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Reader Gregor Mass: Recently I had a chance at a Tokyo dealer to listen to the SIT-2 and SIT-1 which I'm quite interested in. I learnt about them through your introduction. I'm currently coming from a 4wpc SET system but changed to a Kondo M7 preamp and look now for a suitable power amp. Speakers are Hørning Agathon Ultimate (Lowther-based, 99dB). As in principle I'd be willing—and thus luckily also able to—come up with the requested price for the monos, I would appreciate a cross check with your observations before making my ordering decision. As the room and components were completely unknown to me I draw my observations purely from the A/B between SIT-1 to SIT-2 (and unfortunately the SIT-2 was not yet fully up to final operating temperature).

Initially I did not perceive the bias adjustment to have a huge impact. But by focusing not on any change in tone or 'effects' I found the presentation or perhaps what you call gestalt of the music to move from tightly controlled to more cotton padding while never losing the overall tone and timbre. In terms of differences between the two, I found the monos more satisfying with distinctively better tonal colors and separation which I think allowed the individual instruments/tonal events to much better develop and exhibit more air to breathe. For me it also felt more engaging. In conclusion I tend to go for the monos. Would these observations conform with your experience?

Nelson Pass. It's interesting that the harmonic values vary quite a bit on the SIT-1 with operating points but the actual sound not as wildly. Another case where the explanations probably are way too simple. I adjust the SIT-2 for the same distortion waveform at 1 watt as the center point of the dial on the SIT-1 but they are still not exactly the same. The SIT-1 sees about 40 ohms in parallel with the load and the SIT-2 about 150 ohms.

Reader Chris Mercurio had been in the market for a valve amp but also contemplated the transistor appeal of zero maintenance. After exchanging a few emails he took a chance on the FirstWatt M2. He soon reported back that it turned out perfect for his needs. Hence his desire to spread the news: I dropped my FirstWatt M2 into my friend's full Shindo rig the other day. The midrange on the Shindo SET was just a slight bit better and more 3-dimensional but at the expense of everything else (harmonic detail, bass definition, soundstaging, separation of instruments etc). The M2 absolutely did not exhibit any kind of 'solid-state' sound in an otherwise analog vacuum tube system. I'm trying to get him to take a serious look at the SIT-2 because he doesn't need much power (and he could save money versus the Shindo!). With the SIT platform an appreciable step up from the J2 which I rate above the M2, the plot thickened. For more starch my friend Dan was next.

Aries Cerat Gladius 3-way speaker with Raal ribbon, Fostex midrange and 12-inch sealed Fostex woofer

Chez Dan. When I dropped off his black pair of SIT-1s, source was his usual APL Hifi transport based on a fully rebuilt Esoteric UX1. This was leashed to a new prototype 32-bit/384kHz converter with latest-gen AKM chips in multi-paralleled mode and 6SN7 output stage also from Alex Peychev. The Kondo M-77 preamp in the bleachers had handed the game over to Mick Maloney's three-of-a-kind Supratek Predactor (Mick listens to the second unit, the third is with his partner). The Predactor is a three-box high-gain DAC/preamp. Space requirements have located the DAC's output stage inside the preamp control unit. Dan was only using the preamp section with its 6H8C direct-coupled to 71A DHT themselves transformer-coupled to Lundahl amorphous cores. Hence the two smaller inner tubes in the photo below weren't in the circuit. The Predactor's separate power supply runs tube shunt regulation and tube rectification.

Hi/lo gain switches, balance control, remote volume, DAC outputs, preamp outputs

Dan's extensive journey through the upper echelon of single-ended valve amps often including multiple models from the likes of Art Audio, Colotube, Electronluv, Jeffrey Jackson, Jeffrey Korneff, Kondo, Yamamoto Soundcraft, Wavelength and Wyetech had him finally rediscover his old Berning Siegfried. Sasa Cokic's 75TL Vilobha monos are his alternate higher-power valve option. To appreciate the SIT-1 comparison—and appreciate what type of valve amp it would take to match the Pass amps—some Siegfried intel should prove useful. This really is a very unconventional single-ended 300B OTL based on Berning's US patent N°. 5,612,646. Its tube complement consists of a 6SN7 differential input, 6SN7 balanced amplifier, 6J5 follower/driver and 300B output triodes (or the SV811 in a slightly adapted version).

Berning Siegfried between Predactor control and power supply units

"Siegfried uses RF to change the output tube's voltage-current transfer characteristics from its normal impedance plane to one suitable for driving dynamic speakers. RF remapping is implemented with special high-frequency power conversion techniques. The high-voltage low-current tube impedance plane is remapped to the high-current speaker impedance plane through a special transformer at a constant 250kHz carrier frequency. Because the audio signal rides on a carrier, it is no longer subject to parasitic transformer distortions. There is no lower-frequency limit for this impedance conversion and Siegfried is DC coupled with servos to prevent DC at the speakers. In the conventional amplifier the effective turns ratio of the audio output transformer determines the impedance match between output tube and load. Siegfried matches it with equivalent turns ratio of the RF conversion transformer.

Alex Peychev's best two-box source with Stealth Audio Varidig S/PDIF cable

"Audio output transformers have a limited impedance conversion range imposed by parasitic elements. This is especially true of gapped transformers for single-ended circuits. They also have limits imposed by voltage breakdown between primary and secondary windings whilst the required insulation adversely affects the parasitic elements. It is thus difficult to make a high-fidelity transformer with much more than a 25:1 overall primary-to-secondary turns ratio. Siegfried eliminates these restrictions. For the 300B version the effective overall turns ratio is 30:1 (80:1 for the SV811). The effective plate loading is 7kΩ into an 8Ω speaker. Siegfried uses unusual constant-current source loads for each output tube. These are power converters operated at resonance to behave like high-impedance current sources. Unlike conventional current sources that would dissipate large amounts of power as heat, these current sources actually return this power to the power supply."

The upshot of this 300B amp is elimination of the usual output transformer. With that comes a very audible lifting of the usual frequency extremes limits and circuit noise which plague even the best of the conventional breed (we'll still encounter one such example in the Colotube 300B monos in casa Villeneuve on the next page).

In Dan's system the Japanese Kondo Gakuoh 300B monos had performed on the general level with the Colotubes but the latter had gotten his final nod for their more modern not as deeply tinted 'operatic' sound. Either amp performs at a very high plateau. Yet the massive 50kg dead-quiet Vilobhas he'd commissioned and the very lightweight Berning Siegfried work from an even more elevated altitude. During this visit we merely compared Berning and Pass.

The lone output device

Whilst the Berning's treble didn't spell 300B softness by any stretch to prove that the tube itself isn't the bottle neck as one tends to suspect, the SIT-1's grasp over a familiar well-recorded Buddha Bar track with very subdued spiderwebby bells embedded deep in the background was even keener. I could clearly see certain flimmering decays swirl about as the player physically moved the bells in space. The super-potent three-stringed gimbri bass of the Hadouk Trio's Lou Ehrlich had even more growl and snap. If the Siegfried had any advantages on vocal sex as Chris Mercurio had noted for the Shindo SET over his M2, they were truly minor. The degree of tone density and color intensity the transistor monos revealed was stunning.

One of eight 100-watt power resistors to set bias

Granted, the direct-heated 71A triodes in the Supratek preamp were hardly innocent. But Siegfried benefited the same. That's the takeaway. It didn't take a state-of-the-art 300B SET of decidedly unconventional OTL pedigree to achieve this thrilling combination of exploded bandwidth, charged reflexes, lively dynamics and great deep tone. In this impromptu and casual match I'd not declare one or the other the clear winner—that would take more time—but talk of slightly non-identical equals. For adventurous listeners with very broad musical tastes the particular grouping of SITtributes should dominate. In Dan's context this not only put the FirstWatt amps ahead of famous £48.000 valve amps but did so without the so very slippery slope of gradual tube aging.

At $6.950 when still available, the Siegfried was priced fairly on materials but seriously undervalued on actual performance. At €40.000 the giant Trafomatic Audio Vilobhas are direct present-day competitors. That's also the plateau where the SIT-1 roams. In an earlier Dan audition my €5.500 Kaivalya monos had been clearly outclassed by the Vilobhas and SIT-2 prototype. In my system the Kaivalyas meanwhile had solidly bested my Yamamoto A-09S. This paints a map with a few markers. For the SIT-1, listeners halfway between 'deep triode' and 'lit up like a Gryphon' might explore premium valve preamps. If so they'll perhaps focus on direct-heated triodes like the 101D and 10Y which Trafomatic Audio introduced in recent linestage models.

In Dan's system that day we favored the SIT's operating point dead center. There it had just the right balance between softer/more billowy and tauter/leaner/spikier. This shift range was still quite subtle. It perhaps related most understandably to rolling quality tubes of a similar persuasion, say EML to EAT and Synergy Hifi 300B or Full Music to reissue WE. We also favored the 'SITdirect' impedance setting. Different tastes, speakers and ancillaries should call for different preferences. Regardless, the SIT-1 not only on paper but also to the ear behaved decisively like a fast top-class very modern triode amp of the sort that can—but doesn't have to—cost five times more. Having inhabited that bigger picture with some recognizable suspects for context, the more specific assessment would require my own system again.