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Old 23rd October 2015, 07:25 PM   #1
JAY X is offline JAY X  Spain
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Smile wiring and shielding a potentiometer

Hi All!

I have an audio main board, and an external potentiometer attached to the chassis front panel, regarding the wiring, i want to shield both the input and the output wires, but also want to avoid crosstalk, so i use single shielded cable for the wiring.( one for the input and another for the output.

The shield of the input signal is connected to the board gnd. But the shield of the output is not connected to board gnd. I want to make sure this is right or ok. Any comment is wellcome!!

attached is the picture/schematic of the wiring.

Thank you for your help!
JayX
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File Type: jpg FADER WIRING.jpg (36.5 KB, 118 views)
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Old 23rd October 2015, 07:40 PM   #2
rayma is online now rayma  United States
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Quote:
Originally Posted by JAY X View Post
The shield of the input signal is connected to the board gnd. But the shield of the output is not
connected to board gnd. I want to make sure this is right or ok.
Is the fader amp in the same enclosure, with its own connection to ground?
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Old 23rd October 2015, 07:46 PM   #3
JAY X is offline JAY X  Spain
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Hi Rayma!

Yes, the fader amplifier is on the main board. The potentiometer is external to the main board. And everything is inside a metal box. There are wires from the pot to the main board. ( a 3 pin molex connector)

jay x

Last edited by JAY X; 23rd October 2015 at 07:48 PM.
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Old 23rd October 2015, 07:52 PM   #4
rayma is online now rayma  United States
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Quote:
Originally Posted by JAY X View Post
Yes, the fader amplifier is on the main board. The potentiometer is external to the main board.
And everything is inside a metal box. There are wires from the pot to the main board.
( a 3 pin molex connector)
This should be ok, although sometimes you have to experiment with the grounding, when adding parts
to an existing board. Maybe a close photo would be helpful.
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Old 24th October 2015, 04:55 PM   #5
AndrewT is offline AndrewT  Scotland
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I don't like breaking the two wire circuits between modules.

You have a two wire connection from input molex to vol pot.
You have only one wire and a very separated return route from the vol pot back to the PCB. This creates a BIG LOOP in the vol pot output.
That is bad.
Have a good look at the molex and it's connections. Is there a way to get the vol pot output to maintain a two wire connection into the next stage without using that grounding point?

Back to the input.
You show one wire as the input from the previous stage. That should be a two wire connection. Where is the other half of the two wire connection.
Don't say it doesn't exist.
It does, or the connection will not work !
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Last edited by AndrewT; 24th October 2015 at 05:11 PM.
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Old 24th October 2015, 05:10 PM   #6
DF96 is online now DF96  England
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There isn't a perfect way to wire an off-board pot to a board with one ground at that point in the circuit. You have to choose between a ground loop, or separating signal and return for one of the legs.
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Old 25th October 2015, 07:28 PM   #7
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You can make the ground loop as small as possible by keeping the cables closely together (and maybe even twisting them) though. The 3-pin Molex may have been intended to be used with something as simple as a 3-conductor ribbon cable, and that's what you want to emulate.
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Old 26th October 2015, 12:12 PM   #8
JAY X is offline JAY X  Spain
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Quote:
Originally Posted by AndrewT View Post

Back to the input.
You show one wire as the input from the previous stage. That should be a two wire connection. Where is the other half of the two wire connection.
Don't say it doesn't exist.
It does, or the connection will not work !
Hi Andrew!,everybody!

I appreciate your comments, and will take a look to improve this!!

Andrew, the one wire as the input from the previous stage is a trace on the main pcb. I use ground plane on bottom layer, gnd fill on top.

hmmm, as a fast thinking...maybe extending an isolated trace from the gnd of the opamp output...without thermal pad... i could connect this gnd to the wire... hmmm... have to mash/cook these ideas.........


jay x
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Old 26th October 2015, 02:07 PM   #9
AndrewT is offline AndrewT  Scotland
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I recommend you try to maintain close coupled TWO wire connections between modules.
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