i7 875k multiplier overclocking - voltage question

[ivansoup]

I have an i7 875k with a cooler master hyper 520 heatsink/fan I recently overclocked to 3.725 Ghz. Idle temps are 25-30C on each core. 100% load temps following prime95 or Linpack are 69-72C on each core.

I only raised the multiplier to 28 and raised vcore to 1.2v. I didn't change vtt or any other voltages since I assumed they weren't necessary if only changing the multiplier. Should I be changing any other voltages if all I'm doing is changing the multiplier? Or is vcore the only voltage I need to worry about?

Thanks.

 

[Kenmitch]

I'll guess you messed with vcore and left the others on (auto) if that is the case you may want to see what the MB is feeding. It's best to take full of voltages in bios when overclocking and not let the MB guess what is needed as most of the time it'll overvolt.

I'd start by going into bios and writing down your voltages and update your post and we'll see if we can get you setup and stable

And if you are running with hyper-threading enabled then your temps look good to me.

 

[ivansoup]

Thanks for the reply. Yes, hyper threading is enabled. I manually set some of the other voltages to what I thought their default was.

vtt=1.05v
memory voltage=1.5v
pch=1.05v
pll = 1.8v

 

[Kenmitch]

Voltages seem good to me and look like the stock defaults. Now you just gotta do some stability testing to make sure it's stable.

I like to use Intel Burn Test as my first step....Will get the CPU toasty hot so make sure you keep an eye on the temps. Best to stay under 70*C with the lower the better. Best thing about IBT is if you just start with the default settings it'll error out very quickly unlike prime95 which could take hours.

I'd say the voltage you most likely will have to raise would be the cpu vtt voltage. You'll have to just play around with it and see tho. If you fail IBT just bump it up a notch and try again. If it passes already maybe just try more than the default run of 5 maybe 25 and test with max memory also....Just keep an eye on the temps tho!

 

[Kenmitch]

Forgot some info

I use Intel Burn Test as a system optimizer also. If you note the bandwidth during the runs you can use IBT as an optimizer. What I mean is sometimes the system will be stable but starving for voltages. As in maybe just a little more vcore or cpu vtt etc. Sometimes just a little more vcore or cpu vtt etc will increase your bandwidth by alot. Just gotta play around with it and see.

 

[ivansoup]

I tried the intel burn test. The system was stable @ 3.73 Ghz (28x133) w/ 1.15 v vcore and 1.05v vtt. Max Core Temps under full load in intel burn test were between 65-69. To be safe, I upped the voltage so vcore=1.1625v and vtt=1.1v.

My question is does the cpu vtt have any effect on stability if I'm only increasing the cpu multiplier? Or does it have to do with the uncore/memory stability?

 

[MeTechE]

Thanks for the reply. Yes, hyper threading is enabled. I manually set some of the other voltages to what I thought their default was.

vtt=1.05v
memory voltage=1.5v
pch=1.05v
pll = 1.8v

Unless I somehow missed it, have you mentioned what motherboard you're using? The number of phases can be important (up to a point) in overvolting. Some boards are only meant to handle the stock voltages, while others are built to take much more. It may be helpful to post what board/revision (if applicable) you have.

I'm selling another i7 875K here, if anyone wants to get in on the overclocking action .

 

[ivansoup]

I posted a reply earlier, but I guess it didn't send or something.

Anyway, I'm using a EVGA p55 ftw motherboard. I tested with intel burn test, and it was stable at 3.73Ghz (28x133) with 1.15v Vcore and 1.05v VTT. The max temps on cores were 65-69C during Intel burn test. I then upped the Vcore to 1.1625 and the VTT to 1.125 just be be on the safe side. I went through a couple hours of prime 95 also with no hitches. It seems like the chip could probably go a lot higher, but my heatsink (cooler master 520) doesn't seem up to the task.

Vdroop is disabled. Not really sure if I need that or not. Also, I'm not sure I understand what the CPU Vtt voltage is and if I need to raise that if I'm only raising the multiplier.

 

[ivansoup]

I tried posting twice before, but apparently I was doing something wrong.

I am using a EVGA p55 ftw motherboard. The system was stable at 3.73 Ghz with 1.15v vcore and 1.05v vtt. 100% load core temperatures on intel burn test were between 65-69. I also ran prime95 for a few hours. I upped the voltages to 1.1625 vcore and 1.1 vtt to be safe.

I have vdroop disabled currently. Should I have that enabled? Also, I'm not really sure on what vtt is? Since I am only changing my multiplier and not changing bus or uncore speed, does increasing vtt do anything?

 

[MeTechE]

I tried posting twice before, but apparently I was doing something wrong.

I am using a EVGA p55 ftw motherboard. The system was stable at 3.73 Ghz with 1.15v vcore and 1.05v vtt. 100% load core temperatures on intel burn test were between 65-69. I also ran prime95 for a few hours. I upped the voltages to 1.1625 vcore and 1.1 vtt to be safe.

I have vdroop disabled currently. Should I have that enabled? Also, I'm not really sure on what vtt is? Since I am only changing my multiplier and not changing bus or uncore speed, does increasing vtt do anything?

To start from the top, the P55 FTW is an excellent board and should not be limiting your overclock potential in the slightest. Those clocks/voltaegs look good but you have some more vcore headroom if you want to push things a little further.

I would leave vdroop disabled. Since you are putting a lot of extra voltage through the processor, vdroop may end up causing instability by lowering voltages occasionally. As for Vtt, that is the voltage to the 'uncore.' The uncore is, well, not the cpu core . Vtt voltage covers the L3 cache and memory controller.

According to Intel's spec sheed (http://download.intel.com/design/processor/datashts/322164.pdf Page ~67) normal Lynnfield voltages are 1.4 Vcore and 1.155 Vtt. Max voltages are 1.55 Vcore and 1.21 Vtt.

 

[Kenmitch]

My question is does the cpu vtt have any effect on stability if I'm only increasing the cpu multiplier? Or does it have to do with the uncore/memory stability?

Yes cpu vtt will effect stability. If to low the system will most likely not boot into windows or will do the old reboot under heavy loads.

I have vdroop disabled currently. Should I have that enabled? Also, I'm not really sure on what vtt is? Since I am only changing my multiplier and not changing bus or uncore speed, does increasing vtt do anything?

I always leave the C1E, Turbo, SpeedStep enabled as well as at least in my evga it's with vdroop. YMMV. I kinda think that doing the everyday tasks in windows one does not need to be sitting at the max overclock pumping xtra vcore in the chip while surfing the web or doing email, etc.

To start from the top, the P55 FTW is an excellent board and should not be limiting your overclock potential in the slightest. Those clocks/voltaegs look good but you have some more vcore headroom if you want to push things a little further.

True....But I think he's also trying to keep the temps down below 70*C under severe loads.

 

[ivansoup]

Thanks for the replies and help. Yes, I am trying to keep the temps down. I'm sure the chip could do more, but I think I'm happy with the current overclock given my cooler (cooler master 520).