SilverStone Decathlon DA700 power supply

SilverStone, despite its image mostly as a high-end case brand, offers an amazing number of power supplies, probably many more than you might think. The 700W DA700 is part of its Decathlon line, geared to “power users”, but they want to pit it against the quietest PSUs tested by SPCR. Naturally, we’re happy to comply.

Oct 28, 2008 by Mike Chin

The ratings of power supplies for DIY computers have become so routinely high that a 700W unit hardly raises an eyebrow these days. Surprisingly, it is actually possible to assemble a PC that can push such a PSU to its limits, even with all the gains in energy efficiency made in processors. The source of the ridiculous power draw for gamers is the high end graphics card, especially pairs or even threesomes in CrossFire or SLI configuration. The nVidia GTX280 and the ATI 4870 X2 cards both make the power requirements of most current CPU seem positively anorexic.

SilverStone, once a maker of stylish mostly aluminum cases, has also offered power supplies for a number of years. They’ve had good success, tackling both the conventional gaming / performance sector as well as the silent-loving crowd. The fanless Silverstone ST30NF Fanless PSU, a 300W model that dates back to 2004, is still being made in an updated version, and still one of our favorites. The 120mm fan Element ST50EF-Plus model also reviewed well a couple of years ago, though it did not match the quietest reviewed PSUs available then.

The DA700 is next to the bottom model in the Decathlon series, modular cable PSUs oriented to the “power user”. There are seven models, starting at 650W and ending at 1200W. Silverstone actually makes no fewer than six series of power supplies, one of which is aimed at the silent user. The 700W model in that series, ST70F actually sports a lower noise rating than the DA700: 18 dBA versus 23 dBA minimum. Regardless, the DA700 is the model Silvertone sent to challenge “Anandtech’s assessment that Enermax offers the quietest power supplies at the moment.” SPCR’s own review of the Enermax Modu82+ 625W, posted around the same time, made the same assessment as well. Anandtech review of the DA700 stated that “SilverStone is telling the truth and not just blowing hot air” with regard to the acoustics. Naturally, SilverStone is hoping we’ll reach the same conclusion.

One small complication is that the Enermax was tested in a live room, while today, six months later, our testing procedure has progressed to a quieter anechoic chamber where there is no echo and the background noise level is several decibels lower. We’ll make adjustments to make the comparison fair, but a full-blown test of the Enermax was not possible to repeat.

PACKAGING, FEATURES & SPECS

A fairly standard looking retail box.

Inside, there’s the PSU, a manual, AC cable, detachable cables, and a pouch to keep unused cables.

VISUAL TOUR

The DA700 is finished in the usual matte black. It’s a bit longer than a standard ATX12V PSU. The extra length is not unusual among higher power models, especially when space required for terminal connectors for detachable cables.

Matte black finish, slot intakes on the back and a small one on the side.

The DC output side of the unit has a total of 10 plug-in terminals for the modular cables. There are four different types: 24-pins for the main ATX cable, and 4, 6 and 8 pin types of various others. There is a small
vent on this side, the only opening other than for the fan intake and exhaust.

10 plug-in terminals for various modular cables; no permanently attached cables.

The label shows the function of each terminal.

PEEKING INSIDE

Opening up the unit shows a reasonably tidy but packed layout and fairly large heatsinks.

Opening up the unit shows a reasonably tidy but packed layout and fairly large heatsinks.

A relatively high power (0.45A) 120x25mm 7-blade fan by Protechnic Electric.

Naturally, we’re always interested in the details of the fan, as it’s the primary noise source in a PSU. Protechnic Electric, the maker of the fan, does not appear to have a web site, however, so official fan data was not available. Other tech reviews have described this fan, model MGA12012HF-025, as having a “rifle” bearing, and SPL of 38.3 dBA (at 1m?) at 1,600rpm/12VDC. As none of the reviews mention the source of this data, healthy skepticism applies. The struts are well designed, perpendicular to the blades’ trailing edges for low tonal noise. The plastic quality is average, neither extremely brittle sounding when tapped, nor highly damped.

TESTING

For a fuller understanding of ATX power supplies, please read
the reference article Power
Supply Fundamentals. Those who seek source materials
can find Intel’s various PSU design guides at Form
Factors.

For a complete rundown of testing equipment and procedures, please
refer to SPCR’s
PSU Test Platform V4.1. The testing system is a close simulation of
a moderate airflow mid-tower PC optimized for low noise.

Acoustics measurements are now performed in our anechoic chamber with ambient level of 11 dBA or lower, with a PC-based spectrum analyzer comprised of SpectraPlus with ACO Pacific mic and M-Audio digital audio interfaces.

In the test rig, the ambient temperature of the PSU varies proportionately
with its output load, which is exactly the way it is in a real PC environment.
But there is the added benefit of a high power load tester which allows incremental
load testing all the way to full power for any non-industrial PC power supply.
Both fan noise and voltage are measured at various standard loads. It is, in
general, a very demanding test, as the operating ambient temperature of the
PSU often reaches >40°C at full power. This is impossible to achieve
with an open test bench setup.

The 120mm fan responsible for “case airflow” is deliberately
run at a steady low level (6~7V) when the system is run at “low”
loads. When the test loads become greater, the 120mm fan is turned up to a higher
speed, but one that doesn’t affect the noise level of the overall system. Anyone
who is running a system that draws 400W or more would definitely want more than
20CFM of airflow through their case, and at this point, the noise level of the
exhaust fan is typically not the greatest concern.

Great effort has been made to devise as realistic
an operating environment for the PSU as possible, but the thermal and noise
results obtained here still cannot be considered absolute. There are too many
variables in PCs and too many possible combinations of components for any single
test environment to provide infallible results. And there is always the bugaboo
of sample variance. These results are akin to a resume, a few detailed photographs,
and some short sound bites of someone you’ve never met. You’ll probably get
a pretty good overall representation, but it is not quite the same as an extended
meeting in person.

REAL SYSTEM POWER NEEDS: While we test the PSU to full
output in order to verify the manufacturer’s claims, real desktop PCs simply
do not require anywhere near this level of power. The most pertinent range of
DC output power is between about 40W and 300W, because it is the power range
where most systems will be working most of the time. To illustrate this point,
we
conducted system tests to measure the power draw of several actual systems
under idle and worst-case conditions. Our most power-hungry overclocked
130W TDP processor rig with an ATI Radeon X1950XTX-512 graphics card drew ~256W
DC peak from the power supply under full load — well within the capabilities
of any modern power supply. Please follow the link provided above to see the
details. It is true that very elaborate systems with the most power hungry dual
video cards today might draw as much as another 150~200W, but the total should
remain under 500W in extrapolations of our real world measurements.

INTERPRETING TEMPERATURE DATA

It important to keep in mind that fan speed varies with temperature,
not output load. A power supply generates more heat as output increases, but
is not the only the only factor that affects fan speed. Ambient temperature
and case airflow have almost as much effect. Our test rig represents a challenging
thermal situation for a power supply: A large portion of the heat generated
inside the case must be exhausted through the power supply, which causes a corresponding
increase in fan speed.

When examining thermal data, the most important indicator of cooling
efficiency is the difference between intake and exhaust. Because
the heat generated in the PSU loader by the output of the PSU is always the
same for a given power level, the intake temperature should be roughly the same
between different tests. The only external variable is the ambient room temperature.
The temperature of the exhaust air from the PSU is affected by several factors:

The thermal rise in the power supply is really the
only indicator we have about all of the above. This is why the intake temperature
is important: It represents the ambient temperature around the power supply
itself. Subtracting the intake temperature from the exhaust temperature gives
a reasonable gauge of the effectiveness of the power supply’s cooling system.
This is the only temperature number that is comparable between different reviews,
as it is unaffected by the ambient temperature.

TEST RESULTS

Note that the test data shows just one 12V line/load. Our PSU load tester has three separate 12V load circuits, and all three were used: One for the main ATX and drive power output cables, one for
the AUX12V connectors, and one for the PCIe 16X power connectors.

The ambient temperature was 22~24°, and the ambient noise level was 11
dBA.

ANALYSIS

1. EFFICIENCY — This is a measure of AC-to-DC
conversion efficiency. The ATX12V Power Supply Design Guide recommends 80% efficiency
or better at all output power loads. 80% efficiency
means that to deliver 80W DC output, a PSU draws 100W AC input, and 20W is lost
as heat within the PSU. Higher efficiency is preferred for reduced energy consumption
and cooler operation. It allows reduced cooling airflow, which translates
to lower noise.

At the 20W load we first applied, efficiency was at only 51.2%.
This is to be expected; 20W load it’s a harsh efficiency test for a PSU rated
at 700W. Efficiency rose fairly slowly as the load was increased. It was not
until past 150W load that 80% efficiency was exceed. Between 200W and 400W, a fairly flat
efficiency curve was seen, with a broad peak of 81%. This is maximum efficiency power range is probably ideal for a PSU rated at 700W; it’s the typical power range of the majority of systems it will be used in. Efficiency dropped
to under 80% at 500W, and slipped to 76% at full load. By today’s standards, efficiency is OK but not exceptional.

It’s not unusual for PSU efficiency to droop at full load on our test bench, especially high power models such as this one. We subject PSUs to much high
temperature than most test procedures, which are usually conducted at typical
room temperature (under 25°C). At higher tempereature, efficiency almost always suffers; high temperature is what would have in a real computer that demanded 700W, and our test rig simulates that reality. This
sample might not pass the 80 Plus test… but then it might because the 80 Plus test is conducted at room temperature.

2. VOLTAGE REGULATION refers to how stable the output voltages
are under various load conditions. The ATX12V Power Supply Design Guide calls
for the +12, +5V and +3.3V lines to be maintain within ±5%. At all load
levels, voltages were much closer to the mark than required, and even at the
highest loads, the voltages sagged only slightly. This is very good
performance.

3. AC RIPPLE refers to unwanted “noise”
artifacts in the DC output of a switching power supply. It’s usually very high
in frequency (in the order of 100s of kHz). The peak-to-peak value is measured.
The ATX12V Guide allows up to 120mV (peak-to-peak) of AC ripple on the +12V
line and 50mV on the +5V and +3.3V lines. Ripple on the DA700 was exceptionally low on all the lines at all loads.

4. POWER FACTOR is ideal when it measures 1.0. In the most
practical sense, PF is a measure of how “difficult” it is for the
electric utility to deliver the AC power into your power supply. High PF reduces
the AC current draw, which reduces stress on the electric wiring in your home
(and elsewhere up the line). It also means you can do with a smaller, cheaper
UPS backup; they are priced according to their VA (volt-ampere) rating. Power
factor was very good for this model, running no lower than 0.97 at any point
during testing.

5. LOW LOAD TESTING revealed no problems starting at very
low loads. Our sample had no issue starting up with no load, either. The 13.8W power draw seen with the unit running at no load suggests that there may be a dummy load which ensures consistent start even with very low load.

6. LOW & 240 VAC PERFORMANCE

The power supply was set to 500W load with 120VAC through the
hefty variac in the lab. The variac was then dialed 10V lower every 10 minutes.
This is to check the stability of the PSU under brownout conditions where the
AC line voltage drops from the 110~120V norm. DA700 is rated for
operation 115VAC ~ 240VAC ±10%. Most power supplies achieve higher efficiency
with higher AC input voltage. SPCR’s lab is equipped with a 240VAC line, which
was used to check power supply efficiency for the benefit of those who live
in 240VAC mains regions.

Efficiency improved nearly 4% at our 245VAC input level. The DA700 passed the low voltage test without any issues. Neither voltage regulation nor ripple changed appreciably
during the test, and efficiency dropped by about 2% for every 8VAC input reduction.

7. TEMPERATURE & COOLING

Cooling was excellent, with the °C temperature
rise through the unit staying in single digits up past the 500W mark. The 16°C temperature
rise at full power is quite acceptable in our test rig.

8. FAN, FAN CONTROLLER and NOISE

The PSU fan stabilized at around 630 RPM shortly after being powered on. The fan
was clearly audible, mostly a lower frequency, buzzy hum. It’s
not the smoothest PSU noise at idle, but it’s at a fairly low level. In the anechoic chamber it measured 16 dBA@1m, while in the live room it was 22 dBA@1m. The latter was the only measurement taken in the old live test room.

The fan speed remained constant until somewhere past 250W, where it rose slightly. After 5~10 minutes at 300W, it was registering 23 dBA and sounding that as well. Surprisingly, by 400W, the SPL exceeded 30 dBA@1m, our standard demarcation point beyond which lies “too loud”. In contradiction to the data in other web reviews, the fan exceeded 1600 RPM — said to be the top speed at 12VDC — by 500W output. It measured well over 2000 RPM at maximum load. Interestingly, the SPL at full power was substantially lower than with many other PSUs that are actually quieter through most of the range.

The charts below from our SpectraPLUS audio spectrum analyzer should be self-explanatory. Note that the noise floor of the anechoic chamber is 11 dBA. The blue line is the response at moment of screen capture; the red line represents the peak values in the previous few seconds.

In the middle chart above, the area between the black and green traces represent the DA700s acoustic contribution. The sharp spikes at ~180 Hz and 200~300 Hz are audible; they are the tonal hum quality in the sound.

COMPARISONS

How does this compare with the quietest PSUs that SPCR has reviewed? Pretty well, but it is not in the same league as the best. This is a bit awkward to quantify or prove because all the measurements and recordings of the quietest PSUs were done with the previous generation of test gear, without the anechoic chamber. So, extra time was taken to do a quick spot check of the current reigning quiet champ, the Enermax Modu82+. The model we reviewed was a 625W, but one of those was not handy while a 425W model was. Having listened to one before, I know it sounds very similar to the 625W model. Its fan would likely ramp up at a bit lower power level than the 625W model, but that was not a primary concern. Since most systems work at idle most of the time, the acoustics at idle are far more important, and that’s easier to test.

Here’s the comparative data on the Enermax Modu82+ 425W in the anechoic chamber with the current audio test gear:

The SPL reading is not an error. It does say 12.74 dBA, and that’s with the mic a meter away. To give you a better appreciation of just how little above the ambient this is, here’s an overlay of the above curve atop the ambient curve:

In the above chart, the area between the black and green traces represent the Enermax PSU’s acoustic contribution. From a meter away, I have to strain to hear it. The peak at ~15 kHz is audble as a low level “hiss”. You may be able to hear this in an MP3 recording on the next page.

MP3 SOUND RECORDINGS

These recordings were made as 24-bit / 88 kHz WAV files with a high
resolution, lab quality, digital recording system inside SPCR’s
own anechoic chamber (11 dBA ambient), then converted to LAME 128kbps
encoded MP3s. We’ve listened long and hard to ensure there is no audible degradation
from the original WAV files to these MP3s. They represent a quick snapshot of
what we heard during the review.

These recordings are intended to give you an idea of how the product sounds
in actual use — one meter is a reasonable typical distance between a computer
or computer component and your ear. The recording contains stretches of ambient
noise that you can use to judge the relative loudness of the subject. Be aware
that very quiet subjects may not be audible — if we couldn’t hear it from
one meter, chances are we couldn’t record it either!

Each recording starts with 6~10 seconds of room ambient, followed
by 10 seconds of the product’s noise. For the most realistic results,
set the volume so that the starting ambient level is just barely audible, then
don’t change the volume setting again while comparing all the sound files.

Sound Recordings of PSU Comparatives

Caution! It’s important to understand that these recordings cannot be compared directly to the recordings made in the anechoic chamber. The live room in which they were made echoes and has a noise floor 4~8 dBA higher, the microphone has a much brighter sound quality and a different output level, and even the dBA measurements are wrong below ~25 dBA — they are higher by 2~8 dBA than they would be in the chamber with the new test gear. These recordings are here mostly for the record.

Please note that other than the Enermax Modu82+ 425W, PC Power & Cooling Silencer 610 and the NesteQ 700W, all other PSU
recordings were made in the live test room, whose acoustic are considerably
noisier and reverberant than the hemi-anechoic chamber. The comparative
database will get better as we update some previous tests and recordings,
and as more reviews are added to the mix.

Ambient
acoustics of the anechoic chamber vs the live room – Some of
you will be interested to hear this difference. The recording begins with
8 seconds in the anechoic chamber, then 8 seconds in the live room, followed
by a few seconds in the anechoic chamber. The SPL levels, as mentioned before,
were 11 dBA and 18 dBA respectively. It’s interesting to note that the hiss
many SPCR forum members attributed to electronic noise is, in fact, not
so; it’s part of the live ambient, due at least partly, to reflections at
higher frequencies in the room. This is obviously absent in the chamber.
(However, we did make a change to a new microphone which also has considerably
less noise than what we were using before the anechoic chamber, so some
of the hiss in past recordings was caused by microphone noise.)

CONCLUSIONS

The Silverstone delivers very clean power with
tight voltage regulation to its full rated output. AC ripple is exceptionally good as well, among the best we’ve seen.
Its efficiency is a touch lower than many competitors, although this models is admittedly not certified 80 Plus. Cooling is excellent, as the temperature rise through the unit remained in single digits to past 500W in our test rig. The modular cable system is very nice. That every cable can be removed may seem a bit odd because some of them always have to be used, but in some instances, this can ease the installation process.

Acoustic performance is fairly good, staying quiet in our
test setup till around 300W. The noise jumped above 30 dBA@1m at 400W, a little lower than expected, considering Silverstone’s confidence that it would best the Enermax Modu82+ 625W. The sound signature at idle is not particularly smooth, there being a kind of tonal, buzzy quality. The quality may get better as the fan speeds up, with the buzzy quality become less audible over the turbulence noise.

Is it possible that the fan in this DA700 sample is subtly damaged? Nothing is impossible, and damage to fan bearings is quite common, in my opinion. It’s hard for shipping handlers to break a fan and make it inoperative inside a PSU. It seems much easier to slightly damage a PSU fan in transit, enough to make it sound noisier without causing any other significant deteriorations. Over the years, I’ve come to appreciate how often this happens. If SilverStone feels this is the case, we’d accept a couple of replacement fans to try.

In any case, even if the growly quality of the sound could be subdued, the DA700 is not likely to match the Enermax Modu82+ 625W sample which Silverstone pitted it against. The gap is too big. It’s not that far off; for many users, the Silverstone is close enough to their home or office ambient noise level that the difference might be moot. For an aurally sensitive listener in a quieter space, however, the Enermax sounds a lot better. (So do the 850W and 1000W Zalman models, if my acoustic memory can be trusted.) One of the newer, higher efficiency, lower SPL models offered by SilverStone (such as the 80 Plus Silver rated ST70EF) would probably be a more appropriate model to challenge’s SPCR’s short list of top-rated PSUs.

In summary, the DA700 provides excellent electrical performance, keeps itself safely cooled, and doesn’t kick up a noisy fuss. It is not the quietest or most efficient PSU we’ve reviewed… but it could be suffering from a slightly “off” fan. Keep the overall power demand to under 400W, or use it in a case that keeps the PSU intake separate from the rest of the system’s heat, and the DA700 would be a prime candidate for a diehard PC gamer.

Much thanks to SilverStone Technology for this review sample.

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SPCR Articles of Related Interest:
Power
Supply Fundamentals
Recommended
Power Supplies
SPCR
PSU Test Rig V.4
Enermax
Modu82+ 625W
Seasonic
S12 Energy Plus 550 and 650
NesteQ
ECS7001 700W PSU: A Modular Twist
Corsair
HX520 & HX620
Zalman ZM1000-HP: Quiet KiloWatt PSU

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