and build an expansion bus / riser card combo that would fit it. But it gets hard in these days to find time for projects lol. Looks around the house at all the half done projects... hmmm.... maybe next weekend??? ;) Wait... no next weekend I think there might be something in the lake calling me. :D

    As for your advice to the OP... I concur.
  6. m3rob thread starter macrumors member

    Dec 28, 2010
    Thanks for all the feedback guys! Really appreciate it! I might just upgrade and just use one card to save some potential problems. I work with really tight deadlines so probably not worth the risk. :)

    Thanks again!
  7. flyinmac macrumors 68040


    Sep 2, 2006
    United States
    Yes, in situations where reliability and deadlines are important, the least complicated and most stable solution is best. Good luck in your project
  8. bsbeamer macrumors 68000

    Sep 19, 2012
    I've used a hobbled together expansion chassis on a client machine that was connected via PCIe ribbon cable in the past. It's not my preferred connection - do like the PCIe slot expander cable connection better for those setups, but the ribbon cable did the trick for a long time until they moved to different machines.

    Connectors sort of like the ones with green pull tabs on this image:
  9. flyinmac, Apr 15, 2018
    Last edited: Apr 15, 2018

    flyinmac macrumors 68040


    Sep 2, 2006
    United States
    The type of solution I was speaking of for a riser card would resemble (though more appropriate in height / length for the particular chasis) the below image.

    Naturally, if additional slots were added, there’d need to be some circuitry added for addressing purposes.

    But otherwise, if the card was produced at a suitable length / height for a person’s particular application, and perhaps contoured appropriately as well, it could produce a very clean and solid design.


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