Source selecting switch puzzle, a practical question

[JoeAlders]

Building a headphone amp, I am a little bit puzzled about the signal routing from the PHONO and AUX cinch inputs to
the source selecting switch. Particularly the earthing and shielding connections.
For that purpose I studied the wiring picture of a design which is using two AUX and one CD cinch inputs and there my puzzling
started. Unfortunately I do not have the circuit diagram. From that picture and looking at the rotary switch on the left bottom side,
I concluded that there is a rotary switch used with two poles (A and C) and three positions, something like I give here.
AUX2,AUX2 and CD goes to position 3, 2 and 1 respectively, but how about those positions 7,8 and 9? where does the connections go to?

I do not see a separate signal return path. Those wiring connections are shielded and earthed at the cinch inputs.

 

[JonSnell Electronic]

The switch makes or breaks the signal path, no return required as the ground is the screen, 7, 8 and 9 is the other channel if stereo.

 

[JoeAlders]

The switch makes or breaks the signal path, no return required as the ground is the screen, 7, 8 and 9 is the other channel if stereo.

Yes, of course 7,8 and 9 are the other positions for the other channel. I should have noticed this .
But I do not know what you mean with "the screen", not those shields around the wires to the inputs I suppose?

 

[mbrennwa]

Yes, of course 7,8 and 9 are the other positions for the other channel. I should have noticed this .
But I do not know what you mean with "the screen", not those shields around the wires to the inputs I suppose?

Take another look at that drawing. The screens (=shield=audio-GND) of the three inputs are connected to each other at the RCA terminals (top left of the drawing), and to some point (white dot) on the blue PCB. I am pretty sure this "point on the blue PCB" is GND.

In other words: the audio-GNDs of all three RCA inputs are connected to each other, and to the audio-GND of the pre amp. This is a common way to hook up the audio-GND coming from the different input sources.

However, some will argue that connecting the different GNDs in this way is asking for trouble with ground loops. A way out would be to use another layer on the input selector and also switch the GNDs in the same way as the input signals.

 

[MAAC0]

Usually You don't switch grounds, just the hot signals.
I've never seen a switch for switching grounds on many disassembled gear.


Ok .. If You want to go the "Sound Purists" be my guest.

 

[JoeAlders]

Thanks guys for your responses, much appreciated.
Things are now fully clear by me.
And at first I had the intention to do it the way mbrennwa
described and switching the different grounds also but I think that this is indeed a
"Sound Purists" way as MAAC0 responded.