In Chapter 2, we began to design simple circuits, which will later be combined to form complete systems. In doing this, we calculated values for components. We now need to know how to specify voltage or thermal ratings of components.

Correct specification of individual components is extremely important. An underspecified component may fail prematurely, and cause further damage as it does so, whereas an overspecified component may waste money that could have made an improvement elsewhere. To be able to specify components correctly requires knowledge of the stresses that will be applied to the component (electrical, thermal and mechanical), and knowledge of the imperfections of that breed of component. (No components are perfect, although some are more equal than others.)

Much has been said about the sound of components, particularly capacitors. This has caused such polarization of the Engineers vs Audiophiles debate that rational speech has only rarely been heard. This is curious, since there are well-known physical imperfections in components, and it seems reasonable to suppose that they could have an influence on sound quality. On the other hand, whilst components are not magical, there are purveyors of snake oil.

This chapter will help you to avoid the more obvious pitfalls, but it is not a substitute for detailed manufacturers data sheets and the application of intelligence.