You can use an Ohm-meter from the XLR pin 1 connector to the shell solder tab.This is incorrect. Measure a plug.
What measurement can I take which will show (or not) a mechanical connection?
Or by visual inspection, you will see lot's of insulating material between the two connections.
In the stereo pair it will be the same current (leakage & noise) in both cables. You are just connecting chassis to chassis (which are acting as shields). In some rare cases, some experts suggest connecting the shield at the receiving end through a series capacitor (known as a hybrid connection).
If the chassis is non-conductive, then in this modern world you are just begging for interference problems. But i would connect all the XLR pin 1's together with short wires.
When every piece of balanced gear used transformer I/O (40 years ago) with 1000v galvanic isolation the answer was simple, connected the drain/shield at one end to the chassis (which were always conductive and always connected to the third pin of the power cord(ground not neutral) Now we have a dozen different active balanced I/O circuits each with its own dis/advantages and some chassis connected to ground and some conductive chassis not connected to the power ground but connected to the audio ground etc etc. its hard to give global answers. Its no wonder that studio grounding can be a nightmare. Not to mention there is no standard for which pin (2 or 3) is + and which is - .
The standard (where you start) is shield to pin 1 at one end only for all connections. This should be connected in the gear to the ground pin of the power plug. (ohm meter pin 1 to an empty wall plug ground to make sure) or there will be no where for the shield to dump its noise.) If this gives you ground loops its caused by the other connections (pins 2 and 3) and then you need to look at the actual ballanced circuits used to see where the loop is.
The standard (where you start) is shield to pin 1 at one end only for all connections. This should be connected in the gear to the ground pin of the power plug. (ohm meter pin 1 to an empty wall plug ground to make sure) or there will be no where for the shield to dump its noise.) If this gives you ground loops its caused by the other connections (pins 2 and 3) and then you need to look at the actual ballanced circuits used to see where the loop is.
Ah I see we've got crossed wires. I was talking about a mechanical connection on the plug to secure the shield, not a connection between shield and pin1.
OK, with XLR connectors, either chassis or inline, there is a solder tab connection to the shell. In some inline connectors it's made with a small set-screw in others it's a spring type contact. While the cable shield could be made to this shell solder tab, in most cables it's not connected because you never know what the shell might touch.
So far so good!When every piece of balanced gear used transformer I/O (40 years ago) with 1000v galvanic isolation the answer was simple, connected the drain/shield at one end to the chassis (which were always conductive and always connected to the third pin of the power cord(ground not neutral) Now we have a dozen different active balanced I/O circuits each with its own dis/advantages and some chassis connected to ground and some conductive chassis not connected to the power ground but connected to the audio ground etc etc. its hard to give global answers. Its no wonder that studio grounding can be a nightmare. Not to mention there is no standard for which pin (2 or 3) is + and which is - .
I think that most of the experts write - connect the shield at both ends unless you have a good reason for not connecting the receive end.
This is a misunderstanding of how shields work.
The XLR pin 1 should be connected directly to the chassis near the XLR connector.
This has nothing to do with the AC power plug! AC power is connected to the chassis for safety reasons!
Shields do NOT dump noise into the AC power safety ground system where it magically disappears down the ground rod into Mother Earth.
In order to keep the symetry, you will need something like this (R2 being between two pins of the variable potentiometer):
Sorry, but my original question was/is how to wire this up using a quad Alps pot and if that was possible. Apologies if I have misunderstood the schematic - simple as it may be
Credit where credit is due, the above picture is from Rane's Reference section (Balanced L-pad), where the principle is explained in context.
The reason why there's no obvious answer to your question is because - usually - you wouldn't use a four-gang pot for your intended purpose.
The above schematic only involves one variable resistor per balanced channel. It's some special case of my above schematic where there's no ground connection, in which case the two pot tapers functionally become one (common) variable resistance. Given a sufficiently low source output impedance and a sufficiently large input impedance of the next stage (i.e. amplifier), the absolute impedance of the L-Pad isn't critical as long as the ratios between R1 and R2 are maintained.
Perhaps this shows why the question about what to do with the ground connection is not easily answered; it's a question normally not asked.
Have you tried any of the suggested schematics yet? All of them are easy to try out and compare.
Cheers,
Sebastian.
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