What is CPU PLL Voltage for? Please explain.

vwgolfman

vwgolfman

vwgolfman

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Hi,
The February edition of "Custom PC" describes how to run your i7-920's at 3.8GHz on P6T Motherboards.

What I want to know is what is the CPU PLL Voltage setting for?

The article says to adjust it up to 1.9V and then goes on to recommend not going above 1.45V unless you have extremely good cooling.

Is this a mistake?
What is "extremely good cooling"? Water cooling?
I have a Noctua NH-U12P with both fans in push-pull. Is this good enough?

What voltage should I set it to?

Many thanks for any advice.
 
Phase Locked Loop; it's a circuit which gives you your multiplied clock pulse. it essentially takes your bclk and multiplies it by the multiplier you set in bios (or stock). it feeds a input waveform into a differential amplifier (correct me if i'm wrong; been a year since i did my module on PLL) then into low pass filter, leaving only the 'error' margin, this gets amplified, which is what the voltage relates to (and thus higher voltage gives an easier lock-in error margin) and then is fed back (the loop bit :D) into the diff amp (looks at the difference in input A and input B [fed back waveform]) then back through the LPF & amplifier circuit to the output.

i7's seem to be contrary to the usual belief that more volts means more stable waveform, so experiment with higher and lower to see what is more stable.

hope that helps :)

EDIT: if you're on a C2D or C2Q, don't go above 1.6v - by this i mean monitor your volts in bios/everest etc and see if it's above 1.6. don't go sticking it on 1.6 in bios as it might have an error margin of, say, 0.1v, which means you'll be on 1.7v. be careful and make sure you check everything to avoid a raped chip :)

EDIT2: 0.1v error margin was just an example, i doubt there'd be any mobo that had that poor voltage reading :)
 
Last edited:
vwgolfman said:
Hi,
The February edition of "Custom PC" describes how to run your i7-920's at 3.8GHz on P6T Motherboards.

What I want to know is what is the CPU PLL Voltage setting for?

The article says to adjust it up to 1.9V and then goes on to recommend not going above 1.45V unless you have extremely good cooling.

Is this a mistake?
What is "extremely good cooling"? Water cooling?
I have a Noctua NH-U12P with both fans in push-pull. Is this good enough?

What voltage should I set it to?

Many thanks for any advice.
Click to expand...

1.45v was in regards to the vCore, not the CPU PLL
 
Custom PC either know **** all about overclocking or just don't bother to write anything useful. Their general approach of set voltages ludicrously high, minimise time testing then state as gospel that this is what every one of these processors can run at irritates me. It's quite a good thing to read on the train, but it's a terrible source for overclocking guidelines.

Setting PLL to 1.9V is poor advise. For one thing it's over the intel rated maximum, for another the best voltage is chip dependent. For mine 1.7V is best. For others anything down to 1.3V helps. Leave it at 1.8V until neither vcore nor qpi help, leaving you looking for other settings (cpu pll, clock drives, ioh are the most likely).

Twisted has done a good job of describing what it refers to.
 
twist3d0n3 said:
i7's seem to be contrary to the usual belief that more volts means more stable waveform, so experiment with higher and lower to see what is more stable.
Click to expand...

exactly, i7 cpus are very touchy when it comes to PLL

some boards respond very well to pll adjustments but others do not

for example, the UD5, UD7, P6T v1 and P6TSE dont respond well to high pll

the Biostar X58 doesnt like pll changed at all

where as boards like the blood rage, rampage2 and classified work well with precise adjustments

it has as much to do with the board as it does with your chip in my opinion
 
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