The upper deck's low population density reminds us. A core appeal of particularly low-power valve amps without complex micro-processor bias and protection circuitry is signal-path simplicity of tubes + transformers. If you expected more stuff, you've come to the wrong address. This is posh but minimalist.
To revisit basic transformer lore, the double C-core geometry is also known as an ED or, in Japan, a cut-core design. Both its primary and secondary windings are contained within one coil. With all of its grain going in the same direction, there's max permeability for a given flux density. This means less overload distortion than an EI type. Also stray field radiation is lower to begin with. That's because the double C core only has one gap whilst an EI has two.
These photos from James Transformer show a basic ED core without windings at left and with completed windings and mount at right.
Toroidal audio output transformers are far less common with more ambitious high-end amplifiers even though Shigeki Yamamoto of the eponymous Japanese retro firm does use two in his 300B SET. Suffice to say once more that MySound's only look like tall toroids but aren't.
Particularly output transformer design for quality audio amplifiers is considered something of a black art. Their precise winding ratio and layout determines not just their output Ω—the primary duty of such magnetics is lowering a tube stage's high output Ω to approach a modern loudspeaker's load impedance—but bandwidth, phase shift and behaviour under stress. That's when playback pushes a circuit with SPL and bass transients. Few tube electronics brands wind their own. Those who do often start life as transformer experts like Fezz in Poland, Octave in Germany, Trafomatic in Serbia, TruLife in Greece. Boutiques focused on specialty transformer production include names like Hammond, Hashimoto, James, Jensen, Lundahl, Magnequest, Monolithic Magnetics. Sowter, Tamura and Tango. Because a simple tube amp's signal path is mostly glass and iron, the precise makeup of the all-important output magnetics and their supplier is each brand's well-guarded IP.
The obvious upshot? Tube amp sonics are a result of not just its valves. Just as vital is the presence and quality of the output transformers. It's likely why cloning tube-type THD behaviour plus higher output Ω with a transistor amp never sounds the same. Such transistor amps omit the OPT. It's why to make their transistor amplifiers sound closer to their tubed brethren, McIntosh strategically couple their sand amps to autoformers.
We could probably say that classic/typical valve sound relies on output magnetics; and that removing them in so-called output-transformer-less or OTL designs including David Berning's ZOTL equivalents alters the 'classic' bit.
Which leaves the exotic bit of amorphous. The cores of conventional transformers consist of lamination stacks made from silicon steel which exhibits an almost uniform crystalline structure. Made of alloys which have no atomic order, amorphous metals are created by rapidly cooling molten metals. This prevents their crystallization and leaves a vitrified structure. Due to its lack of a systematic molecular lattice, this type of metal is also known as metallic glass.
The price sheet of Belgium's Monolithic Magnetics shows how exotic amorphous and nano-crystalline cores are more expensive than their pure steel equivalents. A benefit of amorphous transformers is lower hysteresis loss. During core magnetization and de-magnetization, less energy is wasted as heat.
Noguchi of Japan on the benefits of their Hitachi Finemet amorphous cores: "…because of the absence of a crystalline structure, amorphous alloys are magnetically soft (lower coercivity, lower core loss, higher permeability). High resistivity and high permeability give lower losses at higher frequencies. Core loss is 1/5th that of iron-based amorphous metals whilst high saturation magnetic flux density is comparable. Low magnetostriction is less affected by mechanical stress to produce very low audio noise emission. Temperature characteristics are excellent and aging effects very small."
In layman's terms, we could think of all this as the transformer-core equivalent to mono-crystal cables where the usual molecular lattice of crystal grains is so elongated that a 1m length of cable will exhibit very few such grain junctures. A typical amorphous alloy for transformer cores is Hitachi's Metglas, a mix of iron, boron, silicon and phosphorus. For hifi applications, there are also cobalt- and nickel-based options. The actual windings tend to be copper but very expensive exotic transformers like Kondo of Japan may use pure silver. Amorphous nano-crystalline core + silver + double C-core geometry would get very costly.
In power utility transformers, efficiency is king. Here amorphous cores are prized for up to 70% lower core losses. How amorphous core audio transformers may sonically differ from traditional silicon-steel cores is described here by amp designer Kevin Carter based on comparing otherwise identical Lundahl specimens. As to what exact type of amorphous core MySound's are, "we don't know. Our supplier won't tell us. He gave us two types to test and we chose the one that sounded best to us."
On the appointed day, Przemyslaw the driver rang to confirm that I'd be in to take receipt. He was still up north in County Donegal so about three hours out. With Google maps and our Eire Code—an Irish location ID system—he needed zero instructions on how to find us. He confirmed that about four weeks later, he'd return to recover the loaners.
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