July
2024

Country of Origin

USA

SIT4

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: $5'000

SITuational awareness. You need it with FirstWatt's SIT4 stereo amp. 8Ω power at 2% THD is just 10wpc or 5wpc into 4Ω, output impedance a high 4Ω. Whilst those figures will scare off or amuse the class D crowd to death—what better way to die than laughing?—there's more here than meets the eye. That's a very good thing too when amplifiers (should) aim at our ears not eyes. Our ears can have a rather different opinion on these matters when copasetic speakers are in play. Those obviously want very little power and damping. The class D crowd tends to be oblivious to their very existence. And to be sure, it's not the classic multi-way tower with its complex reactive crossover and heavy-coned large-excursion woofer/s firing beaucoup back-electromotive force at an amp's output stage. It's a high-sensitivity speaker of light cones and big magnets, a combo which applies all the desired damping already whilst being bloodhound sniffy on noise. Present such drivers with an output impedance of too many zeros and you'll choke off their expressiveness plus cause premature bass roll-off from overdamping. Using the wrong tool for the job makes you the tool and the hyenas heckle.

A few suitable widebander candidates come from AER, Camerton, Cube, Lindemann, MonAcoustic, Rethm, Voxativ & Zu.
That's before we expand our options to front-horn-loaded speakers à la Avantgarde & Co and JBL/Klipsch types.

One Tokin SIT per channel on the top left and right.

On the THD subject, the SIT4 has its own mind, too. As a circuit where a single amplification stage generates all the voltage and current gain, it doesn't upshift the order of THD with cascaded gain stages. It's about low-order distortion which avoids the higher-order products that even at homeopathic doses become disharmonious so annoying. With curves very much like triodes, the class A load line of the SIT4's static-induction transistor is set for the negative-phase 2nd harmonic. That's after the original SIT1 monos had a frontal knob which could shift the load line and with it, the distortion behaviour. Owner feedback signalled a clear preference so subsequent SIT models locked it in. Whilst this amp's industrial Tokin THF51 SIT rates at 600V, 30A, 400W and 50MHz (!), the standard FirstWatt casing limits the size of its power supply and dissipation area of its heatsinks to just ten very carefully curated watts. But the NOS nature of the prior since discontinued SIT models continues. Just as SemiSouth which Nelson Pass commissioned for his original SIT part folded so did the Tokin factory in 2011's Fukushima earthquake. Across the years following, Nelson managed to buy up sufficient inventory of remaining Tokin SIT to author today's amp. It's a solid-state version of a limited-edition valve SET that exhausts an inventory of no-longer-made exotic power triodes until they're gone. But unlike a 10-watt direct-heated triode's limited life expectancy, the SIT4's massively overrated extremely underused output devices should coast for decades to come.

The SIT4 is a single-ended class A amp whose static-induction power transistor in common-source mode is biased by a mu-follower current-source Mosfet. An NOS Toshiba 2SK170 Jfet buffers its input. Despite the single amplification stage there's a virtually standard 20dB of voltage gain and high 100kΩ input impedance. Though this simple circuit was developed to be perfectly stable without any negative feedback, the final iteration applies just 6dB to trim some THD and up the damping. With class A's always-on outputs conducting the same at idle as at full power, consumption is 200 watts. At 32lbs and 17x15x5" WxDxH, the SIT4 isn't a backbreaker as virtually anything is in the parallel Pass Labs catalogue past the smallest models. That main line reiterates Nelson's familiarity with normal speakers and the needs of their owners. It leaves his FirstWatt brand to focus on more exotic transducers and their specialized requirements. Situational awareness. Now you have it for the SIT4.

A 20wpc FirstWatt F7 murders our 250-watt class AB monos on this Cube Audio Lotus 10 load.

Should you still wonder why not just use a classic single-ended triode amp for its target loads instead, I come up with three instantly brilliant reasons: no output transformers; lower circuit noise and zero microphonics; no tube aging and concomitant replacement concerns. It's of course unlikely that these transistors make for complete sonic overlap with actual vacuum triodes. And why should they? Tube output transformers leave a fingerprint which includes phase shift, parasitics and a low-pass filter function. Perhaps some find the sonic consequences thereof the cat's meow not goat's meh? If so, the question still remains whether lower noise and no maintenance don't weigh more. On matters of weight, our review will start with Dawid in Warsaw before I follow up in Eire. Two opinions weigh more than one and our track record with this firm has by now established this recipe and workflow. Having appropriate speakers is a must of course. Otherwise we'd bring a mouse trap to a boar hunt. Oink. I had Cube's below Nenuphar v2 and Zu's Soul VI standing by. Truffles.

19wpc 211 SET from Sicily's Tektron.

Our man in Warsaw had Zu's DWX. More truffles. Over to you, Dawid.