[Allan Speers]

Thanks, Dennis.

I can’t afford a Titan right now. I’ll probably go with a new Mac next year, anyway.

As to my original question, your idea would probably work (clever) but it turns out to be a non-issue. For anyone else needing to know this, here’s what an AMD tech just told me:

### The AMD “ZeroCore Power” technology cannot be disabled or turned off, however it ONLY APPLIES TO A CROSSFIRE SETUP.
With two cards in a Mac, and only one monitor connected, the second card will NOT go into sleep mode, unless the mac itself does.

AMD’s product descriptions do not make this clear at all.

[Allan Speers]

I also just found out that there’s a way to restrict a card’s maximum power consumption (to 225 watts, for instance) via some kind of firmware update. (I don’t know the details) That would obviously restrict some areas of performance. No idea how it would affect FCPx or Motion.

Could your card have this mod?

(straying off-topic a little, but still important)

[Allan Speers]

Wait – I just read that the 280x uses a 6 and an 8-pin connector, with the latter typically providing 150 watts. How did you rig this on a Mac Pro?

If you somehow combined two 75w sources into an 8-pin adapter, then that would explain it, but if so I’d sure like to know how!

[Allan Speers]

Thanks, Mike. That helps me a little, because according to TOM’s :
( https://www.tomshardware.com/reviews/radeon-r9-280x-r9-270x-r7-260x,3635-18.html
The 280 pulls just about the same power, in there highest stress-test (a bitcoin server) as a 7950 running at 950 Mhz. Both cards require over 250 watts. I assume then that your FCPx setup does not stress the card as much as that test.

So: What IS your setup?

Also: The 280 is not on the official FCPx approved list. What was your reason for choosing it? Have you seen any test comparing it to the 7950, using FCPx or Motion?

[Allan Speers]

Here’s a related & kind of obvious question:

If the Mac’s psu is 975 watts, then given normal “safety margin” and aging component concerns, that still gives around usable 700 watts. The other three PCIe slots require 225 watts total, and the cpu is going to pull MAYBE 150 watts on a bad day. Ram & SSD’s might pull 50w, but probably much less.

That leaves a nice safe 275 – 300 watts for the GPU. That would run a maxed 900 Mhz card, maybe even a 1,000 Mhz card under “normal” FCPx usage. Is there some reason one cannot (somehow) put more wattage onto those 6-pin connectors?

[Allan Speers]

Mistake above, and I don’t see how to edit my post, so:

FCP Water Pane FX render:
One 5770: 52.4 seconds. Two 5770’s 3-.8 seconds.

[Allan Speers]

https://barefeats.com/tube05.html

FCP gausian blur test:
One 5770: 38.2 seconds. Two 5770’s 20.2 seconds.

FCP Water Pane FX render:
One 5770: 52.4 seconds. Two 5770’s 3-.8 seconds.

This is an insignificant gain to you?
—————

Other reports (including the BryceX benchmark) indicate that results with two 7950’s are similarly dramatic. Another test showed that two 5770’s blows away a single 7950. FCPx was optimized (not too long ago) SPECIFICALLY to take advantage of two open CL graphics cards.

[Allan Speers]

Thanks, John.

yeah it’s a pretty arcane process. It should be reasonably do-able, if all the needed stuff was available in one place, but I’ve lost 2 days trying to find all the data & such, and some of it seems to be no longer even available. I’m hoping someone might come through here, but if not then I will indeed buy one pre modded. Most lose a port or two, but that doesn’t is actually somewhat common.
——————–

But as for running two of them, of course you can! (and the performance boost is supposedly dramatic.)
You have 2 choices:

1: Use power cable y-splitters, and live on the cutting edge of your psu. (They only draw 190 watts if fully maxed out, which evidently requires running two big monitors. ) Many folks have gotten away with this.

2: Install a second PSU into your spare optical bay. It doesn’t have to be an expensive psu, and you only need a 400 watt model is literally overkill. I have a few on the shelf right now, so ….

[Allan Speers]

Oliver, you are dead wrong on both points, but thanks for playing.

“You can get a Sapphire 7950 Mac card for about the same cost”
– On what planet? New or used, the difference is about $200, typically more.

“This has no effect for FCPX. Only one card will be utilized.”
– Contrary to everything written on the subject, on every forum & every benchmark test one can find.

OK then …..