Take you to get started with tube amplifiers

                                        Take you to get started with tube amplifiers

Amplifier Comparison

Features and Structure

Transistor amplifiers work at low voltage and high current. The working voltage of the power amplifier stage is within tens of volts, and the current reaches several or tens of amps. In circuit design, direct-coupled (OCL, BTL, etc.) non-output transformer circuits are mostly used. The output power can be made very large, up to hundreds of watts, and the electrical performance is very high.

Tube amplifiers work under high voltage and low current conditions. The plate voltage of the final power amplifier tube can reach 400-500V or even thousands of volts, while the current flowing through the tube is only tens to hundreds of milliamperes. The input dynamic range is large and the conversion rate is fast.

Most tube amplifiers use discrete components, manual wiring, and welding, which have low efficiency and high cost. Crystal amplifiers mostly use a combination of transistors and integrated circuits, and widely use printed circuit boards, with high efficiency, stable welding quality, and high electrical performance indicators.

Power and Overload Resistance

The dynamic range of the high-fidelity amplifier should be 120dB, so as to meet the needs of the sound from slight to the peak of the climax, and the amplifier output does not clip, so the amplifier must have sufficient power reserve. If the dynamic range of the audio voltage is 3:1, since the power is proportional to the square of the voltage, the dynamic range of the power is 9:1. That is to say, a power amplifier with a power of 90W can only be turned on to 10W to achieve high-fidelity playback. Therefore, transistor amplifiers need to have a large power reserve so that overload distortion will not occur. Once overloaded, the distortion rises almost vertically, and in severe cases, the transistor can be damaged. Tube amplifiers are far more resistant to overload than transistor amplifiers. In the event of overload, the peak of the music signal will only become smoother than the normal waveform, and the sound will not deteriorate to any extent. For transistor amplifiers, clipping will occur at this time, and the sound quality will obviously deteriorate.

Open loop and transient

The open-loop index of the tube power amplifier is better than that of the transistor, and it can work stably without adding deep negative feedback and phase compensation capacitors, so its dynamic index is better than that of the transistor power amplifier. The open-loop gain of the transistor power amplifier (the gain before negative feedback) is often very large, and its excellent electroacoustic index is achieved by adding a large amount of negative feedback. In order to suppress parasitic oscillation, the transistor power amplifier Lag compensation is often used, which brings obvious transient intermodulation distortion and seriously affects the sound quality.

efficiency life cost

Tube amplifiers have no advantages over transistor amplifiers in terms of weight, efficiency, and lifespan. The life of the electronic tube is low, and some technical indicators will drop significantly after one or two thousand hours of use. Transistors and integrated circuits have much longer lifetimes. In addition, the tube amplifier consumes a lot of power and often works in Class A state, which further reduces the efficiency, but there are basically no factors harmful to sound quality such as transient intermodulation distortion, switching distortion, and crossover distortion. In terms of cost, for amplifiers of the same grade, tube power amplifiers are generally significantly higher than transistor power amplifiers. The main reason is that the cost of electron tubes and output transformers is high, and the production process of electron tube power amplifiers is not easy to automate, and the production efficiency is low. This is especially evident in developed countries.

amplifier speaker

The output internal resistance of transistor amplifiers is often much smaller than that of tube power amplifiers, and its damping coefficient fd is very large, which can reach more than 100-200, while the maximum fd of tube power amplifiers is only 10-20. Therefore, different types of power amplifiers should be matched with different speakers. When the speaker leaves the factory, fd should be marked so that people can choose it. If a speaker suitable for the damping coefficient of the tube amplifier is connected to the transistor amplifier, the resistance damping of the speaker will be too large, the transient response will be deteriorated, and the sound quality will be significantly reduced. Conversely, if a speaker suitable for a high damping coefficient is connected to a tube power amplifier, the sound quality will not be good due to under-damping. In short, the damping coefficient must be appropriate, that is, the amplifier and the speaker are required to be reasonably matched.

sound quality

Due to various reasons mentioned above and not mentioned, the sound quality of tube power amplifiers is obviously better than that of transistor power amplifiers. Transistor power amplifiers sound more high-frequency and less low-frequency. Transistor power amplifiers sound cold and hard, especially the low-frequency sound is not majestic enough, while the high-frequency sound is cold. Sometimes it sounds like there is crossover distortion in the high-frequency band. . These phenomena are more obvious when the frequency is increased and the volume is loud. However, the transistor power amplifier has large dynamics and fast speed, and is especially suitable for expressing more dynamic music. As for the performance of guns and thunder, of course it is better than the tube amplifier.

Generally speaking, the sound quality of the tube power amplifier is soft and pleasant. Specifically, the low frequency sound of the tube power amplifier is round and clear, and the high frequency sound is slender and clean like rain. Expressing vocals is its strength, and therefore more expensive.

Purchase considerations

Since the tube amplifier can share the world with the transistor amplifier, it must have advantages. The new technology used in transistor amplifiers seems to be significantly superior to tubes. Transistor amplifiers still have obvious advantages in the audio field, and because of their own shortcomings, they are trying to reduce and avoid these own shortcomings. For example, more and more applications of various field effect tubes, and the rapid increase of Class A amplification forms are all effective measures to fight against tube amplifiers.

Extended service life

In use, the electronic tube must have good ventilation and heat dissipation. Overheating of the temperature will inevitably shorten the life of the electronic tube, so it is necessary to keep the temperature of the electronic tube as low as possible. Electronic tubes are afraid of vibration, so it is also very important to take anti-shock measures to avoid vibration as much as possible. If these two points are achieved, the service life of the electron tube can be doubled at least. To this end, there should be proper space around the tube equipment, especially above it, so that there is good convection ventilation, and a fan can be used to help dissipate heat if possible.

When the cathode of the electron tube has not reached the required temperature and the high-voltage power supply is applied, its cathode will be damaged, which will also shorten the life of the electron tube. Therefore, if the electronic tube equipment has a preheating device, it must be used. For example, turn on the filament low-voltage power supply to preheat first, and then turn on the high-voltage power supply. If there is no preheating device, don't rush to connect the input signal, you can turn off the volume to the minimum, and wait for 20 to 30 minutes to warm up before using it. If the side-heating rectifier is used to supply the high voltage of the whole machine, it just provides a simple and effective high voltage delay. In addition, during normal use, do not switch the power on and off frequently.

Of course, if the electronic tube circuit is properly designed and misuse is avoided, the electronic tube will not "die young". It should be normal for the electronic tube to use thousands of listening hours. The most common mistakes in circuit design are that the potential difference between the tube filament and the cathode is too high, the voltage of the tube screen or grid grid is used to the maximum value, the voltage of the tube filament is too low or too high, and the improper installation position of the tube causes electrode overheating and high voltage. The power supply does not have a delay device, etc.