Using Stepdown Transformers

by James Leahy

The Real Truth

The number of e-mails I get every week about this topic that brings so much confusion to you guys is staggering. I will endeavour to answer as many questions about this much misunderstood area as I can. The U.S. and some other parts of the world operate on 120 Volts A/C instead of 240V A/C as in Australia. For owners of 110V equipment to be able to be used in Australia a stepdown power transformer must be used. This device will allow the operation of 110V products to be used on a 240V power supply.

The ability of the stepdown transformer to be able to cope with the electrical product it is being used with depends directly upon it's rated output that should be of equal or greater capacity.

Stepdown Transformers & Audio Equipment

While stepdown transformers have their place and are very useful, using them anywhere near a High-End audio system is not one of them. Trying to save a few bucks by using a quality 120V piece of audio equipment on a 240V power supply by way of a stepdown transformer is false economy and will be a shortcut to sonic compromise of varying degrees.

Valve based audio and even transistor products for that matter should NEVER be run on any step down transformers regardless of size if you are at all interested in sound quality. The reason for this is that especially valve powered equipment is VERY dependant on the quality on the power transformer in the unit and the bandwidth of the power transformer is critical to the sound quality. Universal stepdown transformers are not graded for their sonic abilities where dedicated audio power transformers are by good manufacturers.

It might interest you to know that the special transformers most quality manufacturers use account for one third of the total cost of the final unit. Such is the importance they place on this one component. This should tell you something before you decide, you know better. In no uncertain terms putting an universal, step down transformer in front of a High-End audio component would be a total sonic disaster and waste of time/money. I have had customers ask to trade-in their 110V equipment to buy the exact same in an Australian model because they have been so dissatisfied with the performance after trying this cheaper alternative.

Audio transformers are usually the factor which limit sound quality; electronic circuits with wide frequency response and low distortion are relatively simple to design.

A particularly critical component is the output transformer of an audio power amplifier. Valve circuits for quality reproduction have long been produced with no other (inter-stage) audio transformers, but an output transformer is needed to couple the relatively high impedance (up to a few hundred ohms depending upon configuration) of the output valve(s) to the low impedance of a loudspeaker. (The valves can deliver a low current at a high voltage; the speakers require high current at low voltage.)

For good low-frequency response a relatively large iron core is required; high power handling increases the required core size. Low distortion requires iron of adequate properties; special cores with oriented magnetic domains are used for best results. Good high-frequency response requires carefully designed and implemented windings without excessive leakage inductance or stray capacitance. All this makes for an expensive component and one that third party manufacturers like to take shortcuts with. Take it from someone who has tried both ways, this can seriously affect the sound quality more then you realize.

Other components such as CD players and pre-amplifiers suffer similar performance losses but in different ways. The sonic signature of separate stepdown transformers are untested by the audio equipment manufacturer and were not allowed for in their original electrical circuit.