The difference between tube amplifiers and ordinary amplifiers

                         The difference between tube amplifiers and ordinary amplifiers

Advantages of Tube Amplifiers

1. The input dynamic range of the tube power amplifier is large, and the conversion rate is fast.

2. Most of the electronic tube power amplifiers use discrete components, manual wiring, and welding, which has low efficiency and high cost. This is especially evident in developed countries.

3. The open-loop index of the tube power amplifier is better than that of the transistor. It does not need to add deep negative feedback, and it can work stably without adding a phase compensation capacitor, so its dynamic index is better.

4. Generally speaking, the sound quality of the tube power amplifier is soft and pleasant. More specifically, the low-frequency sound of the tube power amplifier is soft and clear, and the high-frequency sound is delicate and clean. Expressing vocals is his forte.

5. The treble of the electronic tube machine is relatively smooth, with enough sense of air, and it has a kind of sound coloration that some people like. The soft and slightly fuzzy sound is very beautiful.

6. The tube amplifier mainly causes even-numbered second harmonics. This harmonic component is very pleasing, just like adding rich overtones and beautifying the sound.

Disadvantages of tube amplifiers

1. The service life of the electronic tube is low, and some technical indicators will drop significantly after one or two thousand hours of use.

2. 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.

3. Compared with transistor amplifiers, tube amplifiers have no advantages in terms of weight, efficiency, and lifespan.

4. 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.

5. Electronic tubes are afraid of vibration, so it is also very important to take anti-shock measures to avoid vibration as much as possible.

Prolonging the service life of power amplifiers using electronic tubes

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.

The performance index of the power amplifier

The main performance indicators of the power amplifier include output power, frequency response, distortion, signal-to-noise ratio, output impedance, damping coefficient, etc.

Output Power

Output power: the unit is W, because the measurement methods of each manufacturer are different, so there are some names with different names. Such as rated output power, maximum output power, music output power, peak music output power.

music power

Music power: refers to the instantaneous maximum output power of the power amplifier to the music signal under the condition that the output distortion does not exceed the specified value.

peak power

Peak power: refers to the maximum music power that the amplifier can output when the volume of the amplifier is turned to the maximum without distortion.

Rated output power

Rated output power: the average output power when the harmonic distortion is 10%. Also known as the maximum useful power. Generally speaking, the peak power is greater than the music power, and the music power is greater than the rated power. Generally speaking, the peak power is 5-8 times the rated power.

Frequency response

Frequency response: Indicates the frequency range of the power amplifier and the unevenness within the frequency range. The flatness of the frequency response curve is generally expressed in decibels (db). The frequency response of household HI-FI amplifiers is generally 20Hz--20KHZ plus or minus 1db. The wider the range, the better. The frequency response of some top-quality power amplifiers has reached 0--100KHZ.

Distortion

Distortion: The ideal power amplifier should amplify the input signal and restore it faithfully without any change. However, due to various reasons, compared with the input signal, the signal amplified by the power amplifier often produces different degrees of distortion, which is called distortion. Expressed as a percentage, the smaller the value, the better. The total distortion of the HI-FI power amplifier is between 0.03% and 0.05%. The distortion of the power amplifier includes harmonic distortion, intermodulation distortion, crossover distortion, clipping distortion, transient distortion, and transient intermodulation distortion.

SNR

Signal-to-noise ratio: refers to the ratio of the signal level to the various noise levels output by the power amplifier, expressed in db, the larger the value, the better. Generally, the signal-to-noise ratio of household HI-FI amplifiers is above 60db.

output impedance

Output impedance: The equivalent internal resistance presented to the speaker is called output impedance.

A good performance index of a power amplifier does not necessarily mean that it has a good tone, which must be recognized by beginners. This is also the pursuit of many enthusiasts.

Amplifier Features

1. Maximum output power As the power amplifier needs to provide enough power to the load, the working voltage and working current of the power amplifier tube are close to the limit value under the premise of safe operation, that is, the tube works at the limit value state.

2. Power conversion efficiency as high as possible. The output power of the power amplifier is obtained by converting the DC power of the DC power supply through the transistor. During the conversion, the power tube and the energy-consuming components in the circuit will consume power. Use P0 to represent the power obtained by the load. PE represents the total power provided by the DC power supply, and η represents the conversion efficiency, then η=(Po/PE)*100%, and the size of η reflects the utilization rate of the power supply. For example, the efficiency of an amplifier is η = 50%, which means that only half of the DC power provided by the power supply is converted into output power and transmitted to the load, and the other half is consumed inside the circuit. This part of the electric energy will increase the temperature of the tubes and components. will burn out the transistor. Attention should be paid to the heat dissipation of the power amplifier tube. In order to ensure the safe operation of the power tube, heat sinks are generally installed on the high-power tube. How to improve efficiency and reduce power consumption is an important issue for power amplifiers.

3. Allowable nonlinear distortion The power amplifier tube will inevitably produce nonlinear distortion when it works in a large signal state. The greater the output power of the same power amplifier tube, the more serious its nonlinear distortion. In different occasions, the requirements for the nonlinear distortion of the power amplifier are different. In the measurement system and electroacoustic equipment, the nonlinear distortion must be limited within the allowable range, and the nonlinear distortion is reduced to a secondary level in the drive motor or control relay. contradiction. In addition, only the graphic method can be used to analyze the power amplifier, and the micro-variation equivalent circuit method is no longer applicable. In order to obtain greater transmission power and efficiency, the power amplifier and the load must be matched. The traditional power amplifier and the load use transformer coupling. The advantages of this type of power amplifier are that it is easy to achieve impedance matching and high output power. Transformers are bulky, bulky, have poor frequency characteristics, and are not conducive to integration. It is rarely used in the power amplifiers produced now, and is gradually replaced by complementary symmetrical power amplifiers. The complementary symmetrical circuit saves the bulky transformer, and has the advantages of simple circuit structure, high efficiency, good frequency response, and easy integration. There are two forms of complementary symmetrical power amplifiers: one uses a single power supply and a large-capacity capacitor to couple with the load, which is called an OTL circuit; the other uses a dual power supply and requires a capacitor for direct coupling complementary symmetrical power amplifiers, called an 0CL circuit.

The difference between the electronic tube amplifier and the ordinary amplifier

1. The production materials are different. The former uses electron tubes and the latter uses semiconductor triodes.

2. Timbre: The former has a wide dynamic range and appears thick in tone. The dynamic range of different power amplifiers of the latter varies greatly, and some sounds appear thin.

3. Volume: the former is large and the latter is small.

4. Efficiency: The former has low efficiency and consumes electricity because the filament heats up and excites electrons. The latter has high efficiency and saves electricity.

5. Lifespan: The lifespan of the former electron tube is in thousands of hours, and the lifespan of the latter semiconductor device is tens of thousands.