Power supply ground

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Hello,

I would like to gradually build the system on the attached image.
I want to build it as a modular system.
In general, each rectangle on the picture to be a seporate PCB.

I guess, the best option is to have galvanically isolated PSU's (seporate windings or transformers).
We have:
- microcontroller PSU
- digital +5v (DAC and spdif receiver)
- analog +5v (DAC analog PSU)
- bipolar supply for opamps (dac output stage and next modules)

First question - is that OK arrangement?
Can I leave out some of the above galvanically isolated PSU's? F.ex. to isolate microcontroller psu, digital and analog +5v with parallel RC chains, seporate linear regulators and only one transformer?
More isolation, without galvanic one, could be achieved (I guess) if I supply 7/8v on the bus, and then have shunt regulators close to each power pin on each chip (dac, spdif receiver).
Except the microcontroller, which is going to be off the shelf arduino nano unit.

Second question - where do we have the common ground?
- I can have the common ground at the PCU unit.
- I can have the common ground at the DAC pcb, where we could have up to 4 psu's and the respective signal lines
- I can have common ground at the 'motherboard', where all the modules (except the psu's) would be inserted on pins.
- Other arrangement?

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It is very important to be clear on the PSU architecutre, so that I can start building the seporate modules(pcb's).
F.ex. the DAC module - seporate grounds or common ground on this PCB...
If not clear - I cannot even start :D:D
Dac volume control is probably not going to be implemented.
Adding it, to show the possible complexity of psu's/signals on that pcb.

jpwe4VU.jpg


Regards - Emil
 
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A Motherboad with plug in Daughter boards might make a good modular system. A 10way dual in line 0.1" plug/socket does not use much PCB area. Lot's of ways give better mechanical "grip" and allow multiple pins for connection that need very low impedance.
Each plug in board can be designed, built, checked & tested before adding to the Motherboard.

The Motherboard can distribute power as well as signals. I wonder if the Motherboard needs to be multi-layered? Have you read H.Ott and his opinions on the minimum number of planes required to implement planes for power (2off) , grounds (2+off), Signals (1+off)?
If I remember correctly all with less than 6 planes have compromises that affect performance.

A separate Daughterboard for the PSU might be easier than trying to integrate the PSU onto a big PCB that has lots of signals passing around.

Do you need to keep noisy power completely separate from quiet power. (Digital and relays could be described as noisy).
 
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Seems that H.Ott paper us smth relevant to read.
I dont know it, but some practical considerations...
- I cannot make more than 2 layers pcb. So probably 2 layers for spdif board, dac board and vol control (digipots) board. Everything else - 1 layer...
- The motherboard is very easy to be ... just a prototype board with 0.1 spacing..

If i have common ground on each daughterboard, and all daughterboards connected to psu's common ground... will that be humfree enough???
I am afraid of buzz, even to a level that could be listenable :( :(
 
That would be empirical study (how 'they' do it). Actually a very sane idea :D
So need to look at some receivers service manuals, including principal and pcb layout.

Seporate psu's... they still need a common ground somewhere..
Probably a single connection point, to avoid ground loops.

Mby possible to have multiple ad hoc connections (per daughterboard) of digital to analog gnd, provided the digital ground is elevated above analog via res||cap.

Mby the analog bipolar might be the 'main' ground, and microcontroller psu, dac/spdif psu to be seporately elevated and connected to analog.

Mby the DAC analog +5v could be common ground with the bipolar ground, on the dac pcb. Directly connected, not elevated.

If we assume digital as noisy (does that include the dac/spdif digital +5v ??), mby common ground on daughterboards is not good?
Isn't it better to have a seporate path for the digital ground, back to the PSU ???

Too many questions... :D
 
And the microcontroller's psu ground, connected to:
- +5v digital psu at the spdif stage
- the bipolar psu at the digipot stage

(That is, if I do not connect the controller to the DAC for some feature)

So still there is a cross psu gnd connection, plus...
- three bipolar supplies... (dac, xover, digipots)
- two +5v digital (spdif, dac)

I would like to have the spdif and dac modules separate, so that I could swap the whole dac :D
And in general it is much easier to design a smaller pcb
 
Some modification.

1. The multicontroller is isolated with optocouplers. Do we still need to connect the microcontroller ground (PSU1) to the other ground?

2. The spdif module gets +5v digital and ground from PSU2.

3. The DAC module gets:
- i2s data
- +5v digital and ground from the spdif module
- +5v analog and ground from PSU3
- +-15v bipolar and ground from PSU4

Here all the ground comes into common ground.
The problem is down to designing the DAC pcb.
All grounds on seporate poligons and a point of connection between them.
Possibly, option for ground potential elevation of any ground to any ground...

4. The analog input selector is ommited, since it is relays. Galvanically isolated.

5. The Xover module gets:
- audio signal from dac
- +-15v from dac
- common ground from dac

6. The vol control module gets:
- audio signals from Xover
- +-15v from Xover
- gnd from Xover
Moreover, it derives +5v (or whatever necessary) from the +15v, to feed the optocoupler and digital control.
Not very clean but... do we need a seporate PSU for this??
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UbtHVYy.jpg


gKbQ0B3.jpg


Is that OK architecture? Most of the interesting stuff happens in the DAC pcb and topology.
 
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