3.8GHz stable, trying to squeeze last bit to 4GHz

laxity

laxity

laxity

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7 Nov 2006
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Hi guys,

I'm having trouble squeezing out the final 4GHz overclock on my 975 system. I currently have it stable at 3857MHz but the final jump to 4 is proving difficult. My current 3857MHz stable settings are :

CPU Multiplier - x29
BCLK 133MHz
CPU Turbo - off
HT - on
uncore - auto (3733MHz)
Performance enhance - standard

CPU Vcore - 1.28750V
Load Line Calibration - disabled
CPU PLL - 1.8V (default)
QPI/Vtt Voltage - 1.315V
DRAM Voltage - 1.64V

Memory is at 9-9-9-24 2T and tRC 48

(All other settings defaults)

Highest temps with Prime95 - 83 degrees

If I take the multiplier to 30x I can't get stability even if I increase the CPU vcore voltage to 3.0V (2 more settings on) so i'm wondering if some other setting needs tweaking as i'd rather not increase vcore more as temps are high as it is. 27x multiplier (3.6GHz) is stable at default voltage of 1.28125V.

Also tried increasing the CPU PLL up by 1 level to 1.84V but didn't help either. :( Any ideas what else I could try here?

cpuz.jpg


Many thanks,
Richard.
 
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Your bus speed is stock (133GHz) - whack it up to 174MHz and reduce the multi to 23 - the mobo should be fine with those settings.

Vcore seems to have dropped to 1.2V due to vdroop - may need to put it up a bit.
 
Just realised 83 degrees at 3.86Ghz? What cooler are you using. I suggest not putting up the speed any more until you find a way of bringing the temps down.
 
cmndr_andi said:
Your bus speed is stock (133GHz) - whack it up to 174MHz and reduce the multi to 23 - the mobo should be fine with those settings.

Vcore seems to have dropped to 1.2V due to vdroop - may need to put it up a bit.
Click to expand...

Thanks for all the replies.

So is upping the bus speed more likely to be stable than just changing the CPU multiplier alone then? I'll give it a whirl but I find that a little odd! lol

If I turn vdroop on my temperatures go even higher. If I turn this on do you think I can throttle back on the voltages a bit assuming this setting keeps voltages from fluctuating so much (well i'm assuming) ?

Also any idea if it is worth increasing CPU PLL even more perhaps? or would that not help here?

The CPU cooler is the Noctua NH-U12P Push/Pull (sorry my sig got pulled for breaking 5 lines earlier should be there now)

Cheers,
Richard.
 
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cmndr_andi said:
Just realised 83 degrees at 3.86Ghz? What cooler are you using. I suggest not putting up the speed any more until you find a way of bringing the temps down.
Click to expand...

Although not great thats not really a problem when running 100% on prime 95...........


also makes you wonder why anyone bother buting the extreme editions.... when a 920 DO is (nearly) as easy to get to 4ghz
 
Caracus2k said:
Although not great thats not really a problem when running 100% on prime 95...........


also makes you wonder why anyone bother buting the extreme editions.... when a 920 DO is (nearly) as easy to get to 4ghz
Click to expand...
My 920 is at 4.2Ghz, if this guy ends up with a 4Ghz 975 how much faster than mine is his?
 
Ok I've tested a few more settings, but I'm not so keen on changing the bus clock rather than just the multiplier as I can't then set my QPI link speed to 6.4GHz which is rather a key feature of this CPU. Also the vdroop settings i'm a little nervous about as I read that this can damage the cpu on wild spikes. I tried it but the vcore still dropped to 1.2V under load and the temps were higher.

Currently trying lowering the CPU PLL voltage to 1.7V which I read could help so will see how it goes. Current settings are (during Prime95 torture test) :


cpuz.jpg
easytune.jpg
coretemp.jpg


fingers crossed!
 
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TheRedZealot said:
Its at 4ghz isnt it :s
Click to expand...
CPU-Z reads 4GHz, Core temp is showing 3.4GHz because the multi is on 26 not 30.

Just drop the multi to 20 & up the bclk to 200 or better still get rid of that cpu & get i7 920 & get back around £300 - £400 & have the same performance.
 
Ignore the frequency output from the coretemp tool as it just picks up on the default multiplier and speed settings from the CPU. The machine is running at 133 x 30 (4GHz) during that test. See the cpuz screenshot.
 
Yay! Finally cracked it. 4GHz fully stable on Prime95 now with vcore of 3.0v and each core temp of around 69-72 degrees (CPU temp 47) depending on the room temperature. The problem was the Noctua NH-U12P heatsink not doing a very good job at cooling the cpu when overclocked. I replaced it with the Prolimatech Megahalems cooler and using the same 2 x Noctura push/pull fans and my temps dropped over 15 degrees on load! Absolutely amazing difference! I also used the NT-H1 heatsink paste instead of the Arctic Silver 5 as I read it was slightly better.

So it appears that the stability problems were all voltage/heat related. I think I there may be plenty of headroom for more too. I went straight to 3.0v too so may even test a lower voltage to see if it is stable. If it is then the stability issues were all completely heat related.

I have to say that the Prolimatech Megahalems is just incredible. It looks almost identical to the Noctura one but boy what a difference. Must be all the additional heatpipes. I am also wondering if the rough surface on the Noctura with the lapping groves could have had an impact. The surface of the Megahalems is just so much smoother in comparison, with a mirror like finish and no lapping/grove marks.

So if your having overclocking problems on air due to heat, go for the Megahalems!!
 
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