Ungrounding an Amp--Any Danger?

Neil, no, I really don't think I wondered from the original point. My post was to explain, in simple terms, why lifting a ground can be a bad thing. Wasn't that what the original poster wanted to know?
You brought up in a follow up to Bob's post about shotgun interconnects. Call it what you want but it is still an unbalanced single ended interconnect. It really doesn't matter what type of single ended cable you use. If you ground one end of a shield only and you have 2 wires left to carry the signal, one of the wires must be considered a neutral because one will still be connected to ground. Neutral ultimately goes back to ground and since the shield is not capable of conducting a flow, one of the other wires will carry the load if a power supply failure occurs. I just wanted to clarify that the type of cable really didn't make a difference when lifting a unit ground. Current during any failure will be required to travel the interconnect if the ground is lifted. That was my point. I also stated, "Balanced was for another day." I think the differences have been discussed and at length here and other places.

Bigtee: So??

Nsgarch, So What?

Skippack, let me answer your (very reasonable) question which is in the spirit of this thread: The signal ground lift switch is used to lift (disconnect or separate) the signal ground return leg in the amp's audio circuit(s) from the metal chassis (which still remains connected to the ground prong of the AC plug. Bryston has done this for years (do you have a Bryston?) This means that your non-shotgun coaxial single-ended interconnect is less likely to become part of a ground loop and pick up hum, while at the same time you are still personally pretty well protected from most shock hazards, even if you're dumb enough to remove your interconnects without turning off or unplugging your amp (just don't touch anything inside because under those conditions, it will take literally hours for the power capacitors to discharge!!)

When the manufacturer provides them, you always see these switches on amps but never on preamps or other components. That's because manufacturers expect you'll always want to ground the preamp to make it the center of a proper "star grounding" layout.

If you are using balanced interconnects between your amp and preamp, meaning the kind with an XLR connector and three signal conductors (plus, minus and ground) with a (optional) shield, then it's not necessary to "lift" the signal ground at the amp or use a cheater on its AC plug because any noise generated in, or picked up by the signal conductors will be self-cancelling.

the problem you're describing may be caused by cable tv. Is it near by? If so you may want to try and disconnect the cable at its first point of entry. then check for hum in your system. if it's gone, all you need is a ground loop eliminator, such as Mondial Magic Box.