No surprises there. After all, a phono transformer requires only a primary-coil impedance that's electrically right for the cartridge in use, and a gain capability—itself determined in part by the transformer's turns ratio (see "Listening" columns passim)—that likewise suits the user's gear. Given all that, one can assume virtually any phono transformer to be more or less wonderful.
But the distance from more to less is greater than usual these days, given the appearance of some truly exceptional new transformers: an unmixed blessing. The latest samples to come my way are from a German firm called Silvercore. Founded eight years ago by an engineer named Christof Kraus, Silvercore designs and builds their own nice-looking tube amps and preamps. And central to everything they design and build—"at their core" were the words that first came to mind—is a belief in the primacy of a well-made transformer.
I had a brief phone conversation with Christof Kraus in January, during which he talked with an expert's ease about various aspects of transformer design. (His English is infinitely better than my German, in which language I can manage little more than "Good day," "Thank you," and "My hat has three corners.") I was delighted by Kraus's enthusiasm for the symmetry of a phonograph-driven, tube-amp–powered playback system in which electromechanical transducers drive or are driven by transformers at both ends: Herr Kraus and I seem to have arrived at the same conclusion, thousands of miles away from one another.
The name Silvercore suggests a reliance on silver wire: generally true, as it turns out, but not exclusively so. Instead, the feature that's common to all of Silvercore's transformers is their toroidal core. "If you wish to make a toroidal [transformer], you need a special machine," says Kraus, "and it's much more difficult to do, especially with very fine wire." Yet somehow or other Kraus manages, and so well that all of his phono transformers are commendably free of resonant frequencies within or even near to the audio range; consequently, Silvercore step-up transformers are among the few that don't require the use of damping resistors (which Kraus quite rightly calls "veiling" resistors).
Tightly wound
Silvercore offers transformer-based products for a number of domestic audio chores: eliminating hum from nonbalanced systems (the Groundbreaker), interfacing single-ended and balanced connections (the Symmetrizer), and even converting stereo sound to mono (the Monokonverter). But the stars of the Silvercore show are their three basic models of moving-coil step-up transformer: the One-to-Ten ($585), the Silvercore MC ($1250), and the Silvercore MC Pro ($4800).
Silvercore products are distributed in the US by Oswalds Mill Audio (footnote 1), whose proprietor, the estimable Jonathan Weiss, loaned me samples of the three models named above. (The middle model, the Silvercore MC, was supplied in a version called the Silvercore SPU Spezial, having been tailored specifically for Ortofon's classic low-output, low-impedance pickup heads.) I hope to write about the two more expensive models by and by, but it's their cheapest phono transformer that's captured my heart in the here and now.
The Silvercore One-to-Ten contains a stereo pair of toroidal transformers, wound from copper wire on proprietary amorphous cores, with a primary-coil impedance of 100 ohms. Given that a cartridge performs best when driving a transformer load that's between two and six times its own coil resistance, this Silvercore model would seem a perfect match for such things as the EMT TSD 15 and variants (24 ohms), the Denon DL-103 (40 ohms), and most Allaerts models (22–32 ohms). You'll be unshocked to know that the turns ratio of the One-to-Ten is one to ten (1:10), which is also the transformer's voltage-gain ratio. Thus the 0.3mV output of the Denon 103 becomes 3.0mV, and the 1.05mV (footnote 2) output of the EMT TSD 15 becomes 10.50mV. (Most hobbyists would consider the former to be fine and the latter to be a little high but not problematically so, as long as the preamp's volume knob stays toward the left of its range.) Remarkably, Silvercore's entry-level phono transformer is built into a substantial case made of polished stainless steel: irresistibly pretty, charmingly nonmagnetic.
Footnote 2: A common misconception is that the EMT's output voltage is 0.21mV—which is, after all, the specification published by its maker. The problem is, that number is based on a 1kHz groove excursion of 1cm/second, whereas the industry standard is a cartridge's output at 5cm/s. Thus, before comparing the TSD 15's output to that of its competition, one must apply a factor of 5.
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COMMENTS
Art,
With all due respect, I don't think you mated the correct SUT to the EMT. It's 1.05 mV, but it can exceed 3 mV if playing loud electronic music as an example. 10x would mean you can have 30 mV going into the preamp, which is very likely at least double what it can handle without distortion.
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