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The anode voltages of all Erato and Ligeia tubes are stabilized. The five-piece architecture here was caused by the necessity to get significantly more power from an accepted no-compromise concept where Ligeia had produced considerably less power. The fact that 400 watts arrive at the anode of this output tube demanded complex and massive output transformers constructed as two separate units each the size of a small subwoofer weighing more than 60 kilos. Erato and Ligeia are otherwise identical in size and design except for a few small details. I call it the pedestal style. Looking at it you can't help but wonder where the statues have gone. Deep vertical grooves in the wooden armor associate us with the crenellations of a column or pilaster to add another classicist motive.
It’s clear that the transformers couldn’t possibly fit inside the main mono cases. There’s no free space. Besides even without the output iron it takes four strong men (weightlifters?) to move these boulders about. The transformers are rated for 8kW of power whilst the feeding power is 3kW and the core section 80cm²!
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The preamp was designed to work with long cables and low loads. Basically it’s a single-ended circuit with about 4 watts of output power. It could have worked as an integrated amp for fairly sensitive speakers. The Erato project relies on only the very highest quality parts like specially selected tubes and paper-in-oil high-voltage Duelund capacitors (aluminum, copper and silver foil inlaid with thick paper soaked in pure mineral oil, with lacquer manufactured from natural materials). I mentioned how many of these elements are of non-Russian origin. The enclosures are made of tinted solid Ash by Belorussian masters. The lacquer doesn't hide but highlights the pores typical for Ash. Ligeia’s cabinets were made of oak, i.e. a structurally similar wood but of a darker shade. In my opinion a high-quality wax varnish would look even nobler since precious oak furniture is varnished only with wax. The output transformers (cores and windings) are of non-Russian origin too.
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Bottles. Power amplifier. The mighty ГУ-80 pentode (Erato uses a Soviet specimen from 1962) is an exact replica of Telefunken's RS384 which was in active use by the Nazi Wehrmacht from 1939 on. This output tube works in triode mode with perfect parameters of 450W anode power, 500mA quiescent current and low internal resistance for a reasonably high damping factor into any load. This tube is very linear. The US VT-25 input triode (late 1950s) was designed and originally used as an output or driver tube in low-frequency amplifiers. It has high linearity and substantial initial current. Here it works as a 300B driver. Because of its high anode voltage and perfect linearity the 300В triode became the chosen output driver. Erato's high-voltage power supply uses modern tubes made in Russia's Saratov. The power supply stabilizers use two 6AS7 (Canada, 1970s), two 6ж4с (Светлана, 1964) and four сг4 (1967).
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Preamplifier. The WE310 pentode (Western Electric, USA 1939) was used in early cinema projectors to drive a 300В. Here this very linear tube works as a pentode whose second grid is stabilized parametrically. The main advantages of the current-production Bulgarian 40 output triode are high linearity of the volt/ampere characteristic and low distortion. The power supply stabilizers are two 6AS7, two 6ж4, two с201г (USSR, 1954) and two VR-150 (France, 1957).
The concert hall. Comparing Ligeia and Erato I must say that as listener I had more empathy with the latter. The sound of Ligeia seemed calm, pacified by a lack of explosive drama, sharply individual and perhaps too beautiful if there is such a thing as an excess of beauty. Ligeia came with its own very strong personality as though commanding the music to obey it. Describing the sound one had to talk primarily about the beauty of replay and only secondarily about music's own beauty. Yet this didn’t harm Ligeia in any obvious ways. Erato meanwhile was imbued with a more dynamic and far more neutral and academic voice.
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Alexei Syomin
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The Erato quintet allowed the music to express itself by moving system personality into the background. Yet personality remained clearly discernible. Writing about Ligeia and Lilt I noted their profound vocal expressivity which off the record I viewed as Syomin’s signature style. With Erato however this quality no longer dominated. The main musical dimensions—horizontal as melody and polyphony, vertical as harmony and color plus the third dimension as spaciousness—came off at such remarkable balance that I'd justly call it the golden mean. Manufacturers of expensive tube audio worry incessantly about not letting their valves run wild. On precise if subjective acoustic scales they weigh the amount of notorious ‘tube sound’. Any excess detracts from realism and makes the sound loose and untidy. Undue lack however raises the valid question of why we'd bother with tubes at all. Erato balances these two extremes in a very artful and even artistic way exactly how it has to be done in my opinion. This is really a neutral sound in the best meaning of the word.
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Last but not least. Once Alexei Syomin called Erato his last amplifier though not literally to imply anything ultimate since he is a modest man. But after a short while he started sharing thoughts on a new amp based again on the ГУ-80 (he obviously likes this tube) in which he’d do something different. One way or another the proverbial ‘never say never’ doesn’t imply that one must say ‘always and again’. In the end Alexei aspired to create something absolutely alien to any adept of tube technologies instead; a transistor mono amp. He already showed me some enclosures which weren’t easy to fit into the trunk of a large car. This won't be opportunism but plain revisionism!
Summary. In Erato many audiophiles will acknowledge a significant achievement in tube amplifier technology (the same holds true for Ligeia). This well-constructed deeply thought-out set is really state of the art. With pathos one wants to call Erato the Lord of Tubes. If there are any compromises, they are known only to Alexei Syomin. The Erato sound is far from any schematic and both multi-faceted and multi-layered. The Erato system will be highly appreciated by the most demanding of music lovers but not at all approved by any ecologists. A single mono consumes almost 1kW after all. Yet I don’t believe that the agenda of any upcoming green conference would ever contain an accusatory lecture on S.A. Lab's Erato and global warming. To warm a listening room with tube heat is quite another matter. It makes a fireplace utterly superfluous...
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aa @ hi-fi.ru |
Specifications
Erato preamplifier
Output voltage: 12V
Frequency response (max. power), 50Hz to 45'000Hz
Output impedance: 9Ω
Signal-to-noise ratio: 90dB
THD (100 Ohm): 0.03%
Input impedance:<100kΩ
Power consumption: 370 watts
Erato monaural amplifier
Output stage mode: Single-end class А1/А2
Output power (4/8А1, 0.4% ): 75/42 watts
Output power (4/8Ω, А2, 0.6%), 102/60 watts
Frequency response (max power), 10Hz to 40'000Hz -1dB
S/N ratio: 95dB
THD (half power): 0.08%
Output impedance: 0.5Ω
Sensitivity: 7.5V
Input impedance: 275Ω
Power consumption per channel: 950 watts
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