* I keep this post technical and assume that whoever reads this is familiar with Maxwell Bios Tweaker and terms I use, such as "voltage table" etc. This is really a post for modders.
I looked at LOTS of GTX 970 Bios and with a good number of cards you can not add more voltage externally, say with Afterburner.
One indication for this is the THIRD slider in MBT's "voltage tab" in the BIOS, When there is one fixed value and no range, it's an indication that you cannot add more voltage.
This means, with many cards, like from EVGA, ASUS, MSI etc. you find yourself in a situation where you overclock, say in Afterburner but CAN NOT add more voltage.
This is bad for some reasons (which I will explain), but there is also a fix for it:
You will know that cards, depending on many factors like ASIC quality, power target, load etc. will boost to a certain BOOST CLK in the boost table, depending on their default given boost clock.
(A lot of cards in the 70%-ish ASIC quality range for example boost to CLK 63 or CLK 64 in the boost table.)
Each CLK entry in the table has its assigned voltage range.
So for example, your card may have a default boost clock of 1316, so it boosts to CLK63. At lower load maybe to clock 60 or 58.
You may find your max stable clock is 1500, so what you do in Afterburner you add 184 to the core.
But once you added core clock in Afterburner, the BIOS voltage table does not reflect the correct voltages.
You added clocks, say, equal to 10 or more boost bins to your card, but the card/bios does STILL USE THE SAME CLK BINS as if you were not overclocking.
Example: Normally, when your card would go to CLK 53 at stock, it might give you (example), 1.000V. But since you added a lot more (you're overclocking)...you would require a lot more voltage than what is specified in CLK BIN 53. (Again: the bios does NOT jump higher in the voltage table when you add clocks externally!)
What you need to do, you must specify your max. stable found voltage as the "default boost clock" in the BIOS and also make sure that the last entry in the boost table is this clock. (Say, 1506, or 1480, whatever you found stable).
By specifying your max. stable clock as "default boost clock" you force your card to the max. boost bin, all the way at the end of the voltage table. (And not, as would be default, somewhere in the middle, like CLK 63 or CLK64)
This is why you would not be stable with MANY cards where you cannot add voltages externally, you MUST modify the bios to get the correct voltages all through the voltage table.
(The instability becomes most apparent when the card CLOCKS DOWN, because it may be ok at your max. stock, default boost clock, say CLK63 and 1.200V, but then it boosts down and the individual voltages etc, are all messed up).
Of course, the best way is if you have a card which simply allows adding a bunch of volts on top of your OC (with Afterburner)...but as said MANY don't allow that.
I looked at LOTS of GTX 970 Bios and with a good number of cards you can not add more voltage externally, say with Afterburner.
One indication for this is the THIRD slider in MBT's "voltage tab" in the BIOS, When there is one fixed value and no range, it's an indication that you cannot add more voltage.
This means, with many cards, like from EVGA, ASUS, MSI etc. you find yourself in a situation where you overclock, say in Afterburner but CAN NOT add more voltage.
This is bad for some reasons (which I will explain), but there is also a fix for it:
You will know that cards, depending on many factors like ASIC quality, power target, load etc. will boost to a certain BOOST CLK in the boost table, depending on their default given boost clock.
(A lot of cards in the 70%-ish ASIC quality range for example boost to CLK 63 or CLK 64 in the boost table.)
Each CLK entry in the table has its assigned voltage range.
So for example, your card may have a default boost clock of 1316, so it boosts to CLK63. At lower load maybe to clock 60 or 58.
You may find your max stable clock is 1500, so what you do in Afterburner you add 184 to the core.
But once you added core clock in Afterburner, the BIOS voltage table does not reflect the correct voltages.
You added clocks, say, equal to 10 or more boost bins to your card, but the card/bios does STILL USE THE SAME CLK BINS as if you were not overclocking.
Example: Normally, when your card would go to CLK 53 at stock, it might give you (example), 1.000V. But since you added a lot more (you're overclocking)...you would require a lot more voltage than what is specified in CLK BIN 53. (Again: the bios does NOT jump higher in the voltage table when you add clocks externally!)
What you need to do, you must specify your max. stable found voltage as the "default boost clock" in the BIOS and also make sure that the last entry in the boost table is this clock. (Say, 1506, or 1480, whatever you found stable).
By specifying your max. stable clock as "default boost clock" you force your card to the max. boost bin, all the way at the end of the voltage table. (And not, as would be default, somewhere in the middle, like CLK 63 or CLK64)
This is why you would not be stable with MANY cards where you cannot add voltages externally, you MUST modify the bios to get the correct voltages all through the voltage table.
(The instability becomes most apparent when the card CLOCKS DOWN, because it may be ok at your max. stock, default boost clock, say CLK63 and 1.200V, but then it boosts down and the individual voltages etc, are all messed up).
Of course, the best way is if you have a card which simply allows adding a bunch of volts on top of your OC (with Afterburner)...but as said MANY don't allow that.
