Several issues in transformer selection

1. In the production of transformers, what are the advantages and disadvantages of machine winding and manual winding of coils?

The advantages of machine-wound transformers are high efficiency and beautiful appearance, but winding a tall toroidal transformer with small holes is more troublesome, and the reliability of the insulation treatment process is not as good as manual winding. Manual winding can make the transformer's leakage magnetic flux very small, and the layout of the number of coil turns can be adjusted at any time during the winding process, so a true Hi-END transformer must be purely hand-wound. The only disadvantage of pure hand-wound winding is low efficiency and slow speed.

2. Which of the toroidal, EI, R, and C power transformers is the best?

They each have their own advantages and disadvantages and there is no saying that one is the best, so strictly speaking, any type of transformer can be the best. From a structural point of view, the toroidal type can minimize magnetic leakage, but in terms of sound, the EI type can do a better job of mid-frequency density. In terms of magnetic saturation alone, the EI type is stronger than the toroidal type, but in terms of efficiency, the toroidal type is better than the EI type. Despite this, the key to the problem is whether you can make the best use of their respective advantages and avoid their weaknesses, and this is the most fundamental thing to do well in a transformer.

In the current imported amplifiers, the application of toroidal transformers is still the mainstream, which basically illustrates a problem. The evaluation of transformers by audiophiles should be objective and fair. You can't use something that is not well made as a reference and say it is not good. Some people say that toroidal transformers are prone to magnetic saturation, so why don't you try to make it not easy to magnetically saturate? This can be achieved through technical means. If you don't put in enough effort or just save costs, it will of course be easy to magnetically saturate. Similarly, as long as you make it carefully, the efficiency of EI type transformers can also be very high.

The quality of the transformer has a great impact on the sound, because the energy transmitted by the transformer is closely related to the iron core and the coil, and its transmission rate plays a decisive role in the impact on the sound. For example, people usually think that the mid-frequency of the EI type transformer is thicker and the high frequency is thinner. Why? Because its transmission speed is relatively slow. And what about the toroidal type? The low frequency is fiercer, and the mid-high frequency is slightly weaker. Why? Because it has a faster transmission speed. However, if you make effective structural changes, you can make both the toroidal type and the EI type very perfect, so the key still depends on how you do it.

However, at least one thing is certain: R-type transformers are not easy to make. It is OK to use it as a power supply for low-current pre-amplifiers and CD players, but it has serious defects if used as a power supply for post-amplifiers. This is because the structure of the R-type transformer itself is not easy to change, while the toroidal and EI types are relatively easy to change the structure to achieve a good sound. The power supply of power amplifiers made with R-type transformers usually sounds very hard and lacks spirit, and the low frequency often has no bounce and seems hard.

3. Is it better if the silicon steel sheet of the transformer core has a higher silicon content?

Not necessarily, the silicon content of silicon steel sheet does not have a big impact on the quality of the transformer, but the orientation and non-orientation are related to the type of iron core. Secondly, even if the iron core is of the same type, if you do not handle it well, the quality difference will be very large, and the difference can sometimes be as high as 40 to 50 percent.

For a good iron core, the heat treatment and wire winding process are very critical for the same material. A good heat treatment only requires a small 10mA excitation current to reach 15,000 gauss, while a bad heat treatment may require a 50mA excitation current to reach the corresponding 15,000 gauss. The difference between the two is very large. From a professional perspective, the quality of the iron core is mainly judged by comprehensive evaluation based on several indicators such as excitation current, iron loss, and saturation parameters.

4. If the strip silicon steel sheets of the toroidal transformer are spliced, does it mean that the quality is definitely bad?

It is not possible to generalize, but it is not advisable to have too many spliced ​​ends, because one more break means one more magnetic leakage point, so it is best not to have more than 2-3 joint points. In terms of manufacturing process, all spliced ​​ends must be pickled in advance, but strictly speaking, it is best to use silicon steel sheets without splicing for the manufacture of toroidal transformers for high-end audio equipment, and its process quality will be more guaranteed.

5. What are the requirements for silicon steel sheet materials in transformers?

Since silicon steel has very little loss in an alternating magnetic field, transformers mainly use silicon steel sheets as magnetic materials. Silicon steel sheets can be divided into hot-rolled and cold-rolled types. Cold-rolled silicon steel strips have the advantages of small size, light weight and high efficiency when used to make transformers because of their high magnetic permeability and low loss. The performance of hot-rolled silicon steel strips is slightly inferior to that of cold-rolled silicon steel strips.

Ordinary EI type transformers are made by punching silicon steel sheets into E type and I type sheets with a thickness of 0.35-0.5mm, which are then inserted into the winding wire package after heat treatment. Most of these cores use hot-rolled silicon steel sheets (high-quality silicon steel sheets with high silicon content are D41, D42, D43, and D301). The cores of toroidal and C type transformers are formed by winding cold-rolled silicon steel strips. The C type transformer is made by heat treatment, varnishing, and then cutting.

The leakage inductance of the transformer is generated by the magnetic flux that does not pass through the primary and secondary coils. These magnetic fluxes pass through the air and form a closed magnetic circuit. Increasing the coupling density between the primary and secondary of the transformer can reduce the leakage inductance. The leakage inductance of a good transformer should not exceed 1/100 of the primary coil inductance, and the output transformer of the tube amplifier used in Hi-Fi should not exceed 1/500.