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Davec113 18th July 2012 02:25 AM

Preamp Grounding Question
 
I have a question about wiring the ground for the preamp I'm working on, it is using an Aikido all in one octal pcb. I am using an input selector switch that switches grounds and have isolated the RCA jacks. The chassis is wood with a .125" aluminum top plate which the PCB is attached to. RCA jacks are on a separate aluminum plate on the rear of the chassis, input and volume are in the wood front panel.

I am considering wiring the safety ground from the mains input jack and the ground from the PCB to the same point on the top plate, along with the ground outputs of the selector switch. Will this work or can anyone suggest an improved scheme? Thanks!

DF96 18th July 2012 10:21 AM

Safety ground should be used for safety alone. All external metalwork should be connected to it. Signal ground is different as it provided the reference voltage for signals. There must be one and only one connection between these two different grounds. The selector switch handles signal ground. The plate with the RCA sockets should connect to safety ground.

Davec113 18th July 2012 05:09 PM

OK, in that case maybe I need to ground the selector switch to the PCB's ground, then the PCB to the top plate where the safety ground attaches to. That will provide one path to ground for the signal.

DF96 18th July 2012 05:11 PM

Yes, for the signal ground there must be one and only one path between any two grounded points. None of these paths should carry any PSU ripple.

Chris Hornbeck 18th July 2012 08:08 PM

And the power supply ripple is the important part. Modern systems with multiple safety grounds are riddled with ground loops; keeping power supply currents away from signal is the best that's possible (without transformers or balancing). And signal ground must be considered to include safety grounds.

All good fortune,
Chris


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