Shorting plugs

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Shorting plugs

*Chapter 19 of my upcoming novel, Resurrection, is posted here.

For many years, the only reference I had to a shorting plug was the handmade kind we built in engineering. Here, we took an RCA connector and to its body, we soldered a wire tying its center pin to the outer shell. We made similar versions for XLR connectors.

We built these shorting plugs to help test noise levels in our products. If one measures the output noise of a preamplifier or power amplifier, for example, there’s a fairly significant difference between an open input connector feeding the amp and when the shorting plug is inserted. This is standard practice on live inputs.

Sometime in the late ’90s, early 2000’s, several cable manufacturers made versions of these for sale. The idea behind them was to cover unused inputs (disconnected from the circuit) on preamplifiers so that “extra noise” wouldn’t somehow creep in. It made sense to some people that a shorted unused input might be quieter if shorted.

Some manufacturers of these protective caps (as they were sometimes called) even went to the extent of employing exotic materials to better conduct the noise away.

On our preamplifiers, there is no measurable difference in noise levels with or without shorting plugs inserted. Part of the reason for this is that an unused input doesn’t go anywhere. The path for noise is so short and the potential noise so low as to be immeasurable.

Still, shorting plugs and their use is a thing. I have never spent the time to see if there might be an audible difference.

What’s your experience?

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Paul McGowan

Founder & CEO

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