6MOONS AUDIOREVIEWS: S.A.Lab SUT & Thunderbird

Readers who have been following us for a few years are probably familiar with S.A.Lab, arguably the premier boutique audio manufacturer in Russia whose electronics, from the affordable yet over-performing Blackbird to the unobtainium Erato, have been showcased in our pages on multiple occasions. I will let you dive into our archives to get a better feel for this 13-year old company, its founder Alexey Syomin and its history. What stands out to me is a propensity for extreme build quality—some might even say over-engineered—regardless of the price point considered; as well as a consistent sonic signature leaning towards the richer and saturated side of things due to the systematic use of tubes and transformers. S.A.Lab have created a name for themselves through custom designs requiring the utmost quality and it shows in everything they do. Tubes, transformers and massive construction will also showcase prominently with the two components under review here, first a phono step-up transformer followed, in part II, by the Thunderbird, a brand-new linestage and phono preamplifier weighing more than most integrated amplifiers I have owned or reviewed.

Step-up transformers (SUT) are certainly not the most common product category and one that does not see new entrants very often. It was intriguing to listen to what such a component, built to extreme standards, could do. I have on many occasions listened to similar components from Bob's Device, Ear and Music First Audio but never in my system; and never for reviewing purposes. Step-up transformers do pretty much just one thing: take the very low voltage output of a moving-coil phono cartridge and amplify that signal sufficiently to be acceptable for a moving magnet phono amplifier that requires higher voltage because its own gain is limited.

Now why in the world would you want to do that instead of using a phono preamp that accepts a very low-level MC signal directly? Two reasons really if we want to keep this discussion simple. First, designing an accurate MM phonostage with low noise and accurate RIAA correction is apparently a lot easier. Hence even phono preamps with a dedicated moving coil input most of the time really place two gain stages in series, the first one bringing the MC signal to MM level. Now the question of a step-up transformer is why not do it externally with an optimized component that's appropriately shielded? The second reason for SUTs is their being purely passive devices just like the cartridges that precede them. Theoretically at least, they should have a significant advantage of noise floor versus active transistor or tube gain. That's one of the reasons why Nagra use transformers for their MC phono stages and why I got interested in checking out a standalone transformer.

Step-up transformers rely on the fact that cartridges, although of very low voltage output, are quite capable producing current. The transformer just reverses that relationship. It produces a higher voltage signal with low current. How much gain and impedance are seen by the cartridge is primarily dictated by the turns ratio between primary and secondary transformer coils. If you are interested in the physics and math behind how transformers work, let me point you to two very informative articles here and here. If you are like me and prefer to get down to the 'so what', know that theoretically a turns ratio of 1:10 to 1:15 will work well with all but the most whimsy MC cartridges; and that it will match fairly well with all cartridges except those with very high or very low internal impedance. In practice, even cartridges that should not really be a good match like a low-output/high-impedance Zu-DL103 end up sounding better than they have any right to anyway. That's because the spirits that govern audio have a wicked sense of humour and enjoy keeping us on our toes.

The S.A.Lab step-up transformer exists only in one version with a 1:15 turns ratio to result in about a 208Ω load suitable for most partridges with an internal impedance of <40Ω unless they have very low or very high output levels by MC standards. Of course your individual mileage may vary. Picking a suitable SUT requires finding the right compromise between loading and gain. Although 1:15 covers a wide range of popular cartridges, it will not be a universal solution. The S.A.Lab transformers are wound in house from pure silver wire to minimize internal resistance of the primary coil. In addition, extreme care was given to electromagnetic shielding with the use of a permalloy inner case.

Part I of this assessment was conducted using the S.A.Lab SUT into my Lounge Audio LCR MkIII. Although this pairing may look completely unreasonable due to the much lower price point of the Lounge MM phonostage, I'll point out that the Lounge sells direct and has been widely acknowledged as providing performance completely out of proportion with its price; and that its neutral sonic signature allowed me to easily pinpoint the contribution of the step-up transformer. I was then able to compare the S.A.Lab to Lounge's unconventional Copla active head-amp as well as benchmark the Lounge + S.A.Lab against my Genesis Phono Gold reference. In part II, I will comment on the combination of SUT with S.A.Lab's own Thunderbird phono and linestage. When comparing the SUT directly to Lounge's Copla head-amp or the SUT/LCR MkIII combo to my Genesis, the very same attributes jumped at me to make a strong case for those qualities being directly attributable to the SUT.

At this stage, my intermediate conclusion became that the S.A.Lab SUT was a significant upgrade over the Lounge Copla active headamp. The differences were significant across the board with a far more organic sound, richer tonal textures, greater macrodynamics and far greater ambient recovery and soundstaging all favouring the Russian, with the exception of upper frequency dynamics where I found it to come up a little short. Overall however, the far greater price resulted in incomparably superior performance. Once paired with the Lounge LCR MkIII, the now roughly $3'000 combo still fell quite short of the Genesis Phono Gold. The differences really focused on the latter's' ability to pass on the raw energy of recordings and provide unedited microdynamics throughout the whole range. Going back to my previous analogy, the S.A.Lab despite being a passive component, sounded like a superb SET. The Genesis doesn't really have a sound. It gives an unedited rendition of the recorded event though like the SUT, it is capable of staging very broad and deep which is not typical of most solid-state components. The degree of honesty of the Genesis may not be the best choice in all systems. There is no doubt in my mind that the tonal saturation and bold sound of the S.A.Lab may be just what the doctor ordered for many leaner systems. It adds a sense of fluidity that escapes most active circuits performing the same function.

These qualities are what SUTs are known for and this one doesn't depart from the recipe. Part II of this review reports on the Thunderbird preamplifier which I paired with the SUT for a full-on S.A.Lab experience

Introductions to the Thunderbird will be short and sweet as it wasn't yet listed on their website upon my receipt and the designer wasn't exactly forthcoming with details. The Thunderbird looks and weighs more like an integrated amplifier and ships in a Russian military-grade flight base but is actually a phono preamplifier for moving magnet cartridges that offers volume control and three line level inputs. I could describe it as a preamplifier with two MM inputs but the Thunderbird lacks many of the features one would expect from a high-end full function preamplifier; things like multiple variable outputs, balanced inputs (those can be added as an option though), mute function, remote control or headphone outputs. On the other hand, the inclusion of two moving magnet cartridge inputs, a sophisticated tubed phono stage and balanced outputs would seem to indicate that the Thunderbird is first and foremost a phono preamplifier with the added convenience of allowing vinylholics to easily integrate a digital source to their system.

Now that we sort of know what the Thunderbird is and to whom it may appeal, it is time to take a look around. The orange Corian faceplate won't be to everybody's liking but I found it very clean and elegant, a feeling unfortunately not shared by anybody else in our household. The power button on the left triggers a loud turn-on noise followed by tube rush for about twenty seconds before the circuit settles down. On fairly high-sensitivity speakers I highly recommend to turn the volume all the way down prior to pressing the on switch. The startup noise is only temporary though and the Thunderbird is very quiet after the initial assault. As always with S.A.Lab, build quality is superlative with solid connectors fastened to the back plate, two MM inputs, three line level inputs, one variable output on RCA and one on XLR plus one fixed output only recommended for recording purposes, not to feed an integrated or headphone amplifier for example. Without an appropriate set of tiny hex keys, I unfortunately wasn't able to get into the Thunderbird to take a direct peek at the two massive transformers in the center of the beast or the six unusual metal tubes I could see through the cooling slots on top.

Speaking of unusual tubes, the first gain stage where RIAA correction happens for the moving magnet inputs, uses a pair of Russian 6Ж4 anode tubes, equivalent to the US 6CA7 type in metallic sleeve. The same tube provides gain for the second stage while the third stage relies on 6П9 pentodes, equivalent to US 6AG7 also in metal dress. Very early tube designs used metallic cases because the technology to actually make glass tubes had not been invented yet. By the late 1930s tube production moved massively to glass as we know it today because it was cheaper and allowed smaller tube sizes and better dissipation. During World War II, metallic tubes made a resurgence because of their better mechanical resistance to shocks as well as expected better shielding from electromagnetic waves. The latter actually turned out not to be that critical as external lead shielding of glass tubes proved to be even more effective than metallic enclosures. Still, metal-sleeve tubes remained in production during the war for their superior physical strength. The tubes in the Thunderbird, selected for their musicality, come from the massive stocks of Russian NOS tubes from that era and can be easily replaced on eBay for about $10 to $12 per tube.

Testing of the Thunderbird mostly relied on the FirstWatt F5 as power amplifier with both the Ocellia and Finale Vivace mini speakers while phono preamp comparisons relied on either the Genesis Gold or Lounge Audio LCR and Copla suite. For initial context and understanding of the sonic signature of the Thunderbird, it is important to understand that the SOtM DAC I used also offers analog volume control and can therefore be run directly into the FirstWatt F5 without the resolution decimation of digital attenuation. When set up that way, the sound of my system is fast, lean, detailed but also somewhat sterile, lacking in weight, texture or flow. I never run my system this way but it is a good reference to know where my ditches are. Other listeners may find this presentation exciting. I find it fatiguing and very far from anything I'd hear in concert. It was therefore quite a surprise to listen to the complete transformation that happened when I inserted the Thunderbird between DAC and amplifier. It was like finally getting the best of both tubes and solid state which is a synergy often talked about but which I have very rarely experienced.

The Thunderbird completely fleshed out the tonal richness of instruments, injected flow without taking anything away on resolution, added weight and drive to the bass and had great macrodynamic ability. Compared to the amplifier being driven direct, the only area that suffered was microdynamics, the little ripples of energy that run through the music and give it its ultimate drive. But even then the effect was not overly negative, just a gentle relaxation that highly benefitted older CDs and poorer digital recordings. Compared to my reference Triode Lab 2A3 integrated, staging was certainly not as deep or wide and the three-dimensionality of triodes was missing but both frequency extremes gained speed, tightness, finesse and drive. The overall flavour of both setups was surprisingly similar in the midrange, with great richness and resolution. The Triode offered greater visual effects while the Thunderbird and F5 combo won on control and extension. For the first time I found a tube and solid-state combination that rivaled and in some aspects exceeded what a great triode can achieve with the Ocellias. That's a sound I could easily live with.

The caveat comes from the fact that the system without Thunderbird leaned to the overly analytical and bleached side of things. I wondered whether the fact that the combination brought back balance did not imply that the Thunderbird itself leaned generously and maybe excessively toward the plushier and meatier side of things. To test my theory, I borrowed a First Watt SIT2 for a day. The much lower-powered and higher output impedance SIT2 is an almost perfect transistor stand-in for the triodes I so much enjoy and is slightly warmer and somewhat looser than the F5, without the upper midrange bite that can turn the F5 whitish at times. When pairing the SIT2 to the Thunderbird, my assumptions confirmed immediately. Pace slowed, bass got looser and the upper midrange closed in. It was still a beautiful presentation, even more tonally intense and rich but clearly turning to liquid chocolate syrup with its ponderous implications. I even tried to run the Thunderbird into my 2A3 integrated. This resulted in an even looser more euphonic presentation very much like a vintage 300B — bloated and slow, characteristics that could not be further from describing the stock Triode Lab amplifier. Towards the end of the review, the LampizatOr Golden Atlantic DAC made its system debut and it too leaned towards a beautifully intense tonal color, thus making it an imperfect mate for the Thunderbird. Keep it lean before and after is all I can say about ideal partners for that bird. It sings with strength and gravitas but don't expect a hummingbird any time soon.

Point made, the Thunderbird is a sublime remedy for systems in search of soul and substance but can easily turn to excess in systems that are balanced or already voiced on the more luscious end of the spectrum like mine. More of the same could be said of the MM phono section. MM carts are typically more beefy and tonally dense than their MC counterparts. Although my Dynavector 10X5 mk4 is a high-output moving coil, its sonic profile is very much MM-like with very dense tone. Played through the Thunderbird, density and weight jumped up another level versus playing the 10X5 through the solid-state Lounge Audio LCR, like a generous helping of heavy cream thrown into chocolate sauce. I wouldn't describe the Lounge LCR as lean for a solid-state phono preamp. It is nicely balanced and extended without excess stiffness but compared to the MM phonostage in the Thunderbird, the Lounge provided nicer illumination and greater separation of instruments. The Thunderbird was not opaque or slow per se—midrange resolution was actually quite stunning—but overall tonal density was pushed farther than natural and that's how I felt about the 10x5/Thunderbird combo. I had to pull the Ocellia pure silver interconnects back into service instead of the Zu Varial to return some light to the picture. Even then it was still a highly saturated image

When I switched to the Ortofon Quintet Black moving coil cartridge using the S.A.Lab step-up transformer into the Thunderbird, things went back to a more central tonal balance although still on the richer slower side of neutral. At the same time as pace slowed down compared to the Lounge LCR and Copla combo, transients using the Thunderbird phono rounded and listening to music felt like settling into a deep cushy couch. The contrast to my Genesis Phono Gold could not have been starker. The Genesis is a speed and resolution demon with magnificent extension yet the most natural-sounding tone I have heard to date in a phono preamp. Conversely, three layers of cushy dynamic behaviour from the full S.A.Lab complement proved just too much comfort even for me. Just like I am not a fan of the full-on vintage 300B aesthetic, I could not get emotionally invested in the full S.A.Lab Monty of Thunderbird and step-up transformer which in many ways managed to turn the spicy First Watt F5 into a NOS Western Electric. On the other hand, the hyper-caffeinated Genesis Gold run into the Thunderbird and F5 sounded positively gorgeous, the tubed preamp managing the fine balance of adding color and soul without killing dynamic drive. I am not an electronics designer but it certainly felt that one tube stage did the trick but three was massive overkill. That said, as a tube preamp sitting between a lean DAC or phono stage and a lean amplifier, the Thunderbird completely took me by surprise and delivered a superb rebalancing act which turned a bleached combo into the most synergistic tube and solid-state association I have had in my system so far.

Reviewer: Frederic Beudot
Digital source: Auraliti PK90 USB file player / SOtM sDP-1000EX
Analog source: VPI Scout 1.1, Lounge Audio LCR MkIII & Copla, Zu-DL103 MkII, Dynavector 10x5 mk5, Ortofon Quintet Black, Genesis Phono Gold
Preamplifier: SOtM sDP-1000EX, Burson Conductor
Amplifier: FirstWatt F5, Triode Labs EL84TT integrated, Triode Labs 2A3i
Speakers: Ocellia Calliope .21 Twin Signature, Rogers LS 3/5a, Zu Essence, Finalé Vivace mini [on loan]
Cables: Zu Varial, Ocellia RCA cables, Absolute Fidelity speaker cables, Zu Event MkII
Power cords: Zu Mother, Ocellia power cables, Absolute Fidelity power cables
Powerline conditioning: Isotek Nova
Sundry accessories: Isolpads under electronics
Room size: 16'x21'x12'
Review component retail: €2'600 SUT, €5'600 Thunderbird