Bitcoin Forum

 I'm currently running my two 6970s at 960/330 core to memory clock at stock performance voltage of 1.175.  Although this is a slight increase in core clock(orig 880), it is a drastic decrease in memory clock(down from 1375). It would seem I can lower my power consumption/heat by undervolting my cards...

 Are there any guidelines for for voltage tweaking, maybe some simple formulas for calculating safe voltages given core/memory clock and fan speed? Do I run any risk of damaging the cards if I undervolt too much? Looking at the bios it looks like the lowest voltage for these cards is .9v when at 250/150. I'm hoping to go somewhere in between. Thanks!

The voltage setting that you see there, is the core voltage! You can't change mem voltage without a modded BIOS and flash!
An OC at stock voltage is fine! If you can lower your voltage, you can raise your core clock instead!
Yes, lowering the RAM speed does decrease temps a bit!
Lowering the voltage won't damage anything! Though it may introduce instability!

Memory and GPU on a single graphics card utilize a separate Voltage regulator?

There's no formula for this, you need to try. Use clocktweak on Windows or atitweak on Linux, lower the voltage to the known lowest threshold (what you see when cards are idle) and put the clocks really low e.g. core@400MHz, mem@300MHz.

Then start increasing the core clock gradually (10-20 MHz at a time) until the system hangs (during mining of course). If you would then use a 10% lower clock you should be fine.

I managed to overclock a 5870 to 900/300 at 1.0V (stock is 1.125V). Much lower heat and power consumption. But it works different for every card, even from the same manufacturer (my other 5870s -same model - need 1.05V and 1.08V for the same overclocking speeds).

I also get a nice 720/300 when all cards run on 0.95V (lowest possible voltage). Very much reduced heat and power consumption but lower hashrate. I configure them like this when I get tired of the noise  :).
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And you can't destroy your cards BTW. It's perfectly safe. If the system hangs, just reboot and they'll be back to stock settings. On the contrary, if you're playing with BIOS flashing you should be very very careful.

My Sapphire 6870's will auto adjust the voltage according to the core speed. I wish there's a way to override this.

400Mhz and below = 0.9v
401Mhz - 775Mhz  = 1.1v
776Mhz and higher = 1.175v

as has been posted, you need to experiment.

I go backwards.. hit the clock I want @ stock volts.  then keep backing off the volts 0.05 or so till instability.  then bump back up one step and youre pretty much done, depending on how exact you want to be.

my ASUS 6870 can maintain 1000 core @ 1.165, stock voltage was 1.200. made a nice difference in cooling.

Same VRM but multiple output.  This is always the case because RAM & GPU operate at different voltage.

As others have indicated I have found no way to lower voltage (other than an unsupported bios flash).  Even utilities like ATI Overvlot and XFX Overvolting tool which allow undervolting core only have options to RAISE memory voltage.