I see a lot of opinions on RCA jack grounding. Many OEM designs use PCB mounted jacks with a common ground. Some recommend the jack grounds remain separate until they hit the input switching. Does it REALLY matter? For context, I have 4 pairs of line level jacks mounted on an aluminum panel, and isolated from the panel. Coax runs from the jacks to a relay switching board a couple inches away. Do I wire all the jack grounds to a common point and leave the shield connected at only one end, or ground them all at the relay board? I would prefer to do this the proper way, the first time.
It's a bit hard to say whether the extra effort is worth it without knowing the entire grounding scheme for your unit, including the actual PCB layouts.
If you have turntable inputs I would certainly try to keep their grounds seperate all the way to the RIAA stage or head amp to prevent noise currents from other inputs contaminating the screens and degrading the noise floor of the phono inputs. That's because the phono inputs have ~40-60dB more gain than the line inputs which will show up any issues with ground noise. The reason for a seperate ground wire for a turntable is to keep noise currents away from the input grounds for the pickup.
If you want the ultimate in stereo channel separation then the grounds need to be completely separated all the way from inputs to outputs and only commoned at one place, namely the power supply 0 volt rail.
If you want to minimise bleed from unused inputs to the selected input then you probably need to switch the grounds as well, or alternatively short circuit the unselected inputs.
The reason for crosstalk induced by common ground conductors is that current cannot flow through a conductor without some voltage drop. That means a ground conductor is not equipotential when return currents from sources are flowing through, and it will have unwanted "noise" i.e. small signals from undesired sources sharing the same ground.
An input stage cannot discriminate between the desired input signal and the unwanted signal in the ground conductors which adds to the wanted signal, so even though the ground voltages are small they are amplified and degrade performance and can be audible.
If you have turntable inputs I would certainly try to keep their grounds seperate all the way to the RIAA stage or head amp to prevent noise currents from other inputs contaminating the screens and degrading the noise floor of the phono inputs. That's because the phono inputs have ~40-60dB more gain than the line inputs which will show up any issues with ground noise. The reason for a seperate ground wire for a turntable is to keep noise currents away from the input grounds for the pickup.
If you want the ultimate in stereo channel separation then the grounds need to be completely separated all the way from inputs to outputs and only commoned at one place, namely the power supply 0 volt rail.
If you want to minimise bleed from unused inputs to the selected input then you probably need to switch the grounds as well, or alternatively short circuit the unselected inputs.
The reason for crosstalk induced by common ground conductors is that current cannot flow through a conductor without some voltage drop. That means a ground conductor is not equipotential when return currents from sources are flowing through, and it will have unwanted "noise" i.e. small signals from undesired sources sharing the same ground.
An input stage cannot discriminate between the desired input signal and the unwanted signal in the ground conductors which adds to the wanted signal, so even though the ground voltages are small they are amplified and degrade performance and can be audible.
Trouble is there are many 0v rail connections in any given audio system, that are inclined to mix then via signal leads. But Yes star earthing works well, as does using back to back diodes to separate signal grounds from psu grounds,
Staying Well Grounded | Analog Devices
Staying Well Grounded | Analog Devices