An amplifier is an electronic device or electrical circuit that is used to boost (amplify) the power, voltage or current of an applied signal. It does this by taking energy from a power supply and controlling the output to match the input signal shape but with a largeramplitude. In this sense, an amplifier modulates the output of the power supply to make the output signal stronger than the input signal. An amplifier is effectively the opposite of an attenuator: while an amplifier provides gain, an attenuator provides loss.
AMplifiers
The four basic types of electronic amplifiers are voltage amplifiers, current amplifiers, transconductance amplifiers, and transresistance amplifiers.
A voltage-controlled amplifier lets you use a voltage to control the amount of another signal that is allowed through, consistantly over time. The higher the control voltage, the more signal is passed. At some voltage level, the entire signal is let through.
One of the most common uses of a VCA is envelope shaping. Think about when you hit a key on a piano; the amplitude starts out pretty loud, then over time it fades away. If you let go of the key then the volume drops off pretty quickly. You can use a VCA in conjunction with an envelope generator to achieve the same effect with notes on your synthesizer.
Types of amplifiers
