Enermax Noisetaker EG701AX-VE SFMA 2.0: 600 Watts!

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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.

REAL SYSTEM POWER NEEDS: One very important point is that the while our testing loads the PSU to full output (even >600W!) 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 65W and 250W, because it is the power range where most systems will be working most of the time. To illustrate this point, we recently conducted system tests to measure the maximum power draw that an actual system can draw under worst-case conditions. Our most powerful P4-3.2 Gaming rig drew ~180W DC 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 SLI could draw as much as another 150W, but the total still remains well under 400W in extrapolations of our real world measurements.

Ambient conditions during testing were 21°C and 19dBA, with input of 120 VAC / 60 Hz measured at the AC outlet. Fan voltage and noise levels were measured with the manual fan controller at its highest and lowest points, although we consider only the lowest points relevant in our analysis.

Enermax Noisetaker EG701AX-VE (W) SFMA Test Results
DC Output (W)
AC Input (W)
Intake Temp (°C)
PSU Exhaust (°C)
Fan Voltage (V, min-max)*
Noise (dBA/1m)
Power Factor

* min-max is the voltage range afforded by the manual fan speed control.
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.


1. VOLTAGE REGULATION was excellent, within ±4% on all lines in any combination of loads. As noted in the introduction, the 3.3V and 5V rails are now regulated independently, meaning that their relative stability are not as closely linked as in an ordinary power supply. Greater fluctuations may be apparent when the Noisetaker is places in a real system.

  • +12V: 12.28 to 12.35
  • +5V: 5.02 to 5.18
  • +3.3V: 3.31 to 3.38

2. EFFICIENCY was very good, although it does not appear to have improved appreciably since the last version. There are now a number of top-of-the line power supplies that can achieve similar levels of efficiency. Regardless of what the competition is doing, however, any power supply that can achieve efficiency above 80% is worthy of special mention. This is a spec worth paying for because it has a significant impact on the amount of heat produced within the power supply, and thus how difficult it is too cool it quietly.

Compared to the previously reviewed 475 Noisetaker, our 600W version was less efficient at the lower end of its output range. However, its peak efficiency was reached at roughly the same point, around 300W, and sustained to a much higher power draw. The differences that we measured between the two models probably stem from the the differences in power rating, not changes in basic efficiency between V1 and V2 Noisetakers

Against other top performers, the 71~77% efficiency of this PSU between 65 and 150W is almost poor. A number of recently reviewed PSUs manage ~78% efficiency from the starting low power test of 65W and continue up from there. Since so many PC systems in the real world remain at or close to idle much of the time, the poorer power efficiency at low power is at least somewhat significant. The efficiency of this PSU does seem optimized for systems with higher idle or minimum power draw.

3. POWER FACTOR was typical for active power factor correction unit, staying very close to the theoretical best value of 1.0. You can't do much better than that.

4. FAN, FAN CONTROLLER and NOISE: The test environment is live, so readings are higher than would be obtained in an anechoic chamber readings.

The fans have not changed since the earlier version Noisetaker. The acoustic signature of 2.0 revision is largely the same: The fans start quiet but not silent. However, the starting voltage is not as low as the Noisetaker 475 tested previously. The extra 0.3V is enough to make an audible difference as it represents a 10% difference in voltage, and results in a 2 dBA increase in the minimum noise level. The reason for the increased fan speed may be the assumption (by Enermax engineers) that the minimum power demand will be higher because this PSU will usually be used in more power hungry systems. Hence, a little more airflow to help with cooling right from the start.

At start, the fans produce a low-pitched background hum that is quite easy to tune out. As the voltage increases, this hum increases in volume but changes little in character. Once the fan voltage reaches about 5V (around the 200W level on our test bench) the hum is no longer quiet enough to tune out easily. The increase in fan voltage appears to coincide with a sudden spike in the exhaust temperature at the 200W level, suggesting that fan controller increases the output voltage precisely when additional cooling is required. These fans are not the quietest out there, but they are acceptable at the low voltage that is supplied when the Noisetaker is under low load.

Shutting down a system connected to the Noisetaker does not immediately turn off the internal fans. As a safety measure, the fans continue spinning for a couple of minutes after shutdown in order to cool the PSU and perhaps exhaust the hot air in the case. It may save a bit on product longevity; it could also be a minor issue in noise-critical applications like audio recording.

The manual fan controller is a strange feature. We have difficulty believing that anybody interested in a low noise PC would use this PSU at anything except with the fan control at minimum. The full adjustment range of the controller is only about 1.5V, and it has a tremendous amount of hysteresis. Typically, we had to wait 10-15 seconds after adjusting the knob before any change in fan voltage was observed. The adjustment range is roughly half of what it was in the previous Noisetaker.

Our quibbles with the manual fan controller aside, it is the automatic fan controller that makes this power supply still worth considering in a quiet system. As with the original version, the fan controller stays at minimum voltage until almost 200W output, at which point it gradually increases as the internal temperature increases.


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

Enermax Noisetaker 600W (2.0) @ 90W (23 dBA/1m)

Enermax Noisetaker 600W (2.0) @ 150W (27 dBA/1m)

Enermax Noisetaker 600W (2.0) @ 200W (30 dBA/1m)

Enermax Noisetaker 600W (2.0) @ 300W (35 dBA/1m)

Reference Files:

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

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

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


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.


Our verdict on the Enermax Noisetaker EG701AX-VE SFMA 2.0 is similar to that reached for the Noisetaker 475. The combination of high efficiency and a well designed fan-controller are strong points. The small improvements made for this new revision are welcome additions and, for the most part, do not interfere with most of the traits that made the Noisetaker 475 a successful product. The EMI-reducing Ring Core may be a good thing. The newly independent 3.3V and 5V rails should contribute to overall stability, especially in a newer system in which the load across the various lines can be quite unbalanced.

Overall, the Noisetaker 701 is fairly quiet, but no PSU designed to deliver this much power has low noise as a primary goal. There are other models on the market that can compete quite capably with the Noisetaker in terms of both efficiency and quality of fan controller. The Noisetaker 701 is a very good PSU choice for low noise, and if you really need — or want, more likely — this kind of power level, then it's probably about as quiet as you can expect. We have yet to test any other PSUs that can deliver 600W.

Much thanks to Maxpoint for this Noisetaker EG701AX-VE SFMA 2.0 sample!

POSTCRIPT: Efficiency Correction
October 22, 2005

Recently, we discovered that our power supply testing equipment and methodology were providing erroneously high efficiency results. In general, the biggest errors occurred at higher output load points above 300W. At lower output levels, the efficiency error was often no more than one or two percentage points. No other tested parameters were significantly affected.

Through a fairly arduous process of discovery, analysis and old fashioned problem solving, we modified our testing equipment and methodology to improve the accuracy of the efficiency results and described it all in the article SPCR's PSU Test Platform V.3. As part of this revision, we re-tested most of the power supplies on our Recommended PSU List. In most cases, the same sample was used in the second test.

The corrected and original efficiency results for all the re-tested PSUs are shown in in the article, Corrected Efficiency Results for Recommended Power Supplies. The relative efficiency of the tested power supplies has not changed. If the tested PSUs are ranked by efficiency, the rankings remain the same whether we use the original results or the new results.

This data is also being added to relevant reviews as postscripts like this one.

Target Output
Actual Output

In this case, our original efficiency calculations were essentially correct through to about 150W output. Above that, the original results were too high, and the error kept increasing with rising output power till it reached over 5 percentage points off at maximum load. The new figures put the efficiency at below 80%. High, but not exceptionally so, about the same as the Seasonic Super Series, the first high efficiency PC PSU models to hit the retail market

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