Seasonic Platinum Fanless 520W PSU

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The Seasonic Platinum Fanless 520W delivers the most exacting performance ever measured on the SPCR PSU testing rig. Its voltage regulation is astonishing, especially on the 5V and 3.3V lines, which remained essentially unchanged from minimal 20W load to maximum 520W load. The 12V line, with a drop of 0.07V between minumum and maximum load, is merely excellent, but also unmatched by any other PSU tested. Noise and ripple were also superbly low, with the oddity of it being slightly higher at mid-power than maximum. Efficiency was the highest I've measured in any PSU thus far. The 95% efficiency seen at 400W load with 240VAC input means this PSU produces no more heat (21W) at that power level than many a low power optimized mobile CPU. The luxuriant packaging, excellent build and parts quality, 7-year warranty and Seasonic's long history of quality products all combine to affirm my own high expections of this remarkable product.

The fly in the ointment is that trace amount of high frequency whine in the first sample at certain loads on the 5V Standby line. Too low to be measured at 1m distance in an 11 dBA ambient anechoic chamber, but probably audible to users with highly sensitive hearing in very quiet rooms who want to place a small, near-silent PC on the desktop. This is the single biggest challenge for makers of fanless PSUs: The absence of masking broadband noise from a fan lays bare any trace of any other noise, while attracting the most aurally sensitive customers. It leaves Seasonic between a rock and a hard place.

The second sample did exhibit some trace tonal buzz, but at a much lower level than the whine of the original, and otherwise performed just as beautifully as the first. So while there's a bit of a question about which sample is exhibiting the more normal behavior, the latter is more likely, and this trace level of buzz is likely to be insignificant for the vast majority of users.

It is not possible to bar the Seasonic Platinum 520W from an Editor's Choice award, given all the other strengths of this outstanding power supply, but I will keep attuned to the web for genuine reports of buzzing or whining from actual users. To end on a positive note, the $149 suggested retail price is really a pittance for such outstanding performance, which was not available at any price a few short years ago.

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ADDENDUM, 5 FEB 2013: Sample Number Three

Last week, some six weeks after this review was originally posted, I received a third sample of the Seasonic 520W Platinum. This one is apparently representative of the current production models. I tested the new sample 3 times, with many hours of steady modest load (<100W) and also standby between high load testing, over a period of 5 days. All this was to ensure that no changes occurred as the unit "broke in".

Overall, the level of whining noise of the third sample is very low and did not change over time or load. It is very unlikely to cause any negative reaction with 99% of potential users. (The 1% who might complain are the ones who would never be happy with any product.) I would call it a residual level of noise — not audible when one's head is more than a foot away, under any load or acoustic background. There is a wee bit of whine associated with the 5Vsb line, and it varies a tiny bit as that load is raised and lowered, but not to any significant or noticeable degree. As a function of 12V load, the level of whine is very low, and does not vary. When the measurement microphone is placed right atop the PSU, the frequency of the trace noise can be seen as spikes at 4kHz and 6 kHz, but even from this intimate distance, the levels are just -10 dBA and -15 dBA.

The very low level of electronic noise achieved in this sample is nice to see. Seasonic reps assure me that the issues which caused the higher than expected electronic noise in the original sample have been resolved. Apparently, it is the quality of the winding process for the transformer that affects the noise I found, and this issue has been identified and corrected, with continuous monitoring assured for the future. Typical production variance of the electronic noise from my sample is estimated to be approximately +7%, -5% — this is very tight tolerance, and a +7% increase will not be audible as any change at all.

The electronic noise with the second sample really wasn't serious, and this one is much better, so all in all, it's a very positive result.

As mentioned in the review, Seasonic reports that adjustments in the BIOS of some recent motherboards eliminates electronic noise completely with many earlier production samples. The settings are:

  • BIOS set up to ENABLE ErP/EuP (S4~S5)
  • BIOS set up to DISABLE Audio Always On

Much thanks to Seasonic USA for the review samples.

Seasonic Platinum Fanless 520W wins the SPCR's Editor's Choice Award

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SPCR Articles of Related Interest:
Power Supply Fundamentals
Recommended Power Supplies
Fanless PSU Torture Test Roundup
Fanless PSUs: Kingwin Stryker STR-500 & Silverstone ST50NF
Seasonic X-400 Fanless PSU
Enermax Platimax 600W
Seasonic G360

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