Jaybe, regarding the safety of using shorting plugs which do not have a resistor (on inputs only, of course), the only situation I can envision in which that might be a problem is the one about which I stated the following in the thread Gdhal linked to in his first post above:
... some power amplifiers which provide both XLR and RCA inputs, the intent being that only one of those inputs would be used. In some of those cases the signal pin of the RCA connector is wired directly to one of the two signal pins (usually pin 2) of the XLR connector. So if the XLR input is being used in those cases and a shorting plug is put on the RCA connector, the output circuit of the preamp or other component providing the balanced signal pair to the amp would have one of the two signals on its XLR **output** shorted to ground.
And I suppose a similar situation could conceivably arise in the case of some subwoofers, if both RCA and XLR input connectors are provided for a given signal type (i.e., for either an LFE input or an input that is intended to receive a full range signal).
Also, as I said in that thread:
Consider the fact that the essentially zero ohm impedance presented to the input by a shorting plug is not greatly different than the very low output impedances (e.g., 10 ohms or perhaps even less in some cases) of some components that might be used to drive that input.
Finally, if which type is used makes any difference at all I would expect the kind that provides a direct short, rather than a resistor, to be more effective. Everything else being equal, low impedance circuit points tend to be less susceptible to noise pickup than higher impedance points.
Regards,
-- Al
