Zoomlion F-9500A preamplifier (a)

(a). The Zoomlion F-9500A circuit is derived from a power amplifier circuit produced by Japan's DENON company. It is designed and manufactured with all discrete components.
Each channel is composed of two independent amplifiers, with a tone control circuit inserted in the middle. The circuit principle is shown in Figure 3-2
. It has the following characteristics:
    (l) The best combination of excellent circuits and high-quality transistors o This circuit adopts a common-base
and common-emitter circuit with excellent performance. This circuit has the high input impedance of the common-emitter circuit and the wide frequency response and low distortion of the common-base circuit. Features. Local current negative feedback is used at all levels of the circuit
, so that the open-loop distortion and frequency response of the entire circuit reach high technical indicators. The left and right channels of the circuit
are composed of four circuits with the same structure, and use high-quality brand-name transistors to take a larger static operating current, so that
the output of the circuit can achieve low impedance and low distortion.
    (2) High-voltage power supply and large dynamic output D. The signal sources currently provided for high-fidelity audio
have a large which often causes clipping distortion in the output of the pre-stage. Therefore, the power supply voltage of the pre-stage is increased.
It is very necessary to solve this problem . This circuit uses a servo power supply composed of NE5532 and integrated positive and negative voltage regulators. Since the servo-type regulated
power supply is limited by the maximum output voltage of the three-terminal integrated voltage regulator, it can only reach ±24V according to conventional methods. However, this circuit
uses The floating power supply method of Sanjing voltage regulator not only retains the advantages of servo-type regulated power supply, but also increases the regulated voltage to
±42V. Such a high supply voltage effectively ensures the high dynamics of the preamplifier (see Figure 7-27).
    (3) The zero-point servo circuit maintains the stability of the circuit. The use of high-voltage power supply solves
the problem of matching the dynamic range and the signal source, but it also causes the circuit stability to deteriorate. To this end, this circuit uses a common-mode current-type zero-point servo circuit composed of an operational amplifier
to ensure both the static and dynamic characteristics of the amplifier.

    Figure 312(a) is of the circuit. The first half is the input part. In this part, Vrl, VT, VTs, and VT6 form a
symmetrical double differential input circuit. VT2, VT3, VT7, and VTs are their constant current source loads respectively. VTg and
VT12 are their Constant current sources oVTg, VTio and VTii.VT14 form a common base and common emitter voltage amplifier circuit.
VT16 and VTis form a push-pull output circuit, and VI~VD4 are the bias circuits of the output stage. Icl, VDs, VI soul
and VT13, VT14 form a common mode zero servo circuit .