Field effect transistor sound control amplifier circuit

It is a field effect transistor sound-controlled amplifier circuit. Since the input impedance of the transistor is low, only lkCZ, it requires a
certain signal current from the signal source to work. This is not the case with the field effect transistor. It is a voltage-controlled device. Within the normal operating range, the gate G
draws almost no current. Field effect transistors have extremely high input impedance (107n), low noise, large dynamic range and high amplification factor.
The voltage amplifier composed of it usually only needs one stage to meet the requirements. Therefore, it is widely used
in various electronic circuits.
    Field effect transistors are divided into two types: junction type and insulated gate type. This section mainly introduces junction type field effect transistors
.
    The picture shows a gate-voltage common-source amplifier circuit, similar to the
common-emitter amplifier circuit of the VT1 transistor in Figure 9-18 . Its working principle is analyzed as follows:
Similar to the transistor amplifier circuit, first of all, the two IN junctions of gate (G)-source (S) and gate (G)-drain (D) must always be kept
in a reverse biased state (for N-type tubes) ), the drain current changes as the gate current k
changes. If the drain resistance Rn is large, a large voltage change can be obtained, thereby
achieving electrical f amplification. Its gate bias resistor does not obtain a bias current for its gate, but
a gate bias voltage. For this reason, in the circuit, its bias resistor is usually an adjustable resistor RP, which facilitates the gate
bias voltage when obtaining a suitable static operating point during circuit adjustment .