4036X1 series internal circuit

The internal circuit structure of the ST KXi series power amplifier circuit is basically the same, except that the power supply voltage differs depending on the output power
, as shown in Figure 2-88. Among them, 4046Xl and 4048Xi have high output power , and the final output tubes are connected in parallel to
form an 18-pin package, while the others are all 15-pin packages.
    The entire circuit consists of an input stage, a voltage amplifier stage and an output stage. VT3 and VT4 form a differential input stage, VTs is
their constant current source, Vrl and VT2 form a mirror constant current source load, which improves the symmetry and stability of the circuit and
increases the gain
    . VT6 and VT7 form a common emitter-common base Amplification circuit , in which VT6 is a common-emitter amplifier and VT7 is a common-base amplifier to
improve the linearity and frequency characteristics of VT6 and reduce the open-loop distortion of the voltage amplifier stage. This is also
one of the differences from the single-tube voltage amplification used in the early production STK power amplifier IC.
    The output stage consists of VTio ~ VT13 to form a two-stage Darlington emitter output. This is also one of the main differences from the quasi-complementary structure adopted by the early ST K power amplifier IC
. It improves the symmetry of the output stage and reduces the distortion of the final stage. o