Edac 30pin MotherBoard for Lunchbox diy

[richiyobs]

Hi folks,
I would like to build a LunchBox for my 500 modules.
I m just drawing 10ch Edac connectors Board....
Knowing that at some point Chassis,GNDA and GND are connected together, how should I develop the PCB?
is it better to create a pwrGND surface to which GNDA and Chassis will be joined? the Chassis will have its own path, I guess...

any suggestions please?

Thanks for attention and support

best

richi

 

[daveb]

My experience (not in audio, in RF stuff) is that designing multiple separate grounds to “star ground” a PCB leads to poorer results than a single ground plane used for everything. I would be inclined to have a single layer dedicated to ground, and keep in contiguous. I’d also heavily bypass each individual board with caps right at the connector.

 

[Rob Flinn]

I have a lot of 38 pin edacs parts if you want some.

 

[sahib]

Chassis/Earth is never connected to analogue ground and power ground on the backplane.

API's practice is that the AGND and PWRGND are joined at the connector. Hence the requirement for 5 pin connector.

We keep the three separate, take them to the power supply in separate wires and tie them together at the chassis/earth stud (bolt) point.

Keep them as straight, linear (horizontal) individual traces. Make the AGND as wide as possible.

I do not mean to disagree with daveb but there is no need to by-pass them.

 

[richiyobs]

My experience (not in audio, in RF stuff) is that designing multiple separate grounds to “star ground” a PCB leads to poorer results than a single ground plane used for everything. I would be inclined to have a single layer dedicated to ground, and keep in contiguous. I’d also heavily bypass each individual board with caps right at the connector.

Hi Daveb
and thanks for your advice....at the moment I am designing the PCB with a single GND plane on the bottom, where the GNDA of the PCBs of each individual module is also included. in fact, in the individual modules we have a different path for GNDA and GND which obviously in the Edac board will be the same point...
I'm leaving at Chassis its own path which at this point will rbe joined the connector that will power all the edac connectors, or even fill the upper plane with the chassis and therefore a solid plane on the top too.
can this be a good practice?

best

 

[richiyobs]

I have a lot of 38 pin edacs parts if you want some.

Thanks Rob,
i just own 30pin connectors, it s fine for my usage...
i will fill the box with only dynamic processors, no needs of extra connection for the moment

best

 

[richiyobs]

Chassis/Earth is never connected to analogue ground and power ground on the backplane.

API's practice is that the AGND and PWRGND are joined at the connector. Hence the requirement for 5 pin connector.

We keep the three separate, take them to the power supply in separate wires and tie them together at the chassis/earth stud (bolt) point.

Keep them as straight, linear (horizontal) individual traces. Make the AGND as wide as possible.

I do not mean to disagree with daveb but there is no need to by-pass them.

Hi Sahib,
so different tracks for GNDA and Chassis, joined together to GND at the main 5/6 pin connector that will supply the entire Edac board.
can top and bottom sides be filled with GND plane?
as I said in another answer, I was planning on using the top side of the pcb to fill with the Chassis, and so include each edac pin1 to that plan, but it doesn t look like a good practice.

Thanks for your support

best

 

[sahib]

Three different tracks for;

Chassis/Earth
Analogue Ground
Power Ground

Below was quickly done but works perfectly. Connections to the 6 way DC power connector are hard wired. You can join the analogue ground and 0V (power ground) at the DC connector and use 5 way connector as in API. But the chassis/earth is never connected to those two at this point. As I mentioned before we take these three separately to the power supply and join them at the chassis stud point.



This is the ground scheme at the power supply.

 

[richiyobs]

This is the ground scheme at the power supply.

GREAT! thank you so much

attached my quick attempt, now I can upgrade it...
I m using 1mm for power tracks is it enough?

 

[sahib]

GREAT! thank you so much

attached my quick attempt, now I can upgrade it...
I m using 1mm for power tracks is it enough?

I would make them thicker. On the example I gave the analogue ground plane is flooded between the power rail pads. You do not have to do that. It gives you more space to make them thicker.

 

[richiyobs]

the enclosure is a remnant from the 80s given to me by an old colleague, who helped me resize this proto-box.... it was still packed with old bubble wrap, hard plastic from those years!!!
now I can better size the Ecad board and place a PSU.
I m thinking to use RJ45 connectors with spider for 4 signals instead of drilling 20 xlr holes.... let s see

best

 

[daveb]

Chassis/Earth is never connected to analogue ground and power ground on the backplane.

API's practice is that the AGND and PWRGND are joined at the connector. Hence the requirement for 5 pin connector.

We keep the three separate, take them to the power supply in separate wires and tie them together at the chassis/earth stud (bolt) point.

Keep them as straight, linear (horizontal) individual traces. Make the AGND as wide as possible.

I do not mean to disagree with daveb but there is no need to by-pass them.

So a true star ground works well then. Do you keep the Analog and power grounds separated on the cards? As I said, all of my experience is at 100 MHz and up, so a very different grounding regime there.

 

[sahib]

So a true star ground works well then. Do you keep the Analog and power grounds separated on the cards? As I said, all of my experience is at 100 MHz and up, so a very different grounding regime there.

Indeed it does and also logical to make a single reference point. On the backplane we have the PWR GND and AGND separate from each other.

I have zero RF design experience but I know that things are different in your world, and it is also not difficult to see that. I have recently dismantled an '80s hi-fi tuner and it was full of ground connections to varying parts of the assembly. This included, I would say at least 4 - 5 different ground points to the metal chassis alone. This would be a suicidal thing to do in pro-audio applications (though there are old guitar amps) . However, the tuner was (naturally) a class 2 product with no safety earth connections to chassis. So, I would imagine this would add another layer to grounding scheme in RF.

 

[daveb]

Yes, very different. The thought of those inches of wire giving a couple of hundred nH of inductance in the ground path makes me grimace, but that impedance is probably comparable to the wire resistance, so it's negligible. The chassis safety requirements are also something I haven't had to deal with, which adds another layer of complexity. Very educational

 

[john12ax7]

It's not uncommon to treat analog and power ground as the same and a single ground plane. Many commercial products do this. The main thing is keep "dirty" currents separate from sensitive analog points. For example for a relay you can run a separate isolated ground trace that connects back at the edge connector. It's mainly about current flow and steering things as needed.

 

[richiyobs]

Thanks for all the info... I'll treasure it...
I take this opportunity to clear up another doubt, what is pin 1 edac usually used for in the individual PCBs of the modules?
to shield wiring or can it also be used to shield the entire PCB?

 

[john12ax7]

Pin 1 of the edac would generally be shielding. Some modules will be enclosed in a metal housing, or have a metal sled, common to tie these to pin 1.

Other options could be the gnd for an rf filter. Or the shield of a transformer. But these can be more debatable and the implementation is important. It would be fine to tie the metal work to pin 1 and nothing else. Connecting the wrong thing in the wrong way will do more harm than good.

Also remember that the mainframe would be metal and connected to chassis gnd. So it can do a lot of the heavy lifting.

 

[Yongyut 97]

GREAT! thank you so much

attached my quick attempt, now I can upgrade it...
I m using 1mm for power tracks is it enough?

Could you please share your drawings? [email protected] thanks.

 

[MidnightArrakis]

Could you please share your drawings? [email protected] thanks.

You mean.....something like THIS???



>> THE SAME THING!!!.....ONLY DIFFERENT!!!.....




/

 

[richiyobs]

Could you please share your drawings? [email protected] thanks.

HI,
I'm still working on it because not much spare time at the moment....
as you can see MidnightArrakis has published useful information about my project.... he is helping me to achieve something better than what I could do...
In any case, the difficult part was to properly space the edac connectors, but with the 3D model and the CAD uploaded you can easily make it.....the dimensions are useful for the enclosure i'm using....
follow the advice regarding GND, Chassis and GNDA..... the rest is easily wired
I'm going to order Mounting Rails for Edac board, so must wait to verify if everything is fine and well alligned

best