While playing the guitar many times there is a problem that unwanted noise can appear. Hence the need for a guitar noise gate. It happened specifically to a high-gain circuit is very sensitive to the surrounding radio signal.
The operational amplifiers built a few dozen transistors attached to direct amplification circuits with high voltage. Often referred to as “op-amp”. Their properties vary widely depending on the model. Balanced inputs and outputs are usually asymmetric, high input resistance and very low output resistance. One of them is typical linearity and low cut-off frequency.
According to their structure can be constructed of discrete components or integrated circuits. The operational amplifier are historical reasons for designation, since this type of circuit during WWII analog computer developed.