Grounding PR99

Revox deliberately made the mains connector to be two-pronged, not three, and they knew what they were doing. All that would happen if you grounded the chassis would be that potentially you've set up a ground loop situation - which could manifest itself in hum. Since the output is balanced already, and transformer-isolated then it probably won't. If you run the back of your hand over the metal parts of the deck and you feel a tingle, then perhaps try grounding it - but Revoxes are pretty good from this point of view and that doesn't generally happen. So it's neither a good nor bad idea really; but it's not necessary.

To avoid signal ground loops you have to make sure that grounding is all in a line, and not joined up at the ends - so that genarally means that in the case of connecting the Revox to a mixer - or a professional sound device - that the grounding for it has come from there, not the Revox itself. If you ground both items, that's when the potential loop is formed. Normally it would be the last powered item in the chain that provides the actual ground connection, so it's often the power amps. Most of the issues with loops come about in unbalanced installations; if you are operating a balanced system all though, you don't have issues unless there are complex routing systems in place - like a patchbay, for instance.