Shorting plugs....

Do these really work well? And if they do does one need to worry about unused Balanced inputs?
wow, nobody has an opinion? I want to order some for my dad for his AR Ref3 pre for Christmas, but not if its a silly snake oil product. ANYONE??
(Oops just noticed your question was for XLR, but I'll leave my response up for any RCA owners that want a cheap tweek?)

Prior to actually buying some...

I'm sure you have a box in your closet full of dozens of cheap generic RCA IC's that come with every electronic component which your likely never ever to use!

Take few sets and cut off the cable, hit the ends with a cigarette lighter to smolder them shut. Now plug all the unused in/outputs and see if you hear a deeper quieter "blacker" background?
I've tried RCA shorting plugs as well as non-shorting caps on the open inputs of one preamp I was having noise floor problems with. Note, you don't want to short open output connectors, only inputs. I noticed very little though some improvement. I made my shorting caps using old generic IC's as Audiobugged suggests (though I soldered the cable ends to ensure they indeed were shorted). This is an easy and free way to test for yourself.

I can't address your question related to balanced inputs.
Made my own shorting plugs to save money and I did notice an improvement despite still having open balanced inputs. You won't notice the difference right away, until you remove the plugs. Then, you'll put them back in immediately realizing that they did, indeed, lower the noise floor noticeably. Definitely not snake oil.
My gear is all un-balanced so I cannot address your XLR question. However, below is a quote from member Nsgarch, which may still be buried somewhere in the archives:

"It is customary to short any unused RCA inputs on preamps. This prevents pops and clicks when switching your source selector between actual sources that are plugged in. Also prevents unused inputs picking up stray RFI. You can use pre-made shorting plugs or make them yourself. I don't recommend the Cardas caps because they don't actually short the input, but only shield the hot signal socket from RFI.

Unused XLR inputs do not require this treatment since they are balanced and self-cancel any noise."
Seems like you got your answer, but I can confirm that covering the inputs and outputs makes a significant difference to the noise floor of my system. I'll have to test the comment about only RCA needing covers as I'm currently using covers for both RCA and XLR. As mentioned above, never use shorting plugs on outputs.
Hmnn, I've never had a "noise" or a humn from most of my system components over the years. Last year I upgraded to a matching Pass Labs amp/pre-amp and they come with shorting plugs on the balanced connectors. I don't hear any difference either with them in or out. that makes me wonder about Jeffcott's answer that XLR don't need them since they're balanced..., then why does Pass Labs, and probably other companies as well, bother putting them in their units? just curious.
With Pass Labs stuff you should use the balanced inputs/outputs when possible anyway.

I tried the shorting plugs on my preamps unused inputs and I really cant tell any difference.
But, what the hey, they are really inexpensive and I already had them.
My father has the AR Ref3 and I ws thinking about these for him, he is going balanced to amps and from CD player but capping the empty jacks still strikes me as curious and a nice stocking stuffer.
You'll actually improve the sound of your system if you unplug all components from your preamp other than the one you are using at any one time (even if the other components are not turned on). This eliminates rf from the unused components.
Thats one school of thought, its impractical and many times next to impossible and inconveient but its a thought.
More than a thought. More even than a feeling. I do this in my system, because the improvement is material.
Concur with Chadlinz, it's an impractical "solution" and just because "the improvement is material" *in your system* does not mean that it will be in anyone else's system.

Also, when you indicate that you turned off components, what does that mean, did you unplug the components, turn off power at the wall or simply press the power off switch on the components?
Interesting responses. Given the lengths to which audiophiles routinely go to try to improve their systems, it's odd to hear the epithet "impractical," which suggests an unwillingness even to try it and see how it works. Of course there is no guarantee that it will work in your system, but anecdotally it has worked in a number of systems.

The idea is not to turn anything off, but rather to unplug from the preamp the interconnects running from those source components that are not currently in use. Ie, at any one time, there would be only one source component with an interconnect plugged into the preamp, though the other source components could/would be plugged into the electricity and turned on.

So, if you are playing a cd, the interconnects from your other components would be unplugged from the preamp.

In fact, my preamp has only one source input, making the issue of shorting plugs irrelevant.
It's interesting the lengths you are going to to avoid the question. Your statement was that simply turning off components did not yield the "material" improvements that unplugging them from the preamp does.

Again, what do you mean precisely when you refer to turning off a component?
well . . . I have multiple inputs on my preamp because I routinely switch between CD and Phono (I actually only need 2 inputs, but my pre has 4, so I short the unused 2). I'm just not willing to go to the inconvenience of unplugging my phono when not in use, and will suffer the sonic trade-off I guess. I suspect most folks are in this school.
Why do you refer to Impractical as a odd "epithet" when many have closed racks or equipment placed in difficult ares to do this everyday, and for folks like me with disability it is far from an odd epithet. Your late to the discusion addition that you only have one input anyway leads one to believe this theory is born more from a "no other choice" method rather than a confirmed improvement.
Bar81: No avoidance of the question. I misunderstood what you are getting at, thinking that you had misunderstood what I was getting at. "Turning off the equipment" means having the power button on the component in the off position, not pulling its electrical plug from the wall. I think this is the standard meaning of "turning a component off."

Chadnliz: The preamp was designed with only one input precisely to take advantage of this finding (based on experience with preamps that had a normal complement of inputs). Sorry to have misled your belief.
I would also note that the point of removing all other inputs from the preamp is to reduce/eliminate rf in the system as a source of distortion. Ie, there is some theory underlying the practice.

Other elements in my system include (i) power cables designed to eliminate rf, (ii) rechargeable dc battery power supplies to the preamp, phono stage and the analog side of the cd player that are unplugged from the wall during operation, and (iii) additional design elements in the cd player to reduce/eliminate rf.

Merely unplugging all other source inputs from the preamp resulted in a clearly noticeable improvement in my system. Adding the other rf-reducers multiplied this effect.
I think the idea behind shorting plugs is that open ended inputs pick up stray rf interference and by shorting the inputs you shunt this to ground. Additionally, if left open the interference picked up can enter your active channels through cross-talk. Thus, there is a sound electrical engineering-based rational for shorting un-used inputs. EE's may argue that this is splitting hairs or going overboard with worrying about noise. I would say that perhaps it is more a matter of the resolution of your system (and I am an EE -- but I am also an audiophile, and no I don't believe in mysticism, voodoo, or snake oil in audio system tweaks that some accessory marketers try to sell us).

An example of real versus voodoo that I experienced comes to mind -- the livery cabs in my neighborhood have illegally powerful radios that interfered so badly with my stereo that I could clearly hear their conversations through it. I live six stories up. The only way to eliminate this interference was to put those magnetic rf elimination protectors around the cables between my amp and pre-amp, close to the amp side of the cables. Nothing else worked.

Now with the input plugs shorted I notice a drop in the noise floor. I only notice this effect in low level passages of music. However, I do wonder if the extraneous noise has an impact on things like signal transients that could have negatives effects on the timbral quality and imaging in the sound reproduction. Input shorting plugs are cheap -- for single ended inputs buy the cheap Radio Shack jobs and solder a wire between hot and ground; $5 and 1/2 hour and no worries from open ended inputs. I saw an ad for very expensive rhodium plated ones from a very high end cable manufacturer. Pshaw!!! Use that money towards a Koestu, or other great cartidge! Or use that money elsewhere in your system where it will make a difference. I can't say it enough; please, give me a break! Expensive rhodium plated rca shorters-- come on! Or rather, go ahead, buy them sucker.

For balanced inputs, contact the repair person at your local high end shop and ask him/her about it. If they don't carry them, they should be able to make them.

Whether equipment that is plugged in and turned off picks up rf and imposes noise is yet another question... I don't know the impedance of my components when they are shut off. I never bothered to think about it. My inclination is that it is not high enough to pick up rf. I may be wrong, though.
Bicycle Man: My EE friend says that anything that acts like an antenna (even a power cable that is plugged into a component but unplugged from the wall) can pick up rf.
O.k. Power cords can pick up rf, depending on the length of the cable and wavelength of the rf. In others words, yes, I agree. That is why cables are generally shielded. That is also why ferrite rings are put around cables (as I described earlier in this thread).

On power cords, here is a nice link. It pertains to accessories, marketing tactics, and specialty power cords. It is a fun read; judge for yourself...
That's not turning it off if it's a unit with a switching power supply (i.e., most consumer electronics these days); the only way to turn off such units is at the wall or unplugging them.

In any case, what was the configuration you used to test on since your current system can't accept more than one input? In addition, how close were the electronics to the system?
The Fisher 400c pre-amp shorts the input rca's that are not in use. Cool! This, from a 1950's design. I learned this from the schematic of the pre-amp.

I cannot say that this was progressive; I just don't know, but that is my thought. However, I can say that this was prudent design. It eliminates spurious noise from entering the active input signal path through cross-talk. And, that is the point of shorting your unused input rca jacks.
You'd best contact the manufacturer. Some products specifically advise against using shorting plugs.
I don't know why they would advise against it. I could understand against using them on outputs, but I am curious as to why they might advise against it on inputs.

I can see no reason not to ever use them. Either your input jacks are open or shorted with nothing plugged into them (based on their design, i.e. the input jacks on the Fisher 400c pre-amp). Shorting an input means zero signal in, no signal, no noise. Any rf spurious signal is shunted to ground. Only the live input is feeding the preamp input stage.

Still, I am curious...