[aCuria]

My current understanding of balanced connections:
 
In a regular balanced audio connection, we have the following:
 
R  Channel: +R, -R, Rgnd
L Channel:   +L, -L, Lgnd
 
The ground the ground wire surrounds the signal wires and is used as a shield against some interference. Unlike an unbalanced setup, the ground wire does not carry a signal.
 
Lets consider the right channel, 2 signals are sent out of phase from each other, say from the preamp to the power amp, we call this a differential signal:
 
+R and -R
 
Along the way from the preamp to the power amp, both signals pick up some form of noise because of electromagnetic induction. The noise is in phase (identical in both signals), so we have
 
(+R + N) and (-R + N)
 
In the power amp, the signals are passed into a differential amplifier, which is a type of electronic amplifier that amplifies the difference between two input voltages but suppresses any voltage common to the two inputs.
 
(+R + N) - (-R + N)
= +R + N +R - N
= 2R
 
In this way, the differential amplifier is able to remove the noise from a signal.
 
What I don't understand
1) For balanced headphones, how does the balanced connection reject noise without a differential amplifier?
2) Why is there no ground built into balanced headphone cables?

 

[Roseval]

The answer is very simple.
Normally headpones have a 3 wire connection: L/R + common ground.
Today you can get them with a 4 wire connection just like you connect a pair of speakers to an amp.
Sennheiser calls this a symmetrical connection.
 
For some reason or other each and everybody in the headphone world calls it balanced.
Of course there is nothing balanced about this wiring schema.

 

[Mediahound]

There's some misinformation here. This article may help:
 
http://www.headphone.com/pages/balanced-headphones-guide

 

[castleofargh]

the problem is how in audio forums we tend to call balanced anything with more than 3 pins, whatever the actual design of the amp.

 

[Mediahound]

  the problem is how in audio forums we tend to call balanced anything with more than 3 pins, whatever the actual design of the amp.

Yep, this is something that sorta pissed me off about the Centrance Hi-Fi M8. Centrance never really mentioned that the amp was not actually balanced, just stating it had a fully balanced output. Turns out, it's a single-end amp and the 4 pin XLR output is there only for convenience. 

 

[Koolpep]

 
Yep, this is something that sorta pissed me off about the Centrance Hi-Fi M8. Centrance never really mentioned that the amp was not actually balanced, just stating it had a fully balanced output. Turns out, it's a single-end amp and the 4 pin XLR output is there only for convenience. 

contrary to their Gloveaudio A1 which is actually a true balanced DAC and Amp....