F-9300 power amplifier circuit

This power amplifier is a famous brand Hi-Fi power amplifier circuit , which is improved based on the products of Japan's DENON company
. The circuit is shown in Figure 2-43. The differences between it and the previous circuit are:
    the input stage uses a field effect transistor double differential circuit and adopts a common source and common emitter structure. Each stage is equipped with current negative feedback,
so that the entire circuit has even open-loop distortion and frequency response. reach higher targets. Common mode current zero servo circuit
    is used . It consists of operational amplifier r-cA741, 2SA733A, 2SC945, etc. When the potential at point D at the output end is out of control, after correction by the operational amplifier tJtA741, the output is fed into the common mode current control tubes 2SA733A and 2S045, so that the sum of the currents of the two tubes in the input stage differential circuit increases or decreases by the same amount, and finally Return the output end to zero. The difference between it and the general differential circuit is that the general differential servo principle is that the input signal increases the current at one end of the differential tube and decreases it at the other end. The total current remains unchanged. As a result, the differential tube works. The points are seriously asymmetric and can easily cause distortion in the output . The common mode current zero servo circuit does not have this shortcoming.     Removing the input stage low-pass filter t allows the input signal to maintain full-band input, which is beneficial to improving the frequency response of the circuit.     Increase the output current of the push stage. Divide the original voltage regulator tube into high-voltage and low-voltage parts. The low-voltage part has a value of <5v and is dedicated to the bias circuit. The high-voltage part is for the op amp. And reduce the base resistance of the push tube to increase the push current. At the same time, the temperature characteristics of the voltage regulator tube are used to compensate for the static operating point of the output tube.     In addition to the original zero-point protection, overload protection, overheating protection and switch shock protection, the power output tube also has a unique feature, namely static protection. When the above-mentioned protection occurs in the amplifier and the relay is released, the normally open contact of the relay is closed , the connection between the base and the output end of the push tube is connected, and the base of the push tube is short-circuited, so that the push tube and the output tube are in a Reliable cutoff status.