The wonderful world of tube amps

                               The wonderful world of tube amps

Vacuum tube amplifiers, commonly known as "tube amps", are no stranger to audiophiles. As early as the 1920s and 1930s, vacuum tubes have been used in fever equipment, from amplifiers behind the scenes in theaters to radios in private homes. Indispensable. So today we enter the world of tube amps.

The tube amplifier plays an important role in the progress and rapid changes in audio equipment in the 1970s and 1980s. The advent of vacuum tubes promoted the development of the wireless electronics industry, and tube amplifiers dominated the audio field for more than 40 years. Later, they gradually declined due to the advent of transistors. Although electronic tubes have been basically eliminated in other fields, the development of tube amps has not stopped there.

In the late 1970s, tube amplifiers began to become active again. This trend became more and more popular in the 1980s. Especially after the emergence of high-quality sound sources, tube amplifiers can neutralize the digital sound produced by these sound sources to achieve better performance. The sense of music is also the most important reason why it has always been sought after by audiophiles.

So why do tube amplifiers have warmer, softer and sweeter sounds than transistor amplifiers? Let’s start with a preliminary understanding of the internal structure of the tube amp.

1. The composition and principle of the amplifier

The bile amplifier is mainly composed of electronic tubes (bile ducts), rectifier tubes and output transformers. The output transformer has a great influence on the indicators and sense of hearing of the whole machine. The bandwidth of an excellent push-pull output transformer is 10Hz-100KHz. Distortion below 1% is no problem at all. Regardless of the structure, process, and materials of the transformer, it still has a great impact on the sound of the entire machine. In fact, after the transformer's index exceeds a certain range, the higher the index, the better it is not necessarily. If the amplifier does not have an output transformer, such as OTL, its listening experience will be different from that of traditional amplifiers. Therefore, the timbre of a tube amplifier has a great relationship with the output transformer. The output transformer is an important part in evaluating the quality of a tube amplifier.

The timbre of the tube amplifier is mellow and warm. The main reason for this timbre is that the tube amplifier can produce rich even-order harmonics. When signals pass through nonlinear components, high-order harmonics, especially odd-order harmonics, will be generated. Odd harmonics are an important reason for the deterioration of sound quality. In contrast, the degree of nonlinearity of electron tubes is significantly smaller than that of transistors, so the odd harmonics generated when the signal passes through the electron tube are much less than when the signal passes through the transistor. Relatively speaking, the content of even harmonics is increased, forming A mellow tone. Since the amplification characteristic curve of the field effect tube is relatively flat, the power amplifier installed with the field effect tube has the charm of a tube amplifier.

Another reason for the tone of the tube amplifier is the use of inductive components in the signal path of the tube amplifier - the output transformer. Inductive components have two functions: first, they have a delay attenuation effect on high-frequency signals. The higher the signal frequency, the more obvious the delay attenuation effect. This kind of intermediate frequency signal is more prominent, resulting in a "dark and warm" tone. In addition, the frequency of odd harmonics in the signal is generally higher than even harmonics. After delay attenuation, the proportion of even harmonics is relatively increased. 2. Clip the peak signal in the signal, resulting in a soft tone.

In fact, in analog sound sources, the magnetic heads of the deck and the moving magnet cartridge of the LP record player are inductive components, so the timbres of these two sound sources are relatively warm and soft. The tube amplifier uses an output transformer, and the tone becomes warm and soft.

2. How the amplifier works

There are single-ended and push-pull working methods in the final stage of the tube amp. The push-pull method is easier to obtain high power, so it is a very common circuit form. However, because the push-pull working method is a superposition method, , so objectively there is some distortion, and there are additions and subtractions in push-pull superposition. In this addition and subtraction, some small things that were not originally there may be added, while at the same time some small things that were originally there are subtracted.

And if a single tube is used in the final circuit to work in a single-ended Class A state, there will be no problems that cannot be avoided by the push-pull working method. Therefore, the single-ended one sounds much better than the push-pull one, especially in some tiny details. However, it is difficult to achieve high power in single-ended mode. For example, using the same type of tube, it can only achieve 8W in single-ended mode, but it is easy to achieve 30W in push-pull mode. However, there are gains and losses. To make it bigger, you have to pay some price for the sense of hearing. At the same time, in terms of technology, single-ended machines are more difficult to handle than push-pull machines. Therefore, single-ended circuits are often used in high-end machines, and push-pull circuits are used in popular machines.

3. Differences between different connection methods of electron tubes in push-pull circuits

In the final push-pull circuit, the electron tubes are often tetrodes and pentodes, so the connection methods used are divided into three types: three-stage tube connection, super linear connection and standard connection.

Theoretically speaking, the difference between them is that the transistor connection has the smallest distortion and the smallest output power; the standard connection has relatively larger distortion and the highest power; the superlinear connection is somewhere in between. Each has its own merits in terms of listening experience. Relatively speaking, the triode connection method is slightly better. However, the triode connection method has a drawback, which is that it reduces the life of the electron tube, so it is rarely used in industrial production.

4. Life span of amplifier

Many people think that the service life of tube amps is much shorter than that of transistor amps, and this judgment is too subjective. In fact, it is not the case. In principle, the lifespan of tube amps is semi-permanent. Compared with crystal amps, tube amps have The life span of an electron tube is determined by the electron tube. The theoretical life span of an electron tube is not very long. Generally speaking, it is only a few thousand hours. However, it is also common for a good electron tube to be used for tens of thousands of hours. For example, the picture tube of a TV is a special electron tube. Of course, the lifespan of many audio tubes cannot be compared with that of picture tubes.

Generally speaking, audio tubes have transportation failure and early failure. Failure can be discovered within 1-2 months after use, or during factory production. For electronic tubes with relatively stable quality, it is not a big problem if used for 2-3 hours a day for 2-3 years. Even if the bile duct is broken , just need to change your courage again, and you can enjoy soft and beautiful music with new energy.

Compared with crystal amplifiers, tube amplifiers have a higher overload capacity. Crystal amplifiers may be damaged in a thousandth of a second when encountering some faults, while tube amplifiers can survive for several minutes without being damaged. Therefore, you don’t have to worry about the lifespan of your amplifier.

5. Maintenance and precautions for amplifiers

As mentioned just now, the lifespan of the tube amp is semi-permanent in principle, but the prerequisite is a good method of use. If any device does not have a good method of use, the lifespan will be greatly reduced. Let me introduce to you the tube amp. Some maintenance and precautions:

1. The load (speaker) should be connected before turning on the power. Do not send signals without connecting the load after turning on the power to avoid burning out the output transformer.

2. Do not use the power supply too high or too low. The power supply voltage should preferably be within 5% of the specified voltage. If the mains power often exceeds this voltage value, it is best to use an AC stabilized power supply.

3. The temperature of the amplifier is relatively high when it is working. Please pay attention to ventilation and heat dissipation when placing it.

4. Do not spill liquid on the electronic tube during startup or just after shutdown (within 30 minutes) to prevent the electronic tube from bursting.

As long as you pay attention to the above points during use, the amplifier can work stably.

6. Comparison of domestic and foreign amplifiers and speaker matching

The start of the amplifier in our country was much later than that in foreign countries, and the amplifier itself is also a representative product of the times that integrates culture, craftsmanship, and technology. Although there is a certain gap between domestically produced amplifiers and some famous foreign amplifiers, after years of continuous efforts, this gap is gradually narrowing. After years of accumulation, domestic excellent amplifiers are much better than foreign no-name amplifiers, and the price advantage makes domestic excellent amplifiers cost-effective and also increases their competitiveness.

The reason why famous foreign amplifiers are good is mainly reflected in the sound adjustment, brand positioning, market strategy, appearance design and product quality stability, etc. This is also the direction that domestic manufacturers need to learn and make breakthroughs. Here are a few well-known brands at home and abroad:

Domestic: Spark, OBO, Tianjin, Lici, Meixing, etc.

Overseas: audio note, Jadis, OCTAVE (octave), EAR YOSHINO, Audio Research (ARC), McIntosh (McIntosh), etc.

Frankly speaking, except for the static intermodulation distortion, the technical indicators of tube amps are not as good as those of crystal amps. And tube amps have not survived by relying solely on technical indicators. In this era, more audiophiles believe that it not only has the function of amplifying signals, but also is more like a work of art that combines craftsmanship and technology.