SALON AV: Integrated amplifier S.A.Lab Hercules SE MK II 15th Anniversary

The new S.A.Lab device is unusual from several perspectives. First, its launch was timed to coincide with the company's 15th anniversary and on that occasion a new schematic —fundamentally different from the ones used for other models — was designed. Besides 15 samples of the amp are to be sold 15 times cheaper than the announced retail price. And, as it turned out during our acquaintance with the new product, it is not only generous but also a very tempting offer.

Let me start from the fact that Hercules Anniversary Edition is a single-ended amplifier (rather a brave decision for a company that manufactures amps in order to actually sell them). As is known power sells the best, but the low (20 – 25%) efficiency of single-ended amp makes each additional Watt very expensive. That's why such a design is popular only among the owners of ultra-sensitive wide-range speakers i.e. the target audience is quite small. But for a real audiophile all flaws of a single-ended amp are more than offset by its advantages, primarily the fact that the output tubes work in pure Class A with constant current-feed and the dominance of the second — so called euphonic — harmonics. Due to the absence of phase-inverting stages the representation becomes much more precise and the signal path turns out to be quite short: one cannel of a 5 W amp can be built with just two vacuum tubes.

But what if one needs more power? To achieve this goal several output tubes are connected in parallel, although this design also brings a problem — the current flowing through the transformer's primary winding increases and to prevent the core from getting into saturation it's necessary to widen the non-magnetic gap. This causes the decrease in inductance and as the result the disappearance of the low bass. In short the main obstacle to overcome while designing a proper single-ended amp is connected to the output transformer: it invariably turns out bulky and expensive to manufacture.

«The main obstacle while designing a proper single-ended amp is connected to the output transformer: it invariably turns out bulky and expensive to manufacture.»

Alexey Syomin, founder of S.A.Lab, developed a unique method of transformer winding, which he is about to patent. The output transformers are clearly visible on the photo below — the power-to-size ratio is about 1 kW (!), the core is made from high quality electric grade sheet. Each output stage has three 6P36S tetrodes switched in parallel and working as triodes. The output power achieved is 2x15 W and doesn't depend on the connected speaker impedance. Low inner impedance of the output stage enabled to achieve good dumping while sustaining the minimal (3 dB) amount of feedback.

The amp has a true dual mono design with separate power transformers, rectifiers and chokes for feeding each channel. It's a direct-current amplifier, i.e. there are no coupling capacitors between stages. These stages are only three in number: input stage based on 12AX7 tube, a driver with 6P14P working as a triode and the parallel output stages mentioned above. To avoid using capacitors the output tubes are fed via a separate source of negative voltage. Volume control with 2 dB step is an array of high quality relay-commutated resistors which in their turn are controlled via remote. The actual volume level is indicated in a circular window on the front panel.

«It's a direct-current amplifier, i.e. there are no coupling capacitors between stages.»

Hercules Anniversary Edition has five line inputs, incl. two balanced XLRs. The signal is transformed into balanced/imbalanced form by means of Texas Instruments INA 137 differential receivers, but it's possible to order a version with input transformers.

The amp is placed on a partitioned steel chassis. Tubes are mounted on thick copper plates; drivers are equipped with heat-sinks in order to decrease distortions.

Design is traditional for newer S.A.Lab products: a tall cabinet on high dumping feet and a front panel made of corian (artificial marble) with circular backlit window. The device weighs 45 kilos.

I have to admit that I've listened to single-ended amps on many occasions. Most of those amps were based on rectilinear triodes – 300В, ГМ70, 845, 211s etc. Despite the mid-range magnificence and incredible musicality they as a rule lacked a proper vigor, a full-blown punch and — even being connected to speakers that had a very good bass response — a bottom end sufficient for playing back live concert. That is exactly why single-ender acquired the reputation of an amp for limited audience —namely lovers of mainstream jazz, opera and chamber music.

But Hercules SE MK II 15th Anniversary (to call it by its full name is a matter of principle now) — is a rare exception to this general rule. Connected to a 145-kilo Magico M3 floorstanders the amp produced such a dynamic sound that I had to ask my S.A.Lab colleague whether we were REALLY listening to a single-ended device. With only 15 Watts of power and at a modest volume level the sound had all the features needed for an adequate representation of any music genre incl. progressive metal and drum-n-bass. And there were no brute force per se: emotional vigor was combined with comfortable (one may even say 'tender') sensitivity in quiet moments and precise articulation of subtle music structure of any particular recording. The feeling of elation, of smooth delivery borders on dense full-bodied sound from the lowest octave to the sparkling silvery twitter. This is that rare occasion when the playback device provokes listeners to replay records that seemed too complicated and too intricate to be interesting. The amplifier's sound is truly captivating for it neither simplifies a convoluted structure (a common flaw among amateur designs), no exerts superfluous brutality — a quality intrinsic to powerful push-pull devices.

«With only 15 Watts of power and at a modest volume level the sound had all the features needed for an adequate representation of any music genre incl. progressive metal and drum-n-bass.»

But the first thing we've noticed — even before the system was properly burned-in — was the incredible stability of the soundstage. No, really: one could wander around the room, stopping even between speakers… still most of the instruments remained in their proper places, only their relative scale changed slightly. Being in the hotspot one could feel both width and depth of the soundstage and also the 3D placing of every single sound.

I must admit that Hercules SE MK II 15th Anniversary is a perfect proof of the fact that the simpler the design is the more profound its implementation should be. A proper single-ender can't be just thrown together — no matter how seductive such an approach may seem. So the 15 lucky ones who get the amp only for 1000 euros are really should be envied.

Output power: 15 W (4 Ω) || Signal|noise ratio: –106 dB (unweighted) || THD: 0,3% || Input impedance: 10 кΩ || Size: 465 х 270 х 480 mm || Weight: 55 kilos || Price: 980 000 rubles.

The editorial staff thanks Sound ProLab for their help in conducting the audition.

• Mark Levinson №512 CD-player
• Magico M3 speakers
• Cables:
– Tellurium Q Black XLR interconnects
– Nordost Red Dawn acoustic cables