Double your pleasure

I had promised in yesterday's post to get a bit more depth of understanding about balanced audio. We learned that balanced audio cables achieve their superior immunity to both radiated electro and magnetic noises by the use of a differential amplifier—a device that amplifies only differences, ignoring anything in common. Since radiated noises contaminate both conductors equally within a balanced cable, they contain noise common to both—noise rejected by a difference amplifier. But if the cure for noise is a difference amplifier, how do we make the musical signal we wish to amplify different? After all, we want to have the same signal without any type of distortion (differences), from our source. The answer turns out to be rather simple. We flip the signal's phase upside down. As one of our two conductor's signals move up in voltage, the second is moving down, in the opposite direction. Just like swapping the red and black wires feeding your loudspeaker. These signals are identical in content, 180˚ different in direction. The difference amp loves these signals and amplifies away, ignoring any noise signals common to the two conductors. But, it gets better. If you measure the distance between two out of phase waveforms, you get twice the voltage, or put another way, 6dB more level, for free. That is why balanced cables have more volume than single ended cables. We've only just covered the balanced input. Tomorrow I want to touch on the benefits of a balanced amplifier.