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Question Undervolting a 9900k (Asus Z390-F)

Mac34

Member
Dec 4, 2012
39
3
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Hi!

I'm new to overclocking and undervolting, and need some advice.

I have an i9 9900K CPU + Asus Rog Strix Z390-F motherboard (using Windows 10), and I would like to undervolt the CPU (I want my PC to run as cool/silent as possible).

I found a CPU voltage parameter in the bios. However, when I changed it to manual, offset or adaptive - I couldn't change the values. Do I have to activate the AI overclocking feature, to be able to manipulate the CPU voltage (a bit hesitant if this automatically changes core and voltage settings)? From what I've read a negative offset is the best for my use (non-overclocking), what kind of offset should I except?

I'm also considering using ThrottleStop, as it seems the most practical way to do it. Any good advice or tips before starting?


I would really appreciate some advice, thanks! :)
 
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Mac34

Member
Dec 4, 2012
39
3
71
AFAIK, you should be able to change those values.
I just read someone mention using the + and - keys to change the values, but I can't test right now, because I'm away from the computer. I'll probably use ThrottleStop first, as it seems like a quicker and easier way to dial in the optimal voltage value.
 

ZGR

Golden Member
Oct 26, 2012
1,830
250
126
I'd use Intel XTU instead. Throttlestop is fine, but I only recommend it on systems with a locked out BIOS.

I would go back into the BIOS when you get the chance.
Choose - instead of + for adaptive, click on the box you want to edit, enter a number, and press the enter key. If you really cannot edit anything then something is not right.
 

UsandThem

Super Moderator
May 4, 2000
11,364
1,906
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While I don't personally understand paying all that money for a 9900k (which Intel has used about every trick they have left to squeeze every drop of performance out of) only to undervolt it in an attempt to reduce heat (you could have bought a 65w CPU instead). If you undervolt it enough (provided you don't affect your stability), it will cause the CPU to run at lower speeds.

That said, you can accomplish what you are after buy creating a power profile within Windows. By setting your CPU's maximum boost state lower than 100%, it will reduce it's heat and energy usage as it won't turbo boost to its full potential.

2.jpg
 

Mac34

Member
Dec 4, 2012
39
3
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I wanted a bit less fan noise, as my PC case doesn't have the best airflow design unfortunately. I thought reducing voltage didn't affect performance, but I'm just getting up to date on PC components again (this is my first PC in nearly 15 years, after solely using Macs).

I was hoping to undervolt by an offset of 0.050-0.100 or something, and getting a cooler-running CPU with the same performance and turbo boost. Is it truly not possible to undervolt, and force the CPU to keep the original performance (until it crashes from not getting enough voltage)?

Thanks for the tip btw, I'll try XTU. So, if I want to undervolt - I should set both CPU core, CPU cache and iGPU at the same volt offset (say -0.050). Then stresstest and go lower if possible. That's it, right? Is there anything else that needs tinkering? :)

Thanks!
 
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DrMrLordX

Lifer
Apr 27, 2000
13,306
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I thought reducing voltage didn't affect performance
It depends on the boost maps in use on the CPU. If you have an old-school CPU that uses a fixed clockspeed, you can dial voltage down to reduce total power at that clockspeed. But modern CPUs like a 9900k use a fairly-complicated boost map that will reduce your maximum boost clocks if you set a negative voltage offset. Yes, you will use less power, but you will also get less performance since the boost will be less aggressive.

You can experiment with various offsets to see how or if performance is affected in benchmarks. I would recommend avoiding AVX/AVX2 benchmarks at least initially, since your CPU will enter an entirely different performance state for AVX.
 

Mac34

Member
Dec 4, 2012
39
3
71
I see... So the only way for undervolting to work properly, is to set 9900k to run at a static clock speed like 4700mhz? What about adaptive undervolting, and setting a specific value to each turbo boost level? Is there any software out there, that can do this? If not, I'll just drop the undervolting all together.

Thanks again for the help, I'm learning a lot here. :)
 

DrMrLordX

Lifer
Apr 27, 2000
13,306
2,820
136
I see... So the only way for undervolting to work properly, is to set 9900k to run at a static clock speed like 4700mhz?
Not necessarily. That's one way to go about it, but you'll find that the voltage required to sustain that clockspeed is high enough that you may wind up exceeding the normal TDP of ~160W for the chip. All you're doing there is guaranteeing a particular clockspeed, and then crossing your fingers and hoping that you have a golden chip that will run at that speed at an abnormally low voltage - something which the boost map might not take advantage of. You're free to make the attempt . . . just be advised that it may not work in your favor.

Really you should just try a voltage offset and run some benches to see what happens. Also be sure to read what @LTC8K6 posted. You can restrict based on power targets instead of voltage. The 9900k performs pretty well as a 95W TDP CPU.
 

Gt403cyl

Member
Jun 12, 2018
126
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I personally don’t have any first hand experience with the 9900k so please take this for what it is...

A friend who runs a 9900k has been playing with Vcore to get his temps lower, his stock voltage was around 1.4-1.42v if I recall, and now he has his chip running at 4.9GHz 1.25v, to my knowledge he isn’t running an offest just setting Vcore and multiplier with speedstep enabled.

That said stability still needs to be checked but from what I’ve read and from what I know of his experience with the 9900k, stock voltages are often a fair bit higher than what is needed, which also means they run a bit hotter, fans run faster ect.
 

legolas_tk

Member
Apr 16, 2008
58
6
71
adjust by going to BIOS -> AI tweaker -> CPU Core Voltage -> Offset -> (negative) -> adjust under-voltage , test voltage in every step and check for stability.
 

Mac34

Member
Dec 4, 2012
39
3
71
OK, thanks again for the help.

I ended up changing the radiator placement of my AIO CPU cooler, and changing some of the fans - now the CPU runs much cooler. I tried a voltage offset of -0.050, but the temperature difference for the CPU was near nill. Anyway, my computer is near silent at this point, with only a very soft fan sound during gaming (mostly from the GPU), so I'm more than happy now, and see no need for undervolting. :)
 
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