50W power amplifier circuit composed of SAP15

This amplifier uses discrete components as the input stage and driver stage, and the output power reaches 50W.

The input stage is composed of VT1 and VT2, which are connected in a fully symmetrical form. It has a higher conversion rate than the general differential circuit, but its temperature stability is slightly inferior to the differential circuit. VT3 and VT4 act as the driving stage, amplifying the input stage signal and driving the power amplifier output stage composed of SAP15N/P.

The output stage adopts current drive mode. The negative feedback voltage is taken out from the sampling circuit in series with the speaker. The negative feedback voltage is added to the emitter of the input tube through resistors R5 and R9. The negative feedback voltage is proportional to the current flowing through the load.

The closed-loop voltage gain of this machine is GV=R12//RL/Rl3×(R5+R6)/R6≈42.