SALON AV: S.A.Lab Autograph Power Amplifiers

Here comes the Autograph, the latest amp design from Russia’s Sound Analysis Laboratory, aimed at audiophiles in love with tube amplifiers. Each monoblock features four GU-50 oscillator pentodes capable of delivering up to 196 watts, making choosing the right speakers a breeze. The tube modes are controlled by a processor that keeps distortion levels at a minimum throughout their entire lifespan.

Now it’s time to reveal the design secrets and, of course, listen to the Autograph.

However, our discussion of tube sound comes with a caveat: Alexey Syomin's tube amplifiers don't always sound the way we're now used to. The unique circuit design, honed through numerous experiments, eliminates the sound flaws considered inherent in triode and pentode circuits. The Autograph monoblocks, Alexey's latest iteration, is tangible proof of this.

Call Your Own Shots

The Autograph aren't the company's first monoblocks, but they've never been so compact and adapted to average living conditions. However, as mentioned above, the new amplifiers have no problems with power — almost 200 watts at 4 ohms — making the sensitivity of the speakers connected to them irrelevant.

The killer feature of the Autographs is the use of GU-50 generator beam pentodes in the pushpull output stage, with two bulbs in each arm in parallel. These tubes are widely known, often used by amateurs in various homemade designs, but few people have been able to fully unleash their potential.

At first glance, their power output may seem modest—only 50 watts at the anode, according to the specifications—but there are nuances. At a standard filament voltage of 12 volts, they do dissipate up to 50 watts, but at 13 volts, it's 50% more, and at 14 volts, it can briefly reach up to a kilowatt. These are standard operating modes, designed for radio transmitters in extreme situations. Of course, the tubes in the Autographs operate at their nominal rating, but the reinforced electrode design, intended to withstand overloads, is a welcome bonus.

«Of course, the tubes in the Autographs operate at their nominal rating, but the reinforced electrode design, intended to withstand overloads, is a welcome bonus.»

The second kicker is that the tubes are connected using an ultra-linear circuit, with voltage supplied to the screen grids not from the primary taps of the output transformer, but from a separate winding fed by a stabilized voltage. This stabilizer can deliver up to 350 mA, and with such a supply, as it turns out, the tubes are capable of truly incredible dynamics. As a reminder, the ultra-linear mode combines the advantages of triode (short harmonic spectrum) and pentode (high output power) modes.

When connecting output tubes in parallel, it is crucial that they operate in unison as inconsistency will lead to increased distortion, including intermodulation. The GU-50's modes are monitored by a specially designed system based on an Altera FPGA, which adjusts the anode currents every 30 seconds with a step difference of 0.1 - 0.5 mA. This is important because even in a carefully selected quartet, the tubes' characteristics begin to drift apart over time.

The Autograph’s driver stage makes a significant contribution to the amplifier's sound. Alexey developed the new driver used in the Autograph experimentally, having tried numerous different circuits and tube types. As a result, he devised his own topology using 6SN7 dual triodes with maximum power supply noise suppression and minimal distortion. Incidentally, the "Sevens" are also manufactured in Russia by special order of S.A.Lab.

The power and output transformers are separated by shielding partitions. You can judge the dimensions for yourself.

The lower level houses a less powerful transformer for powering the digital control circuit and a relay circuit for switching the RCA-XLR inputs. Also located there are the stabilizers for the filament, the driver anode voltage, and the power supply for the output tube screen grids. They are built using chokes and powerful high-voltage MOSFETs.

«The GU-50 modes are monitored by a specially designed system on the Altera FPGA, which adjusts the anode currents every 30 seconds with a step difference of 0.1 - 0.5 mA.»

When connected via XLR, the signal is fed through a broadband balanced transformer with an alpha-crystal core.

Alexey assembles all components of the Autograph himself, thus ensuring both better and faster results.

The Autographs' design is proprietary for S.A.Lab: a faux stone front panel and a large handle with an illuminated logo.

Each monoblock weighs 65 kg, and the price per pair is 3,500,000 rubles.

Music for Everyday Life

For testing, the monoblocks were connected to a new Verus SE preamplifier, using a Marantz SA-15 S1 CD player and a Studer A-812 studio tape recorder as sources. The load was vintage Diatone DS-90 speakers with their rather heavy 40-centimeter bass cones.

«Autographs are unique in this regard – they blast out bass so loudly that you feel the shockwave of excitements throughout your body.»

When preparing to listen to a tube amplifier, it's not uncommon to assume certain limitations in terms of impact energy and speed in the bass band—as a rule, high output impedance prevents the LF drivers from being fully controlled. The Autographs are unique in this regard—they blast out bass so loudly that you feel the shockwave of excitements throughout your body. And not necessarily at high volumes; a comfortable listening level was quite sufficient. Generally, this quality is more typical of well-powered transistor amplifiers, and is a rarity for tube amplifiers. I was surprised by the speed and ease with which the amplifier transitioned from barely audible levels to peaks, without losing clarity across the dense musical spectrum. There wasn't the slightest bit of the tightness typical of amplifiers with deep negative feedback—here it's negligible given the extremely short audio path, giving a feeling of complete openness and freedom.

Of course, in terms of overall dynamics, these monoblocks don't measure up to the Hercules, but those are designed for large halls, but in more realistic home conditions, our current test objects will give most transistor competitors of a similar price a run for their money.

And what is especially valuable is that the phenomenal dynamics of the Autographs are combined with increased attention to nuances and the ability to show the richness of timbres in any music, be it symphonic classics or Donald Fagen's solo album. Moreover, the resolution of the soundstage is independent of volume, meaning the notorious "first watt" problem is completely absent here.

«And what's especially valuable is that the Autographs' phenomenal dynamics are combined with a heightened attention to nuance and the ability to reveal the richness of timbre in any music.»

And literally a few minutes were enough to appreciate the dynamic contrasts on a high-quality studio 38-track played on a studio-quality Studer. It felt like the room had expanded and filled with fresh air. So, the high-quality potential of the Autographs and Verus SE far exceeds the capabilities of CD-Audio; this combination requires either an expensive turntable or a high-end streamer. Otherwise, you simply won't unlock the full potential of these monoblocks.