SPEC's 'house' mica capacitors are just as exotic. Their dielectric is a precious muscovite-type mineral with an extremely stable temperature coefficient and excellent resistance to the dielectric voltage. Their MC-DA capacitors use high-quality white mica from India. Their laminar structure minimizes inductance so capacitance does not fall below 1MHz. Silver electrodes are printed on both sides of the mica sheet. To avoid magnetic interference, the metal support which blocks the laminated dielectric consists of tin-plated brass plates. The capacitor's body is sealed in epoxy resin to minimize vibrations when applied voltages excite the inductor material and electrodes.

The Mosfets in the switching output stage are identical to those used for the integrated RSA-717 EX. They are from Infineon Technologies, formerly known as International Rectifier. It's where Tsutomu Banno worked before co-founding SPEC with Shirokazu Yazaki. These devices are located on the underside of the motherboard. The performance of any class D amplifier obviously depends on its switching accuracy. Here Tsutomu Banno used a hybrid two-in-one approach, integrating the driver and Infineon's DirectFET with a PowIRaudio module. But class D circuits are also particularly sensitive to the quality of their power supply and low-pass filter. Here the output filter is an ultra-simple toroidal/capacitor inductor circuit with custom-made parts of the highest quality including the aforementioned Arizona oil capacitors. To finish our tech, the specs for the RPA-W3 EX are max power of 100wpc into 4Ω; 10Hz-30kHz ±1dB bandwidth (6Ω, 1W); 0.02% THD at kHz to 80% of max power; 0.3Vrms input sensitivity; and high 37.3dB gain at full power (6Ω, 1kHz).

Sound. The RPA-W3 EX/H-VC5 set had all the liveliness and breadth which already characterized the RSA-717 EX four years ago. From the very first note I had the impression of listening to a very good tube amplifier because the sound was so liquid, transparent, fast and holographic. Then I realized that I could ignore the usual colorations of tubes, be those pleasant, unpleasant or invigorating. This in my opinion amounted to the closest transistor approximation of a tube amplifier I had yet experienced. Just so the bass was masterfully controlled, the noise floor very low and so was subjective distortion even at realistic sound levels. I know that it's rather common to compare a good solid-state amplifier to a tube device whenever one spots such liquid behaviour. The RPA-W3 EX however far exceeded this type of consideration. Its sonic DNA was much closer to a triode set and in a blind test, it would have been very easy to mistake it for a pure tube amplifier. This was an unprecedented achievement for a Class D amplifier.

The main changes over the RSA-717 EX integrated seemed to be its ability to drive more difficult speakers as well as a greater authority in the low end. On my two pairs of challenging Vivid Audio Giya—the G1 and Spirit models—the RPA-W3 EX pair provided me with excellent results. For two amps of just 50wpc/8Ω each, that was rather unexpected. What really impressed me was the soundstage depth along with the high level of ambient recovery. Each part and layer of the soundstage was well separated without sacrificing the overall continuity of the panorama. The SPEC combo in fact cast the greatest depth I've thus far been able to obtain in my listening room where the positioning of my speakers already allowed pretty good results. But with the two SPEC amplifiers, the perception of relief was even more striking, especially on recordings of great orchestras. I heard the sense of space, scale and holography that good single-ended tube amplifiers can deliver but now with definitely greater focus and precision of the three-dimensional image. In short, the RPA-W3 EX amplifiers were great fun right from the start. You only have to switch on the front toggles and everything just works.

Another great feature of the set was the stunning immediacy or sense of urgency along with their transparency which reflected the promise of pure digital amplifiers but with greater finesse, greater density in the bass, more air and more refined timbres. Pairing the two RPA-W3 EX with an external preamplifier already gave pretty good results but switching to 'Pure Direct' mode made for even higher transparency. The option of SPEC's external volume controller (be it is the H-VC5 or companion RPA-P7 preamplifier) is therefore highly recommended. I'm surprised to find myself praising the merits of amp-direct when a short while ago I was a staunch defender of analog preamplifiers, especially those with valves. To my ears, the contribution of an excellent preamplifier has always been the soul of my system, the guarantor of its overall performance level. Only recently the most current achievements of French company Acoustical Beauty in terms of digital control code made me realize that there could be an even better solution than a premium linestage; which it to say, no preamp at all as long as volume management was handled with a level of loss almost undetectable by ear. The methods of Acoustical Beauty and SPEC differ radically but their sonic impact can be easily distinguished in either case: the level of transparency increases whilst overall distortion decreases significantly. Bypassing traditional resistive gain management or conventional dithering methods for digital attenuation is very effective. Acoustical Beauty's innovative algorithms still exceed what SPEC Corp have wrought but theirs remains a quite mandatory option if one acquires one or several SPEC power amplifiers given how Acoustical Beauty's patented digital attenuation code has not yet been released (it should be included in Audirvana's next revision).