May 19, 2021
Article on the reviewer's resource

Alexey Syomin's laboratory never ceases to amaze: it recently created a two-block preamp, with its entire signal path, including a powerful output stage, built on nuvistors. Unconventional circuit design engineering with uncompromising implementation has already become the hallmark of this brand but, in this project, the Russian specialists have surpassed themselves.

So, let's review the device, listen to it and share our thoughts.


Perhaps no other company in the world uses such a wide array of active elements in its design projects as our Sound Analysis Laboratory (S.A.Lab). Its innovative breakthrough includes lamps and transistors of various types — silicon, field-effect, germanium and even SITs. Recently, yet another gap has been plugged with the appearance of the Hercules series, a preamplifier based on nuvistors.


It may be worth reminding you that nuvistors are miniature electronic lamps in metal-ceramic design, which are rightfully considered the pinnacle of creation in the field of vacuum technologies. Their service life is several times higher than that of ordinary finger-shaped ones, and the characteristics are excellent. For example, the 6C51N-V triodes that Alexey uses have a guaranteed average runtime of 10 thousand hours, but, in reality, it reaches up to 30 thousand. The gain frequency is up to 60 MHz with minimal noise, and yes — even a slight hiss is not heard in the headphones at the output of the Hercules. A rare lamp in a glass bulb can give the same result, and I have tried a great many of them in my time. Other properties are also well suited for audio — high steepness and linearity, the ability to work at relatively low anode voltages. However, the latter is not so important, since Alexey accelerates the operating modes to the maximum acceptable limits even in the input stages so as to expand the dynamics. The first two stages, for example, in the new Hercules are powered by 420-volt power buses.

«The most interesting thing about this preamplifier is the output stages. They are built on powerful 6P37N-V HF pentodes.»

Some people are saying that nuvistors are strongly microphonic, but this is not so: we tapped on them with a pencil and received a not-so-noticeable response in the speakers - not louder than with ordinary lamps. Nevertheless, nuvistors have a rigid coaxial design with miniature dimensions – conditions that are not suitable for mechanical vibrations.

In fairness, it should be noted that the idea of using nuvistors is not new - despite the high cost, 6S62H triodes were installed in tube coils of Cometa, Astra, etc., and Musical Fidelity even released a whole series of NuVista components. The biggest problem with these mini-triodes is that they are no longer in production, but S. A. Lab has a stock of 2,500 pieces, which will be enough for the foreseeable future.
By far the most interesting thing about this preamp is the output stages. They are built on high-power RF-pentodes 6P37N-V. These are also metal-ceramic lamps that can easily dissipate up to 20 watts at the anode with a radiator. In triode mode, at a current of 75 mA, they have an internal resistance of about 450-500 ohms, which makes it much easier fitting them with the output transformer. The output resistance of the Hercules does not exceed the active resistance of the secondary winding-0.5 Ohms. Such an extremely low value promises high dynamics, which is extremely difficult and expensive to obtain on conventional lamps.

In general, the circuit is very stable with an extremely wide gain bandwidth.

The preamp provides connection for six sources, including three balanced sources. There are also a lot of outputs: six pairs of RCA and six XLR, linear RCA and XLR, as well as RCA for recording. All balanced inputs and outputs are exclusively transformer-based. There is a 6.3 mm headphone jack on the front panel.

«Another interesting feature: there is a Powercon connector on the rear panel for delivering a balanced power supply voltage.»

The volume control is on the relay and the resistance store, the level in decibels is displayed on the matrix indicator. On the left of it, the number of the selected input is displayed, as well as the icons for switching off the Speaker and Standby mode.

The power supply unit of the Hercules is remote, assembled in a case of the same size as the preamp itself. This is explained by the fact that the channels are fed separately on the principle of double mono, and each of them has three high-voltage lines. For the input stage (two-story cascade), it is stabilized, which significantly reduces distortion.
Another interesting feature: there is a Powercon connector on the rear panel for delivering a balanced power supply voltage. In a normal home network, there is usually a phase and zero (in some cases, "ground or earth"), and, in the S.A.Lab components, a "zero and two phases" system is implemented. It is formed by a separate giant Samson unit, which has a 12-kilowatt transformer with a balanced voltage of 2x110 volts at the output. Accordingly, in the power transformers of S. A. Lab amplifiers, the primary winding consists of two equal halves. Of course, they can work from a regular outlet, but when turned on in balance, all network garbage is filtered out without losing the sound dynamics. One of the clients of S. A. Lab in Italy powered his studio entirely from such a source and, in one fell swoop, solved all the problems with network interference.

In keeping with the corporate style, the front panels of both blocks are covered with natural leather with red stitching, the metal surfaces are painted with high-quality auto enamel. S.A.Lab appliances are manufactured with an eye on Europe, so great attention is paid to the quality of the exterior finish.


For our tests, an impressive system — in terms of size and cost — was assembled. The source was a Studer A820 tape recorder connected via a balanced line to the preamp, and that, in turn, to the powerful lamp end of the Samson Mk III. The network power supply is organized according to a balanced scheme. The acoustics are rather old, but the floor-standing Paradigm Reference Studio speakers are very good.

The first thing I did, however, was listen to the preamp in my headphones. In the zero position of the volume control, the silence was absolute, as if the power was turned off. A very unusual, I would even say, unreal feeling. We turn on the Studer, and loaded a good copy of 38/2 from the master tape. The impression is overwhelming, and it's not even the effective sound pressure itself, but what it was made of. Every sound, every note seemed to be shooting out, it seemed that the music was literally hammered into the ears by alternating bursts of energy. And this effect did not depend much on the volume, I slightly reduced it, and the energy attack did not stop.

«The impression is overwhelming, and it's not even the effective sound pressure itself, but what it was made of.»

A very similar effect was observed when switching to speakers. They literally unleashed an avalanche of sounds, and these sounds seemed to bombard and, for want of habit, it made a strong impression.

After a while, it was possible to evaluate other aspects of the sound. The bass was raised, fast, with the right attack, producing a sense of depth and real, not light-weight content. The character of studio phonograms was perfectly conveyed — with the widest, without compression, dynamic range and, as a result, open and free sound.
Vocals are another story altogether. It creates a complete illusion that a person with a microphone and sound is in the same room as you — there seem to be no other hardware intermediaries at all.

In general, I should note that not every system is capable of adequately reproducing a studio recording — you need speed, a margin for dynamics, a wide frequency range and high detail. And not just one of them, but all of them combined. The ear, accustomed to the sound of CDs and even trained on vinyl, is simply no match for the S.A.Lab system — it is so transparent and fast.

Before, I had to listen to circuits on nuvistors, mainly phono preamplifiers. All of them were collected according to the old canonical rules, and sounded quite predictable. And only a departure from routine, and in our own case, a fresh look at the circuitry allowed us to get a real wow effect. And this, by the way, applies to the vast majority of S.A.Lab developments.

«And only a departure from routine, and in our own case, a fresh look at the circuitry allowed us to get a real wow effect.»

By the way, simultaneously with the preamp, we tested another unusual development of the Sound Analysis Laboratory — a feedback module. It allows you to enter the feedback signal from each band of the speaker system into the amplifier and set the optimal damping level. It was still a crude prototype, but it also shows that the idea has a very clear perspective.

Both the Hercules preamplifier and the feedback module (already completed) will be demonstrated at the Hi-Fi & High-End Show 2021, which will be held at Moscow's Borodino hotel on May 21 - 23.

S.A.Lab (Russia)
S.A.Lab Hercules
Frequency Response: 2.5 – 450,000 Hz ± 0.3 dB
Amplifier gain ratio: 4
Signal-to-noise ratio weighted: -110 dB 11
Total harmonic distortion (output voltage 1 V): 0.12% 11
Nominal sensitivity: 1 V RMS 11
Input impedance: 10k Ohm
Inputs: 3 x RCA, 3 x XLR
Outputs: 3 x RCA, 3 x XLR, RCA Recordjack 6,3 mm
Power supply: 220/240 V
Preamplifier net weight: 16 kg
Net weight of the power supply unit 22 kg
Dimensions with supports: 450 x 380 x 210 mm
Price: 1,500,000 rubles.


• Studio tape recorder Studer А820
• Power amplifier Samson MK 3
• Samson symmetrical power supply unit
• Cables: S.A.Lab