Wavelength Audio Cardinal XS monoblock amplifier
Like most audiophiles, I've been peripherally aware of single-ended amplifiers and the high-efficiency speaker systems required to play them as an alternative to the more familiar high-power push-pull setups. (Except in Japan and France, one supposes. My brother-in-law Pierre was cursing the price of 300Bs six years ago in Paris.) I've listened to a number of SETs (single-ended triodes) in my travels for Stereophile, but I'd never been touched by the magic in any of them. They were pleasant, even beautiful—lightweight and warm, plush in the midrange, and perhaps a bit murky. But these systems always did vocals brilliantly.
In the event, I continued push-pulling (it's what I do...), but became aware of what was in store for me when John Atkinson casually mentioned that if I was to review the Forsell Statement amplifier, well then, I'd just have to do Gordon Rankin's special edition Wavelength Cardinals as well, wouldn't I? From the gargantuan to the petite, as it were. I am a fellow of contrasts, after all. I thought to myself, What, Me Worry?
Then JA threw down the gauntlet. SMECK!, as Steve Allen would say. Many were abuzz over JA's stinger footnote in Robert Harley's Cary CAD-300SEI review last September (Vol.18 No.9, p.149): "it's actually a tone control, and an unpredictable one at that." To judge from December's "Letters" column (p.15 onward), the readers were outraged. But I understood—our Editor Most English was requesting investigation and comment. "Go ahead, prove me wrong," I could almost hear him challenge.
As Kathleen and I prepared to send the Symphonic Line Kraft 400 amps for their fateful rendezvous with Unsafe At Any Speed Thomas J. Norton (apologies to Ralph Nader), the Cardinal XS single-ended triode amplifiers showed up. We opened the cases and gently placed them on the floor near the 400s. The giant German amps loomed over the minuscule made-in-Cincinnati single-enders. It was truly a hilarious sight. Contemplating them both raised my Audio Paradox Level to unsafe levels—their natures so radically different, their purpose so similar.
Your grace, the cardinal has arrived...
Gordon Rankin tells me there's nothing particularly ecclesiastical about the Cardinal XS (although, as you shall see, I did hear angels sing); the name simply limns the cardinal number three. (The amps' circuit topology uses a minimalist three-tube complement; and the signal-amplifying tubes are triodes.) The $7500 Cardinal XS stands as the premium edition of the "normal" Cardinal ($5250—see ST's eulogy elsewhere in this issue). Its uprated specs include Siltech and Kimber silver internal wiring, and a new output transformer (designated FS030 XS) which employs greater amounts of silver in its windings. The amplifiers are enjoyably retro-looking, with a simple form-follows-function styling which comes across as very American and quite becoming. They measure a slight 8" H by 12" W by 14" D and weigh in 38 lbs each. The review pair were clad in light and attractive curly maple, and are also available in cherry and walnut.
Designer J. Gordon Rankin: "It is possible to get the amplifiers in more exotic woods with the following understanding: We believe that the woods that we have selected are replenished by today's ecological laws. Woods from the rain forest will simply degrade our planet. For this reason the cost for any of these special finishes are as follows: The cost of the cabinets plus $1000 dollars that will be donated to the preservations of the Rain Forest fund."
Hey...way to go, J. Gordon. (Another one!)
There's a single pair of Cardas binding posts on the rear panel, along with a tiny on/off rocker switch, a long-nose RCA jack, and a standard IEC receptacle for the powercord. The custom transformers (both sourced from MagneQuest) are black, as is the top plate. A small toggle on the rear of the top cover switches between 4 and 8 ohm operation. Just fit the three tubes per side in their sockets (watch the pins on those 300Bs) and you're ready for business.
For the 20-20 on circuit and build details, I'll cut-and-paste from the brief but contemporary and well-turned-out literature, which comes in a classy-looking see-through smoked plastic presentation folio. It included a 3.5" floppy with measurement graphs and the text of the printed instructions and setup guide.
"A run of Siltech LS 4-240 cable is used from the RCA jack directly into the driver gain stage that is fashioned from a modified SRPP (Shunt Regulated Push Pull) circuit. This is a capacitor coupled (Hovland MusicCap) to the VV30B in self-biasing mode. The output transformer primary is terminated in braided Kimber AGSC. The output is wired with Siltech 22/.2 (99.99999% pure silver—approximately 16ga). The FS030 XS does not have taps like other output transformers, but instead has three complete output windings that can be wired in series or parallel to produce 4, 8, and 16 ohms. The Cardinal is available stock with 4 and 8 ohm switchable outputs (16 ohm or any other output is available upon request). The switching is done through a TOKOS silver switch with Kimber AGSS wire. Of course, all the special components that reside in the Cardinal, such as Cardas binding posts, Shinkoh Tantalum resistors, and capacitors from SCR, are included in the XS version as well."
Did he say "tuchass"?
Like all single-ended amps, the Cardinals run in pure class-A. While there is no global negative feedback, small amounts of local feedback are used in the input/driver and output stages.
For the defense
Here's what single-enders would like you to know about what's right with their technology. First, it's simple—usually only two or three stages. The following tidbit was in Gordon's support documentation: "Albert Einstein said it best, 'Make things as simple as possible, but not simpler.'" With SETs there is no need to split the phase, as you must do with push-pull designs. And split phase is often associated with the implementation of an overall negative feedback loop—another no-no in the pantheon of single-ended designers.
Rankin: "We even achieve better damping than push-pull circuits by a factor of four." (Damping is the correspondence between output resistance and speaker load.) "For example, let's say you have a push-pull amp with a 1k primary impedance—I'm choosing 1k for simplicity. The output tube will only see one quarter of that, because the transformer is center-tapped, so that halves the 1k impedance, and push-pull uses a pair of tubes, so each will see only one quarter. A single-ended tube will see the full 1k—and that's where the damping factor comes into play. And our single-ended output transformers run in the sweet spot, because you design them to run in the most linear region of the magnetic core. Speaking of transformers, I might add that I see a lot of designers pushing more into saturation than is correct to get more power. That's a mistake, in my opinion, which is bad for the sound. But they feel that the public wants more power!"
Then there's the interesting issue of distortion products. SETs include even- and odd-order distortion products in their outputs (as in nature, so to speak), while push-pull circuits cancel out even-order distortion by design, leaving only the less musical odd-order products intact. Now look...there's something to this. It's suggested that the sound of single-ended triodes has much to do with their delivery—intact—of the full spectrum of distortion products. "More distortion is better?" I hear you ask. Well, it's less humorous than it sounds. Might "unnatural" proportions of odd-order distortion account for part of the sound of push-pull? Something to think about.