Hi Steve,
Agreed for the most part, and the experience described in your second from last paragraph makes a lot of sense. However, a current will indeed flow in the return conductor of an unbalanced line-level interconnect, that is equal to the current in the signal conductor. Or, at least, the two currents SHOULD be equal. Any slight differences that may exist between them would mean that some fraction of the return current is finding an alternate path, such as the return conductors of other cables that may be connected between the same components, or through the AC safety ground connections of the two components (which would constitute a ground loop issue, to some degree that may or may not have audible consequences).
But if the resistance and impedance of that return conductor is 0 ohms at all relevant frequencies (to a very close approximation), then the voltage drop from one end of that conductor to the other which results from the current flowing in it will be, per Ohm's Law, 0 volts (to a very close approximation). Which in turn will mean that the return conductor and the points in each component to which it is connected will all be at 0 volts, relative to the circuit grounds of both components. (Keep in mind that any voltage number, including 0, is only meaningful if a reference point is defined, at least implicitly. In this case the reference point(s) would be the circuit grounds of the two components).
In any event, thanks for sharing your experiences, which I know are particularly extensive in these kinds of matters.
Best regards,
-- Al
Agreed for the most part, and the experience described in your second from last paragraph makes a lot of sense. However, a current will indeed flow in the return conductor of an unbalanced line-level interconnect, that is equal to the current in the signal conductor. Or, at least, the two currents SHOULD be equal. Any slight differences that may exist between them would mean that some fraction of the return current is finding an alternate path, such as the return conductors of other cables that may be connected between the same components, or through the AC safety ground connections of the two components (which would constitute a ground loop issue, to some degree that may or may not have audible consequences).
But if the resistance and impedance of that return conductor is 0 ohms at all relevant frequencies (to a very close approximation), then the voltage drop from one end of that conductor to the other which results from the current flowing in it will be, per Ohm's Law, 0 volts (to a very close approximation). Which in turn will mean that the return conductor and the points in each component to which it is connected will all be at 0 volts, relative to the circuit grounds of both components. (Keep in mind that any voltage number, including 0, is only meaningful if a reference point is defined, at least implicitly. In this case the reference point(s) would be the circuit grounds of the two components).
In any event, thanks for sharing your experiences, which I know are particularly extensive in these kinds of matters.
Best regards,
-- Al