Power amplifier composed of STK4191

It is a 50w×2 tone-controlled power amplifier circuit composed of ST K4191Ⅱ . Input preamplifier and tone control stage: The input signal enters the preamplifier stage through the equal loudness compensation circuit. cl, island, R, etc. form an equal loudness compensation circuit. When the switch is moved upward, the loudness compensation component is connected in parallel with the volume potentiometer RPi, which can attenuate the mid-frequency component in the input signal at low volume, and relatively increase the high-frequency and low-frequency components. It does not suffer from the additional phase shift produced by the LC resonant coil. This loudness compensation circuit is simple and works well.     The input preamplifier circuit uses a dual operational amplifier TIJ082 with high conversion rate and high input impedance. Since the input stage of TL082 is a junction field effect transistor, its input impedance is very high, making the entire operational amplifier closer to the characteristics of an ideal operational amplifier and ensuring the dynamic characteristics of the amplifier. The gain of this stage Av=Chi2/R3. The feedback tone control circuit is composed     of dual op amp C4558 and RC network, in which (coat, pin) 4, fusion and are respectively bass, midrange and treble control potentiometers.