An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the power of a signal (a time-varying voltage or current). It is a two-port electronic circuit that uses electric power from a power supply to increase the amplitude of a signal applied to its input terminals, producing a proportionally greater amplitude signal at its output. The amount of amplification provided by an amplifier is measured by its gain [增益]: the ratio of output voltage, current, or power to input. An amplifier is a circuit that has a power gain greater than one.
An amplifier can either be a separate piece of equipment or an electrical circuit contained within another device. Amplification is fundamental to modern electronics, and amplifiers are widely used in almost all electronic equipment. Amplifiers can be categorized in different ways. One is by the frequency of the electronic signal being amplified. For example, audio amplifiers amplify signals in the audio (sound) range of less than 20 kHz, RF [Radio Frequency] amplifiers amplify frequencies in the radio frequency range between 20 kHz and 300 GHz, and servo [伺服] amplifiers and instrumentation amplifiers may work with very low frequencies down to direct current. Amplifiers can also be categorized by their physical placement in the signal chain; a preamplifier may precede other signal processing stages, for example. The first practical electrical device which could amplify was the triode vacuum tube [电子三极管], invented in 1906 by Lee De Forest, which led to the first amplifiers around 1912. Today most amplifiers use transistors. 伺 sì: 观察，侦候；cì ～候
Negative feedback is a technique used in most modern amplifiers to improve bandwidth and distortion and control gain. In a negative feedback amplifier part of the output is fed back and added to the input in opposite phase, subtracting from the input. The main effect is to reduce the overall gain of the system. However, any unwanted signals introduced by the amplifier, such as distortion are also fed back. Since they are not part of the original input, they are added to the input in opposite phase, subtracting them from the input. In this way, negative feedback also reduces nonlinearity, distortion and other errors introduced by the amplifier. With negative feedback, distortion can typically be reduced to 0.001%. Noise, even crossover distortion [交越失真], can be practically eliminated.
现实中三级管的门限电压不能为零。输入电压较低时输出电压存在死区，输出电压与输入电压不存在线性关系，产生失真。比如输入从-0.1V到+0.1V，输出都是0.5V.
An audio power amplifier (or power amp) is an electronic amplifier that amplifies low-power electronic audio signals such as the signal from radio receiver or electric guitar pickup to a level that is high enough for driving loudspeakers or headphones.
Key design parameters for audio power amplifiers are frequency response, gain, noise, and distortion. These are interdependent; increasing gain often leads to undesirable increases in noise and distortion.
Tone Winner AD-7300+ $1,899 好评如潮
- Build quality and performance for the money can't be beat ,this is a audiophile grade amp , owning ad 5300 to the ad7300 ver 2 is a great addition to my home theater set up , Amir the best
- You truly cannot beat the value of this amp. In this price range there is nothing that can compete. Anyone experiencing a slight buzz/hiss when you put your ear up to you tweeter, look into a CMX-2 from Emotiva or something like it. Once I added the CMX-2 I hear zero noise from my tweeters, the amp is now dead silent. [The CMX-2 delivers clean power, free of high-frequency line noise and potentially audible DC offsets to your audio components. 加了这个后，功放在没有输入时万籁俱寂，没有交流的嗡嗡声，有输入时动若脱兔，没输入时静若处子]
六级/考研单词: electron, volt, amplify, equip, audio, physics, precede, vacuum, transistor, distort, subtract, eliminate, parameter, seldom, loud, amaze