Which sound quality is good for tube power amplifier

by:Gisen     2020-06-19
1. Working characteristics Circuit 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 amps or tens of amps. The circuit design mostly uses direct-coupled (OCL, BTL, etc.) non-output transformer circuits. The output power can be made very large, up to hundreds of watts, and the electrical performance is very high. The tube amplifier works under the condition of high voltage and low current. The screen voltage of the final power amplifier tube can reach 400-500V or even thousands of volts, and the current flowing through the electron tube is only tens of milliamperes to hundreds of milliamperes. The input dynamic range is large and the conversion rate is fast. Most of the tube amplifiers use discrete components, manual wiring, and welding, which have low efficiency and high cost. Most of the crystal amplifiers use a combination of transistors and integrated circuits, widely used printed circuit boards, high efficiency, stable welding quality, and high electrical performance indicators. 2. Power reserve and anti-overload capability The dynamic range of the high-fidelity amplifier should be 120dB, so as to meet the needs of the sound from the slight to the peak of the climax, the output of the amplifier is not clipped, so the amplifier must have sufficient power reserve. If the dynamic range of the audio voltage is 3: 1, the power dynamic range is 9: 1 because the power is proportional to the square of the voltage. In other words, the power amplifier with a power of 90W can only be turned on to 10W to achieve high-fidelity playback. Therefore, the transistor amplifier needs to have a large power reserve, so that there will be no overload distortion. Once overloaded, its distortion rises almost in a vertical line, which can damage the transistor in severe cases. Tube amplifiers are much more resistant to overload than transistor amplifiers. In the event of an overload, the peak of its music signal only becomes slippery than the normal waveform, and the sound cannot be deteriorated to any extent. For transistor amplifiers, clipping will occur at this time, and the sound quality will obviously deteriorate. 3. Open-loop indicators and transient characteristics The open-loop index of the tube amplifier is better than that of the transistor. It does not need to add deep negative feedback and can work stably without adding phase compensation capacitors, so its dynamic index is better than the transistor amplifier. The amount of open-loop gain of a transistor amplifier (the amount of gain before negative feedback is added) is often very large. Its excellent electroacoustic index is achieved by adding a large amount of negative feedback. In order to suppress parasitic oscillations, the transistor amplifier Lag compensation is often used, which brings obvious transient intermodulation distortion, which seriously affects the sound quality. 4. Efficiency, life and cost Tube amplifiers do not have advantages over transistor amplifiers in terms of weight, efficiency, and lifetime. The service life of the electronic tube is low, and some technical indicators have dropped significantly after using for one or two thousand hours. The lifetime of transistors and integrated circuits is much longer. In addition, the tube amplifier consumes high power and often works in the Class A state, which reduces the efficiency, but there is no harmful sound quality factors such as transient intermodulation distortion, switching distortion and crossover distortion. In terms of cost, for amplifiers of the same grade, the tube power amplifier is generally significantly higher than the transistor power amplifier. The main reason is the high cost of the electronic tube and output transformer, and the production process of the electronic tube power amplifier is not easy to automate and the production efficiency is low. This is particularly evident in developed countries. 5. Matching of amplifier and speaker Transistor amplifier output internal resistance is often much smaller than the tube amplifier, its damping coefficient fd is very large, can reach 100-200, and the maximum fd of the tube amplifier is only 10-20. Therefore, different types of amplifiers should be used with different speakers. The speaker should be marked with fd when leaving the factory, so that people can choose. If a speaker suitable for the damping coefficient of the tube amplifier is connected to the transistor amplifier, the resistance of the speaker is too large, the transient response will be deteriorated, and the sound quality will be significantly reduced. Conversely, if a speaker with a high damping coefficient is connected to the tube power amplifier, the sound quality will not be good due to underdamping. In short, the damping coefficient must be appropriate, that is, the amplifier and the speaker must be reasonably matched. 6. Sound quality For various reasons mentioned above and not mentioned, the sound quality of the tube power amplifier is obviously better than that of the transistor power amplifier. Transistor power amplifier sounds more high-frequency and mid-high frequency, but low frequency feels less. Transistor power amplifier sounds harder, especially the low-frequency sound is not soft enough, and the high-frequency sound is sharp and dry. There is crossover distortion. These phenomena become more pronounced when the frequency is increased and the volume is loud. However, the dynamics of the transistor amplifier is large and fast, and it is particularly suitable for expressing more dynamic music. As for the performance of guns and lightning, of course, it is better than the tube amplifier. The sound quality of the tube amplifier is soft and beautiful overall. Specifically speaking, the low frequency sound of the tube amplifier is soft and clear, and the high frequency sound is fine and clean. Expressing vocals is its strength, and therefore more expensive. Lifetime of tube power amplifier In use, the electron tube must have good ventilation and heat dissipation. The overheating of the temperature will inevitably shorten the life of the electron tube, so the electron tube should be kept as low as possible. The electronic tube is afraid of vibration, so it is also important to take anti-vibration measures to avoid vibration as much as possible. If these two points are achieved, the service life of the electron tube can be at least doubled. To this end, there should be a proper space around the tube equipment, especially above it, so as to have good convection ventilation, and if possible, a fan can help to dissipate heat. When the cathode of the electron tube has not reached the required temperature, that is, when the high-voltage power supply is added, its cathode will be damaged, and the life of the electron tube will also be shortened. Therefore, if the tube equipment has a preheating device, it must be used. For example, first turn on the filament low-voltage power supply to preheat, and then turn on the high-voltage power supply. If there is no preheating device, then don't rush to connect the input signal, you can turn off the volume to the minimum, wait for 20 to 30 minutes to turn on the machine and use it. If the bypass 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 frequently. Of course, if you design the tube circuit correctly and avoid misuse, you can prevent the tube from 'died early in life', and it should be normal for the tube to use thousands of listening hours. The most common errors in circuit design are the potential difference between the tube filament and the cathode is too high, the tube screen or curtain grid voltage is used to the maximum value, the tube filament voltage is too low or too high, and the improper installation position of the tube causes the electrode to overheat and high voltage The power supply has no delay device.
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