External power supplies: it’s like the new audio product! Reason enough for us to take a look at what’s available and put a couple of them next to each other. But we’re not just gonna listen. Anyone can do that. No… we’re gonna measure too. With a little help, because – unfortunately – we do not yet have AudioPrecision and precision measuring equipment in the office. We put two Keces feeds, a Sbooster, Farad and a small ifi feed next to each other. Let the Battle Begin!
We’ve taken two measurements on the power supplies. The first is a noise measurement. This is done via an AudioPrecision System 2 (cascade, dual domain). We provide a load of 0.5 amps on all power supplies. The measurement is both loaded and unloaded. This is to determine how quiet the power supplies are and to see how they react to a load.
The second measurement is more complex. Here we load the power supplies and inject an alternating current (1 kHz square wave) into the chain. So we add a modulated signal. This to see how the power supply responds to this. A load on a dac is not constant. So it is crucial to see how a power supply deals with this varying load. We can see on a scope whether the injected square wave is completely distorted or whether the power supply can follow neatly. The diagram of this setup is shown below.
What we can demonstrate with these tests is: noise level and distortion. These are two critical properties for good power supply. As baseline we have picked up a standard wall plug that you will get with many switches. Below you can see what we get as a result. Downright dramatic.
Both unburdened and loaded, this power supply rushes and ‘swings’ enormously. It just can’t follow the 1 kHz pulse at all. Especially the noise that suddenly shoots up after 20 KHz is worrying. In short: not a suitable power supply to power a decent component in a high quality hi-fi system.
Of course, we also listened to the power supplies. We did this with a Mytek Liberty dac. It can be powered by 230 volts with a 12-volt power supply. The Mytek goes to a Pass Labs XP12 front stage that supplies a Bryston 4B SST3 with signal. This one drives a pair of Focal Sopra No1.
Let’s look at the first candidate!