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Power supply ground
Power supply ground
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Old 3rd February 2018, 09:29 AM   #1
emosms is offline emosms  Bulgaria
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Default Power supply ground

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?

---
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
Dac volume control is probably not going to be implemented.
Adding it, to show the possible complexity of psu's/signals on that pcb.

Click the image to open in full size.

Regards - Emil

Last edited by emosms; 3rd February 2018 at 09:35 AM.
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Old 3rd February 2018, 10:00 AM   #2
AndrewT is offline AndrewT  Scotland
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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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Last edited by AndrewT; 3rd February 2018 at 10:08 AM.
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Old 3rd February 2018, 11:06 AM   #3
emosms is offline emosms  Bulgaria
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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
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Old 3rd February 2018, 11:17 AM   #4
scottjoplin is offline scottjoplin  Wales
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I'd probably start by having a look at the schematics of similar digital audio equipment to see how they do it. Also I'd be tempted to use separate power supplies, why not?
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Old 3rd February 2018, 12:41 PM   #5
emosms is offline emosms  Bulgaria
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That would be empirical study (how 'they' do it). Actually a very sane idea
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...
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Old 3rd February 2018, 01:02 PM   #6
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by emosms View Post
Seporate psu's... they still need a common ground somewhere..
Probably a single connection point, to avoid ground loops.
Do they? It depends what you mean. Is there a "common ground" between your CD player and amplifier for example?
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Old 3rd February 2018, 04:40 PM   #7
emosms is offline emosms  Bulgaria
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Instead of reducing psu's there would be ... six power supplies....

And still, the microcontroller PSU should be ground referenced to 2,3 of them.

A Cd player and an amp are ground connected by the signal cable.

Last edited by emosms; 3rd February 2018 at 04:44 PM.
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Old 3rd February 2018, 05:09 PM   #8
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by emosms View Post
A Cd player and an amp are ground connected by the signal cable.
So, that is all you need between the stages: the 0V signal return/reference
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Old 3rd February 2018, 05:32 PM   #9
emosms is offline emosms  Bulgaria
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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
And in general it is much easier to design a smaller pcb
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Old 3rd February 2018, 07:55 PM   #10
scottjoplin is offline scottjoplin  Wales
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Yes there will be connections via the signal 0V (gnd) and loops are more likely to be created by tying all the supply grounds together at a common ground
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