The basic composition of the listening system

                                        The basic composition of the listening system

The basic composition of the listening system

First, let’s talk about the composition of a complete system. Simply put, it basically consists of the following three parts:

Audio source, power amplifier, speaker.

Sound source:

Regardless of digital or analog signal sources, it includes common mobile phones, CD players, DVD players, computers, various digital players, MIDI, vinyl record players, and even tape players, etc.

It can be roughly divided into two types: digital and analog. Tapes and vinyl records are carriers for recording analog signals, while the 120mm CD records that we commonly use and are common in the market are typical digital signal carriers.

The Cambridge CD player purchased more than ten years ago (Part 1)

If it is a digital audio source, because our speakers receive and play back analog signals, there must be a DAC (digital-to-analog conversion) process to convert digital signals into analog signals. And the conversion quality of this DAC can vary widely. Because we usually use computers a lot, and many people want to build their own Hi-Fi system, so take computers as an example. Nowadays, the motherboard is generally integrated with a sound card, and the sound card has a built-in DAC chip, so there will be a 3.5mm on the back of the motherboard. Analog plug (green is the socket we use when we use the stereo system), of course, many people think that the digital-to-analog conversion quality of the motherboard integrated sound card is relatively low (generally it is true), so many computers are equipped with optical fiber output ports (pictured below At the ring), through this port, the audio digital signal of the computer is output to the next part for digital-to-analog conversion, that is, it is handed over to the power amplifier for processing. At this time, the analog output port of the motherboard becomes a decoration and starts to be dusted.

In short, we think that the quality of the integrated sound card is really mediocre, and the manufacturer knows this, and in order to take care of as many users as possible, they gave us a variety of choices.

The red circle in the above picture is the "Magic Sound USB" interface on the Gigabyte motherboard. This port is specially used to connect us to the USB port of an external DAC. Of course, the DAC with the USB interface can work with any USB port, but this The circuit of the gold-plated "Magic Sound USB" port has been specially optimized, which is more suitable for the external DAC connected to the USB port than other USB ports.

You see, the DAC also comes in the form of an external USB port. At this point, the USB-DAC will perform high-quality digital-to-analog conversion and output an analog signal to the power amplifier.

2. Power amplifier:

The power amplifier is also what we often call the power amplifier. It generally refers to the audio system that amplifies the weak electrical signal from the signal source (in the professional audio system, it comes from the mixer) to drive the speaker (commonly known as the speaker, speaker) for sound playback. .

The power amplifier can receive analog signals and digital signals from the signal source, and there may be an independent DAC device between the power amplifier and the signal source, such as the USB-DAC we mentioned earlier.

For the transmission of analog signals, the common one is the RCA (commonly known as the lotus head) signal line, and the better one is the balanced line.

As shown in the picture below, a USB-DAC is connected to the RCA port (but here is the output to the speaker port, just for illustration, we can see that there is an optical fiber port at the bottom right, which can receive computers, PS4 game consoles, digital players and other equipment digital signal).

For the transmission of digital signals, audio coaxial audio interface (Coaxial), optical fiber interface (optical) and so on are commonly used.

Common power amplifiers also integrate digital-to-analog conversion modules, equipped with coaxial and optical fiber input ports. At this time, we can choose to use an external DAC or directly use the DAC of the power amplifier.

There are many ways to classify power amplifiers. According to the type of power amplifier tube, they can be divided into tube amplifiers (tube amplifiers) and stone amplifiers (transistor amplifiers). Transistor amplifiers are the product of modern technology, but due to the characteristics of electronic tubes, even very old technologies , but it is also more common in today's Hi-Fi systems.

In a two-channel Hi-Fi system, the main power amplifier parameters we need to consider are:

Output power: The unit of output power is watt (W) or kilowatt (kW). Due to the different measurement methods, there are some names with different names, such as rated output power, maximum output power (dynamic power), etc., which are often used by unscrupulous manufacturers to fool users. We mainly look at the rated power.

Frequency range (frequency range): The working frequency band that the power amplifier can amplify, generally 20-20kHz, generally there is a suffix after this data, such as -1/+1dB, which represents the error range of this frequency range, this value is about Smaller, indicating that the frequency response curve in the frequency range is flatter. Today's products generally have a frequency response range greater than the range that can be perceived by the human ear. For example, the Japanese Marantz PM8006 has a parameter of 5-100kHz (±3dB). Maybe some people can perceive ultrasonic and infrasonic waves.

Damping factor: The damping factor is an important technical parameter that directly affects the bass quality. The larger the caliber of the unit, the better the bass, but the larger the cone, the greater the mass, and the greater the inertia of its movement. This inertia makes it difficult for it to move synchronously with the audio signal, often showing a loud Turbidity, especially in the low frequency of 100-400Hz, is likely to cause sound coloration, making people sound vague and unnatural. When designing the power amplifier, engineers took some technical measures to improve the damping coefficient as much as possible, so that it can produce a resistance damping effect against the inertial motion of the speaker, so that the movement of the sound cone and the audio signal move synchronously, and the sound cone moves as much as possible in the driving signal. After the end, it quickly returns to zero position (that is, the center position). This blocking effect is the damping factor (Damp Factor), D=Rs/Ri, Rs=speaker impedance, Ri=amplifier output internal resistance, the larger D, the sound cone The better the synchronization with the signal, the purer and cleaner the bass and the better the reproduction. Still taking Marantz PM8006 as an example, its nominal damping coefficient is 100 (8Ω/ohm load, 40Hz～20kHz).

Signal-to-noise ratio: Signal-to-noise ratio (S/N or SNR or Hum and Noise): refers to the ratio of the signal voltage of the power amplifier to the noise floor voltage. The larger the value, the lower the noise of the power amplifier.

Output impedance: refers to the ratio of the voltage to the current of the input signal of the speaker, and the unit is Ω (ohm). Some power amplifiers are compatible with speakers with a certain impedance range. Mark a specific impedance, such as the most common impedance is 8Ω.

Among the above parameters, with the advancement of technology, parameters such as signal-to-noise ratio and frequency response range can be improved, but we need to focus on rated output power and output impedance.