ABSTRACT
An audio signal can be transmitted either as a voltage or a current. The construction of the universe is such that almost always the voltage mode is more convenient; consider for a moment an output driving more than one input. Given a standard voltage-mode connection, it may be either unbalanced or balanced. The ultimate expression of balanced design is to use two identical paths through a piece of equipment so the signal is balanced all the way through. When the first sizeable audio systems were setup, telephone technology was adopted because it was the only one available. At the most basic level, there are four kinds of amplifier because there are two kinds of signals (voltage and current) and two types of port (input and output). The amplifiers are voltage amplifiers, transconductance amplifiers, current amplifiers and transimpedance amplifiers. Negative feedback is one of the most useful and omnipresent concepts in electronics.
