Comparison between tube amplifier and transistor amplifier

1. Tube
amplifiers and crystal amplifiers The comparison between tube amplifiers and crystal amplifiers only discusses the following two issues, namely, performance-price ratio and sound quality characteristics. For prices below RMB 1,000 (per unit), tube amplifiers cannot be produced at this price, and people cannot buy good tube amplifiers at this price. Although crystal amplifiers can be bought at this price, it is also difficult to buy very good products. In terms of sound quality, generally speaking, for amplifiers of the same price below RMB 30,000, the sound quality of tube amplifiers is usually better than that of crystal amplifiers; in the price range of RMB 30,000 to RMB 50,000, each has its own advantages; above RMB 50,000, crystal amplifiers generally have a relative advantage. At this time, crystal amplifiers are superior in all aspects, while tube amplifiers are superior in characteristics; for crystal amplifiers below RMB 50,000, generally speaking, except for the strength and speed of bass and the brightness of treble, they are better than tube amplifiers in sound quality, timbre, musicality, and listening tolerance. This is the common understanding and experience of many people.

2. About foreign tube amplifiers and domestic tube
amplifiers The start and history of foreign tube amplifiers are far ahead of ours in China. Besides, the tube amplifier products themselves have a certain artistry and a strong cultural background, which is reflected in the sound adjustment of the products, brand positioning, market strategy, appearance design, stable product quality, etc. It should be said that compared with some excellent foreign brands in these aspects, we have a gap with them to varying degrees; but after the efforts of recent years, this gap is narrowing. Compared with some foreign miscellaneous brands, some of our better products are definitely better than them, and we have a great advantage in price. For products of the same level, our prices are at least 1/2-1/5 or more lower than imported machines. Now our individual products are even better than some foreign famous brands in terms of sound quality and timbre at a lower price, which is no longer a strange thing. The direction of our domestic products is to establish brand awareness and enhance product quality and artistic standards.

3. About the shape (appearance) of tube
amplifiers. Most tube amplifiers have components such as tubes (tubes) and transformers exposed outside the casing, which is different from the traditional box-type amplifiers. Does a tube amplifier have to be made like this and cannot be made into a box-type? No, in fact, some tube amplifier products are now made into box-type amplifiers, so why are "naked" amplifiers still popular at home and abroad? This is related to the aesthetic concept of designers and users. The design of modern tube amplifiers is like industrial art design, which pays attention to ups and downs, color contrast, bright lines, and the expression of materials. The shape and processing of an exquisite tube amplifier are like a work of art. It is difficult for a box-type amplifier to embody these aspects, and the free space of a naked amplifier is much larger. Furthermore, after the tube amplifier is working, the filament of the electron tube is lit, giving people a sense of warmth, while in comparison, the box-type amplifier seems a little cold and lacks the "human touch" of the "bare machine", which is one of the reasons why the bare machine is more popular than the box-type amplifier. In addition, the bare machine can better reflect the characteristics of the tube amplifier. Although the bare machine is often not as convenient as the box-type amplifier in use and is more difficult to "serve", this leads to the coexistence of bare machines and box-type amplifiers. In terms of proportion, the amount of bare machines is greater than that of box-type amplifiers.

4. Technical indicators and standards of tube
amplifiers Frankly speaking, except for the static intermodulation distortion, which can be compared with crystal amplifiers, the other technical indicators of tube amplifiers are not as good as those of crystal amplifiers. In fact, the survival and development of tube amplifiers are not due to their technical indicators. If they were to pay attention to technical indicators, tube amplifiers would have no market long ago. In fact, electroacoustic technology is still very imperfect. The existing technical indicators can only explain the problem from one aspect, but cannot reflect the problem in essence. For example, the existing amplifier indicator measurements are all measured under the assumption that the load is a pure resistive (linear) load, while the actual load is a complex resistive (non-linear) load. For example, the measurement of the speaker is measured at a distance of 1M and a power of 1W, but the actual listening cannot be under the condition of 1M/1W. Therefore, such measurement indicators can only be used as a reference, and cannot be used as a standard for selecting amplifiers. It can be said that a product with good technical indicators may not sound good, while a product with good listening may only have average technical indicators (of course not very bad). To ensure the uniformity and consistency of a mass-produced electronic product, there must be a corresponding production standard (technical documents, production process documents and inspection documents). This is common in some more formal product production. However, these standards are only used to guide production and ensure the consistency and uniformity of product quality, and have no other meaning. The production standards of an enterprise are only useful for the specific products of the enterprise, but not for other enterprises, and are meaningless to the artistic quality of the product and the sound quality. To be precise, there is no standard to measure artworks. In reality, the higher the grade of the audio product, the less strict the production standard of the product.

5. Several technical issues about tube amplifiers
1) About single-ended and push-pull
In the final stage of tube amplifiers, there are push-pull working modes and single-ended working modes. Since it is easier to obtain high power by using push-pull mode, it is a very common circuit form. However, since the push-pull working mode is a superposition mode, there are some distortions objectively, and there are additions and subtractions in the push-pull superposition. In this addition and subtraction, some small things that were not originally there may be added, and some small things that were originally there may be subtracted. If a single tube is used in the final stage circuit to work in the single-ended Class A state, there will be no problems that cannot be avoided by the push-pull working mode. Therefore, in terms of listening, the single-ended is much better than the push-pull, especially in some tiny details. However, it is difficult for the single-ended to have a large power. For example, using the same type of tube, it can only achieve 10W in single-ended mode, while it is easy to achieve 30W in push-pull mode. It costs some price to increase the power. At the same time, in terms of technology, the single-ended machine is more difficult to handle than the push-pull machine. Therefore, single-ended circuits are often used in high-end machines, and push-pull circuits are used in popular machines.
2) The difference between different connection methods of the electron tube
in the final push-pull circuit The electron tubes used in the final push-pull circuit are often tetrodes and pentodes, so when using these tubes, there are three-stage tube connection, super-linear connection and standard connection. The difference between them is that the three-stage connection has the smallest distortion and the smallest output power; the standard connection has relatively larger distortion and the largest power; the super-linear connection is between the two. They have their own advantages in terms of listening, and the three-stage connection is relatively better. However, the three-stage connection is rarely used in industrial production because it has a loss on the life of the electron tube.
3) The influence of the driving circuit on the sound quality and tone
Generally speaking, the driving circuit and structure have a great effect on the orientation of the sound quality and tone. Different effects can be obtained through different driving circuits in terms of the low-frequency strength of the sound, the speed of the mid-high frequency and the density of the mid-frequency. There are many kinds of driving circuits. It is difficult to judge the quality of the product from the difference in driving circuits. What kind of circuit to choose is entirely a choice of the designer's tone orientation.
4) The influence of different types of electronic tubes on sound
The electronic tubes commonly used in the pre-stage driving circuit are ELF82, 6F1, EF86, 12AX7, 12AU7, 12AT7, 12BH7, 6DJ8, 6SN7, 6SL7, 6SJ7, 6N1, 6N2, 6N3, 6N6, etc. In principle, these tubes can produce good sound when used in tube amplifiers, but each model has its own characteristics. Designers will decide which model to use based on many factors. Generally speaking, ELF82, 6F1, EF86, 12AX7, 12AU7, 12AT7, 12BH7, 6DJ8, 6SN7, 6SL7, 6SJ7 are the most commonly used electronic tubes in foreign audio, and many manufacturers produce them, so they are interchangeable, so they are commonly used in exported machines or foreign machines. The commonly used electron tubes in the final stage circuit are: KT88, 6550, EL34, 6L6GC, 2A3, 300B, 211, 845. The first four types of electron tubes are side-heated tetrodes or pentodes, which are often used in push-pull circuits with higher power. The last four types of electron tubes are directly heated triodes, which are more commonly used in single-ended Class A (2A3 and 300B are also often used in push-pull circuits). Relatively speaking, the timbre of directly heated triodes is slightly better than that of side-heated quadrupoles and pentodes. However, although they are all triodes or tetrodes, the sound quality and timbre of each model have some differences and characteristics. Since tube amplifiers are plug-in devices, it is convenient to replace them directly, so changing tubes and playing with the machine has become a great pleasure in the use of tube amplifiers.
5) The influence of output transformer on timbre
The output transformer has a great influence on the indicators and listening experience of the whole machine. The bandwidth of excellent push-pull output transformer is 10Hz-100KHz, and there is no problem with distortion below 1%. It can be said that the transformer is no longer a key component that affects the indicators of tube amplifiers. However, the structure, process and material of the transformer still have a great influence on the sound of the whole machine. In fact, after the indicators of the transformer exceed a certain range, the higher the indicators are, the better they are. If the tube amplifier does not have an output transformer, such as OTL, its listening experience is different from that of traditional tube amplifiers. Therefore, the timbre of the tube amplifier is greatly related to the output transformer.
6) About integrated amplifiers and pre- and post-amplifiers
The integrated amplifier has the following characteristics: 1. When the signal source is at a certain input level, the output of the amplifier can reach full power; 2. The amplifier has multiple groups of signal source input options; 3. The amplifier has a level control function; 4. The left and right channels are integrated into one, and a high and low tone control device can also be provided. In the early days, the output level of the signal source was relatively low, generally around 0.2V, so the input level of the integrated amplifier had to be below 0.2V. However, the modern signal source has changed a lot. For example, CD players have been widely used, and the output level of modern signal sources is between 0.5-1V, so the input sensitivity requirements of modern amplifiers have also changed accordingly. Of course, no matter how it changes, as long as the first three requirements of the integrated amplifier are met, it is an integrated amplifier. The front and rear amplifiers are a combination of 1 source selection 2 level control 3 voltage amplification (the one with the third item is an active front stage and the one without the third item is a passive front stage). The pure rear stage is a combination of voltage amplification and power amplification (or two bodies) with one input on the left and one on the right, without level control and source selection (the input level is between 1-2V). This approach is more reasonable in structure, distribution, and materials. Therefore, the grade of the front and rear split amplifiers is higher than that of the integrated amplifiers, and the price may also be much higher.

6. About the service
life of tube amplifiers In principle, the service life of tube amplifiers is semi-permanent. Compared with crystal amplifiers, the relative service life of tube amplifiers is determined by the electron tubes. The theoretical service life of electron tubes is not very long, generally only thousands of hours, but it is also common for good electron tubes 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 life 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 found within 1-2 months after use, or during factory production. For tubes with relatively stable quality, it should not be a problem to use them for 2-3 years if they are used for 2-3 hours a day. Besides, tubes are not expensive or difficult to buy now, and with good after-sales service, the service life of tube amplifiers should not be a problem. Moreover, after the tubes are replaced, the tube amplifiers can be rejuvenated and just like new ones. In fact, many antique tube amplifiers are still sold at high prices in the market. Doesn't this illustrate the life of tube amplifiers from another perspective? Compared with crystal amplifiers, tube amplifiers have stronger overload capacity. Crystal amplifiers may be damaged in one thousandth of a second when encountering some faults, while tube amplifiers can be kept intact for several minutes.

VII. Precautions for using tube amplifiers
1. Before turning on the power, you should first connect the load (speaker). Do not send signals without connecting the load or short-circuit the load after turning on the power.
2. Do not use a power supply that is too high or too low. The power supply voltage should be within 5% of the specified voltage. If the mains voltage often exceeds this value, it is best to use an AC stabilized power supply.
3. The temperature of the tube amplifier is high when it is working. Pay attention to ventilation and heat dissipation when placing it.
4. Do not spill liquid on the electron tube when it is turned on or just turned off for a period of time (within 30 minutes).
Generally, pay attention to the above issues during use, and the tube amplifier can work reliably.