Gain is the increase in signal that is produced by an amplifier. Gain is the factor by which the output of a system exceeds the input. For amplifier circuits, gain may refer to the input and output power, current or voltage.
Feedback is used in controlling the gain of operational amplifiers.
The output of a operational amplifier is fed back into the amplifier via a 'feedback resistor'. if the resistance of the feedback resistor is high a small amount of the output voltage will get through and as a result the gain will be reduced slightly. However if the feedback resistance is low then a large amount of the output voltage will get through and decrease the gain significantly...
Remember gain is found by Av=Vout/Vin
Now if a variable resistor was inplace of the of the feed back resistor couldnt that correspond to the volume dial control of a stereo system whereby as resistance increases gain decreases therefore amplitude of the input signal decreases and as a result volume decreases. Similarly if the variable resistor's resistance decreases gain is increased and volume increases.....
Servomechanisms. These are feedback control systems in which one or more of the system signals reresent mechanical motion. They are usually used to control an output position mechanically in response to input signal changes. Servomechanisms may be regulators. The automatic pilot of an aeroplane is a servomechanism that uses operational amplifiers and feedback systems.
One question, would the stereo you mentioned be classified as an control system?
I found this in the Success one book answers
Discuss how a control system can be used to provide feedback in a circuit.
A control system is a system where a particular input gives rise to a particular output. Such a system is the operational amplifier and part of its output can be fed back to the input, through a control system consisting of a feedback resistor, in an inverting amplifier. The output is out of phase with the input and produces a negative or positive feedback. The control system that provides feedback produces a number of advantages if the feedback is negative. The advantages include predictable voltage generation, increased stability and reduction of distortion.
i dont fully understand that either but it sounds like its describing audio Amplifiers...i think you could just refer to the stereo i mentioned but the components that is, the operational amplifier is the audio amplifiers which in some stereo systems is a unit all by itself...common among Theatre systems