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i5 760 - basic question, CPU Voltage

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mothman0

New Member
Joined
Feb 28, 2011
Brand new guy here, recently bought a new PC, with the i5 760, on an MSI p55A-g55 mobo.

I'm very noob (I mean, VERY noob, this is my first crack at it) when it comes to OCing, but wanted to get a little more bang for my buck, so started looking into a gentle OC of the processor.

I'm not interesting in really pushing anything, I just want a pretty easy OC.


I worked through the guide here: http://www.overclockers.com/3-step-guide-overclock-core-i3-i5-i7/

I found it mostly very straight forward, but have a question...

To give the background on what I've set, (in case it is important)

---

I'm working with an end result of 3.36GHz (160x21). I set the VTT voltage to about 1.2V (can't recall the exact # at this moment, I think it defaulted at 1.097 or something, and I altered it by only a small increment).

RAM is underclocked slightly (638Mhz, stock is 666) because of how the multipliers work out.

Disabled EIST, C1E and c-state settings, as per the guide.

Where I'm a bit stumped is vcore...

The guide talks about setting the vcore (CPU Voltage in my bios) to an "easy 1.3V".

However, on my bios, the CPU Voltage is modified through a +0.000 interface. So, I can't set it at 1.3, but rather can set it from +0.000 to +0.302. And from what I can see, the bios doesn't tell me the default voltage, but rather simply says the default is +0.000.

I tried leaving it set to AUTO, and everything appears stable, though I haven't done an overnight yet... but using AUTO, CPU-z reports the CPU voltage as a number that jumps around a bit... between 1.264 and 1.312.

(stock settings, that value ranged from around 0.88 to 1.1)

Running Prime95 (have run for about 2 hours so far), my core temps (as per RealTemp) all sit at about 60C, maxing at about 62-63C, which from what I understand if fine. At idle, temps are around 33-34C.

So, my question is, what should I be setting my CPU Voltage at? Can I leave it at auto? Is it OK for it to fluctuate slightly? Or should I set it manually? If manual, then what do I set it at?

Thanks for any advice. :)
 
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There is no hard and fast rule that says Vcore / Vcc needs to be set to a certain value at a particular clock. And since the VID of the chip can't be read by software, and leaving Vcc on Auto normally results in an overvolted condition, start by manually adjusting the Vcc to ~1.12-1.15V. With an overclock of only 560MHz, and the DRAM frequency at only DDR3-1280 (x8 DRAM multiplier at a 160 BCLK) neither Vcc or Vtt should need to be altered from their default values. Without knowing which model board you have, the BIOS should have something similar to a Hardware Monitor screen, showing all of the default voltages when their corresponding options are set to Auto.
 
Thanks for the tip re: the Hardware Monitor page. My bios does have that page, I'll take a look there for the default CPU Voltage, and then apply a small + value .

Just to clarify, Vcc = VCore = CPU Voltage?
 
Yes, Vcc = Vcore = Core Voltage. For the time being leave Vcore set to Auto, read the value on the Hardware Monitor screen, then compare that to the value as seen by CPU-Z both at idle and while running Prime. If the loaded Vcore is higher than the value in the BIOS when set to Auto, then manually lower it until it's no higher than 1.12-1.15V, or vice-versa (the lowest value required for stability).
 
just to let u know what ballpark u should be in. my i5 760 is at 191x21 which =4.017 at 1.28 vcore( bios reads like a little over 1.30)

so at 3.3ghz. u should be at like 1.12-1.15

like redduc said
 
OK, thanks.

On the bios H/W Monitor, the default CPU Voltage showed as 1.128v.

In the end, I changed the CPU Voltage setting to manual, and set it at +0.001 (negative changes aren't available, only positive, and this was the only way I could see to manually "lock" the value at/near the stock value).

I also reduced the VTT slightly, to one step up from default (default was 1.097, and again the only way to take it off auto was to increase it one step, I've forgotten the end value, but it's something like 1.102 I think).

CPU-z now reports the CPU Voltage as 1.136 at idle, and 1.104 while running Prime. Is it normal for there still to be that fluctuation? (and for the voltage to actually drop under load?)

I did increase to 166x21 at the same time, and everything is still stable, temperatures are about 10 degrees cooler now than before (maxing at about 52C under Prime).
 
Ok, yes that drop is normal due to "Vdroop". You can remove the voltage drop under load by looking for a setting called "Droop control" or "load line calibration". It's best to set LLC to an average strength, so that the idle voltage and the load voltage will be about the same, and ideally, with no more than a 0.02 difference between idle and load.

Anyway, back to your voltages.

If you can't enter a direct voltage setting, like 1.30v, for instance you can get that voltage by entering in that "vid offset" value, for example, +0.150". Then, if your default voltage is 1.15v, then the offset will give you +1.30v.
Provided, that is, how your BIOS works.

You can test that safely, by entering in a SMALLER value, like +0.050" and noticing how it affects the voltages. It's important to not get the decimal values messed up, though; setting +0.500" would give you a bad hair day for sure, when you realize you're putting 1.65v into the chip.

It looks like the maximum voltage you can set is +.302 which would be 1.45v, anyway, though I'm sure there's a way to override that, if you were using high end cooling, and wanted to push the CPU. (like on water cooling or subzero).
 
Alrighty, thanks. :)

I'll look tonight to see if I can locate the droop/llc setting. If I have further questions after finding it in the bios, I'll be sure to post.

You've all been a great help, thanks a lot!
 
You can just bump the Vcore 0.024V (1.128 - 1.104) to compensate for the droop while under a load. Loaded Vcore for the most part shouldn't be lower than the VID (1.128V) of the chip.
 
Redduc, is that a preferred solution?

I understand the logic behind it, but that would still result in a fluctuating CPU Voltage, which I'm guessing would be a range something like 1.15ish (idle) to 1.13ish (load). No concerns with that?
 
There's always going to be somewhat of a fluctuation in voltage, regardless of whether Vdroop / LLC is enabled or disabled. Some BIOSs don't offer a Vdroop / LLC option, so if the system becomes unstable while loaded because of the lower than set Vcore, then it needs to be compensated for by either raising the Vcore in the BIOS or performing a droop mod to the board. In your case w/ such a small Vcore of only 1.12-1.15V and droop of only ~.02V, I wouldn't be concerned w/ raising the Vcore by that amount, and only if the set Vcore causes instability while running Prime, LinX, OCCT, etc.
 
ALright, I bumped up the CPU Voltage to +0.028, which has resulted in CPU-z reporting the voltage at 1.128 under load and 1.16 idle. Every once in a blue moon, while running Prime, the voltage will drop to 1.120 for a second and then go back to 1.128, so I might bump it up another notch. Or not, I dunno, everything seems perfectly stable from what I can tell.

I couldn't find any setting for LLC/VDroop.

Final question (I think LOL). My bios, in the same page that I'm doing these tweaks in, there is a setting for Spread Spectrum. By default it's enabled, and thus far I've left it enabled. What is that for, and should it be enabled or disabled?
 
Spread Spectrum should always be disabled when overclocking, This is taken from your motherboard manual...
Spread Spectrum

When the mainboard’s clock generator pulses, the extreme values (spikes) of the pulses create EMI (Electromagnetic Interference). The Spread Spectrum function reduces the EMI generated by modulating the pulses so that the spikes of the pulses are reduced to flatter curves.

Important
If you do not have any EMI problem, leave the setting at [Disabled] for optimal system stability and performance. But if you are plagued by EMI, select the value of Spread Spectrum for EMI reduction.

The greater the Spread Spectrum value is, the greater the EMI is reduced, and the system will become less stable. For the most suitable Spread Spectrum value, please consult your local EMI regulation.

Remember to disable Spread Spectrum if you are overclocking because even a slight jitter can introduce a temporary boost in clock speed which may just cause your overclocked processor to lock up.
 
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