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Old 3rd October 2006, 12:46 PM   #1
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Default LM1876 Grounding Question

Hi all,

I'm working on a LM1876 (stereo) PCB design. But i'm not sure on one issue that; do the LM1876's GND pins (pin 5 and 10) Power GND or Signal GND? So should i connect them to Power GND or Signal GND?
I know that all the GNDs will be as one at the end. But i seperated SGND and PGND in the circuit as you can see at the attachment. Right side you can see the PGND and on the left side SGND.
Do you think its a good design for star ground? Or should i seperate SGND and PGND totally?
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Old 3rd October 2006, 01:37 PM   #2
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Both the internal circuitry as well as fig 3 in the data sheet make it clear that the pin 5, 10 connection is for reference purposes only. There is no (load) current through them. Being a reference for the signal, they should be tied to signal gnd.

Your pcb looks good with the star gnd!

Jan Didden
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Old 3rd October 2006, 01:59 PM   #3
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OK! Thanks a lot for your comment! Another question;

I have another stereo board (clone of that) and a buffer+filter board on same case. Should i connect THE STAR GROUND inside of that PCB (as my first PCB) or should i make a common grounding node on metal case then interconnect all of grounds on it? So in that case i will not connect PGNDs to SGNDs on PCB. Like that;
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Old 3rd October 2006, 02:58 PM   #4
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Assuming you have a single power supply for the stereo set I would make a central ground on the case and run the power grounds to this. The signal ground depends a bit how you connect the inputs, are they isolated? Will you run separate input plug gnds to each amp on the board(s)?

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Old 4th October 2006, 07:29 AM   #5
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In fact i'm not sure about that. Which is the best solution? Should i use seperated signal grounds and of course seperated signal lines or should i use one grounding point for all signal grounds then connect all sgnds to there as star gnd?
And should i use shielded cables for line level signal inside of box (it will be a metal box and grounded) Yea i know that i ask a lot but in that case should i connect the shields one sides gnd or both sides?
Sorry about disturbing but i have very bad experiences (two) with gorund loops. And i want no more humms!
Thank you very much Janne..
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Old 4th October 2006, 05:18 PM   #6
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I'd use shielded wire for signals. It may not be necessary without a fan in the box but it wouldn't hurt.

I have done some designs where I star all the signal levels (often called 'clean' GND) then from the star out to the power GNDs (often called 'dirty' GND). I use a small resistor like a few ohms to 10 ohms to connect clean GND to dirty GND. Never had any hum in any of the amplifiers. They were all chip amp types tho so easier to route since few connections.

-SL
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Old 5th October 2006, 02:39 PM   #7
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Thank you SL,

If im wrong pls warn me;
1- I wont connect SGNDs to PGNDs on PCB but they will be star gorund with themselves not with each other.
2- Will connect each SGND of PCBs to a global SGND node
3- Will connect each PGND of PCBs to a global PGND node
4- After all i will connect SGND node to PGND node via a ex:10ohm resistor.
Thats all. Is it?

Then how can i connect PGND to neutral (earth GND) and naturally case?
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