I’ve been thinking about elegant ways to improve the PSU filtering of the Wolfson card and to ensure that any switching noise from the relatively noisy power supplies Raspberry Pi’s are usually used with is effectively filtered.
There’s plenty of possible solutions here, involving various regulators or large capacitors, but all of these require a fair amount of space and I really wanted a solution that met the following goals: –
- Low cost
- As few components as possible
- Easy to implement given reasonable soldering skills
- Fits within the form factor of the existing card
- Effective filtering across the audio band and beyond
- Works within the existing PSU voltage limitations
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.
I’m quite a fan of the Wolfson (later Cirrus) sound cards for the Raspberry Pi – they offer great value for money compared to some of the competition.
Most of the audio cards available for Pi’s offer a DAC only option, with maybe one or two outputs (e.g. Line Out / SPDIF or Headphones).
The Wolfson card offers a DAC and an ADC, SPDIF In and Out, Line In, Line Out, Headphones Out, two on-board stereo Digital Microphones and a 2W Class D amplifier for driving loudspeakers.
I also happen to think it sounds rather good, in particular I like it’s headphone driving capabilities.
The DAC has a 113dB dynamic range, which is much better than CD and the ADC has a 96dB dynamic range. The best HiFi DAC’s can achieve 122dB but the price difference between these and the Wolfson card are significant! The board can exploit 24bit HD audio up to 192kHz sample rate and it also features some very advanced and very complex DSP and mixing capabilities, if you need it.
It’s also worth noting that when Hifi World tested the card with an external DAC, the Wolfson board was capable of utilising the full 121dB dynamic range of a Chord 2Qute external DAC, so as the basis for an upgradeable music streamer, it’s great.