Reviewer: Srajan Ebaen
Financial interests: click here
Sources: 27" iMac with 5K Retina display, 4GHz quad-core engine with 4.4GHz turbo boost, 3TB Fusion Drive, 16GB SDRAM, OSX Yosemite, PureMusic 2.04, Tidal & Qobuz lossless streaming, Fore Audio DAISy1, COS Engineering D1, Metrum Hex, AURALiC Vega, Aqua Hifi La Scala MkII, Questyle QP1R (.aif), Apple iPod Classic 160GB ((.aif), Astell& Kern AK100 modified by Red Wine Audio (.aif), Cambridge Audio iD100, Pro-Ject Dock Box S Digital, Pure i20
Power & integrated amplifiers: Pass Labs XA30.8, FirstWatt S1, F6; Crayon Audio CFA-1.2; Goldmund Job 225; Gato Audio DIA-250; Aura Note Premier; Wyred4Sound mINT; AURALiC Merak [on loan]
Loudspeakers: EnigmAcoustics M1, Albedo Audio Aptica; Sounddeco Sigma 2; soundkaos Wave 40; Eversound Essence; Zu Audio Submission; German Physiks HRS-120, Gallo Strada II w. TR-3D subwoofer
Cables: Complete loom of Zu Event; Ocellia OCC power loom [on loan] Black Cat Cable redlevel Lupo, KingRex uArt double-header USB; Tombo Trøn S/PDIF; van den Hul AES/EBU; AudioQuest Diamond glass-fibre Toslink; Arkana Research XLR/RCA and speaker cables [on loan]
Power delivery: Vibex Granada/Alhambra on all components
Equipment rack: Artesania Audio Exoteryc double-wide 3-tier with optional glass shelves, Rajasthani hardwood rack for amps
Sundry accessories: Acoustic System resonators, Verictum SIlver X Bulk on amp and preamp
Room: Irregularly shaped 9.5 x 10m open floor plan with additional 2nd-floor loft; wood-paneled sloping ceiling; parquet flooring; lots of non-parallel surfaces (pictorial tour here)
Review component retail: €3'900

Beyond Frontiers. Moscode. PS Audio. Tenor. Trilogy. Unison Research. What do amplifiers from these companies have in common? Or KR Audio and Nagra? Or DACs from Aqua Hifi, Canary Audio, Fore Audio and Nagra? They're hybrids. They marry voltage gain from valves with current gain from solid state. Well, only the first group does. The even rarer second one reverses the recipe. Now transistors drive the glowing outputs. Meanwhile these particular D/A converters throw all tube-sourced voltage gain out the window. They use their small-signal bottles purely as buffers, in Nagra's case actually at negative voltage gain. "Big deal" says she who runs a valve pre into a transistor power amp. Quite right. Such folks accomplish the same mutty matter of marrying sonic attributes from either camp. Where purists interject is on the subject of the number of gain stages required to pull it off. A tube preamp may be a 2- or 3-stage affair. Most amps are three stages or more. Here the notion of less is more enters. Each added gain stage complexifies THD, being liable to add higher-order artifacts. The purist goal is to limit oneself to 2nd and/or 3rd order and even there to very low levels. A two-stage solution would be ideal.

The most popular argument in favour of the tube/transistor hybrid (and in that and not the other order) is that it exploits each device for its ideal purpose. That means linear voltage gain for the glow worms. It dedicates the heavy lifting of low-impedance current creation into a non-static load to the semiconductors. Folks who've heard - er, rumours that direct-heated triodes are the most linear of tubes will instantly wonder. Why doesn't one see an army of hybrids which follow up popular DHT like 10Y, 2A3, 300B, 45, PX25 & Co. with transistors? On last count, I found fewer than 15 commercial preamplifiers with direct-heated power triodes to support a hybrid two-box scheme. Once one demands—or is curious about—a one-box solution, the options narrow even more. My November 2014 industry feature of Trafomatic Audio's Sava had been only the second such encounter in 12+ years on the beat. The other was the APL Hifi HAS-M high-power hybrid which spreads the hybrid power-stage concept over three boxes, one for the DHT drivers, two mono current buffers for the transistors. My friend Dan has both. He'd in fact commissioned the Sava from Sasa Cokic to satisfy his own curiosity on the viability of a DHT hybrid.


Because Dan runs hi-eff speakers, either the Rethm Saadhana III or Voxativ 9.87 system, both 100dB, his 38wpc custom Sava doesn't pursue muscle. Instead refinement and zero noise were the overriding targets. Idealists and theoreticians—rather the same in my book—meanwhile point out that the ultimate appeal of any DHT+transistor beast should be to extend 45-SET virtues to power-hungry reactive loads. In short, why not a 100/200/400w into 8/4/2Ω power lifter of vintage Krell herculosity? When Sasa let on that he was at work on a formal production model that would incorporate Sava lessons, my arm shot up. That was prior to having any notion on price or power. Dan's one-up hybrid around his favourite 10Y triode had cost him a cool €20'000. That's a heart-stopping quarter million in Sasa's Serbian dinar currency. I rather hoped for plenty less with Sava's second coming. But to be frank, the prospect of extended (s)mutty pillow talk with a hybrid circuit from a known tube crafter made practical considerations secondary. I committed blind. First rumblings that this assignment might move out of reach was a note from dealer Fred Crane of Stereodesk/Audioprana. He implied that he'd be the eventual recipient of my loaner which would go to market for ~$30'000. This begged for a small tug on my blinds. I emailed Sasa. Was this indeed the projected positioning based on the usual shipping, customs, import and retail margin requirements? What type power rating was he working on this time? What tube type?

"Fred is a bit confused. The amp he thought to send you is the custom 10wpc 75TL-based SE integrated with headphone out [above]. It has absolutely zero connection to the new hybrid. That will make around 100wpc and be a fantastic combination of C3m input pentode and professional Japanese bipolars as phase splitter/drivers for the Exicon lateral output Mosfets, with separate power transformers and supplies per channel. I discovered the Japanese transistor whilst fixing my broken oscilloscope. It's truly special in this parts mix. The retail price will be ~€4'000 and the optics like the image below. btw, during R&D of many different driver stages for the big 450TL bottle—a 140wpc custom amplifier for another Fred customer—I built a truly amazing low-power SE amp with the EML 20B-V4 tubes, one as preamp, one as output. I found some exotic nano crystal IIC cores with 0.03mm metal-sheet windings and got stunning sound from this 4-watt amp, similar to a 71A but with stronger bass and far better treble."

Now things were adding up. One less zero than Fred's custom amp over which Sasa had once again slaved for untold months to drive up fees; 100 watts of real-world power; and instead of a microphonic direct-heated power triode, a proven very linear super low-noise Siemens C3m pentode from Germany's early telephony era. We've seen it as a most excellent driver in many of Shigeki Yamamoto's SETs. Strapped for triode, this high-spec bottle exhibits nearly perfect curves. And aren't curves why people look at tubes in the first place?