Need advice

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Adagio
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Re: Need advice

#31

Post by Adagio »

VoxLupus wrote:I think that you are a little too optimistic with that PSU Fluke.

You must bear in mind that not all of those 500 W are available to the CPU and GPU.
That is powered by the 12 V rail, which for the CX500 is rated at 34 Amps.
12 V*34 A=408 Watts

For the 390, that is a an overhead of 7% for the power available to the GPU and CPU in those bench marking applications (assuming the other components are negligible), and this is assuming that the relatively low-quality PSU is operating at peak performance. I am also not sure if those power draws take into account factory over clocks. Having such a small margin may cause issues with the stability of the system, especially since some applications may lead to greater power consumption than the ones tested here.

I don't know about you but that is a little to close for me to feel comfortable with. I think you will be hard pressed to find many people recommending a 500 W PSU for a R9 390.
Here is a forum post I found relating specifically to this question:
http://www.tomshardware.com/answers/id- ... u-390.html

I think that one of the reasons that the difference in power consumption is not significant in the benchmarks you listed (80 Watts as apposed to the expected 150 Watts) is that the 390 is typically CPU bound due to bad driver optimization. AMD is addressing these issues and along with DX12 I have a feeling that these will lead to improved performance as well as an increase in power consumption.

I know I have oversimplified some things, and while you are right that the 500 W will probably work, I think the potential issues it may lead to will not be worth it. The 970 would be the safer option by far.
I'm no computer expert, but I'm pretty sure all TTL logic works with 5v, and CMOS works from 3.3v to 5....
And on all the microcontrollers/processors I've worked with, this was true...
Another thing I might add. The i5 in my laptop only uses 5 watts... When I'm REALLY using it. It goes up to around 11W...
I KNOW that this won't be the same for desktops. Laptops are designed to use less power...

If it happens to run on 12v, it probably has a regulation circuit inside, but that would be inefficient, and generate unnecessary heat...

My advice.
'Yote. If you can spare the cash. I'd go for the bigger PSU. But it depends on what you want to do...
It leaves a open margin for future upgrades, and it's something that will always be compatible with new hardware...(up untill they bring out new connectors...)

I've never even had a desktop. So I don't know all this overclocking and GPU's and stuff...

But they've been arguing about the PSU so long... You're probably reading this from your new PC aren't you? :lol:
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VoxLupus
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Re: Need advice

#32

Post by VoxLupus »

Most modern MOBOs use LVTTL which uses a voltage of 3.3 V. I think the 5 V is only used for USB, peripherals and hard drives. The MOBO has voltage regulators to drop the 12 V to whatever voltage the CPU needs (usually about 1.5 Volts). This does generate heat and is why most high end motherboards have fancy heat sinks around the CPU.

The i5 2500K has a TDP of 95 W which can increase substantially with overclocking. If you add up the TDPs of the R9 390 and 2500K you get: 95 W+300 W=395 W. Again this is far to close to the 408 W limit, especially if you consider the VRM inefficiencies, which I don't think are taken into account for the CPU and will vary between motherboards.
Here is some more numbers on the power draw of a R9 390 system:
http://lanoc.org/review/video-cards/710 ... l=&start=7

Your advice is pretty spot on Adagio. If Yote has already made his decision then I would like to see how it has turned out. :)
Last edited by VoxLupus on Mon Mar 14, 2016 1:27 pm, edited 1 time in total.
Randall
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Re: Need advice

#33

Post by Randall »

I'm no computer expert, but I'm pretty sure all TTL logic works with 5v, and CMOS works from 3.3v to 5....
And on all the microcontrollers/processors I've worked with, this was true...
No longer the case unfortunately. These days 3.3V is the rage, and the stuff I play with at home, the CPU core voltage is 1.5V. Its been a while since I last had any dealings with anything 5V related.
The MOBO has voltage regulators to drop the 12 V to whatever voltage the CPU needs (usually about 1.5 Volts). This does generate heat and is why most high end motherboards have fancy heat sinks around the CPU.
The heatsinking is used for the CPU and the North Bridge, and South Bridge. The 5V and 12V is stepped down efficiently using switching regulators. Some of the FET transistors used there may need heatsinking but usually that can be done using the PCB.
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Re: Need advice

#34

Post by VoxLupus »

Randall wrote: The heatsinking is used for the CPU and the North Bridge, and South Bridge. The 5V and 12V is stepped down efficiently using switching regulators. Some of the FET transistors used there may need heat sinks but usually that can be done using the PCB.
That is why I said 'high end' motherboards have heat sinks for the VRM. I know there are heat sinks for other components on the motherboard, that is why I specified with "around the CPU"
here is just an example: http://techreport.com/r.x/p67-mobos/asus-socket.jpg

While most VRMs are very efficient they can still get pretty hot, especially with overclocking. This can lead to stability issues and why you shouldn't get a motherboard without VRM heat sinks if you plan to overclock.
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Re: Need advice

#35

Post by Fluke »

VoxLupus wrote:I think that you are a little too optimistic with that PSU Fluke.

You must bear in mind that not all of those 500 W are available to the CPU and GPU.
That is powered by the 12 V rail, which for the CX500 is rated at 34 Amps.
12 V*34 A=408 Watts
I suppose I should have mentioned that a good-quality 500w unit is more than enough for a 2500k OC + 390. Ones like those SuperFlower / EVGA G2/P2 / SeaSonic Gold/Plat units can actually handle ~550w 24/7 just fine. And loading them at ~400w when intense gaming will be the most efficient use of the PSU.

I did state previously that the CX500 is really not a quality unit, I didn't realise it had that poor amperage on the 12v rail. It should be labeled as a 400w PSU then lol.... I wouldn't run that unit fullstop, personally, but seeing that would make me want to upgrade even more.

VoxLupus wrote: I think that one of the reasons that the difference in power consumption is not significant in the benchmarks you listed (80 Watts as apposed to the expected 150 Watts) is that the 390 is typically CPU bound due to bad driver optimization.

AMD is addressing these issues and along with DX12 I have a feeling that these will lead to improved performance as well as an increase in power consumption.
No. Furmark alone shows you it's false (OpenGL).
Also just because AMD drivers are more CPU-bound in DX11 applications doesn't mean that they won't be using 100% of the GPU, 'VRAM', VRMs, etc. in a stress-test like that. It just means that it won't be as efficient into turning in FPS, if you know what I mean.

Also, the 390 actually uses less power than the 290 because they're better binned and lower voltage as a result.
VoxLupus wrote: I know I have oversimplified some things, and while you are right that the 500 W will probably work, I think the potential issues it may lead to will not be worth it. The 970 would be the safer option by far.
I'd for a 970 if you don't want to change away from the CrapXtreme 500 :p

Randall wrote: No longer the case unfortunately. These days 3.3V is the rage, and the stuff I play with at home, the CPU core voltage is 1.5V. Its been a while since I last had any dealings with anything 5V related.
The heatsinking is used for the CPU and the North Bridge, and South Bridge. The 5V and 12V is stepped down efficiently using switching regulators. Some of the FET transistors used there may need heatsinking but usually that can be done using the PCB.[/quote]
+3.3v: Chipsets, some DIMMs, PCI/AGP/PCIe cards, miscellaneous chips
+5.0v: Disk drive logic, low-voltage motors, SIMMs, PCI/AGP/ISA cards
+12v: Motors, high-output voltage regulators, AGP/PCIe cards, CPU

(Motors as in pumps, fans, etc.)

VoxLupus wrote: The i5 2500K has a TDP of 95 W which can increase substantially with overclocking. If you add up the TDPs of the R9 390 and 2500K you get: 95 W+300 W=395 W.
That's a peak plausible. Stock 2500k is actually more around 75-80w when using P95. And gaming is around, I'd say 65-70w. Mildly overclocked (1.3v / 4.3Ghz) you're looking at ~115-120w in P95 and around 105-110w in gaming.
VoxLupus wrote: Again this is far to close to the 408 W limit, especially if you consider the VRM inefficiencies, which I don't think are taken into account for the CPU and will vary between motherboards.
Here is some more numbers on the power draw of a R9 390 system:
http://lanoc.org/review/video-cards/710 ... l=&start=7
See above about my views of the CX500 lol. Also that site is an out-layer, almost every single over reviewer is coming up with 380-400w usage for that GPU. So I wouldn't trust that.

Keep in mind, it's really not possible for it to use 506w with a single CPU+390. My GPU uses ~550w under load. That means ~275w per overclocked 290X core. Around ~700-720w for the whole system under stress-load.


Also lol;

"So the R9 390 pulled 506 at peak, slightly higher than the overclocked R9 290X."
>it has lower voltage
>it has a lower core clock
>it uses the exact same architecture
>less shader cores (massive power reduction factor with AMD Hawaii Architecture)
>result:
>consumes more power???

Yeah, very dodgy right there.
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