Audiosector LM3875 - is this correct Star Grounding?? - diyAudio
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Old 8th May 2014, 08:36 PM   #1
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Question Audiosector LM3875 - is this correct Star Grounding??

Hi,
I am sorry to ask yet another noob question. Which of these would you say is the correct way to ground the Audiosector LM3875 amps? Both instances grounded to the chassis at the "STAR" point..

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Old 8th May 2014, 09:14 PM   #2
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Both are fine.
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Old 9th May 2014, 10:16 AM   #3
AndrewT is offline AndrewT  Scotland
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No to both of you.

The Protective Earth, PE (third wire in the Mains cable) MUST be permanently connected to the Chassis.
Nothing else interferes with that permanent connection.

The audio amplifier operates without any connection to Chassis. It will even operate without a Chassis.

The ONLY reason to connect any part of the audio circuit to Chassis is to comply with:
All exposed conductive parts must be connected to Chassis.
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Old 9th May 2014, 10:31 AM   #4
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HI Andrew,
Thank you for all your help thus far, I have managed to not electrocute myself thanks to you

So if I understand correctly:
- Connect the PE from the Mains to the chassis.

- Create a Ground "star" connection (not connected to chassis) using
-- PG+ PG- from the rectifier
-- OG from each amp

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Currently the ground scheme is as per pic 2, when I use the amp in the computer room I get terrible noise through the speakers? Possible ground loop issues? Is the 3rd pic better?
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Old 9th May 2014, 12:10 PM   #5
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Quote:
Originally Posted by AndrewT View Post
No to both of you.

The Protective Earth, PE (third wire in the Mains cable) MUST be permanently connected to the Chassis.
Nothing else interferes with that permanent connection.

The audio amplifier operates without any connection to Chassis. It will even operate without a Chassis.

The ONLY reason to connect any part of the audio circuit to Chassis is to comply with:
All exposed conductive parts must be connected to Chassis.
The only thing why earth from the mains plug is connected to the chassis, is to stop interfence from other electronics, and in the event of failure to safely lead away the current to ground. It's the same whether you use star ground or you ground the signal diffrently you won't hear a diffrence anyawy.
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Old 10th May 2014, 07:09 AM   #6
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by hangar18 View Post
The only thing why earth from the mains plug is connected to the chassis, is to stop interfence from other electronics, and in the event of failure to safely lead away the current to ground................
NO !!!!
the ONLY reason to connect Chassis to PE is to stop you killing users !!!!

It has nothing to do with audio and nothing to do with interference attenuation.
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