4x 7850 vs 2x 7950 differences (all sapphire standard dual cooler series)

[induktor]

Hello
I will like to know other opinions about this:

I build a rig with 4 x 7850 Sapphire 1GB, they give 250 MH each (at 860 MHz Stock), total 994 MHash
(MEM at 600Mhz, fan at 70%, higher temp of the cards are 60 deg. C )
Total power consumption (PSU is 80+ with APFC at 60% load): 440 W

Now I build a second rig with 2 x 7950 sapphire standard, but each card doesn't give more than 460 MH (total 920 MHash) and this is really pushing with powertune at +15 %, clock at 925 Mhz and the cards running quite hot for my taste, at 66 C with fans at 75%.

also power consumption is higher (same PSU) now reading 520 W.

the black VRM heatsink cannot be touched without burning fingers.
If I run the cards witout OC (at 860 Mhz, like the 7850's are) I only get 420 MH

this looks FAR different that what I have been seen here in the forum , am I missing something?, doing something wrong?

I'm using GUIMiner with -w 128 switch (if I use -v the performance goes below 350Mh), driver tried 12.1, 12.6 and 13.1, Win 7 64 bit
also tried with different -w values, but 128 seems to be the spot.

I'm out of ideas, should I return the 7950's and keep buying 7850's???

thanks
Idkt.

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[bcpokey]

If 66C is hot for your taste, then expect to get low performance out of high end cards. You should never touch a loaded VRM heatsink, they're typically going to be like 30C higher.

Sounds like you want to baby your cards, so yeah, return the sapphires (they run hot and loud) and grab some more 7850s. If you really want to baby a card, you might give the 7790 a look, supposedly does ~240MH/sec, costs ~$140, and can run at about 80W / card. Aw yeah.

[induktor]

Babysitting is not the word i will choose but, it's close
Graphic cards in my country cost twice than in the US, an only have 6 months warranty so I have no choice but to take good care of them because ROI is slow.

Never tested a 7790 I will investigate it, thanks!

I need the GPU to last as long as possible, and produce as much MH per W as possible (even if they are more expensive, I prefer to spend more once, and pay less in the electric bill every month )

EDIT: and no, they are not loud at all, even at 80% fan speed, not the 7850 or the 7950, both are quite silent.
I have a HD 5830 that I use as a guinea pig, with a single massive fan, and this one is loud as hell   (and not practical for mining only 230 MH and consumes as much power as a 7950)

[superfry]

just curious what exactly is the pricing for the 7850's in your area? You might want to consider some of the FPGA's if your GPU pricing is indeed double the cost of the US.

[Bitsaurus]

If you have access to reference design cards and can tolerate the noise go for those. They cool the VRMs and pretty much every component well and are very reliable.  Plus you can undervolt, and then keep tweaking to max out MH/s and still stay in the mid 60Cs.

Only thing is they will be noisy.

[induktor]

just curious what exactly is the pricing for the 7850's in your area? You might want to consider some of the FPGA's if your GPU pricing is indeed double the cost of the US.

Sapphire 7850 1GDDR5 == 330 U$D
Sapphire 7950 3GDDR5 == 670 U$D

I have considered FPGA but the price is ridiculous, for example ZTEX Quad is 900 EURO, in my country will cost 1700 EURO, this price is crazy!

The only way it would be cost effective is if I buy the Spartan 6 chips and assemble the boards myself, which is what I have in mind, I have worked in electronics with microcontrollers and microprocessors all my life but no experience programming FPGA so I will have to learn VHDL (already get the xilinx dev. software )

and since I am a little late for this, I think that design a FPGA that can mine LTC will be the way to go, maybe using 1 DRAM chip of 1GBit or 2Gbit densitiy per spartan, just thinking, i have to investigate it, but I will really do it as far as I can get enough mining profit to buy the DEV board (which are also crazy expensive here (around 2000 U$D).

If you have access to reference design cards and can tolerate the noise go for those. They cool the VRMs and pretty much every component well and are very reliable.  Plus you can undervolt, and then keep tweaking to max out MH/s and still stay in the mid 60Cs.

I have read that fan dies very quickly in reference design cards, I don't mind noise, my room already sounds like a datacenter and I sleep like a baby with it hehe.

is it safe to lower the voltage?, if I kill a 700 U$D card i will kill myself heehehe (well maybe not, but it would be serious hehe)

[Quix]

Voltage seems pretty high to me for only 925Mhz, I can get my cards to run at 1200+Mhz at that voltage. Your video card prices are so high I don't think it's possible to make money Bitcoin mining, unless you can factor in a good GPU resale market... My overall cost for 7950s is about $280 - ~$60 If I manage to sell the game vouchers they come with.

If I were in your position I would be literally terrified of ASICs.

[ssateneth]

Use cgminer or bfgminer, diablo kernel, 11 intensity, 128 worksize, vectors 1 (default), and 2 gpu threads (also default). Should get you more mhash. Also underclock your memory for power savings at very minimal mhash loss (try ~300mhz. i run 340 because I'm too lazy with afterburner to bring them lower), maybe 1% at most. I get 720 mhash from a 7970 at 1200 mhz core, 340 memory using latest driver and look for the thread on how to properly underclock 79xx cards. Should get approx 0.00029297 mhash per MHz per shader, so your 7950 at 925mhz should get 485.6 mhash, or 451.5 mhash at 860mhz. also your 7850 at 860mhz should do 258 mhash. 7950 has 1792 shaders and 7850 has 1024 shaders.

[induktor]

Use cgminer or bfgminer, diablo kernel, 11 intensity, 128 worksize, vectors 1 (default), and 2 gpu threads (also default). Should get you more mhash. Also underclock your memory for power savings at very minimal mhash loss (try ~300mhz. i run 340 because I'm too lazy with afterburner to bring them lower), maybe 1% at most. I get 720 mhash from a 7970 at 1200 mhz core, 340 memory using latest driver and look for the thread on how to properly underclock 79xx cards. Should get approx 0.00029297 mhash per MHz per shader, so your 7950 at 925mhz should get 485.6 mhash, or 451.5 mhash at 860mhz. also your 7850 at 860mhz should do 258 mhash. 7950 has 1792 shaders and 7850 has 1024 shaders.

Very very precise data, thank you!
I will try cgminer, already downclocking MEM, but I'm a little scared to play with VRM voltages.

If I were in your position I would be literally terrified of ASICs.

I know card prices here are VERY expensive, but, since they are very difficult to get, the used market is very good, and pay about 60-70% the price of new, specially if you have the box with all the gadgets.

also, I live in a country with a very devaluated currency, so getting U$D or EURO even if they are only few, is a significant income here.

I'm not really scared of ASICs, I already have some equipments testing/mining LTC, and I plan to develop FPGA for LTC as soon as I can get the dev board. , I can also use FPGAs for BTC, if the difficulty level is not very high.

we'll see, I will be alot more scared, if I buy a ASIC and the difficult grow so high that it is pretty much useless, since it cannot be programmed for another currency, specially for scrypt since they need a lot of ram, GPU's and FPGAs are very versatile, and that is why i think they are the best choice.