That is not the resistor we are talking about. We are (if I've understood the OP correctly) talking about the resistor shown in the first diagram here intended to balance the impdances between the hot/cold wires inside the shield:
And if so, is there anything "less" balanced about such a cable than a mini-XLR to XLR cable? I'm asking in the context of Pro-Ject turntables, as I decide between two different models, one with and one without a mini-XLR output. Finally, if such a cable is possible, is there anything I...
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Personally I would not bother (as Bruno does not). As I point out above, even without that resistor you still gain most of the common mode noise rejection that you can get with it.
I agree and I think the reason why Bruno Putzeys doesn't bother adding the resistor shown above is that this addition only brings on a theoretical improvement that may not eventually be realized or may actually worsen things.
Typically (there are other cases, though), differential active receivers are implemented with 10 kΩ equal resistors. Assuming the use of 1% tolerance resistors (very common in this day and age), that means that each of the four resistors needed to implement a typical differential receiver can have an actual resistance anywhere between 9.9 kΩ and 10.1 kΩ.
If the unbalanced source impedance is low (less than 300 Ω is not uncommon for a source and many preamplifiers have an output impedance of about 50 Ω), the addition of a resistor equal to the output impedance between the RCA shell and the cable shield may actually gives very little benefit (if at all) if the deviation of the resistor values at the receiving end is large. This is all the more true that, as Douglas Self and others have demonstrated, the impedance balance at the receiving end is of more importance in order to get a good common mode rejection ratio than the impedance balance at the sending end, at least when the receiving input impedance is far greater than the source impedance.
And besides resistor value imbalances, other sources of imbalance may exist inside equipment (input or output capacitors, capacitors used as low-pass filters, capacitive or inductive parasitic effects).
So, in order to actually get an effective improvement rather than a figment of the imagination by adding the above shown resistor in a RCA to XLR cable would require some labor to reverse-engineer the output and input stages and to measure precisely at least all resistor values in the signal path to determine the proper value of the added resistor, value that may be a compromise to mitigate imbalances elsewhere. Or, alternately, to replace all relevant resistors with costly precision types (0.1% or better) or resistors matched by measurements.
All those works and costs may be useful for critical applications, but for home audio?
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