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I'm building an amplifier in a conductive metal chassis. The general grounding plan is to have an audio ground, a power ground, and a digital ground that converge at a single point on the chassis. However, my audio connectors are all panel-mount, so the shield of the connectors get grounded by contact when mounted. Technically, should I insulate them from the back panel and wire the ground connection? Practically, does it matter whether I insulate them or not?

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Yes you should insulate the chassis ground also, from the ground star connection at the Poewr Supply.

The chassis should be connected to Earth terminal, right on the Power Input, thus all signals after the transformer should be isolated from the chassis.

Yes it matters if you insulate, because insulation from Earth avoid some "hum" noise often found in poorly designed Audio Electronics.

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  • \$\begingroup\$ Are you saying that the audio ground should never be connected to the chassis? \$\endgroup\$
    – Andrew
    Jul 13 '12 at 4:24
  • \$\begingroup\$ Yes. You should isolate the chassis metal from all circuitry grounds. Some people shunt both Earth and Ground with a Resistor (no electrical isolation) or a Capacitor. I prefer the Capacitor for better EMI performance. \$\endgroup\$ Jul 13 '12 at 12:45
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Often connectors have a dedicated chassis pin so you can add a selection jumper on the PCB to set as desired (e.g. chassis, floating, or circuit grounds) We used a similar connector the one below in one of our products, you can see the 4th chassis pin at the side of the "standard" pins:

xlr

This can be useful as you have the option of choosing in case one grounding system doesn't work in a certain scenario.

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  • \$\begingroup\$ I've seen these; they're nice. Unfortunately the ones I'm dealing with this time are just cheap RCA jacks and binding posts. \$\endgroup\$
    – Andrew
    Jul 13 '12 at 3:32

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