[Phil Allison[_4_]]

Mike Rivers wrote:

=================

Phil Allison wrote:


Note: The internal symmetry of a co-ax cable is the secret to its excellent mag field rejection. Equal and opposite currents inject into the core and shield from a nearby AC mag field - so complete self cancellation.

The ONLY real advantage of a 2 wire "balanced" mic line is when used for carrying phantom power to a mic or device that needs it ( eg a DI unit).


With the assumption that the input is differential,


** The CONTEXT here is microphones - you snipped it out of sight.

The source is *floating* so no ground loops.


what you're losing is common mode rejection.


** Good shielding prevents such coupling with a *microphone*.


You're relying on the construction of the coax
to be all you need to keep EMI from getting to the destination through
the cable.

** Which actually works BETTER than a twisted pair - which does not have such good symmetry cos of having descrete loops.


A differential input fed from an accurately balanced source
is like "belt and suspenders."


** Picks up more hum than a good co-ax.

Try it out just like I suggested, sometime.


A lot of the "unbalanced hums" netlore is a function of improper
grounding

** One word - *microphones*.

Unique case.


...... Phil