CPU PLL effect on overclocking

[boondocks]

At mild overclock (4.5GHz) I went into the BIOS before any testing and got the red screen warning about overclock problems. So, after booting up after the red screen I ran Intel Burn Test for a quick look and it failed.
After a ton of reading and looking at voltages I lowered the PLL slightly from the 1.8V nominal and then was able to pass IBT. (no further testing yet as I had some torrents to seed).

From what I understand CPU PLL is one of those mysterious things that no one short of an EE degree knows much about, either raising or lowering might produce a stable clock.
Does that pretty well sum it up, so is my adjustment smoke and mirrors or a valid step?

[Chike]

Re: CPU PLL effect on overclocking

Does that make it different from other voltages?
What does anyone know about Vcore, Vccio, Vccsa, or even DRAM Voltage other than more or less of any of them may help stabilization?

You can't argue with success providing that your CPU does run at the clock you set it to and you don't get the red overclocking warning anymore. To be sure you can set it back to it's default and see if IBT fails amd/or the warning apears again.

[Lsdmeasap]

Re: CPU PLL effect on overclocking

Are you wanting some information on CPU PLL, or are you just asking if it's normal that lower can help?

Haha, yes, it's normal that lower can help! I often suggest this to users, especially on newer boards as it's generally set too high by auto these days.

If you want info about what CPU PLL does, let me know and I can link you to some information about it.

[boondocks]

Re: CPU PLL effect on overclocking

Does that make it different from other voltages?
What does anyone know about Vcore, Vccio, Vccsa, or even DRAM Voltage other than more or less of any of them may help stabilization?

You can't argue with success providing that your CPU does run at the clock you set it to and you don't get the red overclocking warning anymore. To be sure you can set it back to it's default and see if IBT fails amd/or the warning apears again.

Ah, I don't know. Literally.

[boondocks]

Re: CPU PLL effect on overclocking

Are you wanting some information on CPU PLL, or are you just asking if it's normal that lower can help?

Haha, yes, it's normal that lower can help! I often suggest this to users, especially on newer boards as it's generally set too high by auto these days.

If you want info about what CPU PLL does, let me know and I can link you to some information about it.

No, I don't need any specific info other than verification that this is a normal tweak, as I said I couldn't find much info about it. I had read a bunch of old posts here and there where people were talking about radically increasing that voltage, and a few probably more relevant to Sandy Bridge that suggested the adjustment may go either way, up or down.
I'm not especially paranoid about blowing anything up, I just have a lot to learn.

[Lsdmeasap]

Re: CPU PLL effect on overclocking

OK, yes it's completely normal!

Increasing CPU PLL was only necessary in older boards like P45 or earlier, since X58 and above it's not really needed, nor does it often help to raise it, actually the opposite as stock seems to be a bit high usually.

P45 or below = raise helps stability and increase could help increase OC

X58 and above = lower to start, stock is often too high, going above stock value rarely helps at all, does not tend to affect OC at all unless it's too high and then it brings instability.

[boondocks]

Re: CPU PLL effect on overclocking

OK, yes it's completely normal!

Increasing CPU PLL was only necessary in older boards like P45 or earlier, since X58 and above it's not really needed, nor does it often help to raise it, actually the opposite as stock seems to be a bit high usually.

P45 or below = raise helps stability and increase could help increase OC

X58 and above = lower to start, stock is often too high, going above stock value rarely helps at all, does not tend to affect OC at all unless it's too high and then it brings instability.

Thanks! Sorry about slow replies-been pretty busy around here.

[boondocks]

Re: CPU PLL effect on overclocking

I have been checking email, but not getting any notifications on threads like I usually do. Checked the general settings, instant notification by email is set, so I re-saved it and maybe it will work again.

[Lsdmeasap]

Re: CPU PLL effect on overclocking

No worries about slow replies, we all have real lives and are often busy, so we're never expect instant replies anyway so you're all good!

Yes, sorry about that, email notifications are disable right now. I reminded Mr.Tweak to turn them back on last night, hopefully he'll see that email soon and enable them again

[wevsspot63]

Re: CPU PLL effect on overclocking

I just wanted to confirm that lowering the CPU PLL voltage on my GA-Z68XP-UD4 (revision 1.3) board definitely helped improved stability. Specifically passing 12 hours of Prime95. For the world of me I couldn't pass 12 hours of Prime with CPU PLL voltage set at auto or manually setting it to 1.80v

After reading a lot of overclocking related posts on the Gigabyte Z68 boards I decided to start playing with the CPU PLL voltage. I started at 1.70v and slowly worked forwards and backwards from there. I seem to have found a sweet spot at 1.76v set in BIOS. Now I'm solid as a rock in all apps, games and can even pass 12 hours of Prime95 :)

I also noticed on BIOS F6 that VCCSA is auto set slightly below the Intel "recommended" value. Mine auto set at .920v - Intel says .925 so that is where I manually set mine.

Gigabyte GA-Z68XP-UD4
Intel i7 2700K
G.Skill DDR3 16Gb 1866Mhz
eVGA GTX 570 SC
Corsair HX1000
H20 Swiftech/XSPC

[Acebmxer]

Re: CPU PLL effect on overclocking

I have playing with CPU PLL with my i7-920 on the X58A-UD5 and OC and to be honest I see no change in stability or instability going from 1.8v default to 1.4v, Almost as if it is a broke voltage setting. I keep it at 1.4v just for the fact its a lower voltage. I have tried up 1.84-1.86 but I think I read that 1.9v will kill it or degrade it. I am not sure that that max is for the newer gen i7's .

[Lsdmeasap]

Re: CPU PLL effect on overclocking

It's not broke, well at least it wasn't last time I played with X58

If you turn it down too low it will cause instability for sure, so you can test that way if you think it's broken. Try 0.5-1.0V

[boondocks]

Re: CPU PLL effect on overclocking

Sweet spot for me @ x45 was 1.75V PLL. Didn't help to make further adjustments there when moving the clock to x46, though, so I ran up and down on vtt with no success, vcore on auto was already getting high so I tried working down with no success either.
Finally had to give it up for today, other things to do, and hopefully I can get back to tackling x46 tomorrow.

Funny thing I noticed, with block set at Auto it actually measures a little higher. With block set manually to 100 it drops a little below 100.

[boondocks]

Re: CPU PLL effect on overclocking

....and I definitely was seeing higher temps with the 212+ cooler even with 2 fans push/pull so I had added a vortex 120mm to the side and now the cores are maxing at about 80*C.

[jaggerwild]

Re: CPU PLL effect on overclocking

It's not broke, well at least it wasn't last time I played with X58

If you turn it down too low it will cause instability for sure, so you can test that way if you think it's broken. Try 0.5-1.0V

I seen a warning update some where that the revision XX of Z68 boards had defaulted high CPU PLL voltage, sorry if this iis an old thread.