Internal wiring

[scottjoplin]

In a balanced application the shield is an extension of the enclosure and must be connected at both ends to the enclosures

 

[Speedskater]

Ok, will do some reading.
Does the shield need to be connected at both ends to work?
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Cheers!
/T.

For balanced interconnect shields, the experts have different view-points. Bill Whitlock thinks that a hybrid connection at the receive end is often the best plan. That would be a normal shield connection at the powered send end and a small RF capacitor at the receive end. This of course won't work with microphones.

 

[Robotski]

So, connected at both ends, perhaps... What about a shared screen braid over multiple twisted pairs. I could easily make this happen.

Thanks for the input guys. I'm used to following an assembly drawing at work, but it's a whole another thing trying to design a circuit.

/T.

 

[DF96]

If you have multiple twisted pairs within a shield then you either have to have signal on just one pair at a time, or have different twist patterns for each pair, or put up with crosstalk.

 

[Robotski]

But surely crosstalk between the twisted pairs (balanced line) is not the issue here?
Isn't the shielding mainly for getting rid of possible power supply/transformer hum?

 

[scottjoplin]

No, it's mainly to shield against RFI.

 

[Robotski]

Ok.

 

[DF96]

The shield gets rid of external influences. The downside is that it probably forces the individually twisted pairs to be close together, so you get crosstalk. Whether that is an issue for you is a separate matter, but I mentioned it because I didn't want you to get a nasty surprise.