Resistor and capacitor + A, B, AB class power amplifier in RC coupling

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Resistor and capacitor + A, B, AB class power amplifier in RC coupling [Copy link]

1. Basic RC coupling amplifier circuit voltage regulator resistor: bypass capacitor is set to stabilize the bias voltage: block the AC on the voltage regulator resistor. If it is not added, it will affect the amplification factor and reduce the amplification factor. 2. Power amplification (using transformer) Class B is a basic complementary output stage circuit, which will produce crossover distortion. Solution: the previous preset fixed bias voltage slightly smaller than the threshold voltage. In addition, the Class B power amplifier does not cut off the back electromotive force generated by the speaker. The back electromotive force is even fed back to the previous amplifier circuit, which makes the internal resistance of the power input increase sharply, the damping coefficient deteriorates, or even loses. In this way, the listening experience will feel that the Class B power amplifier has poor control over the speaker, the sound is turbid, and the thrust is insufficient. However, the Class B power amplifier also has its advantages. First of all, its efficiency is very high, which can reach more than 75%, so a smaller power tube can be used to output a larger power. In addition, the push-pull circuit has an effect on suppressing even harmonics to reduce nonlinear distortion. Class AB Class B circuit plus a preset fixed bias voltage slightly smaller than the threshold voltage. Generally, the bias voltage is set higher than the bias voltage, so that the tube is always in the pass state, which is called high bias current class AB. Class A amplifier sets the forward bias at half of the maximum output power, so that the amplifier is in full load working state even when there is no signal input, so that the amplifier is turned on and has current output during the entire signal cycle. Class A amplifier makes the triode always work in the linear region, so Class A amplifier has almost no distortion, and the texture is particularly good in listening, especially when the signal is small, the whole sound is balanced, smooth, and rich in harmonics. But Class A amplifier also has disadvantages. First, the efficiency is low, generally not more than 25%, a large amount of electrical energy is converted into heat energy, and under the same power, the power supply is often much larger than Class AB. Moreover, due to the high working current of Class A amplifier, its working power supply voltage is much lower at the same output power, so its output peak voltage is limited, and its input voltage is also limited by the amplifier amplification factor of the output voltage. Therefore, the large dynamic performance of music is affected. Use transformer: converter coupling method. If a resistor is directly connected to the output terminal like RC coupling, but the current passing through the collector is large, a large power consumption will be generated on this resistor. In order to reduce power consumption, a converter coupling method is used. The load of this circuit is a speaker. The impedance of the speaker is mostly 8~16 ohms, and the resistance is small. In order to convert the resistance into the optimal load of the amplifier circuit, it is more appropriate to use a converter (transformer). The optimal load is the load value that obtains the maximum power. If the output impedance of the circuit is 8 or 16 ohms, then a speaker with the corresponding resistance value can be used. Usually the resistance of the speaker is much smaller than the output impedance of the circuit, so a converter is used to transform the impedance so that it can be matched. The relationship between the number of turns of the transformer and the voltage and current is used for transformation. The maximum output power can be obtained when the load resistance is equal to the output resistance of the amplifier. There is an impedance matching problem here, that is, when the output impedance of the amplifier is equal to the load impedance, the power applied to the load is the largest at this time. Instead of the smaller the load resistance, the greater the output power