Some misunderstandings about tube amplifiers

The tube power amplifier is the oldest power amplifier in the power amplifier family, and it is the big brother of the power amplifier. Before the 1960s, tube power amplifiers dominated the world. From the 1960s to the 1980s, it was the era of rapid development of transistor power amplifiers. By the mid-'80s, tube amps were rare. Since the end of the 1980s, tube power amplifiers have risen again, but they still cannot become mainstream power amplifiers.

Why does the tube power amplifier still have its place in today's increasingly advanced and perfect transistor power amplifier? The main reasons are: first, the tube power amplifier has its warm and sweet tone, and it is more durable and not harsh when replaying music; Sexual over-promotion. Let's talk about some misunderstandings about tube amplifiers

(1) The sound of the tube is warm and sweet

I often hear people say that if you want to get a soft and sweet reproduction tone, you must use a tube amplifier. He also deliberately called this sweet timbre "full of guts". In fact, the above statement is not accurate. The main reason for the "sweetness" of the tube amplifier is the output transformer. Therefore, the accurate statement of "full of guts" should be "full of T" (T is the prefix of English transformer)

Why the output transformer can make the replay tone of the tube power amplifier sweeter and warmer, the main reasons are: due to the hysteresis of the transformer iron core, the transient characteristics of the tube power amplifier have declined, making some subtle and explosive characteristics very Strong, not very harmonious details are eaten up and not fully reflected. Therefore, the tube power amplifier plays a sweetening and beautifying role when replaying some recording products that are originally too rich in details but not too sweet. However, when playing music products that are already somewhat sweet and warm, they will become fleshy and slow

Another reason for the sweet and warm tone of the tube amplifier is due to the frequency response characteristics of the output transformer. In ordinary transistor power amplifiers, since there is no restriction of the output transformer, their frequency response can be basically flat in the range of 20Hz to 20kHz. The frequency response of the high-grade transistor power amplifier can be made from DC to 1MHz

In ordinary tube power amplifiers, due to the constraints of the output transformer's own inductance, capacitance, material, material, structure, etc., it is difficult to make the frequency response curve flat. Even for high-end tube power amplifiers, after the test curve is flat, the degradation of the frequency response curve is relatively serious in actual half-power use. Of course, this is not to say that the frequency response curve of the tube power amplifier cannot be made straight. If you really make great efforts to make it straight, the production cost will become sky-high, and the gain outweighs the gain. Moreover, as long as there is an output transformer, the headroom of the low-frequency end of the tube power amplifier will not be large, and it will never reach the range of DC. Of course, whether this DC low end is of sufficient practical significance is another topic.

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The following is only an analysis of the frequency response curve of a tube power amplifier with a slight decrease in the ultra-low frequency and high frequency, and a slight increase in the mid-low frequency. Why are some product characteristics sweet and warm? This is determined by the sensory characteristics and habits of the human ear when listening to sound

When a person listens in the ultra-low frequency range, such as below 50Hz, especially around 20Hz (the double cello can emit a sound as low as 16Hz), the hearing ability of the ear gradually weakens, while the muscles and bones of the body But this frequency is clearly felt, and then the brain makes a comprehensive judgment. At this time, the bass you feel is loose and real, and the range of diffusion is large. This is like seeing a slowly starting car on the side of the road. You can not only feel the deep and powerful roar of the engine, but also really feel the wind and air pressure changes brought by this moving object. And this change in wind and air pressure is precisely the embodiment of ultra-low frequency and infrasound. Therefore, in a large monitor speaker with excellent low-frequency performance, the roar of cars and trains can be reproduced with pressure, but in a small speaker, a car can never "drive" into the room, which is the reason. After the low frequency below 50Hz begins to attenuate and deteriorate, the part that the human body feels is reduced, and the ear hears relatively more things. At this time, the sound you hear is concentrated and the taste is stronger, but the sound is tight, or it is distorted and unreal.

At the high frequency end of the frequency response, there is a similar feeling. The better the high-frequency characteristics of the sound system, the better and more lively the treble will be diffused. The high-frequency characteristics are not good enough, and it starts to attenuate above 16kHz, or it starts to attenuate after barely reaching 20kHz, which will still reduce the high-frequency overtones of replayed music. At first glance, the high-pitched metal percussion seems to have grown in loudness and the instrumentation has grown in size. But that's because the details are missing, and the sound is a little dead

Some early speaker manufacturers used iron-core inductance coils in their speaker frequency dividers. Its original starting point is mainly to reduce the size of the inductance coil. As a result, after using it, the phenomenon of sweetening the replay tone also occurs. From a lot of scientific research and practice in various fields of audio, professionals have long understood that the tube power amplifier is not sweet on the tube itself, but on the iron core of the output transformer, and on the frequency response characteristics of the output transformer. a basic truth

(2) The tube power amplifier has high efficiency and large power reserve

This is another misunderstanding about tube power amplifiers

Most people think that a 10W tube power amplifier can produce the driving effect of a 30W or even a 50W transistor power amplifier. Therefore, some people say that the efficiency of the tube power amplifier is high. In fact, this is a very vague concept

Because when evaluating the drive capability of a power amplifier, two criteria are very important. One is the voltage amplification of the power amplifier itself, and the other is the power reserve and load capacity of the power amplifier. People who say that the tube power amplifier has high efficiency actually mistook the voltage amplification of the tube power amplifier as a wrong view of the efficiency of the power amplifier. Because in household audio equipment, the average power used is generally between several watts and tens of watts. When listening to music with a relatively average volume and low fluctuations, 10W of power can produce a fairly loud volume. Therefore, some people mistakenly think that the 10W of the tube power amplifier is far greater than the 10W of the transistor power amplifier.

Due to the use of the output transformer of the tube power amplifier, under the action of the iron core hysteresis, the distortion of the tube power amplifier is soft distortion, which is a kind of distortion that is not easy to detect but can be detected. Therefore, the power reserve of the tube power amplifier is relatively small and it is easy to cause a misunderstanding.

Since the transistor power amplifier does not have a transformer, which is the gateway for softening distortion, when the distortion degree of the transistor power amplifier is the same as that of the tube power amplifier, the degradation of the replay tone is much more obvious, so the power reserve of the transistor power amplifier is relatively larger than that of the tube power amplifier, and it is can create false impressions of inefficiency

In fact, whether it is a tube power amplifier or a transistor power amplifier, their true efficiency only depends on the ratio of their own energy consumption to output power. In the case of the same power consumption, whoever has a higher output power will have a higher efficiency. In this regard, transistor power amplifiers often have the upper hand

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(3) The matching characteristics of the tube power amplifier are good

This is another misunderstanding about tube power amplifiers

Many people said with emotion after looking at the output terminals of the tube power amplifier: "The output matching of the tube power amplifier is so detailed, there are often multiple sets of output terminals of 4Ω, 6Ω and 8Ω". In fact, the understanding of this exclamation is just the opposite. The reason why the tube power amplifier has multiple sets of outputs just shows that only one set of outputs cannot adapt to speakers with various impedances. For transistor power amplifiers, there is no such concern. In other words, it is easier to operate with a transistor power amplifier to drive the speaker

(4) The continued popularity of tube amplifiers is a matter of musical aesthetics

Music aesthetics is something that is often heard but difficult to define accurately. This is determined by the personality of art. Different people, people with different qualities, have considerable differences in musical aesthetics

For example, the three well-known tenors of Domingo, Pavarotti and Carreras have different timbres and singing characteristics. Therefore, their respective admirers were born. Since the three tenors are all excellent, but the differences between them are considerable, they represent different beauties in the field of tenors. This will never be unified

Another example is that Mr. Zhou Xinfang, the late Peking Opera master in our country, had a special kind of hoarse voice, so he cultivated a large number of opera fans exclusively for him.

The same is true for the reproduction tone of the tube amplifier. Although it is too sweet and warm, there are many people who like this tone. Coupled with the fact that tube power amplifiers have been around for a long time, many middle-aged and elderly people are used to this kind of sound when they are young. Revisiting this sound after decades, it is easy to remind people of the past and the young age. strong nostalgic color

In short, there is nothing wrong with people's timbre orientation. As long as it is good art, you can enjoy any kind of art. Just don't confuse the concepts of technology and art, because after all, in the most demanding audio field, tube power amplifiers have long been no longer used. There are also many people who like transistor power amplifiers to be cool. For example, young people nowadays like music styles such as rock and jazz. Naturally, they need cool wind equipment. Equipment with a good foundation does not need too much modulation, such as Lannge’s many These power amplifiers are all transistor power amplifiers, and their basic timbre is established. However, in the product circuit structure, many elements have been added to make Lannge's power amplifiers more stable and safe.