c. Amplifier stages designed primarily to raise the power level of the signal-are known as
drivers and power amplifiers. Driver stages usually develop power in the order of milliwatts. Power
amplifiers develop watts or hundreds of milliwatts of power. This distinction based on power levels is
approximate at best. The power levels of drivers and power amplifiers depend on the equipment in
which they are used. A driver amplifier, as its name implies, is used to drive a succeeding stage. Thus,
the driver states delivers power to another driver stage or to a power amplifier. The power amplifier
builds the signal power to the necessary level to operate a device such as a speaker.
d. When microphones are discussed, you will find that the dynamic microphone is determined
to have the best fidelity. However, this microphone requires a preamplifier (preamp) due to its low
output voltage. Therefore, the audio console has built-in preamplifiers, which gives a sufficient signal
level to drive the program and monitor amplifiers. The preamps used in this unit, as seen in Figure 1-1
have external gain controls, which are located on the front of the console along with the other input
controls. These controls are actually labeled mixer. The program amplifier is also a multistage
amplifier which falls in the class of a driver. This amplifier also has a gain control, which is the master
control that enables the operator to adjust for the correct output level, as indicated on the VU meter.
Microphones will be discussed in detail in Lesson 2.
e. The control consoles are equipped with a number of multiple contact double throw lever
switches. These switches are used to perform a number of functions, some single and some multiple
(1) The tape input is an example of a single function. When the switch is in either the
program or monitor position, the only function is applying the tape signal to the respective amplifier.
The microphone selector switches use an additional set of contacts to control the muting relay which
removes the monitor speaker from the circuit. Also, the muting relay controls the on-the-air alert light.
(2) There are other switches, such as S1 which are used to select the various circuits to be
monitored. There is a switch, not shown in Figure 1-1 which enables the operator to select what is
wished to be monitored on the phone jack. It should be mentioned that Figure 1-1 is a block diagram of
a simple console; the more elaborate control consoles have many more switches.
f. The mixers consist primarily of the variable attenuators which are incorporated with the
various amplifiers. In the amplifier circuits, the mixers are nothing more than gain controls. In the tape
input, auxiliary input, and special effects, they serve as gain controls for the cue circuit. or those who
have not actually worked on a control console, there might be some question as to why they are termed
"mixers." This can best be explained by saying that as one input signal is used to replace another, one
signal is increased as the other is decreased. In this instance, the operator increases the gain on one
input mixer control while decreasing the gain for the other. If two inputs are to be used at the same
time, the two mixer controls are set