Toroidal transformers

We have very often talked about toroidal transformers in our Lab reviews. Although we believe that most of our readers have some knowledge of what they are and what they offer, they have the honor of inaugurating this new section in CEC, designed to explain in greater depth and detail how the systems that make up our equipment work.

Let's start by clarifying some concepts. A transformer refers, very briefly, to a device capable of converting high-voltage, low-current alternating current into low-voltage, high-current alternating current, or vice versa, in the words of the Royal Spanish Academy (RAE). In the same reference, we find the definition of "toroidal" as an element shaped like a closed, flat curve rotating around a fixed straight line in its plane that does not intersect it. Put simply, a shape similar to that of a donut. The accompanying photographs explain this term much better. Although we normally refer to these products as toroidals, strictly speaking we should talk about transformers with a toroidal core.

The winding consists of a ring, usually made of artificial ferrite compounds, on which the primary and secondary are combined. They are bulkier, but the magnetic flux is confined within the core, with very low levels of leakage and low losses.

In this way, the energy remains at the center of the transformer itself, so the heat from surplus energy is dissipated better.

Today, they are the most common construction in mid-range and high-end amplifiers. In fact, Faraday, the father of electromagnetism, designed and wound the first transformer on a toroidal core. In this design, the magnetic flux is concentrated uniformly in the core and, owing to the absence of other elements, vibrations are eliminated or, better still, speaking in strictly acoustic terms, noise. Likewise, since the winding is spread over the entire surface of the core, the disturbances caused by friction virtually disappear and heat dissipation is improved. These details make it possible to substantially improve the characteristics and performance of toroidal transformers compared with traditional ones. Many of their virtues are due to their ferrite core, compared with the metal laminations of the other type.

It should be said that both a toroidal transformer and a conventional one can deliver the same power. The main difference lies in their size, so above a certain power rating they are all toroidal. A transformer and its power supply are sufficiently dimensioned to provide the continuous power the amplifier needs. What we call "high current delivery" lies exclusively in the hands of the high-capacitance capacitors (10,000µF and up) that power supplies incorporate at their output, which are responsible for supplying the high current peaks that the amplifier demands and that the transformer would be unable to supply.

The advantages of a toroidal transformer over a conventional laminated one are therefore numerous and important: a smaller leakage field, higher efficiency, low noise, reduced weight and size (we will talk about oversized transformers later), less heating, and ease of assembly. In acoustic terms too, the direct consequence is an increase in current delivery and improved dynamics in an amplifier.



MICHAEL FARADAY AND ELECTROMAGNETISM

For some physical laws, it is difficult to find experiments that lead directly and convincingly to the formulation of a law. One of the few cases is Faraday's Law, one of the fundamental equations of electromagnetism.

Some of these experiments were carried out by Michael Faraday in England in 1813 and by Joseph Henry in the United States at around the same time.

When the ends of a coil are connected to a galvanometer (an instrument for detecting and measuring electric current), there is normally no deflection, since there is no electromotive force in this circuit. But if a bar magnet is pushed into the coil with its north pole facing it, the magnet moves, causing the galvanometer to deflect, showing that a current is flowing through the coil. If the magnet is held still relative to the coil, the galvanometer does not deflect. Conversely, if the magnet is moved away from the coil, the galvanometer deflects, but in the opposite direction, from which it can be deduced that the current in the coil is flowing in that direction. If the south pole end of a magnet is used instead of the north, the experiment works the same way, but the deflections are exactly in the opposite direction.

Other experiments show that what matters is the relative motion of the magnet and the coil. It makes no difference whether the magnet moves toward the coil or vice versa.

The current that appears in this experiment is called induced current and is said to be produced by an electromotive force. From experiments like this, Faraday was able to deduce the law that gives its magnitude and direction.

OVERSIZED TRANSFORMERS

An oversized transformer offers the advantages of a toroidal one, adding greater power delivery thanks to its larger dimensions. However, it also requires more available space, so it may constrain the size of the amplifier and even cause certain overheating problems if it is not accompanied by suitable ventilation or technology. Users, for their part, should take special care with this type of component, since its placement must be carefully considered to keep the ventilation grilles as unobstructed as possible.