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Robert Koda K-15 EX line preamplifier

Robert Koda K-15 EX preamplifier

Uncompromising. Minimalist. These are words that are often bandied around the audio world (I’ve used them far too many times myself) to the point where they have almost no meaning. In some cases, they can be a convenient excuse to justify the absence of a key aspect of a component in some all-too-often nebulous claim to improved performance. But when it comes to the Robert Koda K-15 EX line preamplifier, you begin to see that these terms still have some life left in them. And also, you begin to discover that the terms are not entirely interchangeable.

Let’s break those terms apart, in the light of the line preamplifier; ‘minimalist’ is doing without a remote or a balance control, ‘uncompromising’ is recognising the extent of the damage including either of those circuits has on a preamplifier. ‘Minimalist’ is limiting the preamplifier to five balanced or single-ended inputs and two balanced or single-ended outputs, ‘uncompromising’ is wiring those inputs point-to-point direct to the selector without any form of circuit board to get in the way. ‘Minimalist’ is replacing a potentiometer with a resistor ladder to make a better volume control. ‘uncompromising’ is going for a custom-designed L-pad attenuator instead. An L-pad design means ‘volume level’ isn’t a point on a potentiometer, it isn’t even a ladder array of resistors (because that means the potential for many resistors and solder joints in the signal path); this arrangement means there is just one resistor per channel in the signal path at any given volume level. What’s more, those high-precision carbon composition resistors are specifically designed for audio use and are only ever used in audio applications (Koda stresses that these parts are only used in audio applications).

 

Robert Koda K-15 EX internal image
Only the best components are used in the Robert Koda preamp

Then, there’s Robert Koda’s unique ITC (Inverted Transconductance Coupling) circuit, which uses solid-state semiconductors in the way most companies use triodes. And then there’s the way the K-15 EX acts as, in essence, a single-ended preamplifier and a balanced preamplifier, whose paths only cross should the need arise, creating a ‘best of both worlds’ design.

Continuing that ‘best of both worlds’ approach, the K-15 EX is a solid-state preamplifier that largely eschews printed circuit boards and is built point-to-point like some of the very best valve amplifier designs. The point-to-point circuit design also allows greater control over the materials used in the signal path, and in this case, Robert Koda hard-wires everything with high-grade silver wire (as befits Koch’s Audio Note heritage). The K-15 EX tips its hat to modernity by building each section of the preamplifier into well-isolated ‘rooms’ within the chassis. Some of those rooms are extremely well isolated, too; the zero-feedback, choke-regulated power supply (which, one could argue, is the best the pre-transistor world could offer and remains unequalled today) is housed in what could best be described as a vault, designed to prevent any stray magnetic fields from escaping the power supply’s clutches. Every other stage in the preamp also has its ‘best case scenario’ chamber, whether that be copper, mu-metal, or iron. It’s easy to say that “nothing is left to chance” because, frankly, a preamplifier at this lofty aspect should leave nothing to chance, but the Robert Koda K-15 EX shows just how many of the best preamps still leave some elements left un-addressed because they have always been that way.

However, ultimately none of that is more than ‘surface’ relevant, because it simply contributes to a preamplifier that is discussed in hushed tones among audio’s cognoscenti. This is a product that isn’t just extremely expensive and so exclusive that Robert Koda has a Morgan-like waiting list. It’s a product you have to ‘earn’ rather than just ‘buy’. There are other (granted, not many) preamplifiers that have a similar price-point, and some that are so built-to-order that you might be waiting months to get your sample, but few make such demands on the design and implementation of the system or so crucial a set of listener requirements as the K-15 EX. Frankly, if you aren’t ready for that degree of analysis of system and music yet, the Robert Koda K-15 EX isn’t your preamplifier. The preamp may yet be in your future when you have reached the pinnacle of what ‘mainstream’ high-end audio can achieve and wish to go even further.

What do these demands mean in real-world terms (although at this level of audio, the ‘real-world’ is a long way down)? They mean a potential complete re-think of both your system and how you listen to it, and potentially even the music itself. That last could seem worrying, like creating a filter that only plays some music and renders a lot of sounds functionally unlistenable, but actually, it’s more about the volume levels you are used to playing. Often, even the best systems trade dynamic range for headroom, and we have become used to that trade-off. And when faced with one of the rare designs that go in the other direction, it means you might not want to end up playing music at ear-splitting levels, enjoying the scale of music rather than simply its intensity. If that sounds like a compromise too far, it won’t once you hear what the K-15 EX is capable of in terms of that scale reproduction.

A big function in this preamplifier’s uncompromised stance toward equipment selection is its gain structure. This is not a high-gain preamplifier. In fact, it is closer to a passive preamplifier that brought just enough gain along to wake up sensitive amplifiers and drive reasonable cable lengths. As Robert Koch says, it delivers lots of power gain, but that dictates the choice of the power amplifier; less ‘brute force’ more ‘high-performance lower power’.

Robert Koda K-15 EX
This is the sum total of control surfaces on the K-15 EX. It’s all you need!

Perhaps a mark of its importance, the K-15 EX is one of those rare products where there was something of a clamouring of writers wanting to get hold of this. Once it was announced, a steady stream of requests to review the product arrived, sadly at about the same time as I had already finished up with the listening. While I’m not one to play the ‘rank has its privileges’ card too often, this was something I just could not turn down! But this is almost a once-in-a-lifetime offer given the rarity of the K-15 EX. That rarity is not just because of its cost, but because Robert Koda’s production capabilities are extremely limited and the products are basically built to order. And the K-15 EX is perhaps the easiest for Robert Koda to produce; the MC-One is a much longer build and K-160 is even more labour-intensive. Just a handful of preamps will be built each year along with two or three pairs of power amps. While, “so, get in line” seems inappropriate in the context of a £60,000 preamplifier… get in line!

Those few of us fortunate enough to experience the preamplifier quickly realise that it is just that… the preamplifier. Other designs might be excellent signal attenuators, superb and exciting musical creators or profound examples of the electronic engineer’s art. But they aren’t the preamplifier the way the K-15 EX exhibits from the first musical bar.

There are two reviewer’s traps in describing the K-15 EX. The first is to say the phrase, “Zen-like” because it’s so tempting: the Koda comes from Japan and its stillness and mastery over music replay makes you think of those artisan swordsmiths, ceramists, painters and calligraphers. But it’s the wrong thing to do. Zen Buddhism is inherently inward-focused, and those masters were trying to get past their personhood through perfection of a craft, and the craft was almost secondary to that contemplative position. Zen isn’t just Hokusai, it’s staring at a wall for a couple of decades. The parallel and shared experience here is ‘focus’, but where Zen focuses inwards, the Robert Koda is the result of focus on making the best damn preamplifier it’s possible to make by making what’s important as simple and as good as it’s possible to get, and ignoring the rest. If you are looking for a philosophical construct to describe the K-15 EX, try Aristotle: “Nature operates in the shortest way possible.”

That second trap is to try to pin the sound down in musical terms, using pieces of music to highlight specific aspects of the sonic performance. In other words, the big reviewer trap is to try to do your job and describe ‘how it sounds’. The problem with this is yet more philosophical noodling; it quickly becomes too reductionist. You quickly realise when trying to pin down precisely what the Koda does that you are one of those blind men describing an elephant. The focus you bring to the Robert Koda is your own. If your musical trigger is ‘detail’, you’ll be impressed at the level of detail in your music. If it’s ‘soundstaging’, you’ll start using terms like ‘holographic’. If ‘rhythm’ floats your boat, you’ll be taken by its right, tidy sense of a beat. If you crave a musical presentation that has both space and tranquillity, you’ll start using words like ‘limpid’. And so on.

In fact, what you realise is that any such audio descriptions are pointing at other things. You find yourself describing the performance of the source, the power amplifier, the speaker, the cables, the medium, the recording engineer, even the skills of the guitar tech or the piano tuner long before you latch onto the sonic autograph of the K-15 EX. You also find that those preamplifiers that are supposedly ones that sonically ‘disappear’ often rarely actually live up to expectations. The closest ‘real-world’ parallel is probably a well-produced passive preamplifier, in particular, the current generation of passives that are more than just ‘a pot in a box’. The absence of gain stages do give such devices a taste of what an unsullied audio signal can sound like, but the absence of gain stages also detracts from the tonal and timbral ‘structure’ of the music, which you can only experience when you hear a product that manages to bring along just enough gain to provide musical excellence, but not so much as to swamp that sound. In other words, the K-15 EX.

Everyone in high-end will tell you good preamplifiers are a rare thing. Great preamps can be counted on the fingers of one hand (and, if we’re being really picky, it’s a hand that came off worse in a fight with a threshing machine). Those great preamps balance between a sound that can be ‘lovely’, ‘lively’ or ‘liquid’… picture those three elements like a Venn diagram. Most preamps only hit one of those three targets, or at best focus on one aspect and pay lip service to the others. A few manage to nail two out of three at best. In fairness, many will be comfortable with a sound that delivers a ‘two out of three ain’t bad’ sound because it both fits their system and their requirements. And many of these preamplifiers are truly world-class.

But then there’s the Robert Koda K-15 EX. If you think of that Venn diagram, the K-15 EX’s performance is about as smack in the middle as it’s possible to get right now.

The odd thing about the K-15 EX’s performance is the effect it has on you when you go back to whatever you were used to listening to, more or less irrespective of how good that product was. You can respect its performance and what it is designed to do, but suddenly the shine went off what came before. You hear it in terms of a kind of electronic-y sound or just a little too much warmth maybe it just tries too hard and makes things that bit too legato. The K-15 EX doesn’t do any of those things, and it might take some sonic re-evaluation to get overhearing that fundamentally correct sound.

If listening to the K-15 EX seems to expand to your audio brain in a manner that a steady diet of Beethoven does to your musical brain, or reading a lot of Aristotle and Kant seems to do for your reasoning, the process is reversible; the removal and continued absence of the K-15 EX doesn’t just come with a profound sense of loss; the effect is compounded by something close to a loss of a sense. Your musical ‘proprioception’ is reduced by not having the K-15 EX and listening to music takes a big hit as a result. We unconsciously identify sonic performance into ‘live’, ‘good sound’, and ‘clock radio’ grades (with some considerable amount of overlap between the last two). The K-15 EX simply provides more granularity between ‘live’ and ‘good sound’ and the insight that creates is ‘difficult’ to achieve elsewhere (which is the polite way of saying “I’ve not heard anything that gets this close to the real deal since I spent some time with the Audio Note Ongaku back in 1991”). And it’s taking that step closer to the real sound that is both so heady and so difficult to give up.

The Robert Koda is something of a departure for high-end audio and for the high-end distributor behind the product. The distributor – Ten – is effectively an artisan-led company within the confines of the already quite artisan-led Absolute Sounds company. It’s like a diffusion label in reverse; where Armani has its Emporio line and Prada has Miu Miu, this is what happens when you go in the other direction… Privé Haute de L’Audiophile, if you will. As the equipment here is so uncompromising, it demands people who have a true understanding of the implications of such an approach; not simply retailers, but even the listeners themselves. This is not simply some status symbol product, or some kind of Veblen good. This is the result of a team already thoroughly well versed in what audio can do, and still striving for something over and above that already lofty audio performance.

Robert Koda K-15 EX rear panel
Balanced and single ended inputs are all replicated.

As much as anyone who writes for a living about audio, you get to hear a lot of equipment, a lot of which is exceptionally good. Even the traditionally difficult preamplifier has some really good examples out there. But even set against such exalted company, the Robert Koda K-15 EX stands out above its rivals in pure performance terms. But, it’s far beyond my threshold of affordability, so I have to face up to the fact that the best preamplifier I’ve ever heard is likely always going to be beyond me and I will forever move in reduced circles as a result.

 

TECHNICAL SPECIFICATIONS

  • Type: Line level preamplifier
  • Inputs: Five pairs true balanced (pin 2 is Hot). Five pairs RCA
  • Output: Two pairs RCA, Two pairs true balanced (pin 2 wired Hot)
  • Voltage gain: +8dB at maximum volume
  • Signal to noise ratio: 114dB A-weighted at 1Vrms output, 147dB at full output
  • Frequency response: 20Hz–20kHz ±0.05dB
  • Maximum output: 30Vrms single-ended, 60Vrms balanced
  • Input impedance: 50kΩ single-ended, 50kΩ per phase balanced
  • Output impedance: 60Ω Single ended, 30Ω per phase balanced
  • Total harmonic Distortion: Less than 0.0003% at 2V RMS out, 1KHz, balanced input
  • Dimensions (W×H×D): 389 × 158 × 385mm
  • Weight: 29kg
  • Price: £60,000

Manufactured by: Robert Koda

URL: robert-koda.com

 

UK Distributor: Ten

URL: ten-collection.com

Tel: +44(0)208 971 3909

Meet Your Maker: Robert Koch of Robert Koda

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Tags: K-15 EX LINE PREAMPLIFIER ROBERT KODA

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