HI-FI amplifier 01 made by STK4040x1

STK4040xl is a preferred H. Fi power amplifier circuit has excellent electrical parameters: under
the conditions of Uc=±43.sv, RL-8fl, the rated output power is not less than 70W, the maximum harmonic distortion is only 0.008%, the typical value is 0.003%, 3dB
frequency response is 20Hz~20kHz. Such outstanding performance indicators are indeed rare in power amplifier circuits. As shown in Figure 3-46,
the constant current source circuit composed of internal equivalent circuit ports VT3, R 1 and VDl.VD2 serves as the common emitter impedance of the differential pair tubes VTl, VTZ, which
improves the amplification factor and common mode rejection ratio of the input stage. . The single-ended output signal of the differential stage goes directly to the base of VT8 and serves as
the input of the excitation stage. VT7 and VT8 together form an approximate common-emitter common-base circuit. At the same time, VT7 is an approximate common-base connection method and
has a large voltage gain itself, which is similar to that of VT8. The voltage gain combined to form the excitation stage is still high. More importantly, the base grounding of VT7
has isolation and shielding effects, making it difficult for the output signal of VT8 to be fed back to the input terminal, ensuring a more stable T operation of the excitation stage. To
further reduce distortion o VT6 and R2, VD1, VD2 form another constant current source circuit as the AC load of the excitation stage. It has higher resistance than ordinary
resistive loads (such as STK46:5' ST K4151 and many other integrated power amplifiers ). AC impedance, higher gain,
very stable and reliable operation 6 VT9. R8R9 and VD3 form a "multiplier constant voltage circuit", the constant voltage value is mainly
determined by the ratio of R9 and R8. Compared with the diode series circuit, the voltage stabilization effect is better, the dynamic internal resistance is smaller, the DC bias of the output stage is more
stable, the waveform of the excitation signal is more symmetrical, and the distortion is smaller. VT10.VT11 and VT12.VT13 form a fully symmetrical PN P-
NPN Darlington pair, making the output stage circuit more concise, symmetrical, linear, and low in distortion.