A extremely high amount of gain introduces its own issue, namely noise. When you think about it, it makes sense: in the prior instance, our AVR was supposed to provide a large amount of output, but today it is required to produce a little amount of voltage. This creates noise on the power line, which other devices can detect as an error signal that something is wrong with their circuitry.
To fix this problem, reduce the gain so that less current is needed from the power source. The AVR will then need to work harder to provide the same amount of current, reducing the noise generated when other devices are using the bus.
To summarize, volume controls the loudness of a sound system's output and has no effect on quality, but gain allows you to raise the loudness inside an audio system, which completely influences the quality of the sound or recording. The more gain there is, the louder something will play back with all the distortion and noise that implies.
In an amplifier with a high input impedance, boosting the gain introduces a DC offset that affects the circuit's operating point (it changes the balance of the amplifier). Reading the above, it may appear that individuals seeking the extra output of an external amplifier are stuck in a cruel catch-22. The solution is to use an amplifier with low input bias current.
Increasing the gain of an amplifier will also increase its power consumption. This is because for every additional gain stage, there must be at least one more active device in the amplifier--typically a transistor or field effect transistor (FET)--and these devices consume power even when they are idle. A high-gain amplifier will also heat up more quickly due to the increased current through its terminals. Finally, increasing the gain of an amplifier will tend to cause its dynamic range to narrow; that is, the ratio between the largest and smallest signals that can be accepted by the amplifier tends to decrease.
The most common way of increasing the gain of an amplifier is to use a series of cascaded amplifiers. In this arrangement, each amplifier in the chain receives an input signal that is half as strong as the signal on the previous amplifier in the chain. Thus, if the first amplifier in the chain has an gain of 2, then the second amplifier will have an gain of 1/2, and so on.
As a result, negative feedback tends to limit the impacts of gain change, resulting in what is commonly referred to as "gain stability." Without feedback, a system has a gain of 80dB. If the negative feedback fraction is one-fiftyth of one percent, then the gain will be 70dB. If the fraction were one-tenth, then the gain would be 90dB.
Negative feedback reduces the influence of gain changes by forcing the output signal back into the input channel. This causes the overall effect of the amplifier to remain relatively stable despite large changes in its gain value. The amplifier's gain can be changed only by changing the relative strength of its various inputs; there is no way to increase or decrease the gain without affecting some other variable (such as power) that determines how much noise gets added to the circuit.
In general, amplifiers with positive feedback have unstable gains and amplifiers with negative feedback have stable gains. Gain stability is important for amplifiers used in audio systems because small variations in input level cause large variations in gain which could drive the sound signal below the threshold of pain or completely wash out low-level signals if it is not corrected. Stable amplification allows the artist to play at a comfortable volume without fear of hearing loss from overloading the amplifier.
The no-load voltage gain, Avnl, is computed by calculating or measuring the input and output voltages when no load is connected to the amplifier's output. Avnl is the output voltage to input voltage ratio. This is the maximum benefit you can earn. Loads attached to the amplifier's output reduce its voltage gain. The load impedance must be low enough that it does not affect the input signal.
In general, high-impedance loads decrease the output voltage while low-impedance loads do not influence the output voltage significantly. If an open circuit is used as a load, then there is no effect on the output voltage at all.
Loads are often described as "shunt" or "series". A shunt load is one connected directly across the amplifier's output, whereas a series load is one connected between the amplifier's output and ground.
Shunt loads can only reduce the output voltage; they cannot increase it. Series loads can either decrease or increase the output voltage depending on what type of load they are. A simple resistor will always decrease the output voltage while a capacitor will always increase it.
There are two types of amplifiers: single-stage and dual-stage. Single-stage amplifiers have one transistor for each output stage. Dual-stage amplifiers have two transistors per output stage.