Shorting plugs (RCA phonos)

[DGP]

I have new amp with a whisper of noise on the headphone socket when it's used near computers/disk drives. I had been wondering if it was picking background noise up through an unconnected input and remembered one electrical engineer advising shorting plugs in unused phono sockets to avoid such problems. I've just found a bunch of these at the back of my hi-fi drawer.

Can I call on the collective AOS wisdom - What do shorting plugs do? Are there any hard and fast rules? Does it depend on the quality of otherwise of the circuit design? Is it a good idea to short unused digital outputs? What happens if I selected a shorted input?

DGP

[struth]

should only be used on ins like phono in .....some use a resistor in them

[walpurgis]

Good questions. I have used them and even had amps that came with them new, but I can't say I ever heard anything beneficial or detrimental, with or without them in use.

[Pharos]

All I/Ps are there to receive signals from the source equipment, and have a voltage sensitivity, which may be high or low, usually the latter with the exception of vinyl I/P which has a very high gain, especially for use with moving coil cartridges.

In use we only select one I/P, and so theoretically the others are of no significance because they are not feeding their received signals into the main circuitry, and therefore should be of no consequence, but some do advocate shorting these as a 'belt and braces' approach.

However if the unused I/Ps are subject to a very high source voltage like an accidental touching on something unearthed or a large stray electric field, its following amplification circuit may demand a quite high current from the power supply feeding it, which can be unduly stressing, and may result in some modulation of the used I/P through the power supply.

I cannot conceive of them doing any harm, and they may 'tidy up' things, but I've never used them, and they may be just manufacturers finding something else to sell us to keep the 'churn' going.

This situation is rather parallel to the debate about bi-wiring speakers, in which it is argued that two sets of cables relieve current load in the cable, when in fact the filters already ensure very little intermodulation current in the first place.

[agk]

I've got a pair that came with a Sony amp I bought years ago.
I don't know if they make a difference or prevent something.
I do know I kinda feel like I daren't not use them now just in case.