SALON AV: Интегральный усилитель S.A.Lab Black Knight

The idea of an amplifier featuring Germanium transistors has been thrilling the minds of audiophiles and music lovers for many years, but none of the major manufacturers either in Russia or in the West ever dared to implement it in a modern device. That's why I regard the latest design by Alexey Syomin's laboratory as a brave and promising experiment in this field.

What advantages these 'prehistoric' semiconductors have over modern devices; what implementation issues might arise and how these devices would sound in a 'no-compromise' design? These are the questions we are about to answer.

Amateur designs featuring Germanium transistors are numerous; one can also find a lot of ads for home-made audio produced on a small scale but the overwhelming majority would be copies of designs published in in the Russian Radio magazine in 1960s. Compiled using low frequency transistors with modest feeding voltage they barely yield 20W giving more than 1% distortion. This is caused not only by primitive schematic but also by the mentality of amateur designers that stubbornly try to create something worthwhile from audio parts bought at a garage sale. Nevertheless even these pathetically designed 'Germanium' amplifiers find a lot of supporters and cause tempestuous web discussions.

Before we start discussing the Black Knight let's find out what is Ge the 32nd element in the Periodic Table and what distinguishes it from Silicon. We've already asked this question 15 years before when interest in the subjects of Germanium had just started. Below is a comparative table of the elements and a short commentary by the author of 'Germanium comes first' article published by our magazine in 2003.

This conclusion while not being completely scientific is logical. Voltage drop across the p-n junction is genuinely an important parameter because Germanium transistor opens (begins conducting current) when the base-emitter voltage is much lower therefore the so called crossover distortions are practically nonexistent. In a silicon schematic the only way to eliminate them is making output transistors work in Class A with all subsequent issues and expenditures.

So why none of the modern manufacturers produces Germanium-based amplifiers? There are several serious problems hampering their mass production but quite surmountable for short-run production in Russia.

«Output stage features 50-Watt 1T813 transistors, two in each end; joint collector current is 1A enabling 50W of output power with 10Hz — 20 kHz frequency response.»

First, these transistors are hard to find. In 1960s Western manufacturers started an active transition to Silicon devices and nowadays obtaining the necessary quantity of Germanium transistors is an impossible task. Unlike vacuum tubes nobody thought of restoring the production of Germanium transistors. But in the USSR transistors belonging to П, ГТ and 1T lineups were manufactures until the end of 1990s (well almost) and their supply remains huge and cheap. For instance, in order to match quads for output stages of his amps Alexey easily bought 2000 powerful 1T813 transistors.

Second, low compliance voltages of input transistors don't allow designer to 'accelerate' the signal to the amplitude necessary to obtain output power acceptable by modern standards. Black Knight solves this problem by means of cascodes, 'double-decked' stages featuring МП39Б and МП20 transistors with each 'deck' fed separately. Then there is a phase-inverting stage based on ГТ404/402 transistors. It is connected to a driver utilizing sufficiently high-voltage П605 transistors. Current gain is provided by 50-Watt 1T813 transistors, two in each end; joint collector current is 1A enabling 50W of output power with 10Hz — 20 kHz frequency response. THD at 25 kHz/10W doesn't exceed 0.05% whilst the second harmonic in the output signal's specter is higher than the first one. Clipping at the ultimate volumes is very smooth, almost tube-like. There's no general feedback.

The third issue concerning Germanium transistors is their tendency to generate through-currents when crystal is overheated causing junction breakdown. That's why beside substantial heat sinks Black Knight has an advanced protection circuit featuring Arduino microcontroller. It monitors temperature, the presence of DC in the output signal and output stages current.

The amp is designed on the double mono principle with complete separation of feeding voltage, signal and grounding circuits. Each channel has an individual toroidal transformer (360 VA), a rectifier and a bank of 80,000 µF smoothing capacitors in each end i.e. 320.000 µF in total. When you get 3200 µF per 1W of output power you don't need any voltage regulation.

«The amp is designed on the double mono principle with complete separation of feeding voltage, signal and grounding circuits.»

Up to five sources can be connected incl. a single balanced source. Separate input is provided bypassing the volume control unit. Inputs are switched and volume is controlled by means of relays. Speaker posts (to enable bi-wiring four in each channel are installed) are manufactured in-house from pure silver.

The Black Knight sample we tested wasn't exactly black but a blue one or 'Blue Tour De France' to be precise. Enclosure panels are spray-painted at one of Ferrari service centers so other colors from the supercars proprietary palette are available to order. 'Our' color turned out very dark, changing shade from cyan to pale violet depending on lighting conditions. Paining one set of panels costs 200 euro.

Four Black Knight samples are already manufactured and the very first of them got onto our test bench.

Specifically for this occasion a stationary ATR102 reel-to-reel recorder and several half-inch master tapes were delivered to 'Nota+' audio salon.

The sound was also tested by more habitual means i.e. while listening to CDs played back by Gryphon Scorpio CD Player. Black Knight was connected to Blumenhofer Genium FS1 MK II two-way speakers with 16-inch woofers and horn-loaded tweeters.

«The main difference between Black Knight and the overwhelming majority of Hi-Fi transistor amps is the ideal distribution of virtual sources by their size.»

I've already had an opportunity to listen to Germanium-based amps incl. those describes above in this article. Alongside numerous positive experiences I always felt the lack of power and my attempts to increase volume invariably lead to perceptive growth of distortions and coloring in the upper mid-range. In our case there was nothing of the sort. On a par with smooth and excitable sound Black Knight is capable of reproducing colossal level gradients. The truly enormous dynamic range of a studio recording made on an inch-wide magnetic tape was reproduced with complete adequacy. But the main difference between Black Knight and the overwhelming majority of Hi-Fi transistor amps is the ideal distribution of virtual sources by their size. It doesn't inflate nuances and never tries to downplay large-scale music images. The same is true about dynamic scale: the balance of quiet and loud sounds always remained natural. The third moment concerns comfortable reproduction of upper range without veiling or losses in resolution. The specter components are numerous: percussion sounds the way it does in a real drum kit — bright with transparent aura of intonations. The sound is so natural retaining life even in the quietest moments by the very threshold of hearing that you listen to it with involuntarily relaxation.

Switching to CD Player didn't bring any artificiality. At first you don't find anything special in sound — it's perfectly balanced, even and cute but later there forms a semblance of personal contact with music: it seems to play for you only, capturing your attention completely. And this illusion is hard to get rid of.

At low volumes Black Knight demonstrates resolution level reminiscent of a high quality tube amp or an expensive single-ended MOSFET unit. Its impact and ability to drive large woofers is on par with classic transistor audio. The sound flows so freely and easily that I was completely captivated and it took me some time to be able to appreciate other audio devices again. S.A.Lab's approach to Black Knight's design is so serious that Germanium transistors' potential is brought up to the level of High End Audio. In other words Mr. Syomin did something nobody else has managed to achieve so far.

Amplifier type: push-pull design, Class АВ || Output power: 2 х 50W (4 Ω), 2 х 25W (8 Ω) || Frequency response: 2 Hz – 200 kHz || Rated sensitivity: 300mV || Input impedance: 47kΩ (RCA), 25kΩ (XLR) || S/N ratio: 103dB|| THD: 0.05% (25W, 4Ω, 20kHz) || Inputs: 1xXLR, 4xRCA, bypass RCA || Max power consumption: 460VA|| Size (W х H х D): 480 x 310 x 505 mm || Weight: 31 kg || Price: 800,000 roubles

The editors thank the "Nota +" salon for their help in conducting the audition.

• ATR102 ½" Reel-to-reel tape recorder
• Gryphon Scorpio CD Player
• Blumenhofer Genium FS1 MK II Speakers
• Cabling:
— Interconnects: Cordial XLR
— Acoustic cables: Shinpy Logos
— Power cables: A.Lab Power