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Crossfire default voltage, does it follow top card's VDDC?

post #1 of 8
Thread Starter 
Hi, I got two 7850 cards in crossfire & using Sapphire Trixx.
Card A stock vddc is 1.138
Card B stock vddc is 1.075

Does the default voltage in crossfire depend on which card I put on top?
If that's so, and it sets 1.075 with Card B on top - wouldn't that be below the stable voltage for Card A's 1.138?
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post #2 of 8
Hello,
If both of the cards are the same brand / model they will both have the same everything.

If both cards are diff brand/ model they will be different but no worry's because this is fine! biggrin.gif


-ROG
post #3 of 8
OP each card will run at its own stock voltage and clocks unless you manually increase voltage and overclock. so leave both cards at stock voltage. mild overclocks to 900 - 950 mhz are easily possible at stock voltage.
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post #4 of 8
Thread Starter 
Thanks for the info, guys. I got Card A when 7850 was released, then Card B abt a year ago when Bioshock/Never Settle Reloaded bundle came out. I simply slotted Card B in the 2nd slot, crossfire was great & no problem throughout.

Yesterday I switched Card B to the 1st slot (another story). When playing Skyrim there were times when the screen froze for many seconds (maybe 20-30s), like it semi-hung & had to wait for something to recover. Before, it used to be very smooth & no problems. Everything at stock.

Well it could be new driver 13.11 b9.4. Previously at stock voltages, it could complete Heaven at 1120-1130 gpu clock. Even if it crashed & I needed to lower gpu clocks abit, it would crash sometime during the run. So for more consistent comparison between drivers, I usually run at 1100.

So due to Skyrim problem, I tried running Heaven at 1100 gpu clock, stock voltage. As soon as I clicked RUN, Heaven crashed without me even seeing the Loading screen. At 1.138v it ran fine, even better scores than other recent drivers.

That's why I wondered if crossfire uses the top card's stock voltage & applies it to both cards.
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post #5 of 8
Thread Starter 
Ok I played Skyrim for abt 2 hrs with old default vddc 1.138, and it was very smooth again like before. With new default 1.075, besides screen freezes there were also mini stutters when I looked around quickly. I've to put in more hours to be certain.

raghu78, what you said abt each card will run at its stock voltage - is that certain? I'm thinking crossfire applies 1.075 to both cards, which may be too little for the bottom card (1.138).
REPUBLICOFGAMER mention they will have the "same everything" if they're the same brand / model. My cards are both Sapphire HD 7850 OC, same clocks but different PCB, different heatsink & fan shrouds.

Card A, http://www.sapphiretech.com/presentation/product/?cid=1&gid=3&sgid=1160&pid=1499&psn=&lid=1&leg=0
Card B, http://www.sapphiretech.com/presentation/product/?cid=1&gid=3&sgid=1160&pid=1672&psn=&lid=1&leg=0

Edit links
Edited by misoonigiri - 11/24/13 at 12:21pm
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post #6 of 8
Quote:
Originally Posted by misoonigiri View Post

Ok I played Skyrim for abt 2 hrs with old default vddc 1.138, and it was very smooth again like before. With new default 1.075, besides screen freezes there were also mini stutters when I looked around quickly. I've to put in more hours to be certain.

raghu78, what you said abt each card will run at its stock voltage - is that certain? I'm thinking crossfire applies 1.075 to both cards, which may be too little for the bottom card (1.138).
REPUBLICOFGAMER mention they will have the "same everything" if they're the same brand / model. My cards are both Sapphire HD 7850 OC, same clocks but different PCB, different heatsink & fan shrouds.

Card A, http://www.sapphiretech.com/presentation/product/?cid=1&gid=3&sgid=1160&pid=1499&psn=&lid=1&leg=0
Card B, http://www.sapphiretech.com/presentation/product/?cid=1&gid=3&sgid=1160&pid=1672&psn=&lid=1&leg=0

Edit links

OP you can ask tsm106 who is an enthusiast who has had several multi GPU setups. as far as I know unless you manipulate settings the cards will run at stock voltages and stock clocks. ideally both cards should run at same clock for best performance. so run at the clock which is the lower of the 2 cards.
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post #7 of 8
Thread Starter 
Hi raghu78, both Sapphire cards have the same default clocks 920/1250.

And you're indeed right - Sapphire Trixx does show 1.138 after selecting bottom card from droplist. Don't know why, I thought I did check it yesterday but mistakenly saw 1.075 instead.
So... I think I'll try cleaning the PCIE golden connectors to see if it helps.
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post #8 of 8
Thread Starter 
Played Skyrim smoothly now these 2 days. No more problems with Card B on top (no mini screen freezes, no stutter when looking around).
As for Heaven, at stock voltage crashes DURING runs at 1070-1100 gpu clock, but completes run at 1060. Lower now, maybe its the new driver.

Not sure if cleaning the cards' golden contact regions was the fix or not, but glad gaming is smooth again as before (when Card A was on top).
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