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Covers on unused RCA inputs?

Years ago, I vaguely remember being advised to put little plastic covers on the unused RCA inputs on the back on my preamp. These plastic plugs had a piece of metal that connected the two poles of the RCA input. The theory was, by bridging the two sides of the RCA input, ambient RFI and static electricity were blocked from entering the preamp, resulting in a lower noise floor.

Of course, these plugs could only be used on RCA inputs, not outputs, as this would short circuit and possibly damage the preamp.

Has anyone heard of these gadgets? Does anyone use them currently? Thank you.
javachip

Showing 2 responses by eldartford

eldartford
4,262 posts
 
It's not clear to me how a plastic cover would block those pesky little RFI who are sneaking around all the time looking for a way to get into our preamps!

A well-designed preamp input selector will short out all inputs other than the one selected. This is to prevent "bleed-through" of signal from sources that are not selected but may still be turned on. For example, a FM tuner while you are listening to a record. (Don't ask me why one would do that).
eldartford
4,262 posts
 
Audphile1...The good old fashoned rotary selector switch used to have a "deck" the function of which was to short out all the inputs except the one selected. We no longer see rotary selector switches, and the solid state circuitry common today runs at much lower impedance than old tube circuitry and is less susceptable to bleed through. So, preamp designers don't bother with shorting the unused inputs. I guess you could call it "a common preamplifier design flaw". Gone, like tone controls and Loudness compensation.
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