Shorting plugs

August 4, 2022
 by Paul McGowan

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.

Right?

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.

What's yours?

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41 comments on “Shorting plugs”

  1. I just read Ted’s recommendation (or let’s say agreement that it can make sense) to short USB or I2S on the DS (recent topic in the DS modification thread). Has to be custom made unfortunately.

    But that may be a different matter than RCA jacks.

  2. More nostalgia 😀

    Same as you Paul.
    Over time, engineers have reworked the circuitry to make 'shorting plugs' redundant.

    Both my Marantz - 'CD6006' & my 'SA12 SE' CD players allow the user to switch
    out/off the lights on the display panel, the headphone amp circuitry & the 'digital
    out' circuitry, to improve the SQ from the analogue outputs on both units.

    If my Musical Fidelity - 'M6si500' required shorting plugs on their RCA jacks then I'm sure that the manufacturer
    would supply them.

    1. I agree there's a potential for RF EMI to enter, but just shorting the RCA differentially probably wouldn't do much either. You still have the RCA center and outer connections tied together but still "entering" the component chassis. I'll stick with leaving the unused inputs open circuit.

  3. I see the logic of that, Paul. And for the last few years I have not plugged the RCA in, in my “modern” pres/integr. because I couldn’t hear any difference. With my vintage gear from the early 80ies however there is a slight benefit and “peace of mind” plugging those RCAs.

    1. ps,
      You can get tiny silicon 'socks' or 'teats' that will fit & cover said
      sockets very snugly & completely; protecting them from dust, etc.
      I only care about the 'stuff' that accumulates on said input sockets
      when it's time to on-sell that piece of equipment & for that I use a
      weak solution of HCl acid, acetone, distilled water (in that order)
      pipe cleaners & some cotton sticks.
      The sockets end-up 'brand-new shiny'...inside & out.

  4. It’s ludicrous. Some form of outbound “interference” is going to enter though a tiny hole, but the vents designed into most units are somehow immune to that same “interference”, despite having way more surface area?

  5. I bought into this tweak a number of years ago and purchased some inexpensive ones online to cover the RCA‘s on the back of a small NAD amp I used with my desktop system. I pulled two of them out at one point to plug-in another input device and didn’t realize that the pin from one of them stayed in the opening.

    When I put in the new piece of gear it shoved that pin well inside the connector and apparently shorted out the amp. I was never able to get to it from the inside although I tried a couple of times. The amp never performed or functioned again after that and I eventually sold it on eBay for parts. Oops. So I can’t comment on the merits of these personally other than to say “don’t buy cheap ones”.

    1. Nne years ago I moved from New York to Florida and when I set up my system down here I decided to do a lot of small tweaks that I disregarded in the past. One of the tweaks were these gold RCA phono plugs.I inserted them in to every unused input and I can honestly say I did not hear any audible difference. While I was performing this task I noticed that one of the pins was loose. I discovered that they screw into the cap and so I tightened up any of the loose pins and unscrewed the extra pins and capped unused outputs.

      They look like a finishing touch on the birthday cake now which is fine by me.

      One question that I always ask myself in audio and other forks in the path that I arrive at in my life’s journey is will taking this path hurt anything? Since I already purchased a whole bunch of these plugs and I knew that the answer was they would not, I just left them in place. So, if any of you have made this audio tweak and possibly wasted your money, I suggest that you just keep moving forward. Just keep moving… It’s hard to hit a moving target 🙂

          1. Fair enough.
            I don't call something a tweak unless it actually 'tweaks' my rig.
            I guess that's a difference in definition or interpretation.
            Tomato/Tomarto 🙂

  6. I view input plugs and output caps as a minor investment to insure that the gear sees as little EMI as possible. If they are redundant so what. They are inexpensive and as near as I can tell do no harm.

  7. I use Cardas caps (not the shorting type) to cover all of the unused RCA and XLR plugs on my preamp and power amp. If nothing else, to your point Paul, it may keep dust and whatever from entering the connector. Psychological of nothing else and they look good too. LOL!

  8. When I decided to address this issue, I hired an electrical engineer who did a ton of research and design.
    In the end his advice was to keep all the power turned off.
    This appears to have solved all my problems. 😉

  9. My 1980s era gear had them. I haven't seen any factory-installed in a while. Should I make something of that? Here's something to think about from the folks at Getty. (Sorry, I've wanted to use that advertising catch phrase somewhere for a long time).

    A while back, I upgraded a lot of components in my system. Some folks like to plug it all togather and then spend their lifetime trying to find a problem when it doesn't sound proper. I take the opposite approach. I start small. So I plugged the speakers into the amplifiers and the amplifiers into the preamp, a fine McIntosh C2700, clearly not junk. There were no inputs yet thus no antennas importing rogue signals.

    I fired it all up and was surprised to hear a faint "fwup" at about 3 - 4 Hz coming from the speakers. Say what you say? It turns out the noise was coming from my Linksys mesh router that lived on top of the A/V cabinet. That location was originally chosen as it was best for signal propagation through the, ah hem, estate.

    After lots of experimentation, the solution was to move the mesh router to the other side of the room. It was just that simple. If I had reassembled the entire system all at once, I might still be debugging the issue. As for plugs to shunt the input signals to ground, I think it just complicates finding the solution. It's always best to solve the problem rather than patch the side effects. With the plugs, the issue might still be there, just masked.

  10. Do they make xlr shorting plugs?

    What happens if you have shorting plugs in unused inputs and with the remote you activate the inputs? Does the circuit board fry?

    1. No, you only use shorting plugs on inputs, NEVER on outputs ( caps on outputs ). Nothing happens if you activate a shorted input, disaster if you activate a shorted output ( never use shorting plugs on an output ).

      1. Thanks, Tony, for answering my question and for the warning. I can just imagine a bunch of people (like me?) who don't know better putting shiny gold or silver shorting plug "dust covers" on all unused sockets because they look so pretty, not differentiating between inputs and outputs. LOL

        1. Hence why I made mention of the snug fitting silicone 'teats' that comp-
          letely cover said RCA sockets (in white, red & black) above at 4:11 am 😉

  11. I certainly understand if you got balanced and single ended input leads and to use either or is operated by a toggle switch. My new WA 22 fully balanced tube amp with a pre amp came with those shorting plugs. I don’t use them because I use both leads (balanced / singles ended) for various equipment. If I didn’t use the single ended at all I’d certainly use the caps because the design may require them.
    In any case. If you have open leads it can’t hurt keeping them on. 🙂

  12. At the very least they keep dust out of the center hole and the outer grounded area clean. I think they help keep RF out too. My tuner sounds cleaner. I use the non shorting plugs on the outputs as well. These shorting plugs in the photo can have the center conductor pin removed to use on outputs or inputs that you don't want shorted.

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