Recently I did some measurements on the Wolfson card to get an idea of the dynamic range. When playing a 24bit file @ -100dBfs there was no output from the card.
This was perplexing, as the noise floor is some 20-30dB below that.
I set about making an amplitude sweep test file, sweeping from -60dBfs to -144dBfs and then playing that back on the Wolfson. At -90dB the output would vanish!
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.