Hi Ken,
My feeling is that two paralleled returns and one "hot" conductor would be the preferable arrangement.
With unbalanced (rca) interconnects the return path (which is normally through the shield of a shielded cable) not only conducts the return current, but also connects the chassis of the two components, which in turn are connected to ac safety ground as well as to the internal circuit ground.
Therefore any ac-related voltage differences between the two chassis, which may be caused by differences in potential between the safety grounds of whatever outlets they are plugged into, and also by leakage paths in their power transformers and elsewhere, will result in extraneous noise currents flowing through the return conductors in common with signal return currents. The component receiving the signal has no way of distinguishing those extraneous currents from signal.
Lower resistance of the return path through the cable will tend to "short out" the differences in potential between the two chassis, and lessen any problems that might cause.
Good luck with your project!
-- Al
My feeling is that two paralleled returns and one "hot" conductor would be the preferable arrangement.
With unbalanced (rca) interconnects the return path (which is normally through the shield of a shielded cable) not only conducts the return current, but also connects the chassis of the two components, which in turn are connected to ac safety ground as well as to the internal circuit ground.
Therefore any ac-related voltage differences between the two chassis, which may be caused by differences in potential between the safety grounds of whatever outlets they are plugged into, and also by leakage paths in their power transformers and elsewhere, will result in extraneous noise currents flowing through the return conductors in common with signal return currents. The component receiving the signal has no way of distinguishing those extraneous currents from signal.
Lower resistance of the return path through the cable will tend to "short out" the differences in potential between the two chassis, and lessen any problems that might cause.
Good luck with your project!
-- Al