SPEC Corporation would also remind us that both Spruce and Maple are found on stringed instruments like violins or guitars. Compared to the previous RSA-777 EX and RPA-W7 EX, the RPA-W3 EX power amplifier exploits a newly designed wood structure with increased thickness to improve its sonic performance. Its tripod scheme has reverb characteristics quite similar to those string instruments and thus acts as a damper/resonator for richer sound. The aluminium frame is subject to a specific polyester-based EMC coating with carbon black as conductive filler. The satin finish is particularly stylish and enhances the impression of high standards. It stands well apart from the typical metal chassis of the majority competition. One also notes no unsightly heat sinks or vent holes on the RPA-W3 EX chassis.
Since the class D output stage generates very little heat, there was no need to ventilate the enclosure and allow dust to enter. This case is hermetically sealed. By avoiding heat and dust accumulation, one extends life expectancy and overall reliability among other things.


On the front panel, an aviation-type on/off power toggle must be pulled and snapped into its up position to turn the amplifier on. Two small LEDs indicate status. The red 'off' LED flashes for a few seconds, then the green 'on' LED glows steady. Nothing else adorns the minimalist front of the RPA-W3 EX. After all, it's just a power amplifier.


The rear does get busier. From left to right you'll find the IEC power inlet, a mini jack for the proprietary volume controller, two pairs of AEC speaker terminals and high-grade RCA and XLR inputs also made by AEC Connectors. Then there are three tri-pole selectors. From left to right, one controls gain from regular (max), -6dB and 'pure direct', the latter requiring either the €850 H-VC5 controller supplied to me for this test or the companion RPA-P7 preamplifier with its special provision for such a connection [below].  

The necessary hookup cable came included and the controller itself can supply up to three amplifier units simultaneously to support joint hifi and home theatre installations. Conceptually, this relocates signal attenuation from upstream to downstream, i.e. places it directly in front of the final power stage. The implied promise is one of higher transmission amplitude for less loss and noise. The volume setting of the H-VC5 is thus outside the signal path. It merely sends code to the internal gain block of the RPA-W3 EX which according to its designer Shirokazu Yazaki, maintains a constant S/N ratio regardless of level. The second three-position selector determines stereo, dual-mono or bridged mode via a specific buffer. Dual-mono operation presents the same signal on both output terminal pairs to support bi-amping which isolates a speaker's counter-electromotive force of the woofers from the midrange/tweeter amp.


Already switching amplification means a significant reduction of sensitivity to such feedback. Class D controls its output voltage with the switch duration of its gain devices. Since the output device is only a switch, the output impedance is very low to absorb a good portion of this back EMF which is directed back at the power supply, not the feedback loop of class A/AB transistor amps where it undermines their phase integrity and dynamics. SPEC's design reduces the load on the feedback loop to enable more accurate speaker drive especially in the mid/high frequencies. BTL operation brings signal to just one pair of terminals and doubles the internal DC voltage, creating an even more powerful sound but with a possibly adverse effect on sound quality, which will rely on the loudspeaker's characteristics. The third selector located on the right part of the rear panel activates the desired input of RCA, XLR at full gain or XLR with 6dB attenuation. A closer look inside reveals a cutting-edge switching power supply with electrolytic Hibiki-Ichi capacitors from Japanese supplier Nichicon. These are renowned for their extremely fast response times as well as very natural timbre. They reflect SPEC Corp.'s care at parts selection like prestigious brands like FM Acoustics did in their glory years (and perhaps still do) but with a certainly more modern approach than the Swiss.


SPEC's resistors were specially designed to spec. The high-speed fast-recovery Schottky silicon carbide rectifier diodes are from Japanese company ROHM. They were selected after critical listening tests involving ten different options. The final choice is a type very close sonically to what a rectifier tube would deliver. It should be noted that SPEC don't simply rely on exactly the same diodes for all of their models. They select them on a case-by-case basis to fine-tune the sonic identity of each product in their range.


This design philosophy is radically different from amplifiers by Hypex, Pascal or IcePower. SPEC in fact design class D to closely approach the sound of single-ended tube amps where each component is chosen according to its sonic and not just measurable value yet enjoys the switching benefits of negligible heat and high power efficiency. A broad variety of electrolytic, oil and mica capacitors sit in the circuit with specific anti-vibration treatment by way of an epoxy resin which reduces internal resonances. The military-grade oil-filled capacitors in the output low-pass filter are supplied by Tucson's Arizona Capacitors (previously West Cap). Those in the RPA-W3 EX are the Blue Cactus C50309 units made up of Kraft paper with a Mylar dielectric and aluminum-foil electrode which is impregnated with high-purity mineral oils. Their casing is hermetically sealed into an insulated electro-tin-plated brass tube with soft-soldered glass-to-metal compression seals on the ends and tinned OFC copper lead-outs. These capacitors are said to offer outstanding performance and very long life but also, according to Tsutomu Banno, high efficiency in the bass and a softer response in the treble to handle the harmoniously rich extension of high-resolution music.