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M12D-850W: Seasonic joins the Power Race

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It’s a refresh of the modular cable M12 series, a Silver 80 Plus rated model, and Seasonic’s first entry into the superpower race that’s been raging across the retail PSU sector for the past couple of years. Is it good? Yes. Is it quiet? Of course.

Dec 19, 2008 by Mike Chin

Product
M12D 850W 850W computer power supply
Sample Supplier
Seasonic USA
Manufacturer
Seasonic Electronics
Suggested Price
US$299

Seasonic, one of the most popular PSU brands for quiet computing, has been slow to join the power race that’s been raging for the last couple of years. While competing brands, both old and new, began releasing kilowatt PSUs as far back as two years ago, Seasonic has soldiered on with lower rated models, for its own brand as well as for its OEM lines, such those for Corsair and Antec. Prior to the newly announced M12D series, the most powerful model in Seasonic’s stable was the M12-700W, released in late 2006.

This doesn’t mean the company has been lagging. Its conservative engineering department appears to prefer assured performance over rapid deployment, and a longer development / beta-testing phase is employed than many of its competitors. The new M12D series models are very high efficiency 80 Plus Silver rated, with assured 85% minimum efficiency at all power levels, and in October, Seasonic became one of the first to achieve the Gold 80 Plus award (87% minimum efficiency) — for its upcoming 550LT, 650KM and 750KM models. Seasonic-made PSUs have dominated the top ranks of SPCR’s Recommended PSU list, and still do, with a couple of exceptional entries from Enermax and Zalman.

Most silent PC enthusiasts shrug and roll their eyes at 4-digit rated power supplies; no PC demanding that much power will be able to run quietly. Besides, SPCR’s real-world power testing shows that it’s difficult, even with two high power graphics cards, to put together a gaming PC that really demands that much power. (For example, in the recent Antec Fusion Remote Max case review, a system with an AMD Phenom 9600 quad-core CPU with two ATI Radeon 4780 graphics cards in Crossfire mode drew a maximum peak of 387W AC, which is just ~330W in DC output to the components.) Still, with overclocking now such a mainstream interest, gamers have increasingly discovered the fun and challenge of making their PCs both fast and quiet, so there is more interest in higher rated power supplies that are still quiet.

Seasonic still hasn’t given in to the kilowatt temptation. The new modular-cable M12D series comprises just two models, an 850W and a 750W. The length of the M12D features list is a hint to the high technology that goes into advanced PSUs these days, Yet, a PSU still becomes invisible as soon as it is installed in a system. Most users, enthusiasts or not, don’t usually point with pride to their PSU. The case, the CPU, the video cards…. but not usually the PSU. Makers and marketers of PSUs have been working hard to change this, of course, and Seasonic is no exception. This is especially important when the asking price reaches a lofty $299, the MSRP of the M12D 850W. Admittedly, it’s the same MSRP as the Antec Signature 850W, a bit cheaper than the $330 of the PC Power & Cooling PPCT860, a touch more than the $279 Cooler Master RS900, and similar to the anticipated MSRP of the Enermax Revolution 85+ 850.

With the M12D-850W review sample, Seasonic included a small auxiliary PCB which contains the DC-to-DC converter — this is the actual circuit used in the PSU — and a USB key containing various reviewer-oriented information and data.

PACKAGING & FEATURES


The colorful cardboard retail box is bigger than others from Seasonic in the past.


The contents include a fabric pouch for the detachable cables, paper manual and spec sheet, a hefty 16-gauge AC cord, mounting screws, and the PSU itself.

Seasonic M12D-850W FEATURE HIGHLIGHTS (from the
web product page)
FEATURE & BRIEF Our comment
Supports Latest ATX12V and EPS12V standards The former is the desktop standard; the latter is more for workstations but also provides guidelines on power for dual-graphics cards.
DC to DC Converter Design
Superior dynamic response & greater system stability.
DC-to-DC conversion from the main 12VDC line eliminates the usual additional transformers. This approach is starting to be used on some other high end PSUs as well, such as the Antec Signature series.
San Ace Silent Fan [Sanyo Denki]
Premium quality fan for silent operation.
It’s a brand well respected by engineers but not known to consumers, and have not made low noise fans before. This new quiet fan model is said to be exclusive to Seasonic.
High Reliable 105°C Japanese Capacitors
Exceptionally reliable components extend product life.
Many high end PSUs are flaunting this feature.
Solid Caps on 12Vs for Extreme Stress Operation Conditions
Great stability at higher operating temperatures, frequencies and currents.
These advanced caps are also used for critical circuits on motherboard these days.
Super High Efficiency [up to 90%]
Green solution for lowering energy consumption, noise & heat.
90% is probably only with >220VAC input. 80 Plus Silver status requires efficiency greater than 85% at 20% and 100% load, and 88% at 50% load.
Dual Sided PCB Layout
Better utilization of PCB space to enhance quality and performance.
OK.
Tight Voltage Regulation
Improved load regulation to reduce voltage variations.
±3% claimed for 3.3V, 5V and 12V lines instead of the ±5% recommended by the Intel ATX12V design guide.
Practical Dual +12V Rails
Ample 12v output with OCP for extreme utilization.
OK.
Safety: UL/CUL, TUV, CE, CB, CCC, FCC Class B, C-Tick Very good.
Protection from short circuits (SCP), over voltages (OVP), over power (OPP), over temperature (OTP), and over current (OCP) The more the merrier.
Universal Input, Active PFC Like just about every PSU
on the market… but Seasonic was
the pioneer with these features on computer PSUs.
MTBF: Over 150,000 hours at 25 Deg C. excluding the DC Fan. Very good.
Seasonic 5 year warranty Very good!
Net Weight: 5.82 lbs
Gross Weight: 10.3 lbs
Size: W150 x L160 x H86 mm
Slightly longer than normal.

SPECIFICATIONS

The label on the PSU usually tells us most of what we need to know, but not all.


The manual provides information about both the 850W and the 750W models, as well as an important detail about the output power rating:

Operating Temperature: 0 to 50°C (The rated power will reduce linearly from 100% to 80% from 40°C to 50°C)

The italicized text above states that full rated power cannot be delivered when the environmental temperature exceeds 40°C; it is derated to 80% at 50°C — this means 680W for the 850W model. This is exactly the kind of detail that the conservative engineers at Seasonic would want specified, probably against the wishes of the marketing department. Our standard testing procedures will show whether it is true, because at >600W load, the temperature inside our test box at the intake area of the PSU routinely approaches 50°C; it will impact the efficiency results we obtain at high loads.

Keep in mind that the testing for 80 Plus approval is done at normal ambient room temperature. The 80 Plus Testing Guidelines (PDF) specify only that "ambient temperature shall be maintained at 23°C ± 5°C throughout the test." In contrast, the ambient temperature of our test system is directly proportionate to the load. At low load, the air intake is at or just above room temperature, but as load increases, the temperature rises steadily. Typically, with a fan-cooled PSU, the intake temperature in our test system reaches 45~50°C at >600W loads. This is an extremely tough test condition, as PSU efficiency naturally drops off at high and low loads; combine high load with high temperature and it’s essentially a torture chamber. It does replicate reasonably well the conditions that prevail in a typical tower PC. For full details, please
refer to SPCR’s
PSU Test Platform V4.1
.

Two 12V lines: Note that two 12V lines are indicated. This means there are two separate paths for the 12VDC from the transformer/rectifier to the outputs. Each of these paths has a limiter on it to keep the current from exceeding the stated maximum of 40A per line. A user who seeks the maximum current from this PSU would want to know which outputs correspond to which 12V lines; this would allow the 12V load to be distributed evenly. This information is not provided in any of the standard retail documentation.

VISUAL TOUR

There’s nothing unusual about the M12D’s external appearance. It is standard Seasonic fare: Nicely open hex-shaped pattern grill for the exhaust, a 120mm intake fan, matte black finish, and very tight mechanical fit on the casing.


Standard 120mm fan design.

Despite the modular cables, there are quite a few that are permanently attached. The attached cables are nicely sleeved, as are the modular ones. A row of six output jacks line the bottom of the inside panel.


Matte black finish, modular three output connectors.


Two 8-pin jacks are for PCIe — graphics cards; the rest are 6-pin for standard peripherals.

OUTPUT CABLES

Attached

1 – ATX connector (530mm) 20+4 pin
1 – 12V EPS connector (530mm) 4×2 (8-pin)
1 – Aux12V connector (530mm) 2×2 (4-pin)
2 – PCIe (600mm) 6/8-pin
1 – three SATA connectors (640mm)

Modular

2 – PCIe (530mm) 6/8-pin
1 – three 4-pin HDD connectors (830mm)
1 – three SATA connectors (830mm)
1 – three 4-pin HDD connectors (730mm)

1 – three SATA connectors (730mm)
1 – three 4-pin HDD connectors (500mm)

1 – three SATA connectors (500mm)
1 –
two floppy drive connectors on Y adapter (150mm)

Seasonic has thoughtfully provided drive connectors on difference lengths of cables. This is a nice touch for those seeking the tidiest cabling in their PCs.

INSIDE

The removal of four screws provided access to the innards of the clamshell design. Compared to previous M12 and other Seasonic models, a few visible difference stand out:

  • The heatsinks appear blockier, with less spacing in between them.
  • There are two "daughter" PCBs attached to the main printed circuit board.
  • The San Ace 120 is obviously not an Adda, the fan brand Seasonic has used consistently for years.
  • A small plastic baffle reduces the airflow "short circuit" from fan to exhaust, and forces the air to blow across more of the components before exiting.


Standard clamshell casing design.


One of the two main heatsinks has the interleaved design of previous Seasonics.


The other heatsink has one main bank of fins. In between are the main transformer, the main 105°C Nippon Chemi-Con capacitors, and near the output cables, the back side of the DC-to-DC converter PCB is visible.



Here’s that nifty little DC-DC circuit.



All the visible caps in the secondary stage are also Nippon Chemi-Con. Note 2-conductor fan connector on right.



The fan has good geometry, struts not parallel with the trailing edges of the blades, which are swept forward more than usual, deeply scooped, and nicely rounded to minimize turbulence noise.



The plastic material is hard and perhaps a bit brittle, rather than low resonance.


The end of the fan shaft looks impressive; it can be oiled if necessary. Ball bearings are used, for longer life in high temperature conditions.

The overall impressive look and feel of the fan is more than skin deep. When a 120mm DC fan is manually rotated by hand, it "clicks" into position from one magnetic pole position to another. A finger flick of the blades rarely keep the fan spinning for more than about 1.5 seconds. This Sanyo Denki moves from one "click" position to another more smoothly than any other fan I’ve encountered, and a finger flick keeps it spinning 3~4 seconds. This suggests extremely low friction bearings.

A technical specification sheet included some basic data about the fan. It is rated for a very high 82 CFM (in free air).

Sanyo Denki San Ace S1212H403 fan
used in Seasonic M12D-850
Rated Voltage
12 VDC
Air flow
82 CFM
min. Noise
<36 dBA

We ran some basic free air tests on the fan to glean a bit more information about its performance.

Sanyo Denki San Ace S1212H403 fan
MEASURED DATA
Voltage
RPM
2.1V (min)
320
3V
770
4V
1120
5V
1370
7V
1870
9V
2160
11V
2370
12V
2500

The fan started consistently at an amazingly low 2.1V, with an ambient temperature of 21°C, spinning at 320rpm. At this speed, it still moves a bit of air, and is essentially silent. The start voltage / speed is superbly low for a fan rated at 2500rpm. PWM speed control is increasingly used these days for its ability to start and keep a fan spinning at a lower speed. A PWM control fan has no advantage over this San Ace; its low speed capability with straight voltage control is already much better than most 2500rpm PWM fans can achieve. We’d bet the super wide speed range is directly related to the smooth low friction bearings.

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.

Acoustic 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 software with ACO Pacific microphone 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 PSU 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:

  • Intake temperature (determined by ambient temperature and power output
    level)
  • Efficiency of the PSU (how much heat it generates while producing the
    required output)
  • The effectiveness of the PSU’s cooling system, which is comprised of:
    • Overall mechanical and airflow design
    • Size, shape and overall surface area of heatsinks
    • Fan(s) and fan speed control circuit

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

The ambient temperature was 21~22°, and the ambient noise level was 11
dBA.

OUTPUT, REGULATION & EFFICIENCY: Seasonic M12D-850W

DC Output Voltage (V) + Current (A)

DC Output

AC Input

Calculated Efficiency
+12V1
+12V2
+5V
+3.3V
-12V
+5VSB
12.21
0.97
12.21
0
5.05
0.96
3.43
0.98
0.1
0.1
22
35
62.2%
12.21
1.88
12.21
0
5.05
1.93
3.42
1.92
0.1
0.1
41
56
73.1%
12.19
1.87
12.19
1.71
5.04
1.92
3.39
2.72
0.1
0.2
65
83
77.8%
12.18
1.86
12.18
3.37
5.02
2.84
3.38
2.72
0.1
0.3
90
110
81.6%
12.16
5.52
12.16
3.38
5.00
5.44
3.38
3.68
0.4
0.4
151
180
83.9%
12.15
6.55
12.15
5.49
5.00
5.34
3.36
6.01
0.2
0.6
199
227
87.5%
12.13
6.61
12.13
8.00
4.99
7.90
3.35
8.34
0.2
0.7
249
285
87.4%
12.10
9.48
12.11
7.96
4.98
9.61
3.33
9.88
0.3
0.9
299
343
87.3%
12.10
11.15
12.10
12.32
4.96
12.66
3.34
12.78
0.4
1.2
400
455
87.9%
12.08
15.38
12.08
14.84
4.93
14.44
3.34
15.45
0.5
1.5
501
586
85.5%
12.07
21.29
12.07
20.66
4.88
15.09
3.34
16.30
0.5
2.0
650
769
84.6%
12.05
27.74
12.06
27.54
4.86
19.52
3.35
20.71
0.5
2.5
852
1049
81.3%
Crossload Test
12.07
27.71
12.05
27.42
5.00
0.95
3.3
0.96
0.5
2.5
694
815
85.1%
+12V Ripple (peak-to-peak): <10mV @ <200W ~ 32mV
@ 850W
+5V Ripple (peak-to-peak): <10mV @ <200W ~ 14mV @ 850W
+3.3V Ripple (peak-to-peak): 10mV @ <200W ~ 18mV @ 850W
NOTE: The current and voltage for -12V and
+5VSB lines is not measured but based on switch settings. It is a tiny portion of the total, and errors arising
from inaccuracies on these lines is <1W.
OTHER DATA SUMMARY: Seasonic M12D-850W
DC Load (W)
21
41
65
90
151
199
249
299
400
501
650
852
Intake °C
21
22
24
25
28
32
33
33
35
36
39
47
Exhaust °C
23
25
27
29
33
40
42
43
44
44
51
66
Temp Rise °C
2
3
3
4
5
8
9
10
9
8
12
19
Fan Voltage
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.1
4.7
6.9
10.7
10.8
SPL
15
15
15
15
15
15
15
15
24
37
42
42
Power Factor
0.90
0.92
0.98
0.99
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00

SPL: Sound Pressure Level measured in dBA @ 1m
SPL at idle in 16 dBA live room:
18 dBA @ 1m
AC Power in Standby:
0.7W / 0.1 PF
AC Power with No Load, PSU power On: 7.2W / 0.68 PF
NOTE: The ambient room temperature during
testing can vary a few degrees from review to review. Please take this
into account when comparing our PSU test data.

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 20W load, efficiency was quite good at 62%. 20W load it’s a harsh efficiency test for a PSU rated
at 850W . Efficiency rose quickly as the load was increased. 80% efficiency was reached around the 80W mark, and it kept climbing to a plateau about 87% starting just below 200W to 400W, where the peak of 87.9% was reached. Efficiency began sliding above this point, dropping below 85% at 650W and down gradually to 81.3% at full power.

These are excellent results, expected of a PSU that’s certified Silver by 80 Plus. In our test, the sample did not make 85% efficiency at full load, but this is hardly a miss because of the thermal severity of our test. The 80 Plus testing is done at typical room temperature (18~28°C) while our test conditions feed the heat of the PSU output back into its operating ambient. There is an ideal working temperature for electronics to reach maximum efficiency, but exceed this range even by a bit and efficiency drops off rapidly; like so many other things, it is a bell curve with steep slopes on either side. For a PSU to reach 81.3% efficiency at 850W output with an intake air temperature of 47°C is excellent. Note that this measurement is in keeping with Seasonic’s scrupulous disclosure about full power output at 40°C.

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, the critical 12V lines were with 0.21V (1.75%) of 12V, and even at the
highest loads, the voltages never dropped below 12V. This is excellent
performance. The 3.3V regulation was equally good, while the 5V line was slightly farther off. But a worst case of a 0.14V drop is still very good; it’s just 2.8% down.

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 all the lines was excellent at all power levels, generally staying under 10mV through much of the bottom half of the power range. Even at maximum power, the 12V ripple stayed in the 10~20mV range, with only an occasionally sally into the low 30mVs. It’s close to the best ever measured on any PSU test sample.

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 0.9 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, and the power draw was much lower than normal.

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 5 minutes.
This is to check the stability of the PSU under brownout conditions where the
AC line voltage drops from the 110~120V norm. The M12D 850W is rated for
operation 100VAC ~ 240VAC 50/60 Hz 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.

Various VAC Inputs: M12D 850W @ 500W Output
VAC
AC Power
Efficiency
245V
566W
88.3%
120V
584W
85.6%
100V
599W
83.9%

Efficiency improved around 2.7% with 245VAC input at this load. The sample passed the 100VAC minimum input without any issues. Neither voltage regulation nor ripple changed appreciably
during the test.

7. TEMPERATURE & COOLING

Cooling was good, staying at no higher than 10°C until maximum power was approached. At 650W and above, the low airflow design of our test box was not enough to evacuate the massive heat buildup within. So even with the fan in the PSU running at full tilt, the temperature rise reached nearly 20°C. The hot conditions are the man reason why the unit did not reach 85% efficiency at full power. Nonlinearities in the temperature rise curve are directly related to changes in cooling as the PSU fan began ramping up in speed.

It’s possible that cooling at high power loads could have been better with thinner fins on the heatsinks, as in the S12-600W of yesteryear. Admittedly, this is probably the kind of conjecture that gets engineers riled; there’s no way for us to verify one way or another.

An Aside: Suitability of the Current PSU Test Box for Very High Power PSUs Is it reasonable to expect a single low speed 120mm fan to cool a PC that’s drawing 850W from the PSU? Not really. Loads higher than ~650W push the thermal limits of our test box. Gaming systems that might demand such high power levels (even if only during momentary spikes) are usually built in big cases that have multiple fans, both intake and exhaust, often much larger than 120mm diameter. This means much higher airflow and cooling capability than the current PSU test box, which was designed to replicate the thermal conditions of a quiet, low airflow, modestly powered PC. It may be necessary for us to put together a testing rig specifically for high power PSUs. Such high power PSUs don’t belong in ultra-quiet low power PCs. If we continue to review high power PSUs, then we need to accept that such reviews are catering to gamers, and adjust our testing accordingly to obtain information and insights of value to this audience. More on this in the future.

8. FAN, FAN CONTROLLER and NOISE

The PSU fan stabilized at 3V shortly after being powered on. We know from testing the fan on its own that its speed is 770rpm at this voltage. The fan
was barely audible out in the open, and even in the confines of the PSU and its impedances, it was extremely quiet at 14 dBA@1m. From about 1′ distance, there was a bit of audible electronic buzzing which is typical of PSUs. You can see these noises as the 13kHz and 18kHz spikes in the graphic below, but note that the level is well under 0 dBA.

The fan voltage/speed remained constant until 400W, where it jumped to 4.7V/1300rpm, and SPL went up to 24 dBA@1m. The overall noise level was still modest, and the sound quality was mostly benign, except for a touch of droning hum. At 500W output, the noise level reached 37 dBA@1m, well past the 30 dBA@1m point beyond which we consider "too loud". By this point, the noise was almost entirely wind turbulence. By 650W, the fan was at the highest speed it would reach, with 10.7V across its terminals producing an SPL of 42 dBA@1m.

This is a very steep climb in noise and fan speed from <400W output. As the fan speed and noise level increased, the perceived tone or frequency also increased a bit, but the main subjective impression was increased turbulence or broadband noise. At full power output, it was pretty loud, but not really that annoying, as there was little in the way of a piercing tonal noise.

The graphic below from our SpectraPLUS audio spectrum analyzer should be self-explanatory. Note that the noise floor of the anechoic chamber is 11 dBA. The green lower line is the ambient level of the chamber without any noise sources.


The blue-red line is the frequency spectrum with M12D-850W running, up to nearly 400W.


The frequency spectrum with the M12D-850W at 400W.


COMPARISONS

How does the M12D 850W compare with the quietest PSUs that SPCR has reviewed? It’s just about equal to the best, the Enermax Modu82+ 625W. The M12D is about 1.3 dBA@1 louder at low load, but they’re both so quiet that you may not appreciate the difference. Similar things were said about the Antec Signature 650, which measured 1dBA higher than the M12D and 3 dBA more than the Modu82+ 625W, but its ramp-up curve was a bit steeper, and its highest noise considerably louder, due mostly to the higher rpm of its 80mm fan.

As the power load increases, the Seasonic actually stays just a bit quieter than the Enermax, because the Modu82+ fan creeps up in speed between 200W and 300W load, while the M12D fan stays unchanged from startup till nearly 400W. Which of these two models deserves to be in the top spot? It’s really too close to call.

Here’s a comparative chart on the 12.74 dBA@1m idle Enermax Modu82+ 425W in the anechoic chamber with the current audio test gear.

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 audible as a low level "hiss". You may be able to hear this in an MP3 recording on the next page.

The comparison table below shows the SPL versus Power Load data on all the PSUs tested in the anechoic chamber thus far.

Comparison: Various PSUs Noise Vs. Power Output in Anechoic Chamber
Model
90W
150W
200W
250W
300W
400W
500W
6~700W


Seasonic M12D 850W

14
14
14
14
14
24
37
42


Enermax Modu82+ 625*

13
13
14
15
16
26
36
37

Antec Signature 650

15

15

15

18

18

28

36

47

SilverStone DA700
18
18
18
18
23
32
35
41

NesteQ ECS7001

22

22

22

21

23

25

36

37

PCPC Silencer 610
20
24
24
24
24
30
40
50
The green boxes represent 30 dBA@1m or higher SPL.
*Guesstimates based on the Modu82+ 425’s idle in the chamber and the Modu82+ 625’s load test.

The green colored blocks are 30 dBA@1m or greater SPL readings. The PSU that stayed quiet (under 30 dBA) to the highest load is not in this table because it has not been tested in the anechoic chamber: The Zalman ZM1000, which stayed below 30 dBA to almost 600W load. It’s idle noise is probably not low enough to match the M12D-850W , the Enermax, or the Signature 650; its measured SPL in the live test room was 20 dBA@1m, a dB or two higher than the others.

Caution: Please keep in mind that the data in the above table is specific to the conditions of our test setup. Change the cooling configuration, the ambient temperature and any number of other factors, and you could change the point at which the fans start speeding up, as well as the rate of the rise in speed. The baseline SPL is accurate, however, probably to within 1 dBA.

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
in the Anechoic Chamber

Older Recordings made with Sennheiser microphone in Live test room

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.
  • Enermax Modu82+ 625W at 20~150W output, 19 dBA@1m: One
    meter
  • Enermax Modu82+ 625W at 300W output, 22 dBA@1m: One
    meter
  • Seasonic S12 Energy Plus 550 at 0~150W, 20 dBA@1m: One
    meter
    ,
  • Corsair TX650W at 250W, 21 dBA@1m: One
    meter
  • Corsair TX650W at 300W, 23 dBA@1m: One
    meter

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

This is an interesting time in power supply development, with all the competition amongst brands and the continuing push to ever higher efficiency. The MD12D 850W is the first 80 Plus Silver model to come our way, but others are coming, and by the middle of next year, the Gold models should be in full production as well.

The M12D 850W is a worthy addition to Seasonic’s lineup as its new flagship product in this age of superpower PSUs. The electrical performance of our sample was consistently excellent. Voltage regulation and AC ripple were outstanding. Energy efficiency was excellent, as befits a Silver 80 Plus model. Power factor and cooling were fine, and the build quality, classically Seasonic: Neat and tidy. The technological advancements such as DC-to-DC conversion for the sub-12V lines, high quality Japanese capacitors, and the superb Sanyo Denki fan are well worthwhile.

Acoustic performance is audibly if incrementally improved over all previous Seasonics, mostly due to the excellent low speed performance of its exclusive San Ace 120 fan, and the high efficiency which allows adequate cooling with very low fan speeds. The overall noise at low to medium-high loads is good enough to be tied for best place. By 400W, however, the noise level jumped and continued to rise quickly at higher loads in our test setup. As with most power supplies, the trick for silencers is to keep the power demand below the level where the fan controller pushes the speed up, and to keep the PSU as cool as possible.

It is no surprise that our high power test results don’t match the 80 Plus test results which led to the M12D 850W ‘s Silver rating. The same holds true for the measured efficiency of every PSU we’ve tested over ~400W load. Our test procedure is much tougher thermally than the 80 Plus test, and power supply efficiency is strongly affected by operating temperature. Too low or too high, and efficiency suffers; there is an ideal plateau temperature range that enables PSUs to achieve optimum operation. We believe our test procedure to more realistically replicate the thermal conditions in actual use, although as discussed earlier, at >600W loads, the test box is probably not cooled well enough.

All in all, the M12D 850W is a very good achievement for Seasonic. The company has clearly joined the power race of retail PSUs but without abandoning the acoustics and efficiency conscious design that has kept its products at the top of the SPCR recommended PSU lists for so many years. Whether the hefty price tag is justified depends, as usual, on the perspective and needs of the individual consumer. For a modest power user ot typical silent PC enthusiast, definitely not. For a typical gamer, perhaps not; the sound effects of the games might drown out enough of the computer noise. But for a gamer who wants both high power stability as well as whisper-quiet performance from his PSU, the M12D 850W is a perfect fit.

Much thanks to Seasonic USA for this review sample.

* * *

SPCR Articles of Related Interest:
Power
Supply Fundamentals

Recommended
Power Supplies

SPCR
PSU Test Rig V.4

Antec
Signature 650

SilverStone DA700 power supply
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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