Shorting plugs....

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...
http://www.nvnews.net/vbulletin/archive/index.php/t-106050.html

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?