I’m thinking of getting back to my Raspberry Pi internet radio project again. A few weeks ago I found that the pulsing from the wifi card was caused by a ground loop problem with the USB hub, as I got the exact same problem on the BeagleBoneBlack.
So I’ve bought a Lepai TA-2020A+ amplifier and 12V 2A PSU to power it. I plan on making a little board to tap off 5V 1A via a 7805 to power the Pi. Therefore I won’t need a powered USB hub, as I’ll only have the wifi dongle and USB DAC plugged into the two onboard USB ports and the speakers will be powered by the amp, not USB. And I still manage to keep it to one mains plug.
It also means I can get rid of some cabling and the little volume/power board into the speakers. I may need a bigger box, and I wonder about the heat coming off the 7805. I may screw everything into a wooden baseboard perhaps too.