Help with grounding paths

Hello all,

First time poster. Fairly new to the game, have tried to do some research on this but definitely have not done anything exhaustive. I'm currently building my own phono preamp setup which will include a separate linear power supply in its own case (everything being built by me). I'm far from an electrical engineer and I have a very healthy respect for electricity, so I'm trying to do my due diligence here, and I appreciate your time and any help/advice/input you can provide. Whenever I post in forums, I try to be exhaustive with my details (sometimes to an excessive degree) to be as clear-cut as possible with my questions and in the hopes that the answers will be more easily provided, however this inevitably leads to very long posts, so this will be no exception. Without further adieu, here we go:

The primary concern here is making sure this system is SAFE and will not be hazardous to anyone in my family, under normal operation or in the event of a failure/short within the system. Based on my research, I believe I already know the answers to most of my questions, but I'm coming here for confirmation/expert opinion. Secondary is the potential to preemptively appropriately ground the system in terms of feedback/loops/hum, etc., as I'm obviously going through these efforts to create something I'm hoping is bordering audiophile level, and inherent in that is minimizing/"eliminating" any hum.

The basics of the system are as follows:
Power Supply:
Metal case from eBay (second image is basically the same item with a similar layout to what mine will look like)
1688748311769.png

1688748021863.png

R-core transformer from eBay (15v-0-15v)
1688748076405.png

Sigma22 board from eBay
1688748132471.png

Silkscreen/Circuit sides of board, for reference
1688753630336.png

1688753769333.png



Phono preamp:
Akitika preamp board (https://www.akitika.com/PhonoPreamp.html)
1688748207996.png

Case from eBay
1688748354137.png



My Primary Questions (Safety related):
1. The R-core transformers have a built in GWG (mains ground) wire, I plan on obviously connecting this to the GWG pin of the IEC connector (per the example power supply image), however should I also ground the power supply chassis to the same IEC ground? My thought/plan is: YES
2. Because of the above, and because of the example image above, am I able to bolt the transformer directly to the chassis, or should I use either standoffs (at least for increased airflow around it for heat dissipation) or possibly even insulate it using nylon bolts/washers? My thought/plan is: BOLT DIRECTLY TO CHASSIS
3. The Sigma22 board - should I ground the DC 0v side to GWG, as well? My thought/plan is: NO
4. The Sigma22 board - can I use standard metal standoffs for this or should I try to use nylon hardware for isolation purposes? My thought/plan is: USE METAL STANDOFFS
5. The female 3-pin connector on both the PS and the preamp chassis, should these be insulated from connecting the chassis metal or do I want them contacting the chassis metal for grounding purposes (or does it not matter)? My thought/plan is: DO NOT INSULATE THEM FROM CHASSIS
6. For safety purposes ONLY (both shock hazard and risk to damaging either/both boards - not talking about feedback loops, etc., yet): should any part of the preamp chassis and/or Akitika board be also grounded in some way (obviously the 0v DC ground will be connected to the Sigma22 board)? My thought/plan is: NO, outside of whatever is decided subsequently about potential feedback loop grounding

My Secondary Questions:

7. My turntable has a ground wire (I installed, it originally didn't) that I will be connecting to a knurled nut grounding post on the back of the preamp chassis. I'm having a difficult time discerning how best to ground this from this point based on all the different things I've read (including from Akitika as their board is "meant" to be included in their larger amplifier setup in the same chassis and, ultimately, is grounded to its chassis which is obviously GWG).

I know hum/"ground loop" grounding is a hard concept for most to grasp (outside of those with vast electrical knowledge/experience, of which I am absolutely not) and can be a rabbit hole at times, so I don't necessarily expect an answer on this but curious in case someone has an obvious and (hopefully straightforward) answer. I've read through this article (https://diyaudioprojects.com/Technical/Grounding-Shielding/) and assume something like this would work, however I don't fully grasp what he's talking about and therefore how to implement it (I am entirely a visual person, if this were drawn out I'm sure I'd follow but just reading through text is hard for me to understand exactly what's going on, especially being inexperienced with the nuances of electrical engineering terminology).

8. One final, dumb question - the PSU case I bought has a LCD voltage readout screen that I'm hoping I can hook up. My questions are: since this is just a 2-wire DC unit, do I hook it up to the Sigma22 +15V and 0V, or the -15V and 0V, or does it not matter? And, subsequently, and this might not be obvious without knowing the part, but can it handle/read the ~15V, assuming it's usually used for 12V?

Anyway, as I mentioned previously, I absolutely appreciate any and all help with this, and thank you for taking the time to read this if you've gotten to this point, and even more so if you decide to respond. Please feel free to completely rebut any of my "thought/plans" above, etc., in your responses and just generally tell me where I'm wrong (or right) and any general concerns/red flags you might see with any of the above.

Cheers
 
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Just to start, don't use any nylon hardware, anywhere (other than to isolate RCA jacks from the chassis).
Use steel hardware with lockwashers, properly torqued.

The ground post should use a chassis mounting hole scraped free of anodization on the inside surface,
so the ground post is directly electrically connected to the chassis. Use a lockwasher here also.
 
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The IEC socket ground pin goes directly to the chassis with a dedicated steel bolt like in fig. 3 as posted.
Scrape off any anodization. No other connections to that bolt.

Bolt the transformer directly to the chassis with steel hardware.
The transformer shield ground wire (it is not connected to the mains) goes to a separate steel chassis bolt.
Scrape off any anodization.

Any metal power connector bodies (they are floating) should directly bolt to the chassis.
Generally the audio ground is connected to the chassis either directly or through an impedance
as posted, for safety.

Check to verify that no metal mounting spacers short any pcb ground plane or trace to the chassis.
This can easily happen if the spacer is too large or loose on the mounting bolt.
 
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Connect audio ground to chassis ground at a single point. Preferably with impedance. I usually use a fusible resistor in parallel with an X2 cap. I've also seen a pair of diodes in opposing directions.

Your preamp chassis ground should be connected to your PSU ground. If it is, make sure you are not connecting audio ground to chassis ground inside the preamp as well as the PSU.
 
Thanks, all. Just jumping back in here for right now to say I have not forgotten about this thread, I read your responses as you posted them, I've just been crazy busy and haven't been able to respond.

I believe I understand everything you guys are saying and everything seems straightforward, but I definitely will confirm what you're saying translates properly in my brain. I took pictures of my setup (incomplete, of course) such that I can draw color-coded lines to indicate the different wires and their planned/presumed paths/connection points based on what you guys are saying, and I'll post those for you all to point out any errors or, hopefully, confirm everything looks good.

Thanks again, hopefully I'll be able to post that in the coming days and then button everything up and finish the build in the coming weeks.
 
Alright everybody, finally was able to whip up some schematics. I have the PSU wiring/grounding all sorted (as far as I can tell, obviously please, as always, point out any errors of my ways), and I have the bulk of the preamp wiring sorted/figured out, I'm just still having quite a bit of trouble wrapping my head around the audio grounding aspect. Again, this is down to my incomplete knowledge of electrical engineering, and the use of confusingly similar terminology therein. I'll post the schematics below then discuss the possible ways of audio grounding I feel like are being described, and hopefully someone can point out which one is correct/mostly correct:

PSU:
PSU wiring.jpg


Preamp:
preamp wiring.jpg


Some notes first:
-Preamp audio inputs will either be directly attached to the board with a short bit of snipped resistor lead (per Akitika instruction) and mounted directly to the chassis (with nylon washers for isolation) or will use a short bit of shielded wire
-Preamp audio outputs will also be mounted to chassis with isolation and use shielded wire
-3 prong DC female jacks that are located on both PSU and preamp chassis have metal exterior and will be mounted directly to chassis without isolation, and their male plug counterparts are also metal on the outside, however obviously the 3-stranded, shielded wire I'll be running between them will not be conductive (though this could be used as a grounding connection between the chassis if I run a wire outside that touches from both male connectors' metal housing, if that's what is determined is something that is needed)
-The ??'s in the PSU are the red/black wires coming off the little LCD voltage readout screen, and I'm just wondering if those should go to the PSU board's red/black DC out posts, or its red/green DC out posts (assuming the former, but I didn't even know there was such a thing as 3-wire DC until I started looking into this so just goes to show you how much I know)

Now, onto the audio grounding:

I know I'll need something more than is what's here, but I'm not sure how "audio ground" differs (if at all) from "signal ground" as it seems like I'm being told to use the RCA grounds (either on the input or the output) to ground to the preamp chassis (with impedance), and that the preamp chassis should separately be grounded to the PSU chassis. Is this correct or wildly off?

If the above is correct, can I also put another grounding lug on the back of the PSU chassis and connect the lug on the preamp (that is also connected to the TT grounding wire) to it?

Based on the connections I see available, that's about the only possibility I can imagine, come to think of it, but it just seems wrong given the (what seems like) conflicting requirements to ground audio to chassis but also not ground signal to chassis.

Anyway, apologies again for my relative incompetence, and my sincere gratitude to anyone and everyone helping out with this. Thanks as always for your time.
 
This is quite a useful essay on grounding:
http://www.diyaudioprojects.com/Technical/Grounding-Shielding/

The mains ground goes to the metal chassis on all boxes.
Signal ground is kept isolated from the chassis, except at one convenient point (PSU connections on the PCBs?) where it can be 'loosely tied' via a parallel combo of:

120 Ohm
X2 capacitor 0.1uF-0.22F

I suspect the values themselves are non-critical, but the X2 designation is, as a mains ground fault remains isolated from the signal ground.
The 120 Ohm stops any ground loops having an effect, and also isolates from dirty mains grounds, I think.