I looked at the
circuit I gave you to convert the stereo to
mono and I can see where some confusion could come. The designer talked about shields where we would talk about signal
ground. Sorry I didn't
pick up on this earlier but with a background in electronics I automatically made the adjustment.
I also looked at the rane note and see where you might have got confused. You are thinking about a stereo
jack when no. 13 applies to
mono. You do bring the signal from the laptop as a stereo feed. But after you join left and right channels together by using the two resistors it becomes a
mono signal. And that is how you must think of it when wiring it.
Think of the output of the two resitors being connected to the red
line on diagram no. 13. The black
line is the sleeve from the jackplug.
If you wired it so that the sleeve of the stereo
jack plug ( from the laptop ) is connected to pin 1 of the
XLR and the output of the resistors to pin 2 & 3 you could be setting up a path for hum. To
wire it the original way take the output from the resistors and only
wire it to pin 2 of the
XLR. Take the
ground which is on the sleeve of the jackplug (
ground) and connect it only to
xlr pin 3. In the convertor connect nothing to
Xlr pin 1. This should work and maybe lower the hum
level.
If not we could try wiring it in another way.
In the convertor box at the laptop
wire the
XLR socket so that the sleeve from the
jack plug (
ground ) is connected to both pins 1 and 3. Connect the output from the resistors to pin 2 of the
xlr. This should work but won't necessarily get rid of the hum.
If the hum is really bad you will need some form of
transformer isolation.
Ok the difference between
ground and
shield is:
The
ground, in this case called signal
ground and on
unbalanced line it the path the signal returns on. Sought of like a battery
circuit with a
bulb current flows from one battery
terminal to the
bulb out the
bulb back to the other battery
terminal. That is an over simplification but it gives you the idea of a
circuit flow.
The
shield is meant to do what it says and sheild the audio signal from interfence. It does it by being wrapped around the outside of the signal wires . So when interference comes along it goes down the
shield to a chassis
ground. This
ground is outside the signal path so should help minimise the interference. On the cable you are using you only need the
shield and any two of the other conductors. Just make sure that at the convertor end the
shield is not connected to anything. If the leads are premade
XLR don't worry about disconnecting the shiel from pin 1 Just make sure the
XLR socket on the convertor has nothing wired to pin 1. This only applies if you use the first wiring
circuit ( not the one when when pins 1 & 3 are connected).
Let us know how you get on.