-> I would connect all busboards GND to a central star and connect this star to mains inlet earth.
ProgRocket wrote:What do you mean by mains filtering?
The Meanwell PSUs have a filter at the mains input. That filter is mainly used to prevent high frequency noise from the PSU from flowing back into the power lines. This filter needs a connection to earth, and some of the RF noise is flowing to earth over this connection. If you connect this terminal to the star point, this noise current will flow from the filter terminal to the star point and then to the mains inlet earth terminal and finally through the power cord. There's a small resistance (actually: impedance) in the wires so there will be a small voltage difference between mains earth and the star point and this voltage difference will also appear in your audio signal as that is referenced to the star point (actually to the modules local GND connection on the busboards). By connecting the filter terminal directly to the mains inlet, you decrease the length of wire through which the noisy current has to flow and so your reference point will be less disturbed.
ProgRocket wrote:guessing your meaning, I would connect both meanwells earth terminals to the mains inlet earth. [...]
You would leave the Meanwells COM-terminals empty/unconnect, is that correct? But then the outputs are floating and are not referenced to each other.
Yes to the first sentence.
And No to the second one. The primary and secondary sides of the Meanwell PSU are isolated from each other. The COM terminal is the return path for the current of the other secondary terminals so it must be connected to the star point.
Basically, all you do is: imagine along which paths the currents flow. Then you have to provide a short path for all the currents so that the voltage drops created by the currents become minimal. The ultimate goal is to have your signal reference potential (which is ideally equal to mains earth) as independent from the power supply currents as possible. One way is thick wire and small inductances (short wire runs, no wrapped/coiled wired runs), as less impedance means less voltage drop. The other way is to provide separate paths for the currents so that some of the voltage drop stays away from your reference potential. The star helps here because voltage drops created in one arm of the star do not affect the other arms. Ideally, all ground connection points in the circuit would have their own, super low impedance connection to earth (a star with many, many arms), but that is of course not possible. Using more arms in the star wiring is a practical solution.
All of this applies to GND and also to the supply rails. But in a well designed module, there will be local regulation and a high PSSR (power supply noise rejection ratio). Hence the supply rails are not nearly as critical as the GND wiring.