Preamplifiers

Preamplifiers are a group of devices that allow different types of sound sources, characterised by different electrical signal levels, to be connected to an electroacoustic system.
 

Adjusting impedance and signal level is the primary task of preamplifiers, but additional functionality is possible. The VOX function is the ability to mute signals from selected sources, influenced by the presence of a priority signal. In the simplest situation, the microphone signal of the person leading the discussion has higher priority than all other signals. When the chairman takes the floor, the microphone signals of the non-chairman are muted. Another example is the priority of an external signal over local signals in a public address system, e.g. in a school classroom. Regardless of the signal emitted by the local system, if an announcement is broadcast - for example from the headmaster's office, it has higher priority and will mute all other content.
 

A preamplifier also allows microphones to be connected and the level of their signals to be adjusted; single and multi-channel preamplifiers are encountered. Sometimes a preamplifier is both a mixer and a signal combiner. More advanced preamplifiers may be equipped with signal processors - analogue or digital - allowing for tone correction. Depending on the type of microphones used, preamps can be equipped with phantom-powered microphone inputs for condenser microphones. The preamplifiers can also be used for volume control when adjustment is not possible on the power amplifier. Adjustments can be made available in the form of buttons or knobs on the unit's panel. It is also possible to use an external potentiometer mounted in the installation box on the wall - in a convenient, accessible location for the operator - the preamplifier is then controlled by 0-10V.
The price of the preamplifier depends on the number of functions performed, the number of channels and the quality of the signal - noise, distortion and crosstalk.