Re: STP for unbalanced Stereo
The big thing to understand is what makes a regular twisted pair balanced line preferred over unbalanced.
It is the common mode rejection ratio of the input stage it is plugged into. This CMMR allows balanced lines to be run long distances (think telephone lines) with minimal issue.
Basically since the signal travels on the conductors-a shield is not really needed to keep out the noise. The whole basic concept of twisting the wires is to expose AS MUCH AS POSSIBLE of each conductor TO THE NOISE! I know that sound weird-but if the input stage has a lot of common mode rejection-then anything that is common to both conductors will be cancelled-to the extent of the CMMR.
An unbalanced signal does not have this type of rejection. Since the shield is actually one of the conductors, and it "shields" the center conductor from the noise-there is a much greater possibility of noise getting into the system
If it HAS to be unbalanced-try this little trick.
Use a regular balanced mic line. Hook the hot to the hot (input and output). Now hook the neg/ground to the neg/ground on the input and output.
NOW hook the shield to the OUTPUT or SENDING device and DO NOT hook the shield to the input side.
This way any noise that gets on the shield will find a lower impedance path to ground (outputs are always lower impedance than inputs-these days anyway-it did not used to be that way in years past).
The signal can still travel on the wires-but it will be traveling with less noise.
