For many people working with amplifiers and sound systems, the choice between laminate or toroidal ‘doughnut’ output transformers is a difficult one. As with many questions regarding the specifications of audio technologies, the debate is obfuscated by lazy mythologising and a lack of clear information. Even though as a general rule when it comes to high-end audio toroidal transformers are often recommended over their laminate counterparts, it’s still worth knowing about some of the key differences.
Construction
Though both components serve the same function, they are different in their construction. EI transformers are the most common laminate transformer and consist of an E-shaped section which is wound with wire around its central leg and an ‘I’ section which is installed over the top. Toroidal transformers, on the other hand, are made from stacked metal ‘O’s forming a hollow cylinder which is covered by windings. Laminate transformers are typically made using steel, whereas toroidal transformers are made from a number of materials, including steel, powdered iron and permalloys. A more in-depth guide to their construction can be found here: http://www.learnabout-electronics.org/ac_theory/transformers03.php.
Usage
With regards to audio technology, an output transformer is an integral component responsible for how effectively the audio power of an amplifier will transfer across to the load of the speakers. Its job is to convert an incoming low-voltage, high-current signal to a high-voltage, low-current signal that will power the speakers. In commercial and domestic applications such as guitar amps, people have noted that the type and quality of transformers used can have a great impact on the overall tone.
Practical Considerations
Two main considerations when it comes to choosing laminate or toroidal transformers are cost and functionality. Laminate transformers are often cheaper – due to the relatively easy nature of the their construction, large-scale mass production is feasible. This benefit, however, is offset by a greater level of magnetic field leakage than their doughnut counterparts. Toroidal transformers, on the other hand, are usually more expensive, as each one has to be separately wound. The benefits of using a toroidal transformer, such as the ones made by sigatransformers.co.uk, are primarily less magnetic field leakage, a smaller profile and greater efficiency.
Whatever you transformer needs, when it comes to audio it’s always worth considering these factors to help you choose the right components.