Preamplifier and Servo amplifier

Preamplifier:

A preamplifier is an electronic component that is connected to a low-level signal source for providing suitable impedances and gain in an amplified signal. A singled ended preamplifier amplifies a single ended input signal by a gain factor such that the output signal is equal to the input signal multiplied by the gain factor. Differential preamplifiers are a particular type of preamplifier wherein the differential input signal comprises a positive rail component and a negative rail component. Preamplifier circuits are used in numerous applications. Typically, sound engineers use preamplifiers to amplify and process sound signals to achieve volume boosting while at the same time manipulating certain frequencies. High performance microphones require immediate preamplification of the signal generated by the microphone capsule. Microphones have low-level outputs, but microphone preamplifiers are generally designed to eliminate hum pick-up through the use of balanced-input circuitry, which electronically cancel any noise that is induced on both leads coming from the microphone. The ability of the output signal of a preamplifier circuit to faithfully reproduce the input signal is a function of many factors, including the bandwidth of the preamplifier, the frequency of the input signal, the impedance of the input system and transmission line impedance that provides the input signal, and the input impedance of the preamplifier.

Servo amplifier:

Servo amplifiers are used to drive servo motors in positioning devices. Multiple, servo-controlled DC motors which are reversible to provide a driving force in either of two rotational directions, are employed in various applications, such as magnetic disk device, for example. The motors are controlled by amplifier circuits which are pulse width modulated to provide precise motor control. In a magnetic disk device, the magnetic head is moved in two seek modes, a forward seek mode and a reverse seek mode, each corresponding to the direction of the motion of the magnetic head, i.e., corresponding to which side of the target track position the magnetic head exists when the target track position is commanded. In a servo system for a magnetic head in a magnetic disk device, a servo amplifier circuit having an amplifier portion and an inverting portion which inverts the polarity of the output of the amplifier, is used. Among the numerous general kinds of amplifiers, a common type is a straight DC amplifier with suitable phase-lead circuits to provide system damping, and output stages with the power capability to drive the motor in either direction. Pulse width modulated servo amplifiers are widely used in control systems for aircraft, marine, industrial and computer applications. Such amplifiers are protected against damage from accidental overload only by fuses or circuit breakers which must be replaced or reset before operation can be resumed after a malfunction. Many servo amplifiers are provided with resistors which generate large amounts of heat such as regenerative resistors which function to consume regenerative current. When installing a resistor which generates large amount of heat in a servo amplifier, the resistor is mounted at location separated from the internal components of the amplifier as well as at the rear of the amplifier in order to eliminate the effects of heat on the internal components of the amplifier.