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Old 2nd September 2006, 03:56 AM   #1
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Join Date: Sep 2005
Default Ground shield connections question

Included is a picture of how I intend to make the connections for a single channel of an audio system. The transmission lines represent single center conductor shielded wire.

Am I doing things right?
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Old 2nd September 2006, 06:23 AM   #2
clem_o is offline clem_o  Philippines
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That would certainly be a straightforward attempt to avoid ground loops but...

Chassis grounds will inherently be connected via your power cords, since earth grounds are required in the US... so unless your CD player is not to spec, your schematic "can not" be done... or well, if your player is a DIY...

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Old 2nd September 2006, 07:37 AM   #3
AndrewT is online now AndrewT  Scotland
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your diagram is correct but in an idealised way showing all the different grounds connected together at an imaginary points.

Forget about safety earth, let the maufacturer take care of that. Just ensure you NEVER dismantle the safety earth.

The ground you have shown is the audio ground. It is likely that the audio ground is indirectly connected to safety ground inside each piece of equipment you have. There is an exception, some equipment is built as double insulated and this safety standard allows no safety earth connection.

If the manufacturer has directly connected the audio ground to the safety ground then you may have problems with ground loop hum. Particularly if two pieces of equipment repeat the direct connection fault.

Your diagram of the power amplifier could be expanded to show a signal (clean) gound, a power (dirty) ground, power supply common (very dirty), safety ground.

The incoming RCA ground should not be connected to chassis but can run to either the signal ground on the amp PCB or to the central star ground where all the grounds connect except the safety earth.

Is that any clearer?
regards Andrew T.
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Old 2nd September 2006, 10:46 PM   #4
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Thanks for your inputs! Attached is a redrawn picture with new ground connections.

Let me clarify a few things that I should have before:

The CD player (or input source of any kind, for that matter) will be from a manufacturer (so it will probably have its own ground).

==> The first transmission line (from CD player to PGA2320) is an RCA cable.

==> The second transmission line is just shielded wire.

1) In this included picture, I do not have the negative side of the input source connected to anything because I don't know where it should go. Where should it be connected to?

2) When dealing with a bunch of several components in series (for instance,
shielded wire ==> preamp ==> shielded wire ==> power amp), is it better to "daisy chain" the ground back to the star point (like I did in my first post here), or is it better to give each component its own ground path to the star point (like I have shown in this included picture here)?

Thanks for your help!
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Old 3rd September 2006, 09:12 AM   #5
AndrewT is online now AndrewT  Scotland
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Join Date: Jul 2004
Location: Scottish Borders
each audio source will have it's own audio ground.
Each connector needs two wires (for unbalanced connections).
There is a flow and a return. The flow is the core of the coax (pin of the RCA phono plug). The return is the shield (outer of the RCA phono plug).
You need both connections for a circuit. You cannot and must not break the flow and return.

The central star ground (audio ground) will generally be fitted inside each audio component.
The central star ground must not be connected to the safety earth.
The safety earths of all the audio equipment are all connected back to your earthing point at the distribution board.
If one piece of audio equipment has a safety earth to audio ground connection then it is wired incorrectly, but so far no harm done. If a second piece of audio equipment has the same incorrect safety earth to audio ground connection then you now have an earth LOOP.
From audio ground1 to safety earth1 to distributon board from distribution board to safety earth2 to audio ground2 to RCA return2 to RCA return1. A complete loop causing hum in the output.
This hum is mixed with the signal and transfers with the signal all the way down the chain to the speakers. No amount of clever wiring can unmix the hum from the signal once the LOOP has been established. DO NOT connect safety earth to audio ground.
regards Andrew T.
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