Introduction To Audio Introduction-Analog Audio System

- Mar 25, 2020-

The current audio system is definitely inseparable from digital equipment and digital circuits. However, to briefly introduce the knowledge of audio, we must first clarify the most ancient human audio: analog equipment.


We know that motors and electric motors are actually a kind of thing. Rotating the motor can output current, and the motor supplying current will rotate, and the microphone and speaker are the same thing: the microphone picks up the sound wave to output the audio current signal, and the amplified audio Electric current can drive the horn to emit sound waves. The current sound system is composed of speakers (speakers) and earphones, and microphones and pickups for picking up signals. However, most people do not need microphones and pickups. They are basically digital sound sources now. Analog audio sources, cassette players have become antiques, radios are rare, but vinyl is a bit of a comeback.


The vibration picked up by the microphone and phono head is converted into audio current through magnetic and electrical structures. This is the "analog signal". The audio signal picked up by the microphone and cartridge is very weak and the current is very small. It must be amplified by "microphone amplifier, circuit" and "phono amplifier, circuit" to reach the "line signal" with a level of about 1v. In the current audio system, most of the equipment connected together are mostly "line signals" (identified as LINE in English). The radio head, TV set-top box, CD player, portable player, etc. are connected to the amplifier. Is the line signal. Many audio equipment will be provided with red and white signal lines, which transmit analog line signals.


Many people will use a mobile phone to connect to the stereo, and use a 3.5 to double lotus cable. Because the current of the amp circuit of the mobile phone is not large, it is basically similar to the line signal, so it is also possible. Attentive users will find that some portable players and portable decoding amp all-in-ones have a headphone port and a LO port (either with a lever or a system setting). Although the headphone port can actually be connected to the amplifier, the LO port provides It is the line level (LO is the abbreviation of Line Out), and the sound will be better.


The line signal can be boosted by the amplifier to drive the speaker; the headphone amplifier can be used to match headphones with various impedances. The power of most power amplifiers at normal output is more than ten watts, and the voltage is tens of volts. In traditional analog power amplifiers, the line signal is amplified by the pre-amplifier and the current amplifier stage is driven by the voltage amplifier. These are combined in a chassis is "merged amplifier" For more enthusiasts, the front and rear stages are used, that is, the pre-amplifier circuit is made into a separate device, called the "pre-stage", and the voltage and current amplification is the "post-stage". Note that there is no volume adjustment for the post amplifier. Because the components and output of digital equipment and portable equipment are now very powerful, in fact, mobile phones, players, and decoders can directly drive the rear stage, but pay attention to volume control when connecting. This is an off topic.


In fact, in the 21st century, if there is no vinyl resurgence, basically there will not be a complete set of pure analog systems. In real life, the sound waves picked up by the microphone are converted into digital signals for processing and recording. Even if it is a vinyl record, most of it is digitally recorded and then simulated.


Briefly introduce the pure analog system in the problem map: German clear vinyl record player, Danish high-end cartridge, American new style amp (the one with the earphones inserted below), and Mr. American speaker headphones. The new HPA-9's amps and preamps are single-ended, pure Class A, and have no negative feedback circuits. They are very old analog amplifier circuits; instead, the amps are op amp ICs, which are newer circuits, but It is also a pure analog circuit. This headphone system, coupled with the post-amplifier and speakers, is a pure analog system.