I had a chance to do some quick measurements on the Wolfson card, I was curious as to how well it measured and also to see if the power supply sensitivity, referred to in the HiFi World review was visible at all.
From the Hifi World article: –
A major issue with this audio board is that it’s very dependent upon the quality of the power supply used to drive it. A noisy 5V switch-mode power supply unit (PSU) resulted in 76dB dynamic range from Line Out, but a quiet one (Apple phone charger) gave an excellent 110dB – an improvement of 34dB gained solely by using a better power supply.
More surprisingly, this also cleaned up the digital S/PDIF output to a Chord 2Qute external DAC, allowing it deliver the full 121dB dynamic range of which it is capable.
A good supply would be a battery of some sort, lead-acid or lithium ion, for top audio results, or a smoothed linear supply, bearing in mind that 5V is needed and batteries deliver 6V. Switch-mode supplies generate rubbish and the audio card is sensitive to this (the Apple charger is switch mode, but clean). See p320 of the WM5102 datasheet for more on this.
The effect of this is quite clear in the following trace – the upper trace is the effect of powering the Pi from an Anker multi-outlet USB charger. The lower trace is using the official and very inexpensive Stontronics Raspberry Pi 2.5A supply (available in White and Black).
There’s between 30 – 40dB of difference across the audio band, which correlates with the Hifi World measurements, a big improvement to be had through careful power supply choice!
As can be seen, the noise floor is lowered across the entire spectrum, resulting in greater dynamic range.
An ideal solution here would be to provide the Wolfson card with its own dedicated low noise supply, but this only makes sense in the context of a packaged unit, for most users the cheap Raspberry Pi supply works well. Alternatively, a genuine Apple charger, as mentioned in the HiFi World article, could be a good alternative, especially if running headless.
The official Pi supply holds up incredibly well, given that in those measurements it’s powering the official 7″ display, a Pi3 and the Wolfson Card.
I also did a quick comparison of THD for the Wolfson card vs. an AudioQuest Dragonfly Red, both measure very low levels, with the Wolfson showing lower levels of higher order distortion harmonics.
Both sound great to me, the Dragonfly reveals a little more subtle detail, which may come from its apparent lower noise floor, but it also shows how well the Wolfson card stands up to scrutiny given its very low price.
A few years back, the idea of creating a streaming music player, with 24bit / 192kHz capability at home from parts that can be just plugged together would have been unheard of. I have a number of Slim Devices / Logitech Squeezebox devices around the house, but with the exception of the Transporter, all have limitations with high-resolution files.
A cheap Raspberry Pi, on the other hand, can do a remarkable job, especially when the price of entry is so low.
Never has such high-quality sound been so accessible at such a low price.