Ungrounding an Amp--Any Danger?

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.

Nsgarch: Thanks! Yes, it's a Bryston amp. I use single-ended ICs, so I guess I'll leave the switch on lift. There is no discernible difference in sound or noise-level, however (to my ears).