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The use of transformers in high-end audio systems

In its simplest form, a transformer is a device that converts voltage and current for the purposes of connecting things together. Almost every audio device employs some kind of transformer to convert the voltage from our mains supply into the voltage it requires internally.

Specially designed transformers can also be used to conduct audio signals between stages. The most common examples of such transformers is in the outputs of most vacuum tube amplifiers, interfacing the high impedances of valves to the low impedances of loudspeakers.

Small signal transformers can be used to great advantage in the critical path of audio components, provided they are of suitable quality however this is not common practice, mostly due to cost constraints and lack of expertise in the art of audio transformer design.

Audio transformer design is truly the place where art meets science – it’s not just about curation of exotic materials and requires a deep understanding of the nature of electromagnetism and its interaction within materials and winding structures. To properly comprehend the interplay of inductance, magnetic flux, permeability and music at all audible frequencies requires the mind of a physicist, the ear of a concert violinist, the attitude of a perfectionist and many years of experience.

In addition to inter-stage coupling functions, specialised transformers may also control volume. The weakest link in most audio systems is the volume control stage. As audiophiles, we concern ourselves with special cables and connectors made from precious metals in order to minimise loss of signal quality. Our precious signal is preserved right up to the volume control stage where we typically throw most of it away in the form of heat!

The cheapest and simplest type of volume control is a simple variable resistor, also known as a rotary potentiometer. Potentiometers are used by most manufacturers simply because they are simple and cheap. Even the highest quality resistors that can be used in these commonly applied volume controls have a negative impact on the integrity of the signal. At the other end of the scale, designers of very high-end preamplifiers employ all kinds of elaborate circuitry to create the most lossless, transparent volume control stages. Elaborate volume control stages can often account for the majority of the weight and cost of a high-end line stage. Custom designed, pure silver transformers made in-house by Ypsilon have developed a reputation of being at the pinnacle of performance in this application.

Of all of the possible methods of controlling volume, one ‘classical’ method, the transformer attenuator, has never been surpassed for its ability to provide control without compromising quality. Transformer attenuators were once commonplace in the highest quality vacuum tube based studio mixing consoles of the 1950’s but they gradually fell out of favour due to size, weight and cost as the trend for more densely packaged, multi-channel consoles developed.

So, why don’t more Hi-Fi manufacturers use transformer attenuators? The main reason is that, unlike rotary potentiometers and VGAs (Variable Gain Amplifiers), Transformer Attenuators are not simple and cheap to make. They require a degree of expertise and an uncompromising commitment to audio quality that is only found at the very pinnacle of audio engineering.

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