OCZ ModStream OCZ-520 12U Power Supply

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For a fuller understanding of ATX power supplies, please read our article Power Supply Fundamentals & Recommended Units. Those who seek source materials can find Intel's various PSU design guides, closely followed by PSU manufacturers, at Form Factors.

For a complete rundown of testing equipment and procedures, please refer to the article SPCR's Revised PSU Testing System. It 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 actual output load, which is exactly the way it is in a real PC environment. But there is the added benefit of a precise 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 loads. It is, in general, a very demanding test, as the operating ambient temperature of the PSU often reaches 40°C or more at full power. This is impossible to achieve with an open test bench setup.

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 far to many variables in PCs and far 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 reasonably good overall impression of that person, but it is not quite the same as an extended meeting in person.

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. All other noise sources in the room were turned off while making the sound recordings.

Ambient conditions during testing were 20°C and 18 dBA, with input of 120 VAC / 60 Hz measured at the AC outlet.

DC Output (W)
AC Input (W)
Intake Temp (°C)
PSU Exhaust (°C)
Fan Voltage
Noise (dBA/1m)
Power Factor

NOTE: The ambient room temperature during testing varies a few degrees from review to review. Please take this into account when comparing PSU test data.


We did not test the output capabilities of this power supply up to its maximum rated capacity of 528W, nor did we test its rated peak load (60s.) of 620W. The maximum noise characteristics were reached just above 400W output, and it is difficult to imagine that someone interested in silent computing would be using a system that draws even half of this power.

1. VOLTAGE REGULATION was excellent, within -/+2% on all lines in any combination of loads. The low and high voltage seen on each of the main lines is shown:

  • +12V: 12.24 to 12.35
  • +5V: 4.85 to 5.02
  • +3.3V: 3.15 to 3.31

2. EFFICIENCY was very good. The efficiency / power output ratio curve is quite flat, and efficiency did not start to drop until above 300W - above the highest wattage draw in most systems. For most of the range in which this power supply is likely to be used, efficiency remained between 77~78%. Although there are a few power supplies with efficiency in the low to mid-eighties, these tend to be at 60~80% of rated power, where few system ever reach. In the realistic power draw range, this power supply is close to the best we've measured.

3. POWER FACTOR was typical for a unit with a passive PFC, with a range between 0.62~0.69, increasing with power draw.

4. FAN, FAN CONTROLLER and NOISE: The test environment is live, so readings are higher than would be obtained in an anechoic chamber readings, due to reflections and reinforcement of sound waves off the walls, ceiling and floor.

Despite the modest start SPL of 26 dBA/1m, the fan in the OCZ-520 would not be considered really quiet by most silent computing enthusiasts. Even at 4.6 volts, this fan produces bearing noise in a distinct rhythmic chatter. The problem may be exacerbated by the brittle clear plastic frame. Motor noise is fairly good, representing a low hum that is noticeable mainly at lower speeds when it is not overpowered by air turbulence. At higher voltages, the rhythm of the bearing chatter increases in speed and volume, and air turbulence begins to overpower the hum of the motor noise.

The fan controller of the OCZ-520 is very good from a low noise point of view. The start voltage was 4.6V, and it did not increase substantially until the intake air reached 32° C at around 300W output. At idle, most systems may not produce enough heat to cause the fan to rev up. Even at full capacity, low to medium powered systems with good airflow may not produce enough heat to cause the fan voltage to rise above 5V. At around 300W output, the OCZ-520 begins to produce enough internal heat to cause the controller to rise to 7V. The noise produced at this level is not much different qualitatively from that at 4.6V, although it is slightly louder. Above 300W, however, the fan voltage ramps up to full power, just above 11.3 volts. The noise at this level is still dominated by bearing chatter, and, in the quiet SPCR lab, the noise began to reverberate around the room. At this level, the OCZ-520 is decidedly noisy, but it is difficult to imagine what system would draw above 300W consistently.

Overall, the fan controller buffered the changes in voltage quite well. The transitions between the voltage levels were gradual enough that it not possible to detect a specific change in noise level. The transition between 7V and 10.5V was drawn out over a period of about five minutes. In a working environment, the lack of sudden shifts in fan speed would make the changes in noise level reasonably benign.

MP3 Sound Recordings of OCZ Technology OCZ-520 12U

OCZ Technology ModStream OCZ-520 12U @ <200W (26 dBA/1m)

OCZ Technology ModStream OCZ-520 12U @ 300W (34 dBA/1m)

There was no need to make recordings at higher power levels; it's simply too loud.

Sound Recordings of PSU Comparatives

Seasonic Tornado 400 @ 65W (19 dBA/1m)

Nexus NX4090 at @150W (24 dBA/1m)

Seasonic Tornado 400 @ 200W (24 dBA/1m)

Nexus 92mm case fan @ 5V (17 dBA/1m) Reference


These recordings were made with a high resolution studio quality digital recording system. The microphone was 3" from the edge of the fan frame at a 45° angle, facing the intake side of the fan to avoid direct wind noise. The ambient noise during all recordings was 18 dBA or lower.

To set the volume to a realistic level (similar to the original), try playing the Nexus 92 fan reference recording and setting the volume so that it is barely audible. Then don't reset the volume and play the other sound files. Of course, tone controls or other effects should all be turned off or set to neutral. For full details on how to calibrate your sound system to get the most valid listening comparison, please see the yellow text box entitled Listen to the Fans on page four of the article SPCR's Test / Sound Lab: A Short Tour.


The OCZ Technology ModStream OCZ-520 12U is a capable high power unit packaged cleverly to appeal to the fashion conscious "power" geek. From the perspective of a PC silencer, its best features are the fan controller, which stayed at a low voltage until the output reached a very high 250W, and its detachable cables, which help improve cable management and airflow.

Unfortunately, the benefit conferred by the fan controller is reduced by the clicky fan. Additionally, the advantage of removable cables is countered by their stiffness and short lengths. The cables are not unworkable; users of other stiff-sleeved cables have reported good results using a hot hair dryer to bend the cables in place. The fan is not really loud at typical power levels, but its acoustic character will become annoying in a quiet PC. The fan could be replaced with a smoother, quieter one. In combination with that benign fan voltage controller, this could make for a very quiet and stylish PSU.

At this price level, however, a PSU that needs modding right out of the box seems a bit much. Especially when that's bound to void the 3-year warranty. For the likely target market -- gamers, overclockers, case modders -- there is no need for modding. It looks good, has snazzy features, tons of power and is certainly quieter than your average high power flashy PSU.

The SPCR audience is more demanding, acoustically. Ultimately, it's the choice of fan in this PSU that makes it less than ideal for use in a quiet or silent system. We'd like to see a special quiet fan version. Combined with the slow-ramping voltage behavior of the thermal fan controller, a quieter fan could make this is a very nice quiet high power PSU.

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Much thanks to OCZ Technology for the opportunity to examine this power supply.

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