Assuming there is little to no leakage from either power supply, this should not make any difference, as neither the Pi nor the power supplies provide an additional path to mains ground.Dear All,
after all such interesting discussions it would be useful to have some hints on what are scenario works better, replying to some questions and doubts.
I report here for anyone who wants to elaborate on those helping to choose best scenarios.
Here I have sketched my two possible scenario based on my setup:
View attachment 212332
The solution 1 uses internal DAC of CXA 81 starting from an USB power supply (that has no ground pin) and uses the internal CXA 81 DAC over USB input.
1) In this case I positioned the USB switch on LIFT. It make sense to set USB input as lift even if raspberry pi has no ground pin? I would consider it equivalent since there is no ground pin in the raspberry input.
2) Does the fact that Rpi4 doesn't have a ground pin impact the noise source highlighted in post # 169?
The solution 2 uses my Topping E50 external DAC and hence only XLR inputs are used for CXA81. In this case both Rpi4 and Topping E50 have their own usb power supply and there is no ground pins (and no switch to choose for input).
I tested both these solutions qualitatively from a listening point of view without relevant audible differences. Maybe the second one feels more well-balanced but honestly we are speaking of nuances and I can not say how much these are objective.
Having said that I would like, from a signal integrity point of view, a hint on which solution you think is better and why, just to draw some conclusions on how use this unit at its best.
Additionally, having the USB grounded may in some cases actually be advantageous in this scenario, as it will provide a ground reference for the Pi and the USB PSU.