Love is in the air… core-less transformers

 

An essay by Misho Myronov 💫

It’s never too late to learn, to dig deeper, and to move to the next level.

For many years, I treated transformer cores as a necessary evil. Something unavoidable — helpful in many ways, but also inherently damaging. A compromise we could only try to balance, but never eliminate.

A few years ago, my perspective began to change.

If we cannot eliminate cores across the entire frequency spectrum, perhaps we can eliminate them where they do the most harm — in a narrover band. Exactly in the range where they stop helping and only do the damage to the signal.

Any magnetic core material introduces losses and distortions at all frequencies — even the most exotic cores. They differ in behavior, which is why certain materials are preferred in specific compromises. But the fundamental issue remains.

At low frequencies, we can tolerate these losses. In fact, we have no real alternative — a coreless solution at 10 Hz is unrealistic.

But at higher frequencies, the situation is different.

Here, we do not want anything that steals micro-details, introduces distortion, adds coloration, or affects frequency response.

For many years, I had no interest in multi-way amplification. I have always been — and still am — a big fan of full-range drivers. This realm requires the shortest and most transparent amplification path possible. I hope I’ve learned something along this way.

Discovering Altec two-way systems (and not only Altec, of course — you know), I faced a fundamental challenge: matching two very different transducers — a bass driver and a mid/high-frequency compression driver.

Compression drivers are significantly more efficient than bass drivers. Feeding both from the same amplifier inevitably requires attenuation of the mid/high band — and attenuation practically always means losses.

One solution was to use transformers for level matching. Transformation is always preferable to attenuation. This led me to design a series crossover where the transformer also functions as an inductor — resulting in a minimalistic network with only two elements, performing both frequency division and level matching.

But we are never fully satisfied, even with good results. We keep searching.

This search led me to a rather radical idea — one that seemed crazy at first (and even at second glance): using a coreless output transformer for the high-frequency channel in a two-way amplification system.

Since I had already been designing and building my own output transformers, and conducting extensive experiments, prototyping was a natural step.

This is how the first “Wooden Output Transformer” was born, along with an experimental two-channel amplifier.

It worked flawlessly with a crossover point at 2 kHz — and sounded absolutely fantastic with Altec duplex drivers. In fact, I had never heard the 604 sound this good — and I do have experience with Altecs…

Then the world changed — 2020 and everything that followed. Many things and ideas were postponed, some forgotten.

But the idea of extending the use of coreless transformers to lower frequencies — below 1.5–2 kHz — never left me.

Eventually, a new design was developed. After extensive testing, it proved to be a success.

The result: the first tube single-ended two-channel amplifier with a 500 Hz crossover point, using a coreless (air-core) output transformer.

Both objective measurements and subjective listening confirmed the result: exceptionally positive.

I will continue exploring this path — especially in the direction of multi-way amplification.

Stay tuned.

#WoodenAmp

#WoodenTransformer