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Hey Guys. Can I get your opinions on this mining rig build? I think I'd go with CGMiner.

• Motherboard
  MB ECS|A780LM-M2 760G AM3 R
  http://www.newegg.com/Product/Product.aspx?Item=N82E16813135315

• Video Cards
  HIS H785F1G2M Radeon HD 7850 1GB 256-bit GDDR5 PCI Express 3.0 x16 (x2)
  http://www.newegg.com/Product/Product.aspx?Item=N82E16814161426

• Power Supply
  LOGISYS Computer PS575XBK 575W ATX12V
  http://www.newegg.com/Product/Product.aspx?Item=N82E16817170017

• CPU
  AMD Sempron 145 Sargas 2.8GHz Socket AM3
  http://www.newegg.com/Product/Product.aspx?Item=N82E16819103888

• OS
  Ubuntu 12.04 LTS from a flash drive

No HDD since running from USB

You planning on getting a 1x to 16x riser cable for the second gpu?

Also I would pick a different PSU. If you look at the specs it shows 25 amps on the 12v rail which is only 300 watts, 200 watts of the 500 are on the 5v rail.

I would also get a different motherboard, one that you can add more graphics cards to down the road.  Same for the PSU.  Unless you are pretty sure you're going to just stick with 2 video cards but you already need to pick a different PSU for what you have. 

My suggestion would be to get a motherboard with 2-3 PCIe 16x slots and 1-3 PCIe 1x slots, the more the better with 16x being more preferable. I would also opt for a PSU with at least an 80+ Silver rating and enough power to power 3-4 7850's factoring them at 200 watts each. 

http://www.newegg.com/Product/Product.aspx?Item=N82E16813130679 $70

Searched for all AM3+, AM3, AM3/AM2 boards, lowest price with 2 16x slots, also has 2 1x slots that you can later add gpu's to with powered riser cables.

http://www.newegg.com/Product/Product.aspx?Item=N82E16817139028 $65

Searched for 550w supplies on up with at least an 80+ certification, first decent PSU on the list when sorted cheap to expensive.  You'll also have to look at whether your gpu's have 6 pin or 8 pin connectors and how many so you know how many adapters you need to buy if the PSU you get doesn't have enough.

http://www.newegg.com/Product/Product.aspx?Item=N82E16817182133 $90

This would be a decent compromise - 750 watts 80+ Bronze single rail modular.  Easily run your current set up and you might even be able to squeeze a 3 card out of it later.

http://www.newegg.com/Product/Product.aspx?Item=N82E16814125414 $310

Actually just realized you were looking at the 7850's and not the 7950's!! Their power draw is much more modest.  My advice on choosing a different supply still stands.

I would also advise getting the 7950 over the 7850 even though they are close, the 7950's are about $.10 per KHash/s cheaper and about .02 watts per KHash/s more efficient.

Your build right now totals about $445 not counting ram or the fact that you really should get a better PSU at the very least. My suggestions thus far with the better PSU would put you at $510 with 1 7950 and no Ram as you also left out and could get you about 650 KHash/s or 1.2843 KHash/s per $. Same setup but with your 2 7850's would cost $540 and get you about 820 KHash/s or 1.4818 KHash/s per dollar. This changes once you add more cards for example if you add a second 7950 which brings the build up to $820 and KHash/s to about 1300, your KHash/s per $ goes to 1.5976 which is now a 2 gpu setup compared to a 2 gpu set up as opposed to trying to compare build cost.  Anyway, just my 2 cents... or more :)

I did a cost comparison with Excel file for 2GPU, 3 GPU and 4 GPU builds => they all turn out to be almost the same cost per Kh/s. But you do get slightly better deal by installing AMD 7970 vs .7950 (based on how they are currently priced where I live - NZ).

With 3 GPU builds, however, it may have more resale value, since the motherboard, powersupply, etc are of better quality.

good info.. i've been looking like crazy at cards.  i'm gonna try and setup 4 cards with a 1250 power supply.  any reason most people only using 3 cards instead of 4?

I would have to disagree as for the 7970 being even slightly better.  Here's a link to the spreadsheet I made for this, it factors quite a bit in.

https://docs.google.com/spreadsheet/ccc?key=0Au-5jsYGHc29dG94ekRvbEl1WEUxcnFYMU14eDRRV3c&usp=sharing (https://docs.google.com/spreadsheet/ccc?key=0Au-5jsYGHc29dG94ekRvbEl1WEUxcnFYMU14eDRRV3c&usp=sharing)

The 7970 is about $.06 more expensive per KHash/s and per watt.

7970's in a 3 card setup will take roughly 17 weeks and 1 day to break even where as the 7950's will take about 15 weeks and 3.5 days. Surprising that what seems like such a small difference actually has a pretty big effect? $.06 per MHash/s and per watt equates to 11 days difference in the break even time... 10% faster return on investment.

So are you saying it is better to get the 7970's over the 7950's?

Um... What you quoted answers your question.  The 7970's cost more per KHash/s and per watt meaning you get less for your money than you do with the 7950's.

7970's break even in 17 weeks 1 day, 7950's in 15.5 weeks meaning the 7950's pay themselves off faster and start earning you profit a week and a half before the 7970's. Hope that clears that up although I just re-stated what I already wrote! 

Bottom line - 7950's = money better spent!

Just that everyone saying this and that, But a lot of people have been saying the 7950's are the go. Thanks for the info!

Did you check out the link to the spreadsheet? That might give you a little more to go on than someone just saying this and that... I've spent a FAIR amount of time over the past few days putting it together.  It's not just based on cost of the GPU.  It breaks it down for 3, 4, 5, and 6 card setups, includes the costs of the complete system which can be entered in individually, accounts for cost of electricity which you can specify your electric rate and a bit more.

https://forum.litecoin.net/index.php/topic,2870.0.html (https://forum.litecoin.net/index.php/topic,2870.0.html)

This gives a more in-depth explanation on what it is and how to use it. 

I would agree on the 7950's being a better buy.
Also agree on the better PSU.

Just my 2c

Thanks for the advice guys. I'm going to go with the 750 psu and 4 gpu slot motherboard. I'm still sticking with the 7850's because it's got a lower initial capital investment and it offers some other perks I can sell to recoup $$.  ;D

Yeah my rig has 3 7850's and I love them.  They are easy to setup and overclocking to 1100 doesn't effect temp that much.  Each card gets 330MHash and are running at 58 degrees stable.

+1 for 7950 and better PSU.

Rick

I have a setup with 2 Saphirre 7970.

It was powered with a 750W Corsair PSU.

I upgraded the PSU for a 1500W from Cooler Master for planning to increase my number of GPU from 2 to 4.

I got 2 lessons from that upgrade:

1.

My system is much more quieter and cooler. A big percentage of the heat was coming from the 750W PSU that was close to its limit with 2 7970.

2.

I have a problem. The 3rd 7970 that I purchased didn't fit into the case. Beside milk boxes, what kind of PC cases can host 3-4 GPUs?

Once I find a case, I'll be able to squeeze a third card.

After having found a big PC case for my third card, the motherboard pci port positions will be the limiting problem.

How about the fourth card? PCIe extenders users: Can you tell me if there exist 'off the shelf' cases where I can securely install a 4th 7970 by using a PCI extender cable?

Thanks,

Isn't the single core CPU going to limit the GPU's work in some way? I'm running cudaminer and afaik some of the work has to be done on the CPU, so cudaminer takes up around 20% of the CPU. Is this also true for cgminer?

I really wouldn't advise putting four 7970s in a case. You'll need to either pay for a case with good cooling in the first place, or pay for more fans later on. Cases that can hold 3-4 GPUs are designed for $200+ motherboards and cost at least half as much themselves. Milk crates are the way to go.

ritchan,

cudaminer is a LTC miner right? not very familiar with LTC mining or this particular software but I believe that some part of the computation is done on the CPU, hence for LTC mining with cudaminer the CPU could eventually become the bottlenect.

In my case with 2 7970, CPU usage from cgminer is 1/4 of 1 cpu core capacity on a 6 cores system. So CPU is no issue IMO.

Any chance you can switch out the 7850's for 7950's? Will need to adapt your PSU as well.
How is HIS?

Hi all,

Total Btc Noob, but not so new to hardware.

Is there a particular 7950 do you guys recommend? i.e. Sapphire over MSI over XFX? Does this even matter?

Assuming that I'm slapping 2 of these bad boys into a Haf XB case, does your Mobo recommendation still stand?
http://www.newegg.com/Product/Product.aspx?Item=N82E16811119265

Thanks!  ;D