Where are the pre-amplifier, line amplifier and

by:Gisen     2020-06-18
Line amplifier The line amplifier is located inside the camera lens and can be adjusted by an optical mechanical aperture, which can be used to control the amount of light passing through the lens. Used to drive the audio or video signal amplifier of the transmission line. Power amplifier Power amplifier (English name: power amplifier), referred to as 'power amplifier', refers to an amplifier that can produce a maximum power output to drive a load (such as a speaker) under a given distortion rate. The power amplifier plays a pivotal role in 'organizing and coordinating' in the entire sound system. To some extent, it controls whether the whole system can provide good sound quality output. Where are the pre-amplifier, line amplifier and power amplifier applicable? Generally, the preamplifier first amplifies the input signal, such as the sound signal picked up by the microphone. Because it is relatively weak, it needs to be amplified to a certain level before it can go to other stages. Generally, the front has a higher voltage gain, which can amplify small signals to a standard level. The line amplifier is used for transmission. In order to reduce the transmission attenuation and enable the receiver to obtain a sufficiently strong signal, current amplification and pushing are required during transmission, and sometimes the voltage transmission needs to be increased. For example, constant voltage broadcasting uses this principle. The power amplifier mainly amplifies the current, so as to promote the sound of the low-impedance speaker. Of course, this example is based on the audio example. If it is a radio frequency signal, it will be slightly different from this method, but the meaning is similar. Like the power amplifier of the transmitter, the output is output to the antenna. Where are the pre-amplifier, line amplifier and power amplifier applicable? Single gain pre-stage It was mentioned at the beginning that the active amplifier has an amplifier circuit, and the general gain is 0 to ten times, while the passive front stage uses a volume potentiometer to attenuate, and its maximum output is equal to the input. There is also an active pre-stage, whose magnification is the same as that of the passive pre-stage. This is the single-gain pre-stage. The purpose of the single-gain preamp is to imagine the preamp as a buffer. In the English sense, Buffer has the function of isolation and buffering, that is, it does not change the signal strength of the source equipment, but it is received with high input impedance. , The signal is sent out with the concept of low impedance output, so the single gain front stage has the function of impedance conversion. There are not many single-gain preamps on the market, the main reason is that the gain is often insufficient, and the volume is still at its maximum. The Encore preamp launched by AC and DC studios of domestic manufacturers is the specific representative of the single-gain preamp. This pre-stage uses twin field effect transistors as input and ZTX bipolar transistors as output. It has the characteristics of high input impedance and low output impedance. Because there are very few parts, the S / N ratio is extremely high, and the volume is turned to the maximum , The ear is close to the tweeter, you can not hear any hiss, the sound is transparent and unblemished, the details are natural, and it is a very cheap single-gain preamp with excellent sound quality. Where are the pre-amplifier, line amplifier and power amplifier applicable? Is the simpler preamplifier circuit ideal? There is a lot of nonsense talking about preamps, so now is the time to clarify it. In an ideal environment for listening, the signal path design with fewer components will make the amplifier more completely real and perfect. This is simple is the best theory. Each additional component adds a bit of distortion, but the switch and volume control are the main criminals. However, many good recordings can be achieved. You need to do a little help in the previous tone to eliminate the sharp sounds during playback, which makes people sound tired. In this way, the situation arises: tone control provides precise and sensitive operation (in fact, many advanced level preamps have adopted a stepped resistance selector to replace the commonly used potentiometer). When you try to listen to an amplifier, you may wish to try it: only use the bass and treble knobs attached to it to control the volume, you will hear the corresponding difference. You should have relatively small changes. This phenomenon is not only happening when listening to rock music or pop music, or even listening to classical music. It is also often looking for a 'left-handed down' knob that decreases on the treble, acclimating the natural top of the recording. The volume control has tried its best to still make the amplifier output higher-making the woofer of the bookshelf speaker sound like a monster Cerwin Vega. Remember the additional distortion we mentioned? For the fun of the ball, turn the knob to the position where both the bass and treble are increased, the entire sound wave is improved, but the distortion has begun to blow the horn. Is it best to have both worlds together? Both the pre-amplifier with good volume control and direct sound source output, or a 'volume evacuation' button, can be bypassed when needed. But one thing to keep in mind, purists will even insist that the simpler the better. Output and input impedance matching of pre-amplifier and post-amplifier Both the pre-amplifier and the post-amplifier have output and input impedance specifications. The output impedance represents the internal resistance of the signal output of the pre- or post-amplifier. The unit is ohms. The lower the output impedance, the lower the internal resistance of the amplifier 3. The stronger the driving ability. Similarly, the input impedance is the impedance encountered by the pre-amplifier or the post-amplifier for signal input equipment, and the unit is also ohm. Higher input impedance means that the front-end equipment can be pushed more easily, and at the same time it can reduce the impact of load effects. Each amplifier has an input impedance and an output impedance. Generally speaking, the higher the input impedance Ri, the better, and the lower the output impedance Ro, the better. Impedance matching Ideally, the lower the output impedance of the front stage, the better, and the higher the input impedance of the rear stage amplifier, the better. This is to avoid the effects of load effects. Usually the input impedance of the post-amplifier is preferably more than ten times higher than the output impedance of the pre-amplifier, so that the strength of the pre-amplifier can be maximized. This is like the same reason that the locomotive pulls the carriage. The same carriage allows the locomotives of different horsepower to pull. The degree of ease is naturally different. The larger the horsepower (the lower the output impedance), the lighter the weight (the higher the input impedance). The car is naturally relaxed and happy.
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