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Zalman ZM1000-HP: Quiet KiloWatt PSU

May 13, 2008 by Mike Chin

Product
Zalman ZM1000-HP

ATX12V v2.2 power supply
Manufacturer
Zalman
Market Price
US$250~$325

Zalman has been offering quiet PC components since this market sector first emerged. It's a real pioneer. After starting with innovative quiet heatsink/fans, Zalman moved quickly to offer quiet power supplies, which have been a part of its lineup of offerings ever since. They've never been the quietest PSUs, but competently occupied the noise-reduced middle ground between typical (read: noisy) mianstream models and the super quiet champs. The unit under review is a thousand watt model introduced late last year. It is Zalman's most ambitious power supply to date.

We've reviewed other kilowatt PSUs, the Enermax Galaxy for one, even though we question their utility. No one has ever shown conclusively that a kilowatt PSU is necessary for any DIY PC for personal use. Still, the gaming masses seem to clamor for them, and the entire establishment of tech web sites keep up the hype while manufacturers churn out ever bigger PSUs.

Our lab has seen a few other excessively powerful PSU samples which didn't make our 30 [email protected] maximum SPL cutoff and were thus dropped from our review roster without further ado. The ZM1000-HP didn't suffer such a fate. In fact, it was so quiet at first turn-on that malfunction was suspected. No surprise that it stayed on the review roster.




Yes, it's a huge box, about double the norm: 14"x7"x7".


Inside, there are two cartons, one with the PSU in bubble-wrap, another with all the cables. A user's manual, screws, plastic cable straps, handy 12V to 5V adapter for fans, and AC cable completed the sample package.


ZM1000-HP FEATURE HIGHLIGHTS (from the
Zalman web site)
FEATURE & BRIEF Our comment
Dual Heatpipes for Maximum Cooling Performance and Ultra-Quiet Operation - Dual heatpipes on the main heat sources enable high load operation at low fan RPM for a dramatic reduction in noise levels..
Unusual, used in previous Zalman ZM600 we reviewed. It could be quite useful for very high power operation.
Modular Sleeved Cables provide organized cable management and improved air circulation inside the computer case.
Fairly common for high end retail PSUs.
Ultra Quiet 140mm Fan maximizes the airflow and minimizes the noise level enabling a noiseless computing environment with optimized cooling.
It's bigger than the more common 120mm but seen in other PSUs before.
5V Standby Noise Filter Switch eliminates high frequency noise in standby mode. *The Standby Noise Filter Switch is NOT a power switch. The AC Power Cord MUST be unplugged in order to turn the power supply OFF. Fascinating. Does it work?
Six Independent +12VDC Outputs supply power independently to the CPU, VGA, motherboard, and peripheral components for the highest level of stability and performance.
Independent means that these lines have separate current limiters. See relevant discussion on this page of Power Supply Fundamentals.
Four PCI Express VGA Power 6-Pin & 6+2 Pin Connectors for Nvidia Quad SLI. If you got it, flaunt it, right?
Active PFC for Improved Power Factor & Reduced Harmonics
Common for retail PSUs.
80 PLUS Certified High Efficiency Design capable of reaching a maximum of 86% efficiency (230VAC)
Good, and fairly common, but perhaps not for kW PSUs.
Protection: Over-Voltage, Over-Current, Short-Circuit, Under-Voltage, Over-Temperature. About par for the high end course.
WEEE & RoHS: Compliance w/ EU

environmental directives: Waste Electrical and Electronic Equipment and (Restriction of Hazardous Substances
Both mandatory for sale in the EU
Safety Approvals: UL, CSA, CE, CB, FCC Class B, MIC. The more the merrier.
Three year replacement warranty Very nice.

SPECIFICATIONS

EXTERNAL TOUR

The exterior of the ZM1000-HP is a glossy greyish black. Stylish but easy to scratch. The 140mm diameter fan spans the entire width of the unit. At 210mm, it is far longer than the typical ATX12V PSU of 120~140mm. Given its substantial weight and length, the usual mounting method of four screws off the back of a case seems somewhat inadequate. Without addtional support, the cantilever force of the PSU's weight could easily bend the back panel, especially in an aluminum case. In transit, particularly, this could be a serious problem, so cases with some kind of additional support for the back of the PSU are recommended.



It's black and much bigger than usual.



Note the big 140mm fan and terminals for detachable cables.



The heatsink/heatpipes are visible through the exhaust grill.



...there's also a row of slots on the inside end of the PSU. These would act as exhaust vents, which means some heat will be released from the PSU into the case, generally not such a good thing for keeping components running cool. The switch is not for power; it's for the 5V Standby Noise Filter to eliminates high frequency noise in standby mode mentioned in the highlights.

OUTPUT CABLES

The ZM1000-HP is unusual for a modular cable PSU in that so many of its cables are permanently affixed. In fact, there are enough connectors on the permanent cables to hook up most computers. You'd only need to use the detachable cables if you had a really over-the-top computer... which is really what this PSU is all about. There is a huge number of cables and connectors, as Zalmans drawing below shows.

The main attached cables are around about 20" long, which should long enough for most systems; the exceptions are the HDD power cables, which are around 32". The detachable PCIe power cables are about 20" long, and the detachable HDD power connectors are around 32" long. All the output cables are nicely sleeved.

Another unusual aspect of the ZM1000-HP is that they've identified which connectors the various 12V lines feed. The absence of this information makes most multi-12V line PSUs a bit of a joke. Here, the information is clearly imprinted on the label so the savvy user can balance the 12V load of his computer intelligently. Zalman has to be commended for this attention to detail.



The label identifies 12V lines and what connectors they feed.

INTERIOR

We know for a fact that the actual manufacturer of this model is Enhance. This is a departure for Zalman, who have almost always used Fortron (FSP) in the past. Enhance is known to be a very capable power supply manufacturer, and the platform on which the Zalman ZM1000-HP is based has been used by other brands for PSUs rated up to 1200W.

The build quality of the unit looks commendably high. The internal layout is dominated by the central heatsinks, the copper heatpipes that extend from them, and the thin-fin heatsinks attached to the other end of the heatpipes. There are two AC-to-12V transformers in the center, instead of the usual one. This is to avoid a single huge transformer to handle all the power, which would likely be more costly than two smaller ones. It's the same design strategy used in the Enermax kW power supplies.



Nice clean layout.



The primary uses two PET Matsushita 270uF capacitors rated 105°C.

The smaller caps on the secondary side are mostly 105°C rated Teapo brand.



The dual bridge rectifiers are mounted on a heatsink that looks a bit like an odd antenna.

No connection to the heatpipes.



Finally, the two blocks of thin aluminum fins on the condenser end of the heatpipes.

Obviously they are in the exhaust airflow path.

FAN DETAILS

The 140x25mm dual ball bearing fan is rated at a surprisingly low 0.26A. It has good design basics: Seven smoothly contoured blades with struts at near-perpendicular angles to the trailing edges of the blades for minimized turbulence noise. As in most modern PSUs, the current to the fan comes from a controller that adjusts fan speed in accordance to the temperature in the PSU.



Surprisingly low current rating on 140mm fan.



Neat two-conductor plug for the fan.

TESTING

For a fuller understanding of ATX power supplies, please read the reference
article Power Supply Fundamentals & Recommended
Units
. 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.

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.

SPCR's high fidelity sound
recording system
was used to create MP3 sound files of this PSU. As
with the setup for recording fans, the position of the mic was 3" from the exhaust
vent at a 45° angle, outside the airflow turbulence area. The photo below shows
the setup (a different PSU is being recorded). All other noise sources in the
room were turned off while making the sound recordings.

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:

  • 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

Note that the test data shows just two 12V lines. Three separate loads 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 latter loads were combined and listed under 12V2 for convenience. Otherwise, the table (and the page) get too wide to read with any ease.

The ambient temperature was 20°, and the noise level was 19 dBA.

OUTPUT, VOLTAGE REGULATION & EFFICIENCY: Zalman ZM1000-HP

DC Output Voltage (V) + Current (A)

Total DC Output

AC Input

Calculated Efficiency
+12V1
+12V2
+5V
+3.3V
-12V
+5VSB
12.22
0.96
12.22
1.73
5.08
0.97
3.34
0.94
0
0.1
41
59
70.4%
12.22
1.89
12.22
1.73
5.07
1.95
3.34
2.63
0.1
0.2
65
85
76.6%
12.22
2.84
12.22
3.27
5.07
0.91
3.34
2.63
0.1
0.3
91
152
80.3%
12.21
4.71
12.22
4.95
5.06
3.70
3.31
3.62
0.1
0.5
152
183
83.3%
12.20
6.57
12.18
6.46
5.04
4.46
3.34
4.43
0.2
0.7
202
235
86.0%
12.19
7.72
12.17
8.06
5.04
6.35
3.33
5.22
0.2
0.9
249
288
86.3%
12.19
9.59
12.14
9.78
5.02
8.02
3.29
7.36
0.2
1.1
308
357
86.2%
12.19
7.74
12.15
17.38
5.01
10.58
3.27
9.01
0.3
1.4
399
461
86.5%
12.16
9.56
12.13
23.58
5.00
10.49
3.25
9.65
0.4
1.7
500
584
85.6%
12.09
9.56
12.14
27.57
4.98
16.10
3.21
15.78
0.5
2.1
598
712
84.0%
12.09
15.06
12.04
36.95
4.92
19.11
3.15
18.17
0.6
2.8
799
989
80.8%
12.02
21.07
12.02
45.71
4.88
22.00
3.12
20.78
0.8
3.1
1000
1276
78.4%
Crossload Test
12.00
21.01
12.01
45.66
4.95
0.98
3.29
0.9
0.1
0.1
812
1008
80.8%
+12V Ripple (peak-to-peak): 15mV @ 200W ~ 109mV @ 651W (max)
+5V Ripple (peak-to-peak): 12mV @ 200W ~ 47mV @ 600W (max)
+3.3V Ripple (peak-to-peak): 23mV @ 40W ~ 83mV @ 800W (max)
NOTE: The current and voltage for -12V and
+5VSB lines is not measured but based on switch settings of the DBS-2100
PS Loader. It is a tiny portion of the total, and potential errors arising
from inaccuracies on these lines is <1W.


OTHER DATA SUMMARY: Zalman ZM1000-HP
DC Output (W)
41
65
91
152
202
249
308
399
500
598
799
1000
Intake (°C)
20
22
26
28
29
29
32
36
40
41
42
45
Exhaust (°C)
23
25
30
33
36
39
41
50
55
60
66
70
Temp Rise (°C)
3
3
4
5
7
10
9
14
15
19
24
25
Fan Voltage (V)
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
7.0
10.7
12.1
12.1
SPL ([email protected])
20
20
20
20
20
20
20
20
26
37
40
40
Power Factor
0.63
0.81
0.96
0.97
0.99
0.99
1.00
1.00
0.99
1.00
1.00
1.00

AC Power in Standby: 0.7W / 0.05 PF

AC Power in Standby, No Noise switch On: 1.7W / 0.15 PF

AC Power with No Load, PSU power On: 9.3W / 0.24 PF
NOTE: The ambient room temperature during
testing can vary a few degrees from review to review. Please take this
into account when comparing PSU test data.


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. The latter allows reduced cooling airflow, which translates to lower noise.

Even at the low output load of just 41W, the efficiency of the ZM1000-HP was a reasonably high 70.4%. This is as good as the vast majority of PSUs tested, even those with much lower top rated power (which generally have better efficiency at such low loads). >80% efficiency was seen at 90W output. A broad peak exceeding 86% was maintained between 200~500W. It edges the Enermax Modu82+ 625W for the title of most efficient PSU we've reviewed. That >80% efficiency was not maintained to 1000W output in this 80 Plus approved PSU is no surprise. 80 PLUS testing is performed at room temperature, unlike the thermal chamber of SPCR's test setup. At high temperature, it's normal for efficiency to drop. The ZM1000-HP had been under continuous escalating load for close to four hours when the final full load measurements were taken. That was a torture test.

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 virtually all loads, all the voltages were just about dead on, especially on the all-important 12V line. The worst voltage drop was at full load on the 3.3V line; the drop amounted to 0.18V or just over -5%.

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 kilohertz or megahertz). 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 started low but climbed steadily as output was increased.
Both the 12V and 5V ripple reached close to the maximum allowed at around 600W load. The ripple for the 3.3V line was clearly exceeded at the 800W combined output level.

How important is this? It's difficult to say. We've never seen a system draw more than 400W from the AC line, never mind demand 800W in DC. It's not likely that the higher than allowed ripple on the 3.3V line at 800W would result in misbehavior in a real system; it's hard to imagine how a system could be configured (and then run) to pull that much power.

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. PF on this model was excellent thanks to the active power factor correction
circuit, staying at or very close to the theoretical maximum of 1.0.

5. LOW LOAD TESTING revealed no problems starting at very low loads. Our sample had no issue starting up with no load at all.

6. LOW AND 240 VAC PERFORMANCE

The power supply was set to 600W 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. The ZM1000-HP 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, used to check power supply efficiency for the benefit of those who live in 240VAC mains regions.

Low VAC Test: Zalman ZM1000-HP @ 600W Output
VAC
AC Power
Efficiency
242V
688W
87.0%
120V
712W
84.0%
110V
719W
83.2%
100V
727W
82.3%

The low voltage test was passed within spec. Neither voltage regulation
nor ripple changed measurably during the test, and efficiency dropped only marginally. Efficiency improved with 240VAC input, around 3 percentage points at 600W. In its peak efficiency range of 200W~500W, the unit will reach close to 90% efficiency with 240VAC input.

7. TEMPERATURE & COOLING

Our sample ran quite cool, with the temperature rise through the unit staying below 10°C till past 300W output. The exhaust air temperature exeeded 50°C at 400W, and it rose steadily to 70°C after 15 minutes at continuous full load. Considering the amount of power passing through the unit, the temperature rise seems well controlled.

8. FAN, FAN CONTROLLER and NOISE

The PSU fan stabilized at 4.6V within a minute after turn on. The Sound Pressure Level (SPL) reading on the test day was 20 [email protected], audible at 1m, but quiet and smooth.
It would have measured lower had the ambient in the lab been lower, but it was 19 dBA that day.

There was no audible buzzing from a meter away. There was none at this distance above the fan noise at any load. When the fan was stopped with a plastic wire tie jammed into the blades, a bit of buzzing could be heard from a foot away, but this was about at the same level as fanless PSUs we've tested. When the Standby Noise Reduction switch was turned on, even this buzzing disappeared. In other words, audible buzzing or humming was not an issue.

The fan noise and voltage remained essentially unchanged during testing all the way to over 400W output load. This is extremely quiet performance, the very best we've encountered in any PSU.

Beyond 400W, the fan speed and noise climbed quickly, as expected. The quality of the fan noise was quite decent, despite our anticipation of nastiness given its 2-ball bearing design. Surprisingly, 40 [email protected] was the loudest the unit ever reached. Again, for a kilowatt PSU, this is quite amazing.

In the comparison table below, the >30 [email protected] readings are highlighted in light green.

Comparison: Various PSUs Noise Vs. Power Output
Model
90W
150W
200W
250W
300W
400W
500W
600W
800W
1000W
Zalman ZM1000-HP
20
20
20
20
20
20
26
37
40
40


Enermax Modu82+ 625

19
19
20
21
22
26
36
37
n/a
n/a
Corsair HX520/620
22
22
22
22
22
29
40
40
n/a
n/a
Corsair TX650W
21
21
21
21
23
38
43
44
n/a
n/a
Corsair VX450W
21
21
21
22
26
44
50
n/a
n/a
n/a
Seasonic S12 E+ 650
20
20
20
21
26
38
40
40
n/a
n/a
Seasonic S12II-380
21
21
21
25
31
39
n/a
n/a
n/a
n/a

Antec EW 430
22
22
24
29
37
41
43
43
n/a
n/a

Zalman ZM600
25
27
29
30
31
36
40
40
n/a
n/a

The above comparison table should not be taken as absolute. It shows sound pressure levels recorded on SPCR's test platform. The ambient temperature varies a bit, in a range of 20~23°C, and some of the PSUs may have the small advantage of lower ambient temperature during testing. This can help lower the overall noise curve, and more importantly, increase the power level at which the fan starts getting seriously louder. Still, at higher power levels, the temperature in the test box is determined mostly by the load. There is also some variance in ambient noise. When it's quieter in the lab, the quietest PSUs actually measure lower at idle. The Zalman ZM1000-HP was measured as low as 19 [email protected] but not on the day of load testing.

The top two-thirds of the models in the table above represent the quietest PSUs SPCR has tested. The ZM1000-HP clearly stays quieter to a higher output load and temperature than any other PSU. It is a completely different animal than the ZM600, the last Zalman we tested. It can be fairly described as a truly quiet PSU for power hungry gaming systems.

MP3 SOUND RECORDINGS

These
recordings were made with a high resolution, studio quality, digital
recording system, 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. Two recordings of each noise level
are made in some cases, one from a distance of one meter,
and another from one foot away. More details about how we make these recordings can be found in our short
article: Audio
Recording Methods Revised
.

The
one meter recordings
are intended to give you an idea of how the subject
of this review 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!

The
one foot recordings
are designed to bring out the fine details of the
noise. Use this recording with caution! Although more detailed, it may
not represent how the subject sounds in actual use. It is best to
listen to this recording after you have listened to the one meter
recording.

Each recording starts with 6~10 seconds of room ambience, 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.

  • Zalman ZM1000-HP at up to 400W, 19 [email protected]: One
    meter
    (This recoding is marked 19 dBA because it was recorded on a different day than the rest of the testing. The ambient on the day of this recording was 18 dBA, and the PSU measured 19 [email protected] But the sound that the PSU makes obviously does not change when the abient changes.)
  • Zalman ZM1000-HP at 500W, 26 [email protected]: One
    meter

    The higher level noises were not recorded; you can rest assured they are simply too loud.

Sound Recordings of PSU Comparatives

CONCLUSIONS

The Zalman ZM1000-HP is really irritating. We don't want to like or recommend it because it's a gargantuan power supply of the type we have mixed feelings about... at best. No one needs a 1000W PSU. But...

This PSU is not just quiet, it is incrementally quieter than any other PSU we've tested. Perhaps that phrase doesn't have much impact because we say it often. In our work, a PSU that stays at minimum noise at an output level 100W higher than the best one we tested is significant. That's what this PSU does. At the same time, at the minimum level, it may be just as quiet as the quietest Seasonics, Corsairs and Enermaxes that have come before. Without doing very close A/B comparison listening in the same quiet room at the same time, we can only go by memory — and imperfect recordings and measurements.

Its electrical performance is impeccable in almost every way: The highest measured efficiency, extremely tight voltage regulation, etc. This Zalman is really at the cutting edge of PSU performance. The Enermax Galaxy 1000W PSU mentioned earlier shows its age in comparison; the past year has seen a lot of progress in PSU design and performance. The single fly in the ointment is the higher-than-normal AC ripple. As pointed out earlier, however, we don't really think it's that significant because the out-of-spec ripple is in the less important 3.3V line, and it occurs at such a high output.

Then there's the close attention to details like the label which identifies the 12V line distribution (which has never been done in any PSU we've encountered before!) and the clever 5V Standby No Noise switch. Maybe the heatpipes and thin aluminum fins are more than just gimmicks, too. Maybe it's another example of high attention to detail that helps the PSU's overall overformance. All this from a company that's gone so mainstream in recent years instead of staying at the unwashed edge where it was so likable. It's not easy for an iconoclastic reviewer to deal with!

Despite these positives, we can't recommend the ZM1000-HP without qualifications. Except in the most extreme of systems, many of the other PSUs in the noise comparison table above would actually provide the same acoustic performance; ie, the extra headroom of the ZM1000-HP would not necessarily translate to lower noise. You have to be something of a crazy gamer to want a kilowatt PSU. We've already said many times that no real-world DIY desktop computer needs this kind of power. But maybe you're totally obsessive-compulsive and you feel you should have at least 100% headroom even for the shortest pulse peak. Maybe you're that much of a dedicated gamer and you're going to use a quad-core dual-video card setup with a dual CPU board along with peltier cooling and a mini beer fridge built into the PC. Whatever. If uber power is your thing, this Zalman will do you right.

At over $250 from the lowest priced online discounters, it's a steep price to pay for a macho symbol most people will never even see or understand, but at least you can also brag that it's as quiet as your eco-loving, highly-sensitive cousin's 300W fan-tweaked Seasonic. (The 850W version was deemed the only super powerful PSU quiet enough for the EndPCNoise SPCR-designed Extreme Gamer PC.)

Much thanks to Zalman for this review sample.

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SPCR Articles of Related Interest:

Power Supply Fundamentals

Recommended
Power Supplies

Power Distribution within Six PCs

SPCR PSU Test Rig V.4

Enermax Modu82+ 600W

Enermax Galaxy: A KiloWatt power supply


Seasonic S12 Energy Plus 550 and 660

Zalman ZM600 heatpipe-cooled modular PSU

Seasonic M12-700

Corsair HX520 & HX620

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