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I have a specific question about proper grounding of an old turntable that hopefully has some general merit for such older devices.

This question came up while I was inspecting the wiring of the turntable, because I need to convert the original 5-pin DIN cable to RCA connectors:

enter image description here

With continuity tests, I found out that both cartridge grounds (blue & green wires) are currently connected to the tonearm ground (black), probably inside of the DIN-connector, and to the whole mechanic assembly via the brass colored screw with the cable-holder at the top (the actual chassis is plastic).

My intuition would be that the mechanic parts/chassis grounding should not be connected to the cartridge at all, so I am considering also exchanging the 2-pin AC power cable to a grounded 3-pin cable and connecting the mechanical assembly and shielding elements to the wall while separating the two cartridge ground cables and running them directly to the RCA L/R sleeves.

Would this be a logical conclusion, since supposedly only grounding the mechanical parts should not introduce any ground-loop effects, but aid in shielding from the environment?

Also, the whole tonearm assembly (the center part) appears to be electrically isolated from the rest of the mechanics. Should that then best be included in the mechanics/chassis grounding or connected to one of the RCA grounds or maybe even run to a separate grounding lug for a preamp ground connection, as is the case with other devices (which I then would have to add to the chassis)?

What would make the most sense electronically and sonically in this case and why?

Prototype700
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    Counter question, why do you feel the current grounding arrangement is somehow improper or bad, if you ask how it should be properly grounded? – Justme May 28 '23 at 16:40
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    Also, isn't the tonearm ground connected to audio ground on the PCB, so when the DIN connections come to the PCB, the PCB is the star point of all grounding? Or what's the DIN pinout on your device? Also, why not just make a RCA to DIN cable, why modify a working vintage equipment to have modern connectors directly, as that's not going to alter the sound even a least bit (assuming you have short length of good low capacitance audio cable)? Grounding the chassis to earth might make sense if you know the amplifier is too, but amplifiers still tend to have ungrounded 2-prong plug. – Justme May 28 '23 at 16:57
  • Please justify the suggestions that you make that are different to the current way things are grounded. – Andy aka May 28 '23 at 17:22
  • @Justme: I have an adaptor to RCA. The problem is the current wiring is odd. The 5-pin DIN connector is wired: Pin 1 = R+; Pin 2 = L+; Pin 3 = L/R-, common Ground; Pin 4/5 = Empty. I haven't been able to make it work, but the continuity test seems to suggest the connections are still fine. I just want to make this device usable again, thanks for the vintage considerations, but I've made the choice to modify it for ease of use. It is difficult to see on the image, but the black tonearm ground is not connected to the PCB directly, just to the tongue of the ground lug on the plate. – Prototype700 May 28 '23 at 18:45
  • @Andyaka: The reason is that most wiring diagrams (all I've seen) for vinyl cartridges to RCA suggest connecting the R/L+ directly to the center and R/L- to the sleeve, which is not possible in this configuration. Also, as far as I have read online, there seems to be a consensus that the cartridge "ground" should not be connected to the chassis in any way for acoustic reasons. Since there is no chassis in this case, I assume the mechanical grounding would be the equivalent. Since I have to entirely rewire this segment anyway, I wanted to verify or refute my planned modifications. – Prototype700 May 28 '23 at 18:51
  • Be prepared to scrap any idea you might try and randomly try new points; some of which will work and some won't. Then, in a different building the optimum point may be different again. – Andy aka May 28 '23 at 19:00
  • If connections are fine but it still does not work, what does that mean? Is the needle cartridge OK? Are you connecting to phono or line input? Do note that there are different pinouts for these adaptors. You need to check if your adaptor matches the wiring on the record player. There are different pins used on DIN output and DIN input, maybe Phono input had a separate pinout too. – Justme May 28 '23 at 19:46
  • @Andyaka: I know there appears to be some element of randomness involved in analog connections, but I have wired up quite a few guitars (not the same) and in all cases, grounded shielding lead to a cleaner signal. An unnecessary practice 40 years ago, but useful today. I would just like to know if the same applies here. Is there any flaw in the logic that converting the "chassis" ground to a shield connected to the wall and running the cartridge wires separately should be the cleaner solution? Because that makes sense from my experience and is in accordance with the consensus online so far. – Prototype700 May 28 '23 at 20:24
  • If the amplifier isn't earthed and signal ground floats in respect to mains earth, then connecting the mains earth to the player chassis and having the cartridge wires running close to it will capacitively couple currents from cartridge wiring to earth, and that's hum. That's also the reason why guitars have most of their their metal parts and shielding connected to the signal ground right at the TS connector. – Justme May 28 '23 at 21:06
  • @Justme: That is actually true, I haven't thought of this difference. However, in my case, my amplifier does not have a ground wire to the wall, most guitar amplifiers usually do. Although it does have a phono grounding lug, so not sure how that's supposed to work otherwise. – Prototype700 May 28 '23 at 23:26

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