SIT5

Reviewer: Srajan Ebaen
Financial interests: click here
Main system: Sources: Retina 5K 27" iMac (i5, 256GB SSD, 40GB RAM, Sonoma 14), 4TB external SSD with Thunderbolt 3, Audirvana Studio, Qobuz Sublime, Singxer SU-6 USB bridge, LHY Audio SW-8 & SW-6 switch, Laiv Audio Harmony; Active filter: Lifesaver Audio Gradient Box 2; Power amplifiers: Kinki Studio EX-B7 monos & Gold Note monos on subwoofer; Headamp: Enleum AMP-23R; Phones: Raal 1995 Immanis, HifiMan Susvara; Loudspeakers: Qualio IQ [on loan] Cables: Kinki Studio Earth, Furutech; Power delivery: Vibex Granada/Alhambra on all source components, Vibex One 11R on amps, Furutech DPS-4.1 between wall and conditioners; Equipment rack: Artesanía Audio Exoteryc double-wide 3-tier with optional glass shelves, Exoteryc amp stands; Sundry accessories: Acoustic System resonators, LessLoss Firewall for loudspeakers, Furutech NCF Signal Boosters; Room: 6 x 8m with open door behind listening seat; Room treatment: 2 x PSI Audio AVAA C214 active bass traps
2nd system: Source: FiiO R7 into Soundaware D300Ref SD transport to Cen.Grand DSDAC 1.0 Deluxe; Preamp/filter: Lifesaver Audio Gradient Box 2; Amplifier: Kinki Studio EX-M7; Headamp: Cen.Grand Silver Fox; Loudspeakers: MonAcoustic SuperMon Mini + Dynaudio S18 sub; Power delivery: Furutech GTO 2D NCF, Akiko Audio Corelli; Equipment rack: Hifistay Mythology Transform X-Frame [on extended loan]; Sundry accessories: Audioquest Fog Lifters; Furutech NFC Clear Lines; Room: ~3.5 x 8m
Desktop system: Source: HP Z230 work station Win10/64; USB bridge: Singxer SU-2; DAC: Sonnet Pasithea; Headamp: Kinki Studio THR-1; Speaker amp: Crayon CFA-1.2; Speakers: Acelec Model One Headphones: Final D-8000 & Sonorous X, Audeze LCD-XC, Raal-Requisite SR1a on Schiit Jotunheim R
Upstairs headfi system: FiiO R7, COS Engineering D1, Cen.Grand Silver Fox; Headphones: Raal 1995 Magna, Meze 109 Pro, Fiio FT3
2-channel video system: Source: Oppo BDP-105; All-in-One: Gold Note IS-1000 Deluxe; Loudspeakers: Zu Soul VI; Subwoofer: Zu Submission; Power delivery: Furutech eTP-8, Room: ~6x4m
Review component retail: $10'000/pr

August 28th. "I have SIT5 monos here and they do 40 watts into 8Ω and 60 into 4 again as a function of the amount of heat sinking our standard chassis has. Currently they are sitting in systems here and at a few dealers going through the last evaluation before production. That is anticipated to be without feedback and the prototypes run the part in Common Drain (follower) mode instead of the Common Source mode of the SIT4. SIT1 and SIT2 were Common Source, the SIT3 was Common Drain. With enough sinking, a single Tokin 2SK182es could theoretically deliver ~400 watts of Class A but that would leave no margin for reliability so would likely be half. I know how this sort of sonic signature appeals to the 'lower-power' crowd but I'm not certain of a market for a high-power version. It's also uncertain how well that sound could be delivered at high power levels. What is certain is that it would need a large set of heat sinks. Anyway, thanks so much for the SIT4 reviews. I look forward to getting a pair of SIT5 to you when they are ready."

That was Nelson Pass responding to my what-if question of potential output power were the SIT4 allowed a Pass Labs XA-30.8 chassis and power supply. 400 watts from a single-ended single-stage circuit? Wavac's three-stage 833 SET claims 'just' 150 watts from one direct-heated industrial output triode. Nelson's static-induction transistors with triode curves—chased down and acquired after the Tokin factory vanished in the 2011 Fukushima earthquake—rate at 600V, 30A, 400W and 50MHz. Talk about potential space heaters when at just 10/5wpc into 8/4Ω, the SIT4 stereo already dissipates 200 watts at idle. Power attracts the corruptible, absolute power the sociopaths? A 40-watt monaural amp in true class A is all most of us could ever want. Hoarding more watts is for thirstier speakers and louder listeners catered to by other amps. Into 8Ω though not 4, the SIT5 as a FirstWatt amp actually out-specs two Pass Labs models in the XA25 and XA-30.8 stereo versions. Any more power and we'd have brand warfare on our hands. Must resist corruption and sociopathic tendencies. Thankfully Nelson's built-in FirstWatt limiter—the same chassis, power supply and heatsink for all models—keeps us on the straight 'n' arrow. In the SIT5, all the dissipation surface is hogged by just one Tokin not two. How that SIT is tapped differs too. We end up with quad not double power. If we were adventurous or daft enough to bi-amp, we'd need four monos. Have at it? Not if you live anywhere warm. Even a stereo set dissipates copiously. Who wants to listen whilst the air-con blows in overdrive? It's more excellent reason not to dream of a 200-watt Tokin amp, tripped circuit breakers and flickering light bulbs.

… to be continued…