Balanced Line Driver And Receiver

14 EE MBALANCED LINEDRIVERAND RECEIVER These high-quality audio circuits are intended to overcome all the problems caused by noise picked up by long unbalanced signal lines between signal sources and amplifiers. Applications can be found in public address systems, studios, active loudspeakers, mixer desks and intercoms. The principle of balanced transmission of audio signals is relatively simple as shown in Fig. 1. The unbalanced signal from, for example, a preamplifier is ap- plied to an unbalanced-to-balanced con- verter, which drives two output lines. One of these carries the inverted, the other the non-inverted signal. Noise picked up by the cable between the line driver and the receiver is superimposed on both AF signals. The complementary phase AF signals are added in the line re- ceiver to give an unbalanced output signal, which is a copy of the signal fed to the line driver. In this process, noise is effectively eliminated because its phase is identical on both input lines...