Antec True380S (Sonata) PSU

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Parameters Tools
DC load on PSU DBS-2100 PSU load tester
Ambient temperature
Any number of thermometers
Fan voltages / Voltage regulation
Heath / Zenith SM-2320 multimeter
AC power
Kill-A-Watt Power Meter
Heath AD-1308 Real Time Spectrum Analyzer

The core PSU test tool on SilentPCReview's test bench is the DBS-2100 load tester, made (in Taiwan by D-RAM Computer Company) specifically for testing computer power supplies. The machine consists of a large bank of high power precision resistors along with an extensive selection of switches on the front panel calibrated in Amps (current) and grouped into the 5 voltage lines: +5, +12, -12V, +3.3, -5, +5SR. Leads from the PSU connect into the front panel.

To ensure safe current delivery, the DC output connector closest to the PSU on each set of leads is hooked up to the load tester. This ensures that the current delivered is distributed to as many short leads as possible. When pushing a PSU to its rated output, the heat generated in the wires can be an issue.

The PSU is tested at 4 DC output power levels:

  1. 90W: Established previously as a typical max power draw of a mid-range desktop PC.
  2. 150W: For higher power machines.
  3. 300W: Common maximum power level..
  4. Maximum: The rated maximum power of the PSU.

Care is taken to ensure that the load on each of the voltage lines exceed the ratings for the tested unit. The PSU is left running at least 10 minutes at each power level before VR measurements are made several times.

The DBS-2100 is equipped with 2 individually fused AC outlets and 4 exhaust fans on the back panel. A switch allows the the fans to be turned off for noise measurements. The resistors get very hot under high loads.

Kill-A-Watt AC Power Meter is plugged into the AC outlet on the side of the DBS-2100 in the above picture. The AC power draw of the PSU is measured at each of the 4 power loads. The efficiency of the PSU at each power level is calculated thus: divide DC power output by AC power consumption. It always varies with load, and also temperature. PSUs seem to run more efficiently when warmer, up to a point.

The Heath / Zenith SM-2320 multimeter, a fairly standard unit, is used to measure fan output voltages and the line voltages of the PSU output. The latter is done via terminal pins on the front panel of the PSU tester. It somewhat simulates voltage readings off the wiring on the motherboard.

NOTE: The most "pure" voltage output reading is obtained on PSU output connectors that are not connected; this bypasses the resistance of the wires and the connectors and tells you exactly what the output DC voltages are as it leaves the PSU. However, it is a somewhat artificial measurement as the cables and connectors are part of the PSU as well.

The Test Lab is a spare kitchen measuring 12 by 10 feet, with an 8 foot ceiling and vinyl tile floors. The acoustics are quite lively. The PSU under test is placed on a piece of soft thick foam to prevent transfer of vibrations to the table top. Temperature in the lab is usually ~20C.

In-case Thermal Simulation

Sited next to the CPU, the PSU is always subject to external heat. The low ambient temperature of the test lab explains why the fan in the Nexus NX3000, for example, never reached 12V during testing, even at full power output for over 20 minutes. I have applied a solution first suggested by contributor John Coyle after the publication of his article, Fanless (or Not) with TKPower 300 & VIA C3. Thanks, John!

The solution is a 100W AC bulb in an empty case with the PSU mounted normally. The distance between the bottom of the PSU and the top of the bulb is about 7-8 inches. All the case back panel holes are blocked with duct tape. The only significant exit for the hot air in the closed case is the PSU, which is then subject to a fair amount of heat, probably a bit more than would be seen by a PSU in a real case because there are usually other air exits. The bottom front panel case intake hole is very large. In testing, the front of the case is moved so it hangs over the edge of desk, over free air, to ensure good fresh convection airflow. There are no case fans.

A thermistor taped to the bottom of the PSU close to its right front is used to monitor temperature. It's the little blue nub hanging down off the black wire in the photo above. Its temperature is somewhat affected by the airflow of the PSU fans but not directly in the airflow path.

The simulation means the PSU must cope with the 100W of heat generated by the light bulb plus whatever heat it generates within itself. It is a good simulation when the PSU is actually putting out ~100W of DC voltage, although in real-life systems, there would be other air exhausts paths, resulting in a bit lower case temperature.

No PSU Temperature Measurements were made. Discussions in the SPCR forums have convinced me that there are far too many variables at play to make internal PSU temperature a reliable gauge of... anything. There are way too many ways to interpret the numbers. Check this thread for the full discussion. The most critical parameter for thermal performance is efficiency. If efficiency is high, the size of the heatsinks and vent openings large, and the fan can blow a lot of air at full power, then excellent cooling is ensured.

Noise Measurements

The Heath AD-1308 is a portable half-octave Real Time Spectrum Analyzer with sound level meter (SLM) functions. Below 40 dBA, its accuracy is poor, limited to 3 dB increments, down to ~30 dBA. Some 15 years old, this LED-based unit has long since been displaced by digital devices with better interfaces to PCs. The "A" weighting was used; it most closely approximates the frequency response characteristics of human hearing.

The microphone on the sound meter is positioned about a centimeter to the side of the PSU fan exhaust to avoid fan turbulence in the microphone itself. The dBA obtained here cannot be compared to any other measurements due to the lack of adherence to a repeatable standard and the uncontrolled reflective environment.

The noise measurements are always accompanied by descriptions of subjective perceptions. Without these, the measurements, which are not that reliable, provide only part of the picture.


Measurements were made at 4 power levels: 90W, 150W, 300W and full power. (The 22.5W measurement from previous PSU tests was dropped because it is too low to be useful.) The unit was allowed to run for at least 10 minutes at each power level before measurements were taken. The room temperature was 20C.

AC Power
V Fan
Noise (~1 cm)
42 dBA
44 dBA
47 dBA
49 dBA
Case Temp

VR = With the self-adjusting feedback mechanism built into this PSU, I expected voltage regulation to be dead-on at all times. At all loads, on all lines, the voltage regulation was within 1%, a very impressive performance.

Efficiency is best in the middle and higher power levels. The 64% efficiency rate at 90W is a bit low, but the PSU may be optimized for operation at higher power output. The 74% calculated at the 300W output level is close to the highest achieved by any PSU tested thus far. Even at full power, it stayed above 70%.

V Fan: The voltage to the fan started at 5V and climbed in a more or less exponential curve to 10V at maximum power. The maximum fan voltage available is 11.2V.

Noise was measured ~1 cm from the edge of the PSU fan exhaust, not in the airflow path. At all power levels ~100W or lower, fan voltage remained around the minimum of 5V. Measured to be 42 dBA, it is about the same noise level exhibited by the Zalman at the 90W power level. Several alternatives among the Recommended PSUs are quieter at the same power level -- by 2 to 7 dBA. Morever, the competitors actually drop to lower noise levels as power output declines from the 90-100W range. This Antec does not; its fan voltage stays at 5V from turn on at any temperature to ~100W power level. The noise level at 150W is audibly higher than at 90W. At full power, at 49 dBA, it is not bad, even though 11V is being fed to the fan.

The fan was forcibly stopped while the PSU was supplying idle power. Some very low level coil buzzing could be heard up close, but it was quiet enough not to be audible in any normal circumstance. Even the air turbulence noise from a low speed Panaflo would mask this noise.

Case Temp hardly changed between 90W and 380W, which suggests the PSU fan control does a very good job of keeping itself cool. The temperature would have climbed if the light bulb wattage was changed to match the output power at all times.


The Antec True 380S is a high performance, low noise PSU. It provides stable, tight voltage regulation on all rails to full rated power. Its fan is a bit noisier at the default start voltage of 5V than most of the single fan models on our Recommended PSU, with a bit more turbulence noise, and some subdued bearing chatter as well. It does, however, appear to actually blow more air through the PSU and provide a somewhat higher level of cooling, at least at idle.

The emphasis here is less on minimal noise and more on adequate cooling and stability. If you want quiet, there are quieter PSUs available, but for good power delivery with reduced noise, the Antec True 380S is a good choice. Recommended.

Much thanks to Antec for the review sample and their kind support.

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