Solid State Power Amp Reviews

I'm a jazz lover. To be specific: I'm a lover of jazz on vinyl. I'm referring not to my sexual proclivities but to 33¹/₃rpm LPs from such venerable labels as Blue Note, BYG Actuel, Contemporary, ECM, ESP-Disk, Impulse!, Prestige, and Riverside. Nothing hits the sweet soul spot of this former jazz drummer and devout jazz head harder than Tony Williams's riotous ride-cymbal beat, Hank Mobley's carefree tenor-saxophone shouts, Charles Mingus's gutbucket double-bass maneuvers, or Bill Evans's haunting piano explorations. Jazz and vinyl both may constitute narrow slivers of music sales, but millions of us around the globe are on a constant hunt for exceedingly rare, grail-like jazz LPs, which we spin on our turntables with an equally holy reverence for the musicians' achievements.

My love of jazz and jazz vinyl has strongly informed my choice of playback gear: a Kuzma Stabi S turntable (known informally as "the pipe bomb"—a reference to its brass-rod chassis) with Kuzma Stogi tonearm and Denon DL 103 cartridge, Shindo Laboratory tubed preamp and power amp, and DeVore Fidelity Orangutan O/93 full-range speakers. This collection of wood, metal, glass, and wire has helped me experience sensory and musical bliss. Tubes rule. Life without Sylvania, Telefunken, and Mullard is life lacking proper aural nourishment.

Probably like you, I've worked for years to refine my audio system, perched in my bachelor pad high above the bridge-and-tunnel-crowd din of Greenwich Village. I've spent as many years collecting LPs, and purchasing, ripping, and selling CDs—and listening, listening, and more listening. My choices of tubed over solid-state, analog over digital may not be yours, but I hope we can agree that what dictates the choices of all of us is the music—or, at least, that it should.

Many a listener has gone from solid-state to tubed amplification, including Spec Corporation founders Shirokazu Yazaki and Tsutomu Banno. Combine a mad audio DIYer (Yazaki) with an adventurous circuit designer/engineer (Banno)—they respectively helmed technological breakthroughs at TEAC/Pioneer Japan and International Rectifier—then let them share their wisdoms in novel class-D amplifier designs, and . . . the Spec RPA-W7EX Real-Sound amplifier ($5995) is ready for show time (footnote 1).

Description
The RPA-W7EX Real-Sound is the only stereo power amplifier in Spec's USA product line, which includes integrated amplifiers, a turntable, Real-Sound speaker attenuators, and Mica capacitors. As with most amplifiers based on class-D circuits, Spec claims for the RPA-W7EX high resolution, an exceedingly low noise floor, extremely efficient heat dispersion, abundant power, and the ability to drive practically any speaker. Shirokazu Yazaki has had more than 40 years' experience in building and refining audio products for his own use, including a single-ended tube amplifier built around a GEC DA30 directly heated triode, which drives a horn speaker system comprising Altec 414A woofers, Onken OS-500MT mid/high drivers, and matching SC-500 wooden horns. However, he envisioned something unique for Spec's first class-D stereo power amp.

Like all class-D designers, Yazaki and Banno worked to overcome class-D's typical problem of brittle, bass-deficient sound—what Michael Fremer has described as "all outer shell, very little creamy center." Yazaki's solution began with the choice of capacitors used in the RPA-W7EX's low-pass filter—the exit point in a class-D amplifier's output stage. Yazaki is well-versed in the sounds of various capacitors: In the early 1990s, he used vintage Black Beauty and Black Cat caps to upgrade his own Marantz 7K, a '70s-era kit preamplifier that has long impressed him with its musicality (footnote 2). He also experimented with West Cap's oil-filled capacitors in his homebrew DA30-based SET amplifier, and in his early class-D prototypes. West Cap eventually became Arizona Capacitors (footnote 3), some of whose paper-in-oil capacitors are used in various Spec products; Yazaki says they have a "gorgeous and rich mid-to-low range" and a "pure and beautiful mid-to-high end."

Other noteworthy choices in the RPA-W7EX's design include Tsutomu Banno's "ground-plane branching" circuit-board layout, mica-dielectric capacitors sourced from India, and Tepro-Vamistor resistors. Fast-recovery ROHM/Schottky silicon-carbide (SiC) diodes were, in Banno's words, used to "eliminate" the high-frequency noise generated by class-D pulse-width-modulation (PWM) switching, a perpetual problem in class-D designs. Additionally, while many class-D amps have a single amplifier module, Banno used in the RPA-W7EX a hybrid two-in-one approach, integrating the driver and DirectFET MOSFET of International Rectifier's AUDAMP4 with a PowIRaudio IR4301 module. As a result, the RPA-W7EX can output up to 100Wpc into 4 ohms.

The RPA-W7EX measures 13.7" wide by 3.7" high by 14.6" deep: not much bigger than a stack of three large notebook computers. Its case and chassis are made of steel—it looked svelte in my Salamander rack, felt lighter than its 13.6 lbs, and seemed to produce no heat at all. This is evidently what made it possible for mechanical engineer Yasuhiro Yamakawa to use large slabs of natural wood for the side panels and footers, effectively sealing the RPA-W7EX in a sleek, minimalist cocoon.

"The switching operation doesn't produce heat," Banno explained in an e-mail exchange, "so using a wood base is effective for creating natural, REAL SOUND [his emphasis]. In addition, because there is no heat we can fully enclose the case. No dust enters the unit. No heat leads to long reliability because cyclical heat is not good for parts and solder.

"Wood dampens vibrations and resonates with the audio signal. Accordingly, the tone becomes more natural, rich, and melodious because of the wood. Intriguingly, I think of it like a musical instrument. [Banno is a cellist.] After many experiments, we found that the combination of spruce and maple worked best. In the RPA-W7EX the wood is of three-layer construction: spruce for damping the main chassis, maple and spruce for the three footers."

I popped the RPA-W7EX's lid, uncovering five circuit boards connected by tidy, all-copper wiring. On the largest board was the International Rectifier AUDAMP4 class-D amplifier module, which contains four large Nichicon caps, a small potted IRAUPS3 transformer (or choke), and a tiny, side-mounted circuit board. On the second board—directly connected to the RPA-W7EX's power receptacle, fuse, and on/off switch—are smaller Nichicon caps, a Talema potted toroidal transformer, and a single Arizona C50309-6223K Blue Cactus capacitor. The third board comprises many large and very small caps, two inductors, numerous diodes, and two tiny elevated boards, all wired directly to the amp's speaker terminals, input-selector switches, and RCA and XLR jacks. All in all, it's a beautifully constructed amplifier, inside and out.

Engraved on the center of the front panel is Spec's logo, which seems to depict the sun rising low on the left flank of a Fuji-like mountain—or maybe it's just a lower-case d and an upper-case A, representing the designer audio slogan that Spec puts on many of their products . . . ? At the far right is an inch-long, On/Off Power toggle, sourced from the aircraft industry. To power up the RPA-W7EX, you gently pull the spring-loaded toggle, then snap it into its up position. The red Off LED flashes for a second or two, and then the green On LED glows steadily, to confirm power engagement. The switch operation felt professional and elegant—as if I were powering up my own personal Learjet.

On the Spec's rear panel are, from left to right: the power receptacle, a fuse plug, and a mini-plug input for Spec's H-VC1 hardwired external volume control ($400). To the right of that jack is a gain switch with three positions: maximum gain, –6dB, and the setting for use with the H-VC1. In my system, the maximum setting provided way too much gain—I couldn't turn the volume knob on my Shindo Allegro preamp, itself a high-gain device, past 7 o'clock!—and the –6dB setting didn't provide enough attenuation: The H-VC1 was practically a necessity.

Then come two pairs of banana speaker terminals made by Aec Connectors Co., Ltd., of Taiwan, and a three-position switch for choosing between normal stereo operation, mono operation with the same signal appearing on both pairs of output terminals (useful for biwiring a system with two RPA-W7EX amplifiers), or strapped monoblock operation, with signal on only one pair of terminals. Finally, on the far right are Aec RCA and XLR input jacks, with a three-position selector switch for choosing between single-ended inputs (RCA), balanced inputs (XLR, with pin 2 hot), and balanced inputs with –6dB attenuation.

Listening
New York City provides ample diversion for the LP collector. With new vinyl-only stores opening practically every month, even a hardened jazz collector like the late writer and cartoonist Harvey Pekar would have had a great time searching for sides. Pekar swore off collecting LPs long before he became famous for his wonderful American Splendor comics and the film of that title. Like the pre-Hollywood Pekar, I visit my favorite vinyl vendors weekly. After cleaning my new sides, I often invite friends over to listen to them.

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Footnote 1: The company prefers that its name be written in caps, ie, SPEC. However, we reserve that usage for company names that are actual acronyms.—Ed.

Footnote 2: Later that decade, Yazaki led the design team that created one of the first universal SACD/DVD-A/DVD-V players, the Pioneer DV-AX10, thus the old Marantz 7K played a role in voicing one of the most noteworthy products of 2000.

Footnote 3: The products of Arizona Capacitors are now distributed in Japan exclusively by Spec.