Whatever happened to the shorting plug?
For those of you scratching your head, a shorting plug is an RCA connector with its signal and ground wires shorted together. Here’s a picture of some fancy gold-plated versions.
The idea is to stuff these shorting plugs into the unused inputs on a preamplifier. The goal is to make sure no noise gets into that unused input. I mean, after all, without the shorting plugs there’s an empty hole where whatever we don’t want can get in and contaminate things.
Now, of course, as audiophiles we’re going to want to make sure we use gold-plated versions because despite the fact no signal goes in or out of them (that’s the point of them) gold is always better.
We have several sets of them (not gold) in the lab. They are essential for the testing of noise on a phono stage.
Are they useful for their intended purpose on a preamplifier? Well, consider that most modern preamps use PC mounted RCA jacks and those jacks are connected only to the switch or relays that selects the input you wish to listen to. When not selected it’s nothing more than a short piece of conductor going nowhere. Any potential noise is not going into the preamp because there’s no electrical path for it to travel. So no, I do not believe they are useful.
But, that’s just my take based on my experience with preamps.