What is a professional home theater power amplifier?

                                What is a professional home theater power amplifier?

A professional home theater must be composed of products dedicated to home theater, and home theater power amplifier (commonly known as AV power amplifier) is the most important part of it.

What exactly is the AV amplifier doing?

The current AV power amplifier has become the information management center of the home theater, and even the center of the home streaming media, but the core work is mainly three categories - decoding, pre-stage signal amplification and post-stage current amplification.

Decoding means that the AV power amplifier receives the digital signal from the disc player or high-definition player through HDMI, encodes the core (core) audio, and decodes it into a multi-channel digital stream. Next, let's take a look at what is marked on the panel of a truly professional home theater power amplifier?

We see the DTS, AC3, AURO 3D, Dolby TrueHD, DTS HD, Dolby ATMOS and DTS X formats marked on the power amplifier. These are the sound formats that home theaters should support now.

What is the difference between these formats?

To put it simply, DTS and AC3 are products of the 5.1-channel era, and they were products more than ten years ago. When Dolby TrueHD and DTS HD appeared in 2007, they supported up to 7.1 channels, which belonged to products seven or eight years ago, but they are also mainstream now.

Seven or eight years ago, Dolby TrueHD and DTS HD needed HDMI to transmit sound, but coaxial was not supported. HDMI has long been popular in ordinary people, so everyone should be careful not to buy devices that support formats that are too old.

Now there are more and more movies in panoramic sound format (sound format with sky channel), the main formats are Dolby ATMOS and DTS X, the number of supported channels is more than 7.1, and the sky channel is added.

The latest home amplifiers have already supported a terrifying 32 channels, allowing users to hear clearer tracks and higher-density sounds.

To put it simply, professional home theater power amplifier products currently have at least Dolby TrueHD and DTS HD logos on the front panel, and the products launched this year will basically have Dolby ATMOS and DTS X logos.

Even if you don't understand power amplifier products, you should be able to know the formats supported by this product when you see these logos when purchasing.

For AV power amplifiers, this is the simplest. Because there is no support for these decoding formats, it means that you cannot fully play the latest sound formats. When purchasing, look at the logo on the front panel of the product to understand everything.

After decoding, the signal is pre-amplified

When the decoding is complete, the digital signal is converted to an analog signal, and then the signal is amplified. However, after the signal is amplified, it cannot be used directly connected to the speaker. At this time, it is necessary to use the post-stage amplification.

Amplifying section after power amplifier

To give a simple example, we still use motor vehicles as an example, which is easier to understand. If we compare the power amplifier part to the powertrain of a car, then the front part of the power amplifier is equivalent to the steering wheel part, which controls the direction of the entire vehicle. The sound style of a power amplifier is determined by the preamplifier. We all know that the engine part is the power source of a car, and the post-stage part of the power amplifier is responsible for boosting the power for the whole set of audio, which is the engine of the audio system.

An important indicator of the post-amplification part is the wattage, which is generally marked in RMS (continuous output power). This is like the displacement of a car engine. A 3.0 displacement engine must be more powerful than a 1.0 displacement engine. The same is true for the power amplifier. Under the same objective nominal conditions, the 300W (watt) nominal power will be stronger than the 100W output current, and the greater the power to push the speaker, the higher the undistorted sound pressure can be obtained. .

The technology of post-amplification in power amplifier

There is more than one way to amplify current, just like there is more than one technology for a car's engine. Let's take a look at what technologies can amplify the current to push up the speakers.

Class A

Class A, also known as Class A, is the simplest type of amplifier in which the transistors in the output stage are always on (not completely off) for any output waveform. These amplifiers have excellent linearity characteristics, but are very inefficient.

Class AB

The combination of class A and class B is class AB amplifier, which has higher efficiency than class A amplifier and lower distortion than class B amplifier. By biasing the two transistors in the circuit, the two transistors are turned on when the signal is close to zero (the non-linear operating point introduced by the class B amplifier); when the signal is large, the transistor switches to the class B working mode. It can be seen that when the signal is small, both transistors keep working effectively, similar to a class A amplifier; when the signal is large, corresponding to every half cycle of the waveform, only one transistor remains active, similar to a class B amplifier.

Class D

The output of the Class D amplifier is a switching waveform, and the switching frequency is much higher than the highest frequency of the audio signal that needs to be recovered. After low-pass filtering, the average value of the output waveform is consistent with the actual audio signal. Since the output stage transistors are fully on or off during operation and do not enter the linear operating region of the transistors (this is the reason why other types of amplifiers are inefficient), Class D amplifiers have extremely high efficiency (up to 90%, even higher). Modern Class D amplifiers can achieve the same level of fidelity as Class AB amplifiers.

Class H

To understand Class H amplifiers, the principle of Class H amplification is similar to that of Class AB, but the control circuit is more advanced. When a class H amplifier circuit works at a small signal level, the amplifier is powered by a lower power supply voltage. As the signal level increases, the amplifier automatically switches to the appropriate supply voltage. Class H amplifiers are more efficient than Class AB amplifiers because they are only powered at high voltage when necessary, compared to Class AB amplifiers which are always powered at high voltage. The design of Class H amplifiers is more complex than other amplifiers, and additional control circuits are required to predict and control the supply voltage.

Practical significance of various amplification technologies

Let me translate, the efficiency introduced above does not fully represent the final sound quality, but it will definitely be converted into heat. The lower the efficiency of the power amplifier, the higher the heat generation and the higher the power consumption; the higher the efficiency of the power amplifier, the smaller the heat generation and the lower the power consumption. Therefore, in audio, the actual power consumption of the nominal RMS power is not completely proportional.

Let's not talk about the advanced technology, but directly talk about the conclusion. Class A power amplifiers have small distortion but low efficiency, so they generate a lot of heat, and almost no manufacturers use them in advanced AV power amplifiers. Class AB and Class D are the mainstream of the market. Class H amplifiers are mainly used in independent post-stages.

Switches for home video and audio sources

The aforementioned is the traditional function of the home theater power amplifier, but now, almost all playback sources in a family (Blu-ray players, boxes, closed-circuit TV HD set-top boxes, game consoles, etc.) will be connected to the front end of the AV power amplifier, and then they Subsequent switching is directly controlled by the AV amplifier remote control board or the amplifier APP.

At the same time, AV power amplifiers above mid-range are equipped with multiple HDMI input interfaces and two HDMI outputs to handle switching between playback sources and display devices (TVs and projectors). The high-end AV power amplifier can also output multiple HDMI signals at the same time.

Types of AV amplifiers

Among the AV power amplifiers, there are also subdivision types. One is the most common form of integrated power amplifier, which has complete functions of decoding, pre-amplification and post-amplification. The second type of AV power amplifier products are composed of two parts: pre-amplifier and post-amplifier.

The upper part of the integrated power amplifier has many signal access interfaces, while the lower end is the terminal for connecting the speaker wires

The front and rear power amplifiers also have great differences in appearance. The front amplifier does not have an interface for connecting speaker wires. The rear amplifier does not have the HDMI interface that the front amplifier must have. The role is to amplify the current.

The finer the signal processing of the front stage, the better, and the greater the ability to amplify current for the latter stage, the better.

The greater the current, the greater the interference to the front-end signal, so when the requirements are extreme, the two can only be installed separately in two chassis. The simple explanation is this.