Measures to improve listening effect of tube amplifier

Even if there are astronomical test data, it may not necessarily have an ideal listening effect. This phenomenon is sufficient to prove that the test items and test levels of audio amplifiers are far from the current requirements. In terms of the current brand amps with high prices, there are not a few people with the following sound effect defects.

1. The soft sound is hoarse, and there is no detail expression at normal volume, such as many high-power amplifiers of KT88.

One of the reasons for the above-mentioned shortcomings is that there are serious low-level failure phenomena in the power amplifier, involving various capacitors of signal coupling, bypass, and decoupling. The traditional lead-out form by pressure contact is one of the causes of low-level failure. This type of capacitor is completely normal when the signal voltage is large. Once the signal voltage is lower than 2V ~, the lead-out leads to similar open-circuit consequences. It is slightly larger and can be recovered in white lines. As a result, the output signal of the amplifier forms heart-shaped distortion, especially when the volume is turned off. Even if the volume is sufficient, the music will be hoarse during the low ebb period, and there will be intermittent phenomena in severe cases. The low-pitched area is hoarse and discontinuous, so that the normal music playback details are completely lost, and even some low-pressure orchestrators are completely absent. This phenomenon is a common problem of pressure-induced capacitors. Regardless of coupling and decoupling bypass capacitors, and electrolytic capacitors and film capacitors, almost all have the characteristics of low-level failure. The culprit is caused by the tablet type.

There have been enthusiasts who have suggested that tightening the above-mentioned capacitors with string wires can improve the sound quality. It is obvious that the reduction of contact pressure caused by crimping is the main reason.

The countermeasure is to use famous brand capacitors. Or carefully observe the structure of the two ends of the film capacitor, choose the Robo type assembly (or winding) capacitor, and the film capacitor passes through the plastic film. It can be seen that the polar plates on both ends are longer than the insulating layer. The end face of the pole piece protruding from the insulating layer is extracted by ultrasonic welding. The capacitors produced by this new process have no distributed inductance components (such as common speaker crossover capacitors) even when they are wound, and there is no low-level failure. Whether it is a fever or not, as long as you choose a capacitor of this structure, you can greatly improve the sound quality.

2. Hairy hair, accompanied by intermittent noise

Regardless of the volume, the sound is hairy, and there is no roundness in string music and vocals. It sounds like the feeling of a few pig hairs mixed in the delicate delicacies, which is extremely disappointing. Unlike the general noise, the noise disappears during the intermittent period when the music stops, and the static noise output of the power amplifier is detected. Less than 0.6mV is detected at the 8Ω terminal.

The above-mentioned adverse effects are often caused by low-quality signal cable connectors, especially RCA plug sockets. Cheap products are basically made of iron, and the outer layer is copper-plated, zinc, silver, etc., and there are titanium-plated products and gold-plated products. Fish head mixed beads. The above connectors are oxidized by the moist air when they cooperate with the base, causing electrochemical corrosion. The signal transmission is blocked. The hand-held plug was turned several times in the socket, and it improved slightly in a short time. But it will be the same as usual in a week. Although it can be solved by changing to a better signal cable, it should be noted that the power amplifier input socket must be replaced at the same time. Otherwise, the galvanized socket on the base and the coating on the high-grade signal cable plug will accelerate the electrochemical corrosion rate in a humid environment. Wire plug plating.

Another culprit for the formation of sound hair is the carbon film potentiometer for volume and balance adjustment. In addition to the friction noise generated by the sliding contacts of the potentiometer, the carbon film lead-out method of riveting and bonding can not always keep the contact excellent. The pressure contact follows It is difficult to avoid noise caused by poor contact after long-term use. When the potentiometer is welded to the connection line, the pad is subject to high heat, and the bonding point between the pad and the carbon film is more likely to loosen. As a result, the signal transmission is not smooth, and sometimes the above-mentioned weak sound is hoarse.

Another reason for the distortion of the signal by the potentiometer is the existence of the PN junction effect between the contact of the carbon film and the sliding contact. Its low-level unidirectional conductivity characteristics cause distortion of small signals, poor clarity, and poor signal-to-noise ratio. At the same time, the Miller effect occurs between the carbon film and the contacts, which also deteriorates the frequency transmission characteristics.

Eliminate the effect of carbon membrane potentiometer on sound quality. The simplest and most effective way is to use a multi-position switch to control the attenuation of the attenuation resistor. More on the market is the 24-speed switch volume controller. The maximum attenuation ratio can reach -60dB, the minimum attenuation error of the same gear between the two channels can reach positive and negative ldB. It is the best solution.

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