"Mike Rivers"
Phil Allison:

** That not a correct example.

A bad penny always returns. Welcome back, Phil.


** Typical ****head reply from the NG's parrot.


RF interference is defeated firstly by
the use of shielded cable and secondly by the use of filters to reduce
such
signals at the inputs of the balanced pre-amp.

However, what doesn't get caught by those crude mechanical methods
will be reduced by common mode rejection.


** What pig ignorant drivel !! Shielding and filtering are not "crude"
and CMR has no effect on FRO interference.


That was a bad rebuttal.


** What Rivers posted was as worthless crap.



Common mode rejection operates across the audio band and maybe a little
beyond but is usually most effective at the lower frequencies since the
main
aim is to eliminate ground hum from audio systems. A ground hum voltage
will
appear equally on the two wires and so be rejected.

In theory it can operate in any frequency range, even DC.


** Irrelevant reply - as usual for a parrot.


Did anyone say anything about audio here?


** Not Mike Rivers anyhow.



** A voltage injected into a balanced audio line by external magnetic
fields ( like nearby high AC current cables and transformers) creates a
hum
signal in differential mode that the pre-amp *will* amplify - its CMRR
has
no effect.

Whoa! This is EXACTLY where common mode rejection is useful in audio
circuits.


** More pig ignorant drivel. The two wires in a balanced line form a loop -
loops pick up induced hum just perfectly.


It's what lets us connect microphones with zip cord. The
reason why it doesn't work as well as we'd like it to is that it's
rare that the noise voltage at both inputs is rarely exactly the same,
so there will always be some difference, which will be amplified.


** The voltage induced in a loop is a differential signal - same as the
wanted signal on an audio line.


This sort of interference is reduced by the fact the two wires are
*twisted* inside the cable which reverses the phase of any hum signal
picked
up every inch or so along the line and hence cancels it out. Where
multiple
twisted pairs are used in the same cable the twisting reduces crosstalk
in
the same way as above.

A very twisted explanation.


** More pig ignorant drivel.


I suggest that anyone really interested in
the theory behind this statement read the book about cable written by
Steve Lampen of Belden. It's pretty easy to understand.


** Polly want another cracker ???


"Star Quad" cable uses four twisted wires instead of two to enhance
the
effect of the twisting and virtually eliminates induced hum problems
even
when used near to high current AC cabling.

This is correct.


** And does kinda prove that twisting of the cable is responsible for the
rejection of induced hum from external fields.


Knowing who I'm talking to,


** Mike - you have NO idea who you are talking to.


I feel compelled to make this statement.


** What a posturing ass you are Mike.


I've offered the correct answer,


** Not one thing about that post was correct.


explained to other readers why your
response isn't quite correct, and tried really hard not to make you
look like a jerk this time around. That's all I have to say on the
subject until someone changes it.



** LOL - how pathetic.




............ Phil