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I used RBE to overvolt to 1.25V. It seems like at that voltage I can get pretty near 1100Mhz before it locks up. My question is, anyone gone higher? I am curious about what bumping up the voltage another .1 will offer given my temps are fine. I am on air cooling using poclbm -f 15.

If there is interest I can update with my rejected percentage after a few hours of running.

That's the same voltage that AMD GPU Clock Tool sets the GPU to any time you move it off stock clock settings.  I just got one of those $190 HIS 5870s from NewEgg and it seems pretty stable at 1050.  Anything over that it starts getting a little shaky though.  1050 is good for around 460MH/s but I scaled it back to 1030MHz for stability.

Nice I'll do that too.

I've not seen anyone claim a hash rate that high on a single GPU before but people do occasionally get higher core clocks.  Last night I took my 5850 (non-reference, Sapphire 5850 Xtreme) to 1.25 V and managed to get 461.1 MH/s out of it for 3 hours.  The card crashed immediately when I started up a second miner on another card in the same system.

• 1110 MHz core clock
• 370 MHz RAM clock
• 55*C GPU temperature

This is on Linux with Catalyst 11.6, SDK 2.1, and phoenix (latest phatk kernel).  Here's a screenshot (http://img195.imageshack.us/img195/339/72screenshot2.png) of me about an hour into the pooled mining test.

This same card went to 1140 MHz before crashing and is perfectly stable at 1030 MHz at stock voltage so you might put this down to luck.

I only have experience with 5850s but I'm hoping they are similar enough to 5870s that some of the following can be of help.

I'm assuming you're using the very latest phatk kernel; check out http://forum.bitcoin.org/index.php?topic=25860.100 (http://forum.bitcoin.org/index.php?topic=25860.100) if not.

I found that SDK 2.1 is a few MH/s faster than SDK 2.4 on my card so I'm guessing you'll see a similar improvement with SDK 2.1 (yes, that's with phatk).

Have you tried increasing your RAM speed a little.  I know 300 MHz known to be good but I've found that as core clock rises, the maximal RAM speed rises.  You may well find another 3 MH/s or so by bumping up to 355-360 MHz.

Another idea I have is to use Catalyst 11.4.  On my card this gives a straight up 9 MH/s boost to my 5850 clocked at 900 MHz.  Over 1GHz I'd expect 10 MH/s or more.  Windows users have claimed 12-13 MH/s over me by using Catalyst 11.4 instead of Catalyst 11.6 (same card, clock, RAM, kernel, SDK, miner settings).  Unfortuately, no-one seems to know of a way of overclocking a card past BIOS limits using Catalyst 11.4 in Linux but it seems like you've solved this by flashing your BIOS to increase the limits.

May I ask how much variance you get with your hash rate?  You may need to look at your command line options (for phoenix '-a 1' - for poclbm '-e 1' maybe, I'm not sure).  If your MH/s is varying by more than 1 MH/s then you can surely manage further gains through configuration, especially if you are using Linux.  I'm guessing that this is not a dedicated miner given that you are using the '-f 15' option but if it is and it's running Linux then PM me for some further tips.

If all goes well you should be able to comfortably climb past 480 MH/s, maybe touch 490 MH/s.

You guys are nuts to try running a 5850 or 5870 at nearly 500mhash/s.

Those cards cost $150 to 200 bucks at the least & 1.25-1.3 voltages will 100% surely kill the card due to electromigration or VRAM failure within a month or two.

It'd last years if you ran it at 420-430mhash and the monetary 'loss' is negligible considering you don't have to buy a new GPU

Also the power consumption will skyrocket if you go past 1.25v

Don't worry, I'm sure we're all aware of the various issues with overclocking/overvolting.  This thread is more about finding and establishing the limits of the cards for fun and to satisfy curiosity.  Furthermore, what we learn can be applied to design very efficient setups.

My occasional forays into the world of high voltage have all been experimental and my discoveries have allowed me to reach a stable 430 MH/s on stock voltage (5850).

Also I've noticed you like to make the assumption that miners are primarily interested in profit but perhaps this is not a safe assumption of the people using a thread with 'voltage mod' in the title.  I expect there are some passionate overclockers on this board that are taking great joy in the sudden interest Bitcoin is drawing to overclocking.

I was wondering if you would be willing to play around with some electromigration numbers. The Mean Time to Failure (MTTF) due to electromigration has been estimated empirically using:

http://upload.wikimedia.org/math/7/c/5/7c541184cbe9c3cff95489596287fc16.png

Where A is the cross-sectional area, J is the current density, n is a scaling factor that is usually set to 2, k is the Boltzmann constant, Ea is the activation energy of the material, and T is the temperature. (link (http://en.wikipedia.org/wiki/Electromigration#Electromigration-aware_design))

Lets take a VERY conservative MTTF based on your estimation of two years. You are welcome to provide your own adjustments, but based on my experience the temperature has not changed much raising the voltage and overclock. This may just be due to favorable cooling circumstances but I will assume the temperature sensor readings are accurate.

So Ea, T, k, and A are all constant or nearly so. This leaves us with the current density being the most important change. For non-ohmic materials like semi-conductors J can be expressed as:

http://upload.wikimedia.org/math/a/5/5/a55f0a18b99ebf8b587fc8228a9ebc1f.png

Where sigma is the capacitance, E is the electric field, D is the diffusion constant, q is elementary charge, and n is the electron density. Therefore in calculating the current density D, q, and n are constant for the same component. Then we can look at the electric field inside our component. For the sake of simplicity we assume that we are dealing with a small wire where E = V / d. Again d remains the same and the electric field grows linearly with voltage.

The purpose of the analysis above is to show that current density grows more or less linearly with increasing voltage in our case. This means for for n=2, MTTF will reduce by the inverse square of the change in voltage. Doubling the voltage reduces the MTTF of the junction by 4, quadrupling by 16, etc.

Therefore by increasing the voltage by .1V we reduce the MTTF by roughly 15%. For the given two years the MTTF for any given junction will reduce by 3.5 months.

(change in MTTF) ~ (modded V / stock V)^-2

Given 2 years is a fairly conservative estimate of the life of your card you may be reducing the total lifetime by a much higher amount, but the percent reduction in mean time to failure will be the same. For the sake of completeness I will estimate the difference in hashes over the life of a card in the two circumstances. I will give a very bullish reduction in life based on the calculations above of 2 weeks (even though in fact it was about 100 hours).

Overclock at stock voltages of a 5870, 425 Mhash/s for 2 years (104 weeks) ~= 27 x 10^18 hashes
Overclock at 1.25 V, 470 Mhash/s for 90 weeks ~= 26 x 10^18 hashes
Untested! 1.35 V, 490 Mhash/s for 77 weeks ~= 23 x 10^18 hashes

Therefore, you are correct you will reduce the overall hashes your card will be able to perform based on the MTTF. Also, there are numerous other points of failure and I believe electromigration in the junctions is just one to consider.

I would like to further complicate this picture by suggesting that having an extra 20 MHash/s now will be worth much more than the entire hashing power of the card at the end of two years given difficulty increases. I have not calculated this and difficulty changes are not predictable that far ahead. But you can see that increasing difficulty is an exponential and decreasing MTTF is quadratic.

I look forward to other considerations in ramping up the voltage before I do so.

Ok, you will satisfy your curiosity and find what is the maximum stable clock for mining, but is it worth it apart from that? Probably not.

A quick comparison: mine are @ 960Mhz Core = 440Mhash/s, so you get 35Mhash/s more = 0.6BTC more a month than me for the much higher chance that your card will die much sooner than mine. What about electricity?

The highest I run mine are in my sig.  No issues for the past few months.  I do have occasional disconnects from pools but that isn't the cards.

Wow, nice. Have you used poclbm's failback for handling the disconnects?

Have you posted more info about what blocks/water cooling setup you have? What temps are you getting?

I will almost certainly try bumping up at least one of my cards now.

Haven't tried it yet but may consider.

My H²O setup is as follows:

CPU Block: EK Supreme HF (Gold)[/li][/list]
GPU Blocks: EK-FC5870 (Acetal/Copper) and (Plexi/Nickel)
Radiators: Black Ice SR1 480, Feser XChanger 480, and Feser XChanger 240
Pump: Laing DDC 3.2
Reservoir:  Danger Den 5.25" Dual Bay Res
Fan Controller:  Sunbeantech Rheosmart 6

GPUs average around 34-38°C.  VRMs don't get above 85°C.

Excellent, 490 MH/s from a single GPU is the highest I've seen on this forum by a margin.

Also, thank you rethaw for the highly informative post.

Honestly, the only reason I don't overvolt all the time is due to noise.  Profit/Loss are card longevity are practically irrelevant compared to my quality of life.

That's exactly what I did with my HIS 5870s :D

I'm still giddy about getting my hands on such an awesome card for that cheap!

Broke 500MH/s.

http://img688.imageshack.us/img688/3104/unledfe.th.jpg (http://imageshack.us/photo/my-images/688/unledfe.jpg/)

very nice, here is what i'm getting:

Clocks:
Temps
Ye ol' Mega Hash

I'm sure i could get better though, aint touched the voltages yet :P

what watercooling block are you using on the card?

Look above.



I knew you could do it! 1.35V?

air cooling and only 60c at that speed? what's the ambient air temperature? you must have a ton of fans in that case

I was impressed by the temperature as well. The reference designs are heavier due to better heatsinks. I found that extracting air at the edge of the case near the ports works really well.

That being said he didn't post his fan speed. It could be he's forcing it to 70% constantly.

I've been having a hard time keeping my 5870 below 80c with the fan at 100% atlhough that could be because as an eyfinity edition i have a rather small vent on the card (1/2 of one slot) i've been thinking about simply replacing the case side with a box fan though!  :D

I also have an eyefinity 5870. What I like about it is that all of the ports are recessed (minidisplay port). Because of this you can place a fan right up against the back which helps immensely with the exhaust. This is what I did:

https://i.imgur.com/KVhd9.jpg

i'll look into that however mine still has some DVI ports on it(not a flat surface) but that shows an answer to my question

Congrats!  A significant milestone!  You also beat my highest stable core clock: 1110 MHz (I say stable but in reality I only ran it for 3 hours so who knows).  I see that you took your screenshot shortly after starting the miner.  How long did you run it for at that speed?  Perhaps you are still running it at that speed.

I did get my 5850s core clock up to 1140 MHz (473.4 MH/s) in testing but it only lasted for 30 seconds.  I'd love to try and compete but with a 5850 and air cooling I'm a little out of my depth.

Do you have other cards right next to it in the case?  If so, get one of those "vortex" type fans ($15 or so at Target) and force some air across your boards.  It'll make a world of difference.

Actually there are no other cards in the case. it's an ITX size motherboard in a full ATX case with the one video card

I ran it about an hour after taking the screenshot.  After checking my Kill-A-Watt, I'm saving ~40w by lowering the clocks to 1100/300 @ 1.300v.

It's hard messing with overclocking while mining because every second counts.   :'(

Haha so true. That's why I'm trying to get as much data before I start flashing again.

1) You're sucking air away from the card right?
2) Idk what that cover on the backside of the PCB is made of but you might be able to lower your temps even further if you can remove it (i say if because it might be an integral part of what keeps the fan attatched)
3) what RPM/CFM fan is that? :P

1) Yes removing air.

2) Interesting thought, though temps are not so much of a problem that I would do that. Perhaps it even conducts some heat away from the card?

3) It is a .1 A Antec silent fan of some kind. It is running at 100% and is still silent so I'm sure you could easily outperform it with any other kind of fan. Having trouble finding the specific model it came from an Antec Sonata case.

I really think you should take a look at your VRM temps though... Because my asus 5850 had no issue overclocking up to 1050 mhz on the core when i increased the volt to 1.2 however my VRM's were incredibly hot, even with 100% fan, 125-129 degrees wich is just under the 130 degrees max supported operating temp...

But then again there are only 3 of them running in phase on a 5850, there might be more on a 5870 since it's able to go to as much as 1.35v...

Did you measure the VRM temperatures manually?

Wow.. this post its without doubt the best argument reasoning that I have read about the topic. Kudos to you  ;)

Little update. This is 1055Mhz at 1.25V. Not all cards are created equally. The other 5870 will not stay at over 1020 MHz for any significant length of time.


I also wanted to make a little attempt at arguing that 20 Mhash/s now is worth more than two months of mining two years from now.

Here is one an excellent graph of network computational power by sipa available here (http://bitcoin.sipa.be).


As you can see that over the course of two years it is extremely steep, especially in the last six months. Whether this will be maintained is anyone's guess.

You can very quickly see the importance of speed now. 20 MHash/s may seem small, but it is not difficult to imagine 200 Mhash/s being small in a matter of months. Current estimates project the next jump to be modest, however, just in the last two increases we've seen the same hardware giving half the payout. If this maintains it means that in say, 4 months, a 400 Mhash/s card will be paying out as much as 25 Mhash/s does today. Even if the difficulty increases slowed dramatically, evidence would suggest that in less than 18 months that extra 20 Mhash/s would be significant.

Obviously this does not take into account resale value of the card, and I wouldn't attempt to guess the exchange rates down the road. Neither is it a given an overvolted card will fail, but it does increase the likelihood.

Perhaps I am doing something wrong, better ask.

I have a couple of 5850's and a 5870 in a system, and whenever I try to OC the cards to 900 core, I seem to get more stales etc. The weird thing is, both the 5850's and the 5870 are hitting the same "wall" 900/300 they seem to get more stales, they restart a tad more often I think, 898/300 they seem fine.

I haven't done extensive testing, but somehow I feel it's not really the cards, but more my way of OC'ing. Any tips and tricks? How do I see if I pushed the card to the limit, only 1 of them is connected to a monitor, so I am guessing it's the only one that could make the system "hang" or am I wrong? Im using Trixx to OC, Afterburner to monitor temps, gpu load. The 5850's are Sapphire Xtreme's and the 5870 is a XFX.

Windows 7 32bit, AMD 11.7, AOCLBF 1.75, Phoenix 1.5, PhatK 07-17-11 (BFI_INT, Vectors, Aggression 13, Worksize 256)
5850a   898/300  ~369MH/s
5850b   898/300  ~369MH/s
5870     898/300  ~408MH/s

Thanks for any help/tips in advance.

WTF, I was getting 495 MH/s @ 985/300 for about an hour.  I'm not sure what it is I did, but was mining Namecoins in GUIminer, then switched back to mining Bitcoins with Phoenix.  I've done it 2 or 3 times now and it will mine around 495 MH/s for about an hour before it locks up.  I wish I could repro this stably.

You can get the $190 5870's from newegg up to 495? 0.o Even if its only for a hour at that speed that's a huge bargain. Wish I had the money when they had that sale.

This was with a 5870 reference card.  The $190 5870s run normally at around 460 MH/s at 1010/350.