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: $11'000/pr

Running at a constant 200 watts, actual use rather than a promo pic would probably not really want to stack these to run them cooler.

August 28th. "I have SIT5 monos here. 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're sitting in systems here and at a few dealers to go through the final evaluation before production. That's anticipated to be without feedback. 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 am 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 and Dawid when they're ready."

One of two mighty Tokin in the stereo SIT4.

That was Nelson Pass on 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 200W 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 still thirstier speakers and louder listeners already catered to by more conventional amps. Into 8Ω though not 4, the SIT5 actually out-specs two Pass Labs models, the XA25 and XA-30.8 stereo amps. Any more power and we'd have us brand warfare on our hands. Confucius in his crumbly dry fortune cookie say, 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, one Tokin not two hog the available dissipation surface. How that transistor is tapped differs too. We end up with quad not double power and far bigger low-impedance support. If we were adventurous or daft enough to bi-amp, we'd need four monos. Have at it? Not if we live anywhere warm. Even a stereo set will dissipate copiously. Who wants to listen whilst the air-con blows in overdrive? More excellent reason not to dream of a 200-watt Tokin amp, flickering light bulbs and related excesses. Once more, on specs the SIT5 already sits smack-dab between the familiar FirstWatt and Pass Labs catalogues. For FirstWatt the SIT5 are unusually hulky. For anything more, Pass Labs have many answers. And to return to the designer, Nelson isn't even sure that, a/ the device's special single-ended sound would scale intact to max power and, b/ that people needing or wanting such power wouldn't prefer a different sound. As a proper artist, Nelson knows his audience. He's learnt what kind of tuning between his two different brands best meets it. Given prototype status of the above specs and whatever feedback beta testers returned, we could still learn of changes once this circuit went into formal production. Those changes were a minimal downrating of the 8Ω spec to 35 watts. The published highlights then again list zero feedback, 100kΩ input like that of the SIT4, 0.25Ω output impedance 16 x lower than the SIT4, 0.1% distortion so a 6 x lower value, 36µV of noise so half that of the SIT4 and at 19dB, just one decibel less voltage gain. Finally, the SIT5's upper -3dB bandwidth is 200kHz not 80kHz.

Voxativ Hagen2 5-inch widebanders crossed over to 2×15" cardioid subwoofer, FirstWatt SIT1 monos driving the monitors from Berlin.

By mid November I met the company's Desmond Harrington in Killarney to hand over my loaner SIT4. He told me how a set of SIT5 had already dispatched to Warsaw to give Dawid Grzyb first dibs before forwarding to Ireland. If the SIT4 had your full attention but didn't properly peg your power meter without first selling off your existing hard-of-hearing speakers, today we might have something more suitable for your needs. Given the stereo version's departure, you obviously won't expect a side-by-side comparison.

That said, Dawid's award and my equal enthusiasm for the SIT4 suggested that if the same or similar sound can be had with usefully more power, we'd recognize it even without a SIT4 in standby. Or as it says above the arched entry of FirstWatt, "there's no such thing as a perfect amplifier but there is a best amplifier for each type of speaker, music and listener. Each FirstWatt piece is a unique design and "best" in some particular way. They look alike because all use the same basic chassis and power transformer. On the upside, it makes it easy for me to test ideas and compare different designs with the hardware being a fixed constant. Looking for tomorrow's faceplate with yesterday's circuits? You're in the wrong place."