Why is the Class A machine amp better than the Class B amp?
In static state, Class A power amplifiers and Class B power amplifiers are connected to purely resistive loads. The test may have similar indicators, and even the thermal noise class A is larger. However, in actual application, the real load (dynamic load) is connected to the speaker, and the impedance of the speaker is different at different frequencies. At this time, the comprehensive electroacoustic index will be inferior to the index of the pure resistive load, generating transients. distortion. Since the existence of negative feedback is fed back to the pre-stage, the key to this transient distortion is that the speaker system quality-off design is caused by effective, uninterrupted damping (control), and the higher the voltage rise rate of the signal, The more severe the distortion. For high fidelity, it is important that the mass inertia of the speaker system is effectively damped (controlled) by the amplifier.
The damping of Class B power amplifier can not effectively control the speaker. For any half-cycle, only one arm output is working, or push or pull, but it can't work at the same time, so its damping is unidirectional, that is, whether it is positive half or negative half, he only has The power that drives the working of the speaker is generated, and the pulling force that controls the back is not generated. To all-round damping, the driving current must be reversed in time, and the problem is here.
Taking the input square wave as an example, the input signal may be more complicated than the square wave when working. When the signal rises, the speaker can work according to the signal waveform, but when the signal suddenly stops, the speaker will not stop immediately due to the inertia of mass. At this time, its voice coil generates a back electromotive force, causing the A-arm output tube that is being turned on to be turned off and turned off, while the B-arm that was originally turned off is turned on, and this back-EMF is sent back to the previous stage by negative feedback. In this way, the B-arm output tube is energized to accelerate the conduction, and the special damping of the Class B power amplifier is completed together, because this process has to cross the zero point, and there is a moment of loss of the damping free oscillation. After this process is completed, the B-arm conduction is turned off, and the A-arm output tube, which was originally turned on and reversed, is restored to conduct, and the damping is restored only when the zero-crossing point loses damping. Therefore, the damping of the class B power amplifier is unidirectional at any moment, and the damping of the speaker is realized by the reciprocal zero-crossing phase commutation, and the distortion is generated almost at all times.
Class A power amplifiers are both positive and negative, and the damping coefficient is bidirectional. When the sudden high voltage rises, the voice coil moves according to the waveform. When the signal stops, the back EMF completes the path through the conductive B arm. It is damped, unable to generate free oscillation, and the back EMF can not be established. The omnidirectional damping of the Class A power amplifier forces the vibration of the Yang Dynasty to the generator to always vibrate according to the waveform of the signal. This is like a motorcycle that is pre-emptive. If you leave, stop and stop.
From the above analysis, we understand the reason why the sound quality of Class A power amplifiers is moving. More fresh and fun home theater information, please pay attention to home theater network (WeChat: cnhifi) http://, the country's most influential home theater audio player interactive media website.
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