Seasonic Super Silencer 400 - ATX12V 1.3

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The Seasonic Super Silencer 400 represents a couple of major firsts for an ATX12V power supply.

1. It is the first to be compliant with the ATX12V v1.3 PSU Design Guide - as far as we know.

2. It is the first to reach an efficiency performance of 78%. That it achieves such high efficiency at a price no higher than many run-of-the-mill PSUs is a testament to Seasonic's intelligent engineering.

The noise level of this new model should be substantially lower in normal operation than previous Seasonic models. The Super Silencer also runs cool enough that in many systems, it is probably quite feasible to dispense with a case fan, thus eliminating another noise source.

It's clear that in real applications, inside a case powering a real system, the Seasonic Super Silencer 400 will probably run quieter than any other high power PSU we've examined or reviewed at SPCR.

Combine low noise with high performance, high efficiency, high current capability, handy "Doctor Cable" kit, 3-year warranty and a modest $99 price, and this new Seasonic looks like a real winner. The US$59 300W model is an even better deal for those with more modest power needs.

For diehard silencers and molders, the Super Silencer 400 is a perfect platform for fan swapping with the quietest fans available. Because of its super high efficiency and modest heat dissipation, the risk of overheating with low airflow fans is low. The end result with such modding would be loss of the generous 3-year warranty... and gain of the coolest quiet 400W PSU in the world.

Low Noise by Definition?

Regular visitors to SPCR may be aware that Intel's ATX12V v1.3 PSU Design Guide has guidelines for low noise PSUs. Section 5.7 on page 54 of the Guide calls for a maximum sound power level in a PSU designated as low noise to emit no greater than 4.0 Bels sound power at 50% load and ambient intake air temperature of 43C.

While 4.0 Bels is not exactly super quiet, the conditions of 50% power load and 43C air temp makes this a very tough standard to meet, especially for high power PSUs. Few PSUs even on our Recommended quiet PSU list would pass this test. Most quiet PSUs are quiet at power loads under 150W. But the high efficiency of the Super Silencer 400 made us wonder if it would pass.

It is very difficult to make a precise conversion of Bels (sound power) to decibels (sound pressure level), but 4.0 Bels would usually fall somewhere between 30-34 dBA @ 1 meter in most environmental conditions. In order to achieve the required 43C intake temperature, the 100W light bulb in the case was raised and brought closer to the intake vents while the PSU was running at 200W load.

This was an awkward process as the cover to the PC case had to be replaced, and a few minutes allowed to pass for internal temperature to stabilize. It was made even more difficult because of the thermal fan speed controller: It would adjust the fan speed up at first, causing temps to drop temporarily, then it would slow the fan down, causing the temp to go back up and so on... In the closest match to specified conditions, at an intake temperature of 41-45C, the noise level measured was 35~36 dBA @ 1 meter. The fan voltage was ~8V.

Given this SPL, the Super Silencer 400 probably would be borderline to pass the section 5.7 low noise guideline in Intel's ATX12V v1.3 PSU Design Guide. But it's likely to pass at 150W. The Super Silencer 300 at 50% load would be producing 150W. If its efficiency is anything like the 400, the Super Silencer 300 is a very good candidate to pass (with a better testing setup!) this demanding low noise guideline.

Our thanks to Seasonic and Seasonic USA for the review samples and for their kind support. They say Seasonic's new "Super" line of PSUs will be available any day now at 24 Fry's Electronics store locations around the US. They are also available online at quiet PC specialist Silicon Acoustics.

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Despite all efforts to avoid testing errors, a Seasonic engineer did find a factual error (regarding the rating of the 12V line, already noted in the text of the review) and a procedural error:

"On page 4, the loading combination of 400W was over our specification of 3.3V & 5V combined load (not exceed 180W):

  • +5V~145W (29A) and +3.3V~81W (24.54A): The total power load of 226W exceeded the combined power limit of 180W
  • We suggest this load combination for 400W: +5V/110W (22A), +3.3V/69W (21A), +12V/216W (18A)
  • High combined load might cause shortened life, voltage out of regulation, high ripple noise...."

The most likely change in the result, according to Seasonic, is that the efficiency at full power may be improved somewhat. So the full power test was run again as per their suggested line loads:


The end result did not change much. Instead of the 527W AC power consumption measured and reported with the overload on the +5V and +3.3V lines, AC consumption measured on 6 tries with both 400W samples was 523W to 526W. This was with the AC at 118~119V.

Although 523W is lower than any AC power consumption figure measured in previous tests, because the maximum was only 1W lower than before, it's hard to consider statistically significant. Even if the 523W figure is used for the efficiency calculation, the final result improves only from 75.9% to 76.5%. Thus, our original assessment of 76% efficiency at 400W remains unchanged.

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