For several years now, under the impetus of its eminent technical director Bruno Vander Elst, Toulouse-based manufacturer Kora has been enjoying a new lease of life. The products are increasingly ambitious and, above all, feature new, practical functions. A case in point is this brand new phono preamplifier, as clever as it is musical, which left us wondering when we heard it at the last High End in Munich, and which we are delighted to present to you as a preview: the Kora Phono Stage.
Over the last few years, we’ve had the opportunity to test the TB140 integrated amplifier (VUmeter no. 27) and the TA480 power block (VUmeter no. 38), two infinitely musical products. The new Phono Stage uses the same chassis as the TB140 for an elegant, compact visual effect.
It is the brand’s first independent phono stage. Previously, Kora had only developed a pre-amplification section for moving-magnet (MM) cells found in its integrated amplifiers.
The specifications that governed the design of the Phono Stage are in keeping with the spirit of Kora: to meet the technical requirements of the phono format in order to obtain an uncompromising result without giving in to any fashion. The requirements defined by the developers were firstly to obtain the lowest possible noise level, without circumventing the problem with an input transformer. Secondly, the team wanted to maintain great respect for the RIAA correction, but also offer excellent flexibility of use.
Finally, of course, as with all Kora devices, to guarantee the quality of the components and manufacture, without ostentation, but without compromise.
The most delicate part of the development was undoubtedly the input stage. To achieve the lowest possible noise level, Kora used some of the quietest input transistors on the market. In addition to the ultra-low-noise operational amplifiers, all the resistors in the signal path use ‘foil’ technology, guaranteeing the lowest possible noise level and absolute precision. These are Vishay VSRJ resistors, offering accuracies down to 0.01%.
This stage has a gain that can be programmed to 50 or 100. It is a fully symmetrical stage that can also be used with an unbalanced input. Noise theory predicts a 3 dB reduction in noise in this case.
Once properly amplified by the input stage, the signal is less fragile. Still symmetrical at this stage, it will be converted into an asymmetrical signal by an analogue subtraction operation. This eliminates some of the so-called ‘common mode’ noise, which is the whole point of balanced cabling. We take advantage of this stage to apply a gain of 3.
It is within the RIAA correction that the first part of the signal correction is implemented. This section processes the high end of the spectrum and is therefore essential for the overall quality of the preamplifier. This first correction is totally passive, essentially entrusted to precision capacitors in polystyrene technology, the best according to Kora. An active circuit handles the second part of the correction, which deals with the low end of the spectrum, again using polystyrene capacitors.
The output stage intervenes when the signal is restored in its entirety. It gives the signal all its strength to ‘attack’ the links to the amplifier. The output is unbalanced on two RCA sockets, but an additional circuit (called a phase shifter) will create the second signal in phase opposition which will feed the two XLR output sockets. Both RCA and XLR outputs can be used simultaneously. This last stage has four programmable gains (1; 3.33; 5 and 10). All these gains distributed along the amplification chain allow you the wide range of gains of the preamplifier, always taking into account the noise and requirements of each stage.
The set up
The Phono Stage allows you to meet all the requirements of your cartridge(s), as it has four inputs. Two are equipped with XLR sockets, allowing you to connect the cartridge in balanced or unbalanced mode, depending on your needs. Each input can be individually programmed to best suit your requirements. The configuration is stored in memory and will be recalled automatically each time you select that input.
The various programming choices available to you concern the input impedances and the total gain of the device. For your cell, select the value given in the manufacturer’s manual if it is specified. For moving magnet (MM) cells, the value 50 kilo-ohms is standard. For moving coil cells, the value is often given as ‘> 40 ohms’. In general, the value of 200 ohms meets all requirements!
Don’t hesitate to do a few tests, there’s no danger to either your cartridge or your Phono Stage. The selection of the capacitance of each input is valid for all types of cartridge. Your choice covers from 100 pF (0.1 nF) to 1.5 nF in steps of 0.1 nF, i.e. 0.1 nF; 0.2 nF; 1.3 nF; 1.4 nF; 1.5 nF. Here again, either the manual for your cartridge recommends a value, in which case you choose the closest value (for example, if the recommended value is 470 pF, program 500 pF), or the manual doesn’t specify anything, in which case you can try things out ‘by ear’ to fine-tune your listening!
The Phono Stage has a wide range of gain settings to match your installation. This output voltage value should be in the order of magnitude of the sensitivity of the following amplifier.
Kora comes with two handy extras. A Demag function allows you to demagnetise your pick-up if necessary. Finally, for a record that’s a little foggy, you can use the Rumble function, which eliminates very low frequencies outside the audio range.
The sound of the Kora Phono Stage
It doesn’t take long to realise that the Phono Stage is a rather special product. Once you’ve set it up according to the indications of your cartridge, all you have to do is let the sound blossom in the room to understand what kind of product you’re dealing with. Listening to these electronics is truly ‘liberated’.
You instantly feel the way the energy takes over a space in the room. Obviously, analogue media favour physical listening. But here there’s a little something extra, a little extra soul. Firstly, the notion of control is very palpable. The energy is there, very much there, but it’s channelled to perfection. Do you want to vibrate to your favourite tunes? No problem, but with an above-average level of demand. So, lots of spontaneity, beautifully controlled.
This is the powerful foundation on which Kora builds its musical edifice. Because this flow gives a superb sensation of carnal presence. On a double bass, the material waves are present and vibrant. If we reason coldly in terms of bandwidth, it’s worth pointing out that the bass descends very low, with astonishing aplomb and superb legibility.
In the various rhythmic lines, it’s easy to distinguish between the playing of each instrument (bass, drums, etc.). The timbres are natural, accurate and never overly brushed. The treble runs very high with a delightful smoothness. What’s also very striking about this device is the notion of space it imposes. Depth is unusually great, with a very legible gradation of the different planes.
The result, obtained with a very fine cell, is of remarkable quality. But what’s far more astonishing is that the Kora manages to push the performance of a simple MM cell to unsuspected limits. With our trusty Nagaoka MP150 (under €400), the Kora surprises in terms of fluidity, attack and perspective. Never before have we heard this cell sound so realistic and effective.
In other words, its potential is much better exploited by the Kora. With our Dynavector XX-2, the performance is superb. The coupling between the two products is very successful. The preamp makes full use of the resolving power of the cartridge, which seems to scan the bottom of the groove as rarely as possible. The tonal colour of the different recordings is immediately apparent. The vocals are suave and delicate, the instruments highly embodied. The swing is formidable and the dramatic intensity of each disc is perfectly rendered. Each time the tonearm is lowered, a new world of sound is revealed.
Our conclusion
This compact, elegant product conceals mature technology and great adaptability. With its four fully configurable inputs, the Phono Stage offers uncommon operational flexibility. But what really counts is its lively, powerful, controlled and extremely subtle sound reproduction. This is Kora’s first separate phono preamp (with the exception of the MM stage of integrated amplifiers), but it has already made a very strong impression on us. In a field where the offer is wide and sometimes very well made, the Kora should have no trouble making a place for itself, as its flexibility and musicality are absolutely indisputable.
Author: Laurent Thorin
Technical sheet: Kora Phono Stage
- Origin: France
- Price : €6,600
- Dimensions : 315 x 90 x 260 mm
- Weight : 5 kg
- 4 fully configurable inputs :
- 2 balanced
- 2 unbalanced
- Input impedance :
- MM: 50 kΩ
- MC: 10 Ω to 1,270 Ω in 10 Ω steps
- Input capacitance : 100 pF (0.1 nF) to 1.5 nF in 0.1 nF steps