Silent & noisy grounds on a RIAA preamp

The input RCA ground shells are directly connected to the audio board common (sometimes called "ground")
It is not necessary to connect the chassis to the audio ground for the circuit to work.
The chassis functions as a shield, and for protection against being able to touch a live circuit.
It also functions as a low inductance dump for input conducted RF in this case.

The chassis is normally connected to the utility ground, through the IEC outlet and power cord, for safety.
Usually the audio ground is connected to the chassis at one point, but that part of the schematic is not shown.

You could have the pcb just laying on the bench, connected to a power supply, and it would
work just the same, perhaps with a little noise pickup from the lack of shielding.
The RCA jacks are often isolated from the chassis in an attempt to avoid 60Hz ground loops.
 
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I see the OPA192 listed with a price of €3,75 for 1 piece.
Of course you are right. I don't know how I missed it. One more option to listen to. It also comes as a dual, certainly slightly worst in specs.
The input RCA ground shells are directly connected to the audio board common (sometimes called "ground")
It is not necessary to connect the chassis to the audio ground for the circuit to work.
The chassis functions as a shield, and for protection against being able to touch a live circuit.
It also functions as a low inductance dump for input conducted RF in this case.

The chassis is normally connected to the utility ground, through the IEC outlet and power cord, for safety.
Usually the audio ground is connected to the chassis at one point, but that part of the schematic is not shown.

You could have the pcb just laying on the bench, connected to a power supply, and it would
work just the same, perhaps with a little noise pickup from the lack of shielding.
The RCA jacks are often isolated from the chassis in an attempt to avoid 60Hz ground loops.
Yes, the RCA ground has to be isolated from the input point, but it should go to the star ground. The pcb I bought already has the ground paths, but I can those I want to modify.
First I will use them as it is, checking if there's no blatant mistake, and listen to it. And look for any hum at maximum volume.
 
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so at connector j453 why are the grounds sent off board as LG and RG?
 
why are the grounds sent off board as LG and RG?
The designer has kept L and R grounds separate all the way to the Phono RCA jacks, except the RF cross-connect to two 0.01uFd caps and the phono green-wire screw.

Is that necessary? I do not know. Is it an affordable thing to do on a fairly expensive box? Certainly. Another 5 minutes on the layout table, after that it is print, etch, repeat, repeat, repeat.... no added labor and only penny parts.