SALON AV: S.A.Lab Hercules Phono Amp

The problem of amplifying a signal coming from LP cartridge is quite easy to solve: throughout the life of vinyl an enormous number of solutions were designed. Nevertheless the most exacting audiophiles often complain about the absence of a 'proper' Phono amp capable of realizing the full benefits of analogue recordings. Let's find out if the new fully balanced unit designed by Alexey Syomin can fill this gap.

The situation with balanced Phono circuit differs a great deal from the one that takes place, for example, in a line pre amp or power amp. In the latter case the main problem is finding a way of eliminating the overall distortions by suppressing the second harmonics plus the ability to make up for the losses while sending signal over a long line cable. But in a Phono amp the balanced circuit serves a fundamentally different purpose. Symmetrically connected cartridge not only lowers Phono cable interferences (such circuit is immune to common-mode interference) and background noise caused by ripples in feeding voltage, but also ensures a special structure of RIAA correction circuit. The latter is very important: placement of elements that form standard RIAA equalization and the way they're introduced into the circuit make radical impact on sound.

«Symmetrically connected cartridge not only lowers Phono cable interferences (such circuit is immune to common-mode interference) and background noise caused by ripples in feeding voltage, but also ensures a specific structure of RIAA correction circuit»

Let me explain this in detail. As you probably know the RIAA frequency response is defined by three time constants of 3180, 318 and 75 microseconds that match 50, 500 and 2120Hz respectively. Each value is set by an RC circuit i.e. a combination of resistors and capacitors. The correction may be an active one (conducted in a feedback loop) or a passive one and the corresponding circuits either comprise a unified schematic or are allocated to different amplifying stages. Each approach implies a compromise between signal/noise ratio and overload capacity. The second parameter is equally important for it defines the circuit's response to high amplitude signal. When the needle strikes a scratch on the record or while playing back a percussion hit the voltage on the needle's output can be ten of even a hundred times higher than the Phono amp's sensitivity. That's why the overload capacity must be as high as 20 dB otherwise a very discordant clipping may occur.

Tube balanced circuit ensures a very neat solution to a lot of problems because the cartridge initially has a symmetrical output. The first schematic of this kind entitled Siren Song was published in Sound Practices (Vol.#3, 1993) audiophile magazine and became a cult item among the DIY enthusiasts of that time. The inclusion of HF circuit between anodes of the input tube ensured not only overload capacity of more than 30 dB but also an absolutely linear phase response. Unfortunately J.C. Morrison, the author, didn't have the stomach to build a totally balanced circuit: the output stage with LF correction unit was a single-ended one.

«The new Alexey Syomin's Hercules Phono amp has all frequency-dependent operating in balanced mode.»

The new Alexey Syomin's Hercules Phono amp has all frequency-dependent circuits operating in balanced mode. Signal from the cartridge received by grids of 6SL (6Н9С) octal dual triode passes through HF correction circuit and is amplified in balanced mode by the second stage featuring 6Н7С tube, a very linear triode with common cathode. The LF correction circuit is also placed between its anodes. Due to balanced correction mode the proper frequency response is achieved over the whole operating range (deviation from the standard RIAA equalization doesn't exceed 0.5 dB) with minimal phase shift. The third stage is a single-ended one utilizing 6F6 pentode working as triode terminated on the output transformer. This circuit acts as an extremely linear and broadband buffer with low output impedance. The main transformers' size is the same as in a respectable tube push-pull unit; Hercules Phono is capable of producing up to 3W of output. The transformer's secondary winding is connected to a smaller transformer that turns signal into a balanced mode and carries it to XLR outputs. Alexey Syomin is sure that this circuit sounds better than a universal output stage operating with RCA and XLR outputs simultaneously.

The sound path is assembled by means of point-to-point wiring and mounted on a 2-mm thick copper plate.

Power supply is a different story — as is the case with all S.A.Lab designs. Toroidal transformer is encased in a special screen machined from brass. Rectifiers, chokes and filters are placed inside the Phono amp itself — separate for each channel. The rectifying capacitors' energy reserve would make even a power amp jealous.

Hercules Phono is designed for simultaneous connection of two MM cartridges; inputs are switched by means of a large handle on its front. As is the case of every recent S.A.Lab model Hercules Phono's faceplate is machined from Corian marble. Chassis and top are 2-mm steel that effectively screens sensitive stages from outer interference.

«It was exhilarating to witness sound engineers' experiments with channel separation, panning and other spacious effects.»

To test the new Hercules an impressive audio system was built. Its source was 65-kilos J.C. Verdier La Nouvelle Platine turntable with Tri-Planar tonearm and Lyra Titan i MC cartridge connected to the Phono amp via S.A.Lab Special Edition step-up transformer with amorphous iron core.

The major feature of Hercules Phono became evident almost immediately — when we put familiar records just for a trial run. Not all expensive CD Players are capable of building such a tidy and effective sound space. The audio stage was spacious and neat, each virtual source perceived as a real physical object. When a record was changed the overall picture changed too but depth perspective and clarity of sound images' placement remained the same. It was exhilarating to witness sound engineers' experiments with channel separation, panning and other spacious effects. On some tracks the instruments were grouped centrally, on others they were located so wide apart that appeared beyond the boundaries of stereo base.

The second point worth mentioning is the sensation of an absolutely uninhibited music flow with natural transitions from piano to forte and drum parties played with instantaneous attack. This is a typical quality of feedback-less tube pre amps featuring high overload capacity. One has a feeling of music living on its own independent of playback devices.

«One has a feeling of music living on its own independent of playback devices.»

And surely we can't avoid talking about lower register. In many respects its character depends on the room acoustics but nevertheless its foundation is laid in the signal path. In our case the room's input was quite substantial but even that didn't stop us from properly appreciating the speed of bass, its detail and vigor. The point is that the source and the Phono amp set the quality bar so high that you can further experiment with other links in the audio chain. By the way, one of these links is the listening room itself.

The third feature of Hercules Phono is its ability to transmit everything the needle extracts from a record. Due to extremely high spectral resolution of the amp micro dynamics is defined exclusively by the cartridge quality. Minute details in timber, dynamics or rhythm are clearly perceived; they don't exist on their own but constitute an intrinsic part of music giving it the very realism that make analog sound so likable.

Signal/noise ratio (unweighted): –82dB || Rated sensitivity: 5 mV || THD (1kHz): 0.06% (output voltage 2 V RMS) || Size: 40 х 152 х 405 mm || Weight (w/o adapter): 13 kilos || Price: 610 000 rubles.