A10-5800K: The Undervolt And Overclock
It would have been easy enough to drop the clock rate on our A10-5800K and nudge its voltage down as well, triggering lower power consumption. But this exercise wasn’t about cramming a 100 W APU into a mini-ITX chassis. Rather, we wanted to maintain stock performance at the lowest voltage possible.
A BIOS-set 1.25 V seemed like it was going to be stable. After the system hung a couple of a times in our multi-hour benchmark suite, though, we settled on 1.275 V instead. With all of the platform’s power-saving features already enabled, further cuts would have taken a more efficient power supply, different memory, perhaps, or maybe a minimalist motherboard. Really, though, we were most interested in power cuts directly attributable to the processor.
Overclocking was a little more exciting. Based on our conversation with Sami Mäkinen in Professional Help: Getting The Best Overclock From AMD's A8-3870K, we began our quest with a graphics tweak, pushing the integrated Radeon HD 7660D core from 800 MHz all the way up to 1083 MHz in AMD’s OverDrive utility (this required a 1.275 V northbridge setting). From there, we edged the processor clock up to a stable 4.4 GHz at 1.5 V.
The A10-5800K in our preview story managed a stable 4.5 GHz with all four cores under full load. We tried the same thing this time around, but discovered that, at just under 70 degrees Celsius, cores would jump back down to 1.4 GHz at .91 V to throttle heat if we were using AMD’s reference FX cooler. Even switching over to AMD’s Asetek-designed closed-loop liquid cooler wasn’t enough to get the chip stable at 4.5 GHz this time.
So, we settled for 4.4 GHz across all cores—as high as we could go without triggering performance-debilitating issues throughout our suite. But we noticed another strange behavior that might affect the peak overclock of an aggressive enthusiast. As soon as we crested 4.5 GHz and started trying to push 4.6 and 4.7 GHz, slowly increasing voltage along the way, MSI’s FM2-A85XA-G65 motherboard forcibly pushed down our multiplier (as low as 29x in some cases), despite UEFI and OverDrive ratios that read otherwise.
We’re not sure if this is a deliberate mechanism to protect the motherboard’s power logic, but it’d make sense when you get to our power analysis and see how quickly consumption ramps up as you increase clock rate and voltage.
At the end of the day, it looks like there might be a couple of different protection mechanisms in play: AMD’s thermal monitor keeping the APU from exceeding a ceiling, and what appears to be MSI’s motherboard from jumping over a certain power level, even with temperatures well under the aforementioned limit.