OCZ ZT 650W power supply review - Stability Testing the PSU - Sound levels (dBA)

Stability Testing the PSU

So during our tests we also monitor the voltage fluctuations as shown below in both IDLE and LOAD states of the PC. We write down the lowest and highest value we see within a certain PC state. The difference is the fluctuation. If a PSU is unstable we'd see a lot of fluctuation, differences and discrepancies which can result in system instability.

Once we gathered all voltage results we can place them in an easily understandable chart. Look at the chart, the two lines show both the Idle and Load state of a specific voltage rail, the dark blue one the lowest voltage dip measured, the red one the highest fluctuation. That's your baseline.

So then, ATX specification requires that the PSU needs to stay within a 5% fluctuation; for example, each +12 Volt rail should remain between 11.4 - 12.6 Volts.

As you can see, the PSU when utilized stays consistent as you can hardly even see the blue line, meaning that the PSU is functioning within ATX specified limits. During the load test, I checked several times to see if the PSU was warm, it was cold to lukewarm really.

Sound levels (dBA)

As usual we grabbed our dBA meter. The human hearing system has different sensitivities at different frequencies. This means that the perception of noise is not at all equal at every frequency. Noise with significant measured levels (in dB) at high or low frequencies will not be as annoying as it would be when its energy is concentrated in the middle frequencies. In other words, the measured noise levels in dB will not reflect the actual human perception of the loudness of the noise. That's why we measure the dBA level. A specific circuit is added to the sound level meter to correct its reading in regard to this concept. This reading is the noise level in dBA. The letter A is added to indicate the correction that was made in the measurement.

(reference photo).

As always we measure 75 CM away from the product (usually the distance between you and a desktop computer).

The ZT 650W once we stressed towards 500 Watts started to make a bit of noise, audible at best. In fact there was a ~41 DBa audio pressure coming from the PSU, which is audible. In idle or desktop mode, you can silently hear the fan. Nothing important.