Microphone Technology 667practice to employ balanced circuits for both input and output in those instances where
the signal levels are low and susceptible to electrical noise or cross talk interference.
Indeed, many systems maintain balanced linking circuits throughout regardless of the
signal levels.
If one excludes miniature microphones that constitute a special case, the de facto standard
microphone connector is the XLR-3. The male and female versions of this connector are
illustrated in Figure 22.14.
Through the years the assignment of functions to the various pins has varied. The present
standard assignment of the male connector at the microphone has pin 1 connected to
the microphone case. Pin 2 is connected to the microphone circuitry such that a positive
pressure on the microphone diaphragm drives the voltage at pin 2 in the positive sense.
Pin 3 is connected to the microphone circuitry such that a positive pressure on the
microphone diaphragm drives the voltage at pin 3 in the negative sense. Pins 2 and 3 are
balanced with respect to pin 1.
Quality microphone cables consist of a twisted pair of insulated, color-coded inner
conductors formed from stranded copper wire covered by a tightly woven copper braided
shield with the combination encased in an insulating jacket. The conductors may be
tinned, although this is not always the case. The cable is fi tted with a female connector at
one end and a male connector at the other. The connector pin assignments in this instance
have pin 1 connected to the shield with the option of also strapping the connector shell to
pin 1. Pin 2 is connected to the positive signal conductor while pin 3 is connected to the
negative signal conductor. Microphone cable is also often used as the connecting cable in
link circuits between mixers, subsequent signal processing units, and power amplifi ers.
2 13Male1 23FemaleXLR-3 connectors
Figure 22.14 : Pin arrangements of XLR-3 connectors.