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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.

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