CS8420 SPDIF grounding question

studiostevus · 21st April 2010, 10:53 AM

Hi all,
I am about to improve the SPDIF input on my Berhringer SRC2496 by connecting a new RCA directly to the CS8420.

I'm just a bit puzzled on the grounding. The CS8420 datasheet shows different ground points for the RCA and the chip, and I could imagine a ground loop if I would connect the ground pin of the chip (pin 5) to the cold of the RCA (RCA is grounded to the star point). On the other hand, what other ground point should I connect pin 5 to?

Or should I just leave it on the board as it should be grounded correctly in original state (in other words just connect pin 4 to the hot of the RCA and that's it?)

Thanks for helping me out here...

SoNic_real_one · 21st April 2010, 11:42 AM

What ground loop are you imagining?
The ground ring of the RCA shall be connected to the board, on the ground, closest to the point where the middle is connected.

studiostevus · 21st April 2010, 12:20 PM

Ground loop:

Star point - PCB - CS8420 - RCA ring - Star point

studiostevus · 21st April 2010, 03:43 PM

Capture.JPG

So, where does the RCA ground go to? Star point?

And where does the RXN ground go to? Leave it as is as it already should be grounded properly on the PCB? Scratch the laquer off the PCB and ground it to the ground plane? Or ground it at the RCA (via cap)?

bocka · 21st April 2010, 03:47 PM

Quote:

Originally Posted by studiostevus

So, where does the RCA ground go to? Star point?

Star ground with RF? This will never work. You need a well defined 75ohms transmission line from your RCA connector to the SPDIF receiver. Use a solid ground plane.

marce · 22nd April 2010, 11:55 AM

Digital should always have a GND plane, star grounds are no good (understatement) with digital. If nothing else the signal is closely coupled to the ground as at these speeds the return path follows the path of least inductance, i.e. dircectly under the signal track, no ground plane means the return has to meander all over = noise, EMC problems etc

21st April 2010, 10:53 AM	#1
studiostevus diyAudio Member Join Date: Oct 2009 Location: The Hague	CS8420 SPDIF grounding question Hi all, I am about to improve the SPDIF input on my Berhringer SRC2496 by connecting a new RCA directly to the CS8420. I'm just a bit puzzled on the grounding. The CS8420 datasheet shows different ground points for the RCA and the chip, and I could imagine a ground loop if I would connect the ground pin of the chip (pin 5) to the cold of the RCA (RCA is grounded to the star point). On the other hand, what other ground point should I connect pin 5 to? Or should I just leave it on the board as it should be grounded correctly in original state (in other words just connect pin 4 to the hot of the RCA and that's it?) Thanks for helping me out here...

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21st April 2010, 11:42 AM	#2
SoNic_real_one diyAudio Member Join Date: Jan 2008 Location: Virginia	What ground loop are you imagining? The ground ring of the RCA shall be connected to the board, on the ground, closest to the point where the middle is connected.

21st April 2010, 12:20 PM	#3
studiostevus diyAudio Member Join Date: Oct 2009 Location: The Hague	Ground loop: Star point - PCB - CS8420 - RCA ring - Star point

21st April 2010, 03:43 PM	#4
studiostevus diyAudio Member Join Date: Oct 2009 Location: The Hague	Capture.JPG So, where does the RCA ground go to? Star point? And where does the RXN ground go to? Leave it as is as it already should be grounded properly on the PCB? Scratch the laquer off the PCB and ground it to the ground plane? Or ground it at the RCA (via cap)?

22nd April 2010, 11:55 AM	#6
marce diyAudio Member Join Date: Jun 2007 Location: Blackburn, Lancs	Digital should always have a GND plane, star grounds are no good (understatement) with digital. If nothing else the signal is closely coupled to the ground as at these speeds the return path follows the path of least inductance, i.e. dircectly under the signal track, no ground plane means the return has to meander all over = noise, EMC problems etc

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