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XLR (balanced) Chassis ground and signal ground question

EB1000

Active Member
Joined
Jan 8, 2020
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Israel
#1
Hi

When connecting panel mounted XLR connector to a balanced power amp (BTL), I usually leave the chassis ground connector unconnected. The pin 1 (signal ground) is connected to the amp's signal ground input.

Now, the amp module (125ASX2 for example), once mounted to the chassis, it connects the signal ground to the chassis, via the mounting screws. My question: Should I connect the XLR's 4th external pin - the chassis ground to pin 1 or directly to the chassis, or should I continue to leave it unconnected to anything?

I do not have any hum or noise, but I wonder if bridging chassis and signal grounds will be a better practice, provided that the amp module will always bridge the signal ground to the chassis. Searching for this issue returns contradicting results.

Thanks
 

somebodyelse

Major Contributor
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Dec 5, 2018
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#2
Unless the amp module's docs say otherwise you should probably be connecting pin1 to the chassis at the socket. Some of the XLR sockets have this built in, with a spike to pierce paint or anodizing, so that the mounting screw connects the shell and pin 1 to chassis. Have a read of AES48 if you can find a copy that's not behind a paywall, The G Word and/or the Jensen Transformers application notes - AN007 is probably most comprehensive.
 
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