Many believe having no active preamp or linestage in the signal path is the “purest” appproach to home audio. However, the electrical parameters of the cables themselves can result in colorations. The balanced line standard Ralph often discusses provides benefits in reduction of common-mode noise and in cable drive abilities (due to noise cancellation) but must meet certain requirements, which would be difficult to meet when using components from different manufacturers, because of differences in impedance and because not all equipment that has balanced connectors is actually a differential balanced design. Some additional information for anyone who is curious.
A balanced transmission line consists of two conductors of the same type, each of which have equal impedances along their lengths and equal impedances to ground and to other circuits.
Circuits driving balanced lines must themselves be balanced to maintain the benefits of balance. This may be achieved by transformer coupling or by merely balancing the impedance in each conductor.
Compared to unbalanced lines, balanced lines reduce the amount of noise per distance, allowing a longer cable run to be practical. This is because electromagnetic interference will affect both signals the same way. Similarities between the two signals are automatically removed at the end of the transmission path when one signal is subtracted from the other.
Lines carrying symmetric signals (those with equal amplitudes but opposite polarities on each leg) are often incorrectly referred to as "balanced", but this is actually differential signaling. Balanced lines and differential signaling are often used together, but they are not the same thing. Differential signaling does not make a line balanced, nor does noise rejection in balanced cables require differential signaling.
