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The circuit features of XA8800MNE
Designed as a separate mono-channel structure,XA8800MNE is a full symmetrical current negative
feedback Class A amplifier. The main circuit theory and technical features are as following:
The input buffering amplifying stage adopts fast and wide-frequency amplifying circuit with cross coupling compensatory
structure. It could connect the push-pull amplifying dynatron as Darlington circuit and control base current at a low level,
ensuring the stabilization of the middle point voltage. Meanwhile, the adoption of transistor Constant Current Source as
load ensures the steady and liable work on the stage.
Darlington complex structure on the Voltage amplifying stage not only ensures enough voltage gain but also raises the
input impedance to reach excellent match between the different stages. Besides, the adoption of Cascode circuit offers a
good solution of the effect on the high frequency by the transistor junction capacitance. Thus the frequency width could
be raised, the output characteristic curve of the bipolar transistor could be improved, the distortion of this stage could be
reduced and high stabilization could be achieved.
On the current drive stage, it adopts high power FET to supply drive current for the end stage. The parallel output
transistors on the end stage could reduce the output impedance, increase the output power, and improve the load
capability with low resistor. The static working current of 6 pairs high power transistors on the end stage as parallel output
is about 300mA and each transistor works in the special linear area where current is higher. This could eliminate
crossover distortion and switch distortion efficiently and reduce the output impedance. Equipped with impedance
compensatory network including L, Rs, Rz and C on the output terminal, the load of this unit will be closer to pure resistor
and difficult to cause self-excitation. Meanwhile, it could afford bigger damp to enhance the controlling ability of this unit to
the loudspeaker.
In order to ensure the middle point voltage of this unit approximately to be zero, high quality operating amplifying
components, high frequency non-inductance resistor, silver isinglass capacitance and so on are put to good use to the
loop current servo feedback circuit.
As for the power supply for the complete unit, each channel adopts 600W high quality annular transformer while the other
parts adopts winding group on the power supply separately. Additionally the power supply for the power amplifying,
voltage amplifying and protecting circuit are separated: the power supply for the power amplifying part is equipped with
50A bridge rectifier and 60,000 microfarad Rubycon filtering capacitance and supplies power directly after commutating
and filtering; the power supply for the voltage amplifying adopts stable power supply with fast speed, low noisy, low
impedance and strong ability to avoid the “ripple” to avoid the modulating disturbance caused by fluctuation of the power
on the following stage and make the sound purer.
Additionally, this unit adds protection functions, including power-on delay concussion protection, zero point floating on
the output terminal, over current and over voltage of the power transistor protection. In order to avoid the noisy when
power-off, this circuit adds transient release circuit, power-on delay circuit and glittering indicating circuit for protection to
make this unit more intellective.
2.1 Product Features
Introduction
Chapter 2
XA8800MNE
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