I don’t know if Nicolaus Copernicus was eating oxtail soup, looking at an apple falling from a tree, or cleaning his astrolabe when he thought up his theory of the revolution of celestial spheres, set down in his book De revolutionibus orbium coelestium in 1543. But his superior insight, partly derived from mathematical expertise, changed everything, putting the sun at the center of the universe and not the earth, as most of the governing clergy insisted was the case at the time, and became the defining epiphany of the scientific revolution that followed. After Copernicus, clergy could no longer so readily dismiss a Galileo or a Giordano Bruno by saying, Are you gonna b’lieve me or your own eyes? Scientists came to believe in their own eyes— observation before theory the new motto. Likewise, I’m not sure if Alfred Wegener, a German climatologist and arctic explorer, was peeling an orange in 1915 when he thought—Hey! The coastlines of Africa and South America fit together! He may have just been working on a jigsaw puzzle, but, somehow, he came up with the idea of continental drift—that the earth’s landmasses were once one big supercontinent that then broke apart and moved away from one another, giving rise to the oceans and, some eons and eons later, a new revolutionary paradigm in geology. What is certain, though, is that, every once in a while, we get a shift in the way we think of organizing things, be it astronomy, geology, or fried green tomatoes. Stuff we start noticing just doesn’t make sense using the old way of looking, so we have to change the lenses through which we’ve been seeing as through a glass darkly, clean things up, and come up with fresh new approaches.
Kevin Hayes, President of Valve Amplification Company (VAC), has taken fresh approaches to preamp design at least three times since the inception of his company in 1990. I spoke to him recently and the discussion told me much about the “revolutions” in VAC preamps over the past twenty years. Rather than sitting back, practicing science of the caretaker variety and simply refining his existing circuits, Hayes has spent most of his R&D time “interrogating the gross flow of electrons,” identifying where the electronic turbulences are in each given circuit. He wants to see not only what might be improved by parts substitutions, but what entirely different approaches, new topologies, completely different flows of those electrons might bring. For example, in 1998, when VAC issued the aptly named Standard preamp, it altered the VAC lineup, shaking the sun and stars, replacing the original 1991 CPA-1 preamp, and staying in production until 2007—nearly ten years. But, the advent of the Renaissance Signature Mk I pre in 1999 marked a sonic breakthrough for VAC that introduced a new circuit topology—an extremely high-gain, three-stage line section with direct-coupled interstage and transformer-coupled inputs and outputs—and the reliable Standard was eclipsed (if not yet discontinued). Then, very quickly in 2000, Hayes released the Signature Mk II with major changes to 11dB gain and a fully differential circuit with transformer coupling at the inputs. It established yet another major shift in preamp design for VAC and stayed in production another ten years until the recent release of the Signature IIa.
Introduced in 2011, the Signature IIa ($15,500, linestage; $19,500, with phono) represents the first new iteration of VAC’s flagship, transformer-coupled preamp in over a decade. It sports a small boatload of improvements over the prior Signature II. New are the volume control, key passive parts, variable phono loading, and the character of the chassis (better damping, new “energy termination” solutions). Also new is the option to roll tubes in the linestage.
That linestage has 12dB of gain, a frequency response claimed to be flat over the audio band, and an output impedance of 96 ohms. It comes stock with two 12AU7 twin triodes and two E88CC tubes (designed to be swappable). From input to output, the Signature IIa contains no coupling capacitors in order to protect the purity and detail of the hand-wired, direct-coupled triode tubes. There’s no loop negative feedback either, as Hayes wanted the output interface to be completely stable and free from dynamic interactions with an external load. The preamp does not invert phase.
As for the fully differential circuit, because the preamp achieves this through transformer coupling, there are fully balanced inputs and outputs. It also means the Signature IIa should sound the same with either RCA or XLR hookups. And, significantly, the transformer isolates the Signature IIa’s sources from the amplifier it is driving.