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I'm trying to design a double-layered PCB audio DAC. At some point, I've started with "reverse" engineering best 80-90s Sony's CD players that uses the same DAC ICs (PCM58) and digital filter and found interesting thing, the "higher" player in hierarchy (more expensive, heavier, slightly better supply, etc), the less ground plane on the top layer.

CDP-228ESD -> CDP-338ESD -> CDP-X7ESD

CDP-228ESD (¥59,800/$466.5 - 1988 - 6.2kg/13.67lb) enter image description here

CDP-338ESD (¥89,800/$700.6 - 1988 - 12.5kg/27.56lb) enter image description here

CDP-X7ESD (¥200,000/$1560.4 - 1988 - 17.0kg/37.48lb) enter image description here

And pictures of PCB's grounding for each of them:

CDP-228ESD

CDP-228ESD

CDP-338ESD CDP-338ESD

CDP-X7ESD

CDP-X7ESD

As you can see on the last picture PCB is single-layered and it was their almost the most expensive player. Initially, I planed to left the whole top layer for the ground plane (don't split digital/analog/power ground), but now I'm not that sure. And then I come across a Rick Hartley seminar on proper grounding (https://www.youtube.com/watch?v=ySuUZEjARPY&t=4405s) that he suggest to split the ground for <20 kHz. What strategy will be the best in my case:

  1. Cut the ground plane after the middle of the DAC IC;
  2. Cut the ground plane after the DAC IC;
  3. Cut the ground plane after the I/V converter opamp;
  4. Left whole top side for the ground plane?

DAC PCB

UPDATE (schematic):

The PCB I want to design is a classic R-2R dac with op amp based I/V converter and third order low-pass filter with Sallen-Key topology. Basically,

WM8804 (spdif receiver) -> SM5847 (digital filter) -> PCM58 (dac) -> ad842 (I/V) -> LME49870 (LPF+buffer)

enter image description here

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    \$\begingroup\$ What do you mean when you say "higher"? Do you mean a more expensive model, or a later model? It looks like that last one you show a picture of is on a single-sided board, a classic sign of cost-cutting measures that are commonly taken as a product is refined and unnecessary (at least according to the finance department!) expenses removed. \$\endgroup\$
    – Hearth
    Commented May 20, 2021 at 4:27
  • \$\begingroup\$ @Hearth right, roughly speaking, the last one is much more expensive, heavier and has separate digital/analog supply from transformers to regulators. All of them are pretty close in terms of release date. For me the idea of using single-sided board is more than controversial, but I'm just seeking arguments for splitting the ground in my case. \$\endgroup\$
    – almnk
    Commented May 20, 2021 at 10:28

1 Answer 1

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Splitting planes is useful when there is common mode noise that creates large currents running on the ground plane. The split plane allows you to re-direct the current away from ground pins of the part.

If a current (especially a changing current) is running adjacent\past the ground pins it will create a small voltage from the resistance of the ground plane (there will also be a voltage created from any wires running back to the power supply).

A 5mA switching noise would create 10uV of noise if the resistance of the ground plane were 2mΩ (1oz copper is about 0.5mΩ, so 4 linear inches would be about 2mΩ)

There is no full schematic posted so I can't comment on the layout.

Also consider this: if you split the plane, you actually increase the resistance of the ground plane (especially if the current is run through a "star point" connector or jumper.)

A better way is to rearrange the components so large currents (returning back to the source through a ground in a power connector or to a supply mounted on the board) are directed away from sensitive parts. This can be done with proper layout.

Another thing that would help is to decrease the resistance of the ground by moving to a higher oz copper or larger grounding wires (going from 1oz to 2oz would decrease common mode noise by a factor of 2x).

Short story, don't cut the ground plane. It's almost never useful (there are a few cases where it is, isolation is one of those cases where it is useful). If you do cut the plane a good reason is to redirect large currents away from parts.

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  • \$\begingroup\$ Thank you for your answer, I'll better left the ground plane untouched. I just was curious about potential benefits of Sony's approach (in that fancy expensive player) and Rick's statement about splitting below 20KHz. \$\endgroup\$
    – almnk
    Commented May 26, 2021 at 15:57
  • \$\begingroup\$ Yes, that is what I meant \$\endgroup\$
    – Voltage Spike
    Commented May 26, 2021 at 17:35

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