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 3.01, Tidal & Qobuz lossless streaming, COS Engineering D1, AURALiC Vega, Aqua Hifi La Scala MkII, Fore Audio DAISy 1, Apple iPod Classic 160GB (AIFF), Astell& Kern AK100 modified by Red Wine Audio, Cambridge Audio iD100, Pro-Ject Dock Box S Digital, Pure i20, Questyle QP1R
Preamplifier: Nagra Jazz, Esoteric C-03, Vinnie Rossi LIO (AVC module), COS Engineering D1
Power & integrated amplifiers: Pass Labs XA30.8; FirstWatt SIT1, F5, F6, F7; S.A.Lab Blackbird SE; Crayon Audio CFA-1.2; Goldmund Job 225; Aura Note Premier; Wyred4Sound mINT; AURALiC Merak [on loan]
Loudspeakers: Albedo Audio Aptica; EnigmAcoustics Mythology 1 w. Sopranino super tweeters; Sounddeco Sigma 2; soundkaos Wave 40; Boenicke Audio W5se; Zu Audio Submission; German Physiks HRS-120; Eversound Essence
Cables: Complete loom of Zu Event; KingRex uArt, Zu and LightHarmonic LightSpeed double-header USB cables; Tombo Trøn S/PDIF; van den Hul AES/EBU; AudioQuest Diamond glass-fibre Toslink; Arkana Research XLR/RCA and speaker cables [on loan]; Sablon Audio Petit Corona power cords [on loan], Black Cat Cable Lupo
Power delivery: Vibex Granada/Alhambra on all components, 5m cords to amp/s + sub
Equipment rack: Artesania Audio Exoteryc double-wide 3-tier with optional glass shelves, Exoteryc Krion and glass amp stands [on loan]
Sundry accessories: Acoustic System resonators, Verictum RF/EMI blockers
Room: Rectangular 5.5 x 15 metres with gabled 2-storey ceiling and stone-over-concrete floor
Review component retail prices: €9'000

What if one wanted transistors to sound like hollow state?
In many ways, it's an entirely Quixotic proposition. No matter what, transistors will never be tubes. Or vice versa. It's Rudyard Kipling's never the twain shall meet. Transistors will never have swarms of electrons zip through a vacuum. Whether, Bob Carver like, one models their transfer function or ends up with equivalent output impedance; uses output transformers or McIntosh-like autoformers... treating two inherently different output devices in the same way, eve arriving at similar THD via other chicanery can't offset that these parts will always be fundamentally dissimilar. Many of the Nelson Pass FirstWatt amps in their topologies share things with basic tube-amp circuits but they neither sound like them nor were they intended or claimed to do so. To end up with a badly hobbling sentence: Similar isn't the same as same.

What if one rebiased the question? What if an experienced tube-amp designer was tasked—or tasked himself—with designing a sand amp? How would he approach it? In the case of one Alexey Syomin from Russia, extensively chronicled in these pages already, his resultant class A/B White Knight integrated does get massive output transformers. It even uses a 5Hz-300kHz stepup transformer for passive 32V gain. Transformer gain we know of from low-output cartridges. It's rarer in power amplifiers though FirstWatt and Audio Consulting are two easy precedents. In typical SET fashion, the White Knight uses no negative feedback. But then, neither do solid-state electronics from Ayre Acoustics or others. For balanced power, the overbuilt bipolar supply runs on four vertically aligned toroidal line transformers. This array pursues maximal noise rejection on the AC mains. It also contributes heftily to the final weight.

"Each channel has two power transformers, one for '+', one for '-'. To wind these, we use high-precision machines. They guarantee perfect symmetry of the power supply poles. Transistors suffer distortion when rising temps lead to higher current conduction and eventual failure. My aim was to create a constant quiescent current regardless of temperature. Other parts require their own thermal stabilization to operate best. In our case, transistors operate at 70°C, capacitors at 60C° and resistors between 40-50C°. We stabilize our transistors with Beryllium oxide couplers. Our output module runs 24 powerful transistors, 6 for thermal control, 18 for current gain. Capacitors too alter behaviour with rising temps. We stabilize this with different thermally conductive compounds. Partitions inside our module prevent these compounds from mixing. This locks in optimal working parameters for different parts. The only downside is extreme complexity for assembly of our potted modules. It's time consuming and uses 6kg of exotic compounds to add serious labour and parts costs." Military-grade sealed relays act as input switchers. 'Direct' mode bypasses the volume control for the first input. It converts our integrated into a pure stereo power amp. Delivering 90/180wpc into 8/4Ω, the first 20 watts operate in class A. The attenuator is a simple variable resistor at the amplifier input.

Whilst one wouldn't expect the White Knight to sound like a traditional valve amp, it was designed by a classic valve-amp expert. It's thus accompanied by very specific sonic expectations; runs on 'heavy irons' like a premium tube amp; and combines a passive stage for voltage gain with a single current buffer where transistors are exploited solely for what they do best: amplify current. This mirrors SET lore with a minimum-stage architecture. Diverging from common SET specs meanwhile are 10-250'000Hz bandwidth ±0/3dB, a damping factor of 950, claimed SN/R of -140dB and THD of below 0.001%. Given these figures, one knows going in that the White Knight doesn't really behave like a tube amp. Knowing who designed it, one simply wonders what, exactly, it does sound like.

When Alexey emailed that he'd delivered the amp to Russian customs in Moscow for export, a smiley face added that "I hope they don't break anything". Given what looked to be a Blackbird-type chassis loaded with heavy iron, I seconded his thoughts. Two prior S.A.Lab deliveries had incurred shipping damage; one with a broken transformer bolt to suffer a free radical donut; one with broken stand-offs to net a very precarious heavily loaded PCB. "After quite the experience trying to send you the White Knight amp, I finally succeeded. I don't know why but customs requested a fumigation treatment. We had to unpack it from the original box (customs said it looked too military, hence suspicious) and repack it in two other boxes so total ship weight decreased from 68 to 56kg." So much for smooth governmental cooperation with small domestic entrepreneurs trying to do the export business.