Review: Kora TB 200 integrated amplifier: I had known the brand name Kora for a long time, but this French brand was scarce here in the low countries, so I had no experience with it. When I delved into the history of the company, I learned that it disappeared from the market in 2014, but that it was revived in 2017 by Bruno Vander Elst, a Frenchman with a very Belgian-like last name. Vander Elst is not only the new owner of Kora, he and his team are also developing highly sophisticated measuring equipment used in civil, military laboratories and the aerospace industry. And he is a great music lover and audiophile who seized the opportunity to fulfill his long-cherished dream by acquiring the Kora brand name. The company is based in Toulouse, which is also known as the Silicon Valley of France. Here Kora’s amplifiers are completely handcrafted. So no Oriental semi-finished products, but ‘entièrement fabriqué en France’. Currently, the range consists of three integrated amplifier models, but separate pre and power amplifiers are being worked on, according to the website.
Square Tube is (isn’t?) what it’s all about
You can’t talk about Kora amplifiers without mentioning the unique and patented technique that Vander Elst has developed. My dilemma is about how deep I want to go into it. Because even though we definitely have to talk about it, the audible end result is what matters for the music lover or audiophile. But the end result in this case is so closely related to the particular circuitry that I will nevertheless attempt to explain it, while at the same time trying to keep it quite simple. To give full disclosure in advance; I’m not a highly educated electronics engineer myself, so excuse me if we’re all going to get a bit lost in a moment. That said…here we go…
The Square Tube technology is a completely new way of using tubes as a reinforcing element. As the name implies, it takes four tubes; mini triodes in this case. A 12au7 (ecc82) at the input, and a 12ax7 (ecc83) at the output of the circuit. These tubes are only used for voltage amplification and are set in such a way that they last for a very long time. Kora does not specify how long, but colleagues talk about a lifespan of at least ten years, but probably at least double that. And that is indeed much longer than in a traditional tube circuit. Because the tubes in this circuit have fixed polarization points, their influence on the final sound is nil. That’s a shame for the inveterate Tube Roller, but it gives the average user a beneficial mental peace. In the example I received, the input stage contained two NOS Philips ECC82s and the output stage contained two OEM (ie unmarked) modern production 12ax7s, almost certainly of Chinese manufacture. And that’s it. That small printed circuit board with four tubes that is mounted behind a half-obscured window in the front plate of the Kora TB 200 could be called ‘the actual amplifier’ with some poetic freedom.
Now I can already hear the better-trained electronics among my readers say: “Wow, Delissen, you can’t drive loudspeakers with a 12ax7!” And that’s true, but we have now arrived at the most brilliant part of the patented Square Tube technology. The amplifier contains six extremely linear Motorola power transistors per channel, hidden behind an enormous battery of capacitors that, with 60,000uF per channel, take care of ‘differential mode’, among other things, with 60,000uF per channel. mains filtering (the power supply circuit also includes ‘common mode’ mains filtering). These transistors are set up as ‘followers’ and supply the necessary current for the final amplification, but they themselves do not participate in it. The input impedance is high, the gain is about 1, and the output impedance is low. So they actually form the impedance buffer between the output stage (the 12ax7s) and the loudspeakers, just like the output transformers do in a traditional tube power amplifier. But without the disadvantages of those output transformers, such as phase shifts, a relatively low current throughput and a rather low damping factor. Because the transistors are not really in the signal path, the Square Tube technology is not a hybrid circuit in the traditional sense of the term. We are dealing here with a genuine, albeit rather unusual, tube amp. Are we all there yet? Okay, then on with the…
Features and Connections
The Kora TB 200 is an analog integrated amplifier. On the rear panel, next to the IEC mains entrance (use a good power cable, Kora strongly recommends) you will find two pairs of speaker terminals that are suitable for banana plugs and spades, but have a slight preference for the ‘fruity’ variant in an ergonomic sense, and four unbalanced line level analog stereo inputs. No phono stage, no built-in DAC, only amplification. The case itself is made of aluminum and steel and has been sprayed with a beautiful spatter structure in the color ‘mineral grey’. The front consists for the most part of a sheet of ‘smoke’-colored acrylic in which the barely transparent viewing window for the tubes is located in the middle. Slightly to the right of center, on the border of the acrylic and the metal, you will find a multifunctional turn/click button and above it is the ocher yellow VFD display. That’s all, the appearance is beautiful, very sleek in finish but also very minimal. In addition to the recessed rotary knob, which feels very pleasant when you operate it, a relatively simple remote control is included for things like volume and source selection, mute and on/standby. The background settings, such as the brightness of the display, the balance and the gain adjustable per input, can be adjusted via the menu that is only accessible with the turn/click button. That is a bit cumbersome, but in practice you will not often make changes to it. Unfortunately, there is no option to give each entrance its own name. There are only four, so remembering won’t be a problem per se, but you do expect such a function at this price and quality level. It’s not bad, it’s a pity.
And then the big moment is finally here. My own tube amp (the suddenly very traditional looking PrimaLuna EVO 400i) goes aside and the AudioQuest Blizzard power cord is plugged into the Kora. My AURALiC ALTAIR G1 streamer and Thorens TD125 turntable with Jelco SA750E arm and Holistic Audio HA-103C element – on an AudioCreative PhonoDude tube phono stage – are connected to the TB 200 with AudioQuest Water interconnects. The banana plugs of my AudioQuest William Tell Zero speaker cables disappear into the speaker terminals of the Kora and then the amplifier was turned on by pressing the turn/click button once. When the amp is ‘off’, it is effectively in a deep standby sleep where only the most important parts are left energized. Not the tubes, which start their stabilization cycle after the amplifier wakes up. A progress bar in the display indicates the time remaining. Only when the tubes are at sufficient temperature and function stably – which takes less than a minute – are the supporting transistors connected by means of a relay. After an hour of warming up (not more than lukewarm, by the way, when I feel the cooling fins after that hour) with internet radio at whisper volume, the listening finally starts.
Listening to the Kora TB 200
The peak was kicked off by the album by the magnificent Goldbrun of the Yuri Honing Acoustic Quartet. Calm yet incredibly richly recorded acoustic jazz with saxophone, piano, bass and drums. The first thing that struck me was how incredibly smooth and easy the music sounded. Now this relaxed jazz may not be the most demanding challenge dynamically, but in terms of tonality and rhythmic coherence I heard some incredibly beautiful things. What also struck me quite quickly was that the sound had no clear ‘signature’. It sounded neither tube-like nor solid state. Or perhaps a beautifully balanced combination of both? Warm and rich in sound, fast and dynamic, broad, deep and high in the spaciousness, and above all extremely clean and transparent in the lavish detailing. Best of both worlds then? To give the amp a little closer look, I – très François – started Suzanne Belaubre’s wonderful electronic album (DIY), which was released on the rather obscure but often surprising French internet label La Souterraine. The name of the album actually says it all; this is bedroom studio music (three times word value), with a charming rawness that came out very well through the Kora. I heard the imperfections but they didn’t bother me. On the contrary, they were quite logically part of the recorded artistic achievement. Third surprising fact that stood out: with the Kora I was always very quickly ‘in’ the music.
To fully exploit that phenomenon, I stayed in the French spheres for a while with the infamous Le Temps Passé by Michel Jonasz, from his album La Fabuleuse Histoire De Mr Swing. Besides a godforsaken pit deep layer, this track also has a very tangible and special live atmosphere. That atmosphere was there immediately, the stage was so clearly audible that I had the feeling that I could walk over it, between the musicians. This amp can create an image folks, phew… but here’s another thing that struck me. The bass was indeed deep and super tight, but it was also very clean. Even so clean that I had to get used to it. I might have liked that a little bit bolder. So the TB 200 turns out not to be French, but a French one. Who makes music very sovereignly and with extreme precision, but I started to get a suspicion that the heavier music might need more an Obelix as an amplifier than a Valhalla.
To put this to the test, I played another piece of French music, namely the new album by the progressive metal band Gojira from Ondres. Pretty extreme music, that has to be said right away. There is little audiophile about it. The Kora once again carried out its task with gusto, but here it did indeed sound just not dirty enough. Incidentally, I am the first to look for the cause of this in the system synergy with my extremely high-resolution Kharma prototype loudspeakers. This music doesn’t sound as brutal with my own tube amp as it does on stage, but that small dash of extra distortion that more traditional amps add does ensure a slightly higher air guitar and skull swish factor in my set. However, I can vividly imagine that this music on a thick JBL monitor does sound fat with the Kora. Because there was no shortage of power and control – and insight into the recording – despite my minor reservations. But every now and then you just want to have a nice brutal beating. All in all, I suspect that the target audience of this amplifier will ask: “GoWatte?” when they hear the band name.
Conclusion – Kora TB 200
The Square Tube amplifier, the innovative and unique brainchild of Bruno Vander Elst, is a success. Music is played with great ease and great fluidity and immediately grabs your heart. With a few very serious exceptions, the Kora TB 200 devoured everything I presented to her in recent weeks. The relatively small number of – exclusively analog and not renamable – inputs is not a problem in an average audiophile set with a record player and a streamer (respectively via a phono stage and an internal da-converter or not), but it may be something for some. to keep in mind. But that, in addition to the somewhat minimal operating facilities, is the only thing I can say about it. What remains is a beautiful-looking, beautifully robustly built, wonderful-sounding and truly innovative amplifier. This Kora TB 200 is very beautiful. A more than worthy revival of the brand. Thank you and good luck, Monsieur Bruno!
- Kora TB 200 integrated amplifier: €10,000