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Old 9th April 2014, 06:03 PM   #1
Crumboo is offline Crumboo  Sweden
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Join Date: Dec 2007
Default Help with grounding (connect the black dots)

Hi!

I wonder if anyone could help me out with proper grounding of my preamp/dsp/dac build. I've read about star ground, ground busses, separation of signal and power ground, etc. but I still don't get how I should do it in my build.

Please see the attached picture: I've drawn the main components of the build and their interconnections regarding signal and voltage supply. The black dots represents GND connections on each board, and I wish that anyone could guide me how to properly connect those.

About the components: the DAC is Buffalo3, the DSP is miniSHARC, toslink module is the one from TPA and I/V stages (there are 8 channels) are my own boards but based on IVY3 from TPA. For PSU I use Placid BP for the I/V:s and LCDPS for the rest. I also have a couple of other components (uC, display, relay boards) but I leave them out in order to not complicate the drawing too much.

Best regards,
Mattias
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Old 9th April 2014, 06:41 PM   #2
chaparK is offline chaparK  Luxembourg
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Hi Mattias,

As your strategy is to have a star ground layout, well you need to connect all the black dots to one same point somewhere in your build.

The problem gets actually a bit more complicated because your build mixes analogue and digital circuits. So you need to check if they have separate grounds. You also need to check how the analogue and digital grounds are connected together on a same board when this happens.

Have you looked at this application note from ADI?

Nick
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Old 10th April 2014, 01:00 PM   #3
marce is offline marce  United Kingdom
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How are you connecting the signals between the toshlink module, the DSP board and the DAC and the I/V boards as all will have high frequency content and the return path for these will be critical for noise control. Using just a star would be the worse scenario without a solid return path for all the signals between these boards.
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Old 10th April 2014, 08:20 PM   #4
Crumboo is offline Crumboo  Sweden
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Thank you guys!

@Nick:

Actually, I don't have a strategy yet - was hoping for some advice on that! I think (need to double check) that digital and analog grounds are interconnected on the dac board - I believe that I measured near 0 Ohms between the ground pins on the input and output side (as well as at the power connector). But I don't how those are connected on the board itself. Maybe someone knows, since this is a commonly used dac? Thanks for the application note - I will study it carefully!

@marce:

From the toslink module a single wire is connected to the dsp, carrying stereo SPDIF. The dsp outputs 8 channel I2S to the dac (4 data lines and 2 clock lines). For simplifying this connection I made a small board containing these lines that stacks onto the corresponding header on the units. On this board I made a solid ground plane (since I believed this would be good for these sensitive I2S-lines). That ground plane is also connected to the ground pins on both the dsp and dac currently. The dac is connected to each of the 8 I/V's using 2 wires (balanced connection).

Regarding star ground - since the boards have multiple ground connectors, I guess only one should be connected to the star point so no loops are created?

I believe I read somewhere about a "star of stars" layout, maybe this should be used?

I use a wooden chassi - should the star connect to the safety earth on the AC inlet?

I added a new picture with one example (yellow are signal lines, red are power lines, black are ground lines and the black rectangle is the ground plane on the small connector board). What do you think?
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Last edited by Crumboo; 10th April 2014 at 08:23 PM.
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Old 12th April 2014, 10:04 AM   #5
marce is offline marce  United Kingdom
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A twisted pair for power from each supply to each board.
A ground between each board with the signals, to provide a low impedance return path for the high frequency content.
The input of the PSUs where the ac goes in can be fastened to PE.
A wood box wont offer much in the way of shielding, ether way.
This is a mainly digital set up star ground is not the best solution.
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