Country of Origin



Reviewer: Srajan Ebaen
Financial interests: click here
Sources: Retina 5K 27" iMac (4GHz quad-core with Turbo boost, 32GB RAM, 3TB FusionDrive, OSX Yosemite. iTunes 14.4), PureMusic 3.02, Audirvana 3, Qobuz Hifi, Tidal Hifi, COS Engineering D1, Denafrips Terminator, Soundaware D300Ref as USB bridge/SD transport
Preamplifier: Vinnie Rossi L2 Signature with Elrog ER50; Nagra Classic, Wyred4Sound STP-SE Stage II, COS Engineering D1, Vinnie Rossi LIO (AVT module)
Power & integrated amplifiers: Pass Labs XA30.8; FirstWatt SIT1, SIT3, F5, F6, F7; Goldmund/Job 225; Wyred4Sound mINT; Nord Acoustics NC500 monos; LinnenberG Audio Liszt monos, Crayon Audio CFA-1.2, Bakoon AMP-13R; Simon Audio i5 & AIO
Loudspeakers: Audio Physic Codex; Acelec Model One; Cube Audio Nenuphar; Albedo Audio Aptica; EnigmAcoustics Mythology 1; Boenicke Audio W5se; Zu Audio Druid V, VI & Submission; German Physiks HRS-120; Eversound Essence; Fram Midi 150
Cables: Complete loom of Allnic Audio ZL 3000 & 5000; Zu Event; KingRex uArt double-header USB cables; Tombo Trøn S/PDIF; van den Hul AES/EBU; AudioQuest Diamond glass-fibre Toslink; Black Cat Cable redlevel Lupo; Ocellia OCC Silver
Power delivery: Vibex Granada/Alhambra on all source components, Vibex One 11R on amps/sub
Equipment rack: Artesania Audio Exoteryc double-wide 3-tier with optional glass shelves, Exoteryc Krion and glass amp stands
Sundry accessories: Acoustic System resonators
Room: 4 x 6m with high gabled beam ceiling opening into 4 x 8m kitchen and 5 x 8m living room, hence no wall behind the listening chairs
Review component retail: €TBD

Plate amp layouts for Acelec Model Two MkII

In late April, Cees Ruijtenberg asked me for John Darko's current email. I took the opportunity to ask Cees about progress on his planned 50-watt class A/B Kratos monos for Sonnet. Their original target specs included output noise of 300µV RMS, slew rate of 50V/µSec, 30dB of gain and bandwidth of 10-300 Hz/kHz -3dB. "I'm actually busy with the new active sub. Instead of nCore I decided to create my own new amplifier to have more design flexibility. That new amp turned out so good that it'll replace the Model Two's current nCore electronics. And it's now even influencing my ideas about Kratos. So next week I must compare the current Kratos to this new design, then make a decision."

1-watt distortion measurement of new amp circuit

To step back one, Cees, ex Metrum Acoustics, now helms the brands Acelec for speakers, Sonnet for electronics. To activate his Acelec Model One monitors which play in my upstairs system and evolve into a Model Two—and for an active sub stand to eventually augment our Model One—Cees needed electronics. nCore/Hypex offer numerous modules dedicated to such tasks. Now we take one step forward again. Cees' own plate amp for the upcoming subwoofer had bested not only nCore to enforce a Mark II revision of the Model Two. It even threatened to overturn his original design for the Sonnet Kratos monos. Added to his existing R2R Morpheus DAC with true variable gain and the Hermes server, those will complete a compact Cees electronics chain.

By May 1st, our industrious Dutch was still optimizing his amps for the Model Two MkII. "As a result we now have extremely low distortion and noise. It's clear that such specifications are not just reserved for PWM amplifiers." Which way would Kratos go?

First Kratos version at left, new prototype module at right

Until our story continues, we're left looking over the shoulder of a gifted engineer. To escape restrictions of a proven OEM solution, he minted his own only to surprise himself. As a result, other models already finalized or just about to would benefit as well.

Ingenuity can be a real pain in the arse.

So can moving house. That's currently on Cees' agenda. So this R&D will slow down for a few months. But something is definitely in the works.

… to be continued…