Output Transformer Taps

Output Transformer Taps

This is a topic rarely mentioned by anyone. Are 4 – 8 – 16 Ohm output transformer taps good? This is usually present on potted transformers (another reason not to use potted transformers!) It gives us convenience alright, having being able to connect 4 Ohm, 8 Ohm and 16 Ohm speakers just with changing taps. Good eh? 

Well, it is good for convenience but it is bad for sound, especially if you’re not using 16 Ohm speakers, where the full secondary winding is utilized. With 4 or 8 Ohm taps being used, the remaining unused taps / windings are wasted, meaning that the energy is lost to thin air, or down the drain, or in other words, the secondary windings to receive the energy from primary windings will be insufficient. Also, these open windings will change the electrical properties of the output transformer, and therefore the effect is really unimaginable but calculable with complex mathematical equation, or measurable with various analyzers. 

Now, compare this to an output transformer with only a single secondary! Isn’t things become simpler, where lesser is better? All the windings on the transformer are dedicated to only a single set of output. The energy transfer is complete instead of being partial. As a result of this, the output signal will be cleaner and the efficiency is higher, which is equal to – better sound! 

If multiple output transformer taps are absolutely required, a configurable 4 or 8 or 16 Ohm by rewiring will be a much better option, using switches or manual wiring. This way, all the secondary windings can be utilized. This is what is being used by Lundahl where the secondary windings are configurable for various loads. Check out their datasheet and see how the secondary windings are sectioned and combined in series or parallel or series & parallel to cater for various speaker impedances. 

These types of transformers are more complex to build and design. The sectioning of the windings need to be equal and the ratios need to be correct for each windings to get the desired output or correct primary / secondary ratio, with respect to the speaker impedances. 

If you cannot change all that, then just get a 16 Ohm speaker, or use output transformer that has only a single tap. Simple as that. 

J&K Audio Design

20/12/2013

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