It’s a pity that I couldn’t post a drawing of best grounding technics (something didn’t work here). I will try to explain it as best I can.
There are 3 “grounds” that need to be connected correctly in order to make sure that potential differences between audio equipment don’t chose the path through the circuit which will become audible as hum or buzz : the ground for the audio signal on the circuit board or star ground if point-to-point wired (let’s call it reference ground), the power supply ground which of course needs to be clean (normally is with HighEnd gear), and the ground which connects each piece of equipment (shield ground). If these 3 grounds are connected in the right way and grounded to Earth there will be no audible ground loops. I will only talk about SE (RCA) grounding for simplicity sake because that’s also what most people have.
If we look at a single unit it doesn’t matter how the “grounds” are connected together and the electrical standards/code is only concerned about correct grounding to Earth for safety reason. So the manufacturer can do everything right and the buyer can still run into ground loop problems (more or less audible but it will always create IMD and impact SQ). If we connect two or more devices together, different ways of grounding in each unit and potential differences between “reference grounds” can create audible ground loops. We must make sure that the path for the current caused by potential difference will always go directly to Earth and not through the audio circuit where it becomes audible as hum or buzz.
So how to connect these 3 grounds then? Unfortunately we would need to open each device and find out how it has been grounded. Ideally the ground of the power supply (which is ground for the circuit board or connected to star ground in tube gear) should be also connected directly to shield ground (ground from RCA connector) and chassis ground (if that was part of the original ground) in one single spot which is then connected to Earth ground (via ground of the power cable). All power cables should be as close as possible together in one power strip/conditioner. Shield ground and power supply ground stay of course connected to the circuit board as it was in the original circuit. But now the difference is that potential differences between audio equipment will take a short cut to earth ground instead of running through the circuit. Only one extra cable from psu ground (power common) would need to be added. Don’t know if that can be done without losing the warranty? Cheater plugs and open Earth ground can help but never remove ground loops hundred percent and are unsafe.
Another issue is if power conditioners use different grounds between their power outlets. I use a Furman IT 20 Reference for analog (prefer the sound with balanced mains power) and a Power Plant for digital. Both systems are totally separated (otherwise the different grounds have some audible influence) and I switch only the speaker connection. If there are still ground loops with the above grounding scheme a separate grounding cable (power cable grounding needs to stay as is for safety!) to the ground of the other receptacle can do the trick and stop the ground loop.
I know that might sound a bit overwhelming at first but it resolves all the problems with ground loops and helps to improve the SQ quite a bit (more clarity and subtle details). I hope it is helpful.
