Tube amplifier single tube output and push-pull output

Tube amplifiers are different from transistors (but they also have similarities). Strictly speaking, different tubes produce different sounds. Different circuit designs also have different changes in timbre. Among them, the push-pull amplifier circuit occupies the mainstream position in the market in terms of quantity. Its biggest feature is that it has higher efficiency and larger output power than single-ended amplifier circuits. Of course, the power supply utilization rate is also higher. For example, the common KT88, KT100, 6550, EL34, 6L6, etc. are more commonly used in the output stage of push-pull amplifier circuits. Since the push-pull amplifier circuit amplifies the positive and negative half-cycles of the signal respectively, in the primary circuit of the output transformer, it has a certain inhibitory effect on the noise, AC noise and other noise signals formed by the induction in the circuit, because the signal that has not been inverted cannot be coupled to the output terminal of the output transformer in the push-pull amplifier circuit. Therefore, the signal-to-noise ratio of this circuit is relatively good. At the same time, since there is no DC magnetization effect in the push-pull output transformer, the output transformer can be made by cross-stacking silicon steel sheets like the power transformer. This can reduce the size of the output transformer and reduce the cost compared to single-ended amplification. Due to the above-mentioned significant advantages, tube amplifier manufacturers are more willing to adopt it.

In the push-pull amplifier circuit, at least two output tubes are used to amplify the positive and negative half-cycles of the signal respectively, so an inverter circuit must be designed in the circuit to distribute the appropriate corresponding signals to the power output tubes, so as to meet the basic working conditions of the push-pull amplifier circuit. In the inverter circuit of the tube amplifier, there are transformers for inversion and tubes for inversion. For example, we often see the screen-shaded inversion and the long-tail inversion circuit, etc., but no matter which method is used for inversion, there are certain advantages and disadvantages. The design of the inverter circuit using a transformer is high in cost and cannot use large negative feedback to improve the sound quality, so few people use it. However, it is difficult for the electron tube inverter circuit to ensure the consistency of the positive and negative half-cycle division of the signal from low frequency to high frequency. These shortcomings of the inverter circuit have added an obstacle to the reproduction of sound quality in this link.

The power output circuit of single-ended amplification is lower in efficiency than that of push-pull amplification circuit, which makes the circuit much simpler than that of push-pull circuit, uses fewer components, and has a much lower failure rate than that of push-pull amplification circuit. Since the single-ended amplification circuit does not have the phase inversion circuit, the signal directly reaches the input stage of the final power amplifier tube, so there are no troubles of the phase inversion circuit. In the push-pull amplification circuit, the positive and negative half-cycle signals after phase inversion are sent to the "upper and lower" push-pull tubes for push-pull amplification at the gate level. Since at least two power tubes are used to coordinate the work, this requires that the consistent performance of each pair of power amplifier tubes must be good, so as to ensure that the waveform after push-pull amplification is complete and undistorted. In fact, the performance of each pair of push-pull tubes is difficult to ensure consistency from low frequency to high frequency. The so-called pairing is just pairing within a certain frequency range. If the push-pull amplifier circuit works in Class B state, there is also the risk of crossover distortion. In the single-ended amplifier circuit, because the positive and negative complete waveforms of the signal are amplified in a power amplifier tube machine, and because most single-tube amplifier circuits work in the Class A state, and the working point of the Class A amplifier circuit is the middle part of the straight part of the curve, there is no crossover distortion and other problems. Another comparison is that the reason why tube amplifiers sound better than transistors (relatively speaking) is that although the indicators of transistor machines are relatively high, the third harmonic distortion is larger than that of tube amplifiers, that is, the odd harmonics are relatively large, and the second harmonic distortion of tube amplifiers is larger than that of transistor machines, that is, the even harmonic vibration wave distortion is greater than that of transistor machines. However, from the perspective of hearing, the human ear is more sensitive to odd harmonic distortion, which gives people a harsh impression and is more annoying, but the even harmonic distortion gives people a soft feeling. The human ear is more receptive, just like the right amount of seasoning, which is also a major factor in the good sound of tube amplifiers.

As for the push-pull amplifier circuit and the single-ended amplifier circuit, compared with the two, the odd-order harmonic distortion of the single-ended amplifier output circuit is lower than that of the push-pull amplifier circuit. Most of the distortion it has is coupled-order harmonic distortion, so it sounds better.

Although the single-ended amplifier circuit is simple and easy to make, it has strict requirements on the arrangement of components between circuits. If the design is unreasonable, it is very easy to produce AC noise. The transformer with single-ended output is more complicated to make than the push-pull output transformer. This is because the primary of the output transformer of the single-ended amplifier circuit has DC high voltage passing through it, which will produce magnetic saturation. Although the push-pull output transformer also has DC high voltage passing through it, it can offset this phenomenon. Therefore, when the silicon steel sheet is put into use, a certain gap and air gap should be left. The size of the air gap should be adjusted according to the circuit requirements and the output power. Because the silicon steel has an air gap, the magnetic permeability of the entire output transformer is greatly reduced, so it is necessary to use a silicon steel sheet with a larger cross-sectional area to make it. The cost is greater than the volume and difficulty of making a push-pull output transformer with the same output power.

The single-ended output amplifier circuit is very popular and pursued by senior audiophiles because of its simple circuit, good sound quality and extremely low failure rate. Don't forget that many tubes in the world have become famous, all thanks to the charming sound produced by the design of the single-tube output circuit. For example, the WE300B, known as the "Prince Charming", and the King of Tubes 845, the noble sound quality they reproduce can only be exerted to its maximum potential when single-ended output is used.