Gaining on GaNTubes. Here's what 250/350w into 8/4Ω tucked into a small glass bottle look like from the front and rear. The 120KT's base diameter exceeds the actual KT88 socket Alberto uses so he surrounds it with a machined PVC ring until the injection-molded equivalents arrive. Eight vertical 1.5mm bores act as air exchangers. It's another reminder that this isn't a vacuum but vented glass bulb. Neither is the amp chassis hermetically sealed. It exploits three slit vents beneath its smoky acrylic crown to create some air flow. As we knew going in, Alberto's industrial design with its orange back lighting for bulb and case is quite the talkie. For those familiar with tubes, spying a KT120 lookalike that's filled not with filaments and getters but capacitors, finned transistors and miniature resistors is another wake-up call. Nothing new under the hifi sun is a thin-worn cliché. Different and novel do still happen. One must just know where to look.

What initially throws even educated audiophiles is, again, the solid-state-as-tube thing. Many assume that it just has to be a dubious marketing gimmick for the sake of being different. As numerous reviews have shown already, gimmicky is the last thing this family of power amplifiers is. If this output stage didn't live inside a removable tube, you'd not easily swap it for a true long-term investment. A hot-swappable concept demands an externally accessible output stage that unplugs easily. Why make it an invisible slide-in card? Why not dress it up to look awesome? Don't ask a stylish Italian that and expect a boring answer. Why doesn't Alberto publish a 2Ω figure when shoppers of high-power amps tend to use it as an arbiter for low-impedance stability? It's something measurement-centric reviews like Stereophile's check on. In some quarters, power doubling into 2Ω is even regarded as a badge of 'proper' amplifier excellence. "It's irrelevant. It's not 'watts' which drive the variable motor that is the loudspeaker. It's 'amperes' aka current. Here Grand Vivace is capable of 50 amperes. Vivace does 32A. The real challenge is how fast any amplifier can deliver that current to drive the motor. A tractor has huge power and traction but doesn't go fast." This returns us at minimizing a circuit's inductance, using 0.1% tolerance parts with ultra-low stray inductance, keeping it maximally compact and using gain devices which switch much faster than traditional silicon Mosfets. To sustain its bigger headroom, Gran Vivace's power supply has twice the capacitance of Vivace. To deliver its higher current, it uses far bigger 600V GaN devices and two per bottle. Unlike traditional amplifiers whose circuits occupy far more physical mass, Gran Vivace is thermally stable "within five minutes".

Asked how in Vivace the 88KT and 120KT compare, "at standard volumes where we consume from 1 to 5 watts, very similar. It's when SPL increase that the bigger tube's higher current comes to the fore even though in the original circuit, you won't tap its bigger power. Still it'll sound more dynamic, with a more potent sense of sustained power." Alberto also shared how some of his clients feel that the 120KT in that lower-power mode sounds a bit warmer. The things he learnt during the design of the 120KT output stage he also applied to the next generation of 88KT to remain as sonically similar as possible. "I think that the sense of holographic ambiance which good recordings capture has benefited in particular." He's already working on a smaller EL34-encased version which could show up in a headphone amp. And as an aside, among his Audion clients are Avantgarde hornspeaker owners to reflect highly on the amps' ultra-low noise floor. On the subject of commercial OEM power modules which dominate public perception on class D, "they're designed for cheap very high-volume manufacture by companies which specialize in switching power supplies. It sets a design path very different from mine. Mine isn't about cost-efficient mass fabrication of the power modules at all. Mine is purely about the very best possible performance."

Here we remember. Class D's primary commercial edge has always been power conversion efficiency and compactness. Class D powers your TV, laptop, PC and cellphone. These devices are used in the millions if not billions. Imagine them driven in class A or AB. If made maximally compact like a 25wpc Bakoon AMP-13R, they'd get very hot. For mobile, low efficiency kills battery life. Sizing up to accommodate larger batteries defeats miniaturization and thinness. Remember the old satellite phones with antenna? Thus the smart streamlined modern tech we take for granted relies on class D. Here premium sound quality has never been any priority. Only our comparatively small high-end community demands it where very few designers comfortable with the tech's fundamental differences to traditional topologies challenge themselves to push beyond class D's mass-market imperative. Alberto sees himself as such an evangelist. He's committed to fight class D's bad rep in the upper high end. He wants to prove the doubters wrong. His are unapologetically expensive but proprietary circuits. They are not ICEpower, Pascal or nCore modules with Jeff Rowland, Aavik or Bel Canto Black badges. To some shoppers looking at class D past Apollon, NAD, Nord & Bros., that makes a difference to then grant interest; to not be written off as cheap OEM tech repacked for far too saturated green.