Robert Koda Takumi K-10 Preamplifier

by Marc Mickelson | May 24, 2012


If you ever have the chance to review these, I would love to hear your impressions. I'm told they are amazing!" This is the entire text of an e-mail I received from Kevin Tellekamp, the head of Silent Running Audio, more than two years ago. He pointed me to the website for a brand of electronics I'd never heard of: Robert Koda. Kevin was referring to a peculiar pair of mono amplifiers, the Takumi K-70s. The amps' unusual physical layout -- two amps that share a power supply, for a total of three chassis -- was the first sign of a highly original design. The K-70s are actually referred to as a single amplifier, one that operates single ended but offers an un-single-ended-like 70Wpc in "class A1." The K-70 is a hybrid, using solid-state output devices along with a pair of 5842 triode tubes at each input.

In a follow-up message, Kevin revealed that he had made a few sets of his Ohio Class XL+ isolation bases for the Robert Koda amps -- make that, amp -- and this was what brought the K-70 to his attention. Curious, I wrote the company and received a quick reply from Robert Koch, who does all of the design work in addition to running the entire enterprise. After a bit of e-chit-chat, we discussed a review of the K-70, the only Robert Koda product at that point in time. Koch told me that he was working on a preamp and that he would be more apt to offer it for review, as it would be brand new and in need of some exposure.

So here we are two years later and the subject of this review is that preamp -- the Takumi K-10. After researching the K-70, I would have wagered that the K-10 would have tubes lurking somewhere within its single, hefty chassis. It only stood to reason, given that the K-70 was a hybrid, and, frankly, the preamp's $31,000 price is a neighborhood where tubes are pretty much de rigueur in audio electronics. But the K-10 turns de rigueur on its head -- it's solid state from input to output, though with a few interesting wrinkles that are in keeping with a maxim that strongly informs both Robert Koda products: eschewing conventional thinking in favor of the best circuit for the purpose.

"Best," in Robert Koch's words, means "dynamic simplicity" and "total freedom from power-supply sound." Koch has been working in the audio industry for many years, his entry being like that of so many manufacturers: following his father into the ever-deepening waters of audiophilia, a preoccupation from his childhood in South Africa onward. Beginning in his teens, Koch worked in audio retail, mixing this with formal study of electronic engineering with an emphasis on addressing the big issues: "I spent most of my time studying AES journals and the like and concentrated on equating subjective performance with measurable electrical performance."

"Then I went over to the UK, worked for Audio Note UK a bit -- I wanted to find out more about the other side of products (i.e., production) as it had been my childhood dream to have my own high-end audio brand." Infected with the sound of low-power single-ended amplifiers, Koch gutted a pair of van den Hul amps he owned and used the chassis to house his electronics. "There were several more moves between South Africa and Japan. Several comings and goings from Audio Note Japan, where I helped engineer the M1000, the M1000 Mk II and various other items before I finally said goodbye to them and started Robert Koda," which launched in 2008.

An intriguing question for me, given Koch's globe-trekking, is whether his design philosophy grew out of his vast and varied experience in the audio industry, or if that experience was directed by his maturing design philosophy. In other words, was nature or nurture responsible for the making of this audio engineer and his products? Koch provided some insight during e-discussion: "I had realized at a very early stage that circuits with great specifications would more often than not not yield high-fidelity music reproduction." Nature it is, but with a twist, one that doesn't elevate "great specifications," such as they are understood today, above "music reproduction." In other words, Koch listens as much to music as he does his own ideas about designing audio electronics, what my experience tells me is the highest of approaches and the one most likely to succeed.

Which brings us back to "dynamic simplicity" and "total freedom from power-supply sound." For Koch, these tenets don't simply coexist in his amp and preamp, they enable each other. The former is the product of some well-known design ideals, including eschewing feedback and ensuring low output impedance, but the larger notion, as Koch expressed, is removing "uncontrollable variables." These include the local bypass capacitor in the power supplies of his amp and preamp, which, according to Koch, has a tremendous effect on the sound. To overcome this, the K-10 "runs two loops through the power supply, each modulation being of the same intensity but mirror-imaged. The result is that there is almost no audio signal flowing through the power supply and related regulators, bypass capacitors, etc. due to a near-perfect cancellation effect." Koch also uses a very good bypass capacitor "in any event" along with a Japanese-made R-core transformer and four chokes.

While most designers who cite the power supply as a particular concern house it in a second chassis, Koch discovered through trial and error that this led to no sonic gains. But the implementation of the K-10's power supply inside the chassis is anything but usual, housed as it is within 2mm of soft iron plate. "We tie the problem up at every end and then tie it up again," Koch says.

The K-10's fully balanced audio circuit is the product of a clean-sheet design process focusing on new circuit concepts. Koch's ITC (Inverted Transconductance Coupler) solid-state circuit uses all of ten transistors and no integrated circuits. There are no relays and minimal circuit boards, which are connected with silver wire. There is also no remote control, which, given the K-10's volume control and input selector, would have required motors, logic circuits, and extra power supplies. The K-10's volume attenuator uses resistors created for sound reproduction and its source selector is a rotary switch built specifically for audio use.

Functionally, the K-10 is as bare bones as a preamp can be. Only the volume control, input selector, on/off indicator and a bit of explanatory script adorn the faceplate. There's no balance control, so if you adjust channel balance often (I don't), you'll want to look elsewhere. There are four inputs: three single ended and one balanced. Outputs are both single ended and balanced, their use determined by a rear-panel switch. The other rear-panel feature is a grounding post, which Koch includes because "ground noise can be very destructive to sound quality." Perhaps to prove his commitment, all K-10's available now have two grounding posts on the back panel: one each for chassis earth and signal earth, a configuration that gives more flexibility than the single post. The K-10's chassis is as deep -- 15" -- as it is wide, and it weighs a lot -- nearly 60 pounds. The weight is centered within the chassis, giving the K-10 a cannonball-like feel when you pick it up.

Although the K-10 is all solid state, Robert Koch doesn't recommend keeping it on at all times. I suspect this is due to heat, which is minor on the exterior but possibly major within the tight quarters of the fully sealed chassis. Twenty minutes of warm-up are recommended, and I would consider that a minimum, as the K-10 sounded even better -- more liquid and dynamic -- after 45 minutes. I was never anal about the on/off status of the K-10. I left it on a few times over the course of a couple of days, and there were no issues, even here in toasty Arizona.

I was able to use the K-10 with a lineup of amplifiers that embodies the phrase "a wealth of riches": Lamm M1.2 Reference and ML2.2, Atma-Sphere MA-2 Mk 3.1 and Audio Research Reference 250, all monoblocks. I used all but one of them extensively. Because the K-10 has extremely low voltage gain -- a mere 6dB -- it didn't work well with the Lamm ML2.2s, which also have rather low gain, creating a situation with some phono stages where there wasn't enough gain for analog playback to sound anything but dynamically limp. The Lamm M1.2s, on the other hand, have very high gain, with the MA-2 Mk 3.1s and Reference 250s occupying the middle ground. All were very good matches with the K-10 in this respect -- and in sonic terms as well. While I often discover that a certain amp simply sounds best with a preamp I'm reviewing, that wasn't the case here, as all three combined for stellar outcomes, with some sonic differences of course. This went hand in hand with my initial feelings about the K-10 -- that its performance made the act of reviewing it a challenge. While it sounded tight and polite right out of its box, it broke in quickly, and in short order I was listening for hours on end without thinking -- or remembering -- that I was supposed to be dissecting what I heard.

The K-10's performance was immediately explained by what it didn't achieve -- that well-worn audiophile concept, hi-fi sound. Hi-fi sound can be initially impressive, hitting the marks for resolution, dynamics, speed and spaciousness, but never resembling anything more than competent reproduction. While I agree with Brother Roy Gregory that audio systems, no matter how exceptional, fall far short of reality, they can nonetheless display many of the earmarks of live music, and this is why they are compelling to us. In the terms of another well-worn audiophile concept, they suspend disbelief, even if we know that's all they are doing, and they achieve this through a preponderance of those live-music earmarks.

The K-10's sound was abundant with qualities that suspend disbelief, all presented in a manner that never called into question their hi-fi credentials. The K-10 was about poise more than fireworks, even as its finely drawn treble extended to nothingness and its fleet, well-defined bass plumbed whatever depths were on each recording. Its sound had weight, both in the traditional sense of producing substantial images and in terms of the musical consequences and meaning conveyed. It made me lean into the music, becoming engrossed in it and forgetting the equipment that put me there. If there's a higher audio ideal, I'm not aware of it.

The K-10 displayed a skillful balance in perspective and especially tone. It was neither forward nor recessed, and it cannily combined the inherent linearity of solid state with a touch of golden glow, giving the mids and treble an endearing approachability. There was none of the arid leanness that can often color solid-state sound (though some audio reviewers inexplicably call this "neutrality"), none of the exaggerated speed that gives transients an artificial snap that obscures decay. From this you might be thinking, just as I was, that the K-10 sounds as though there are tubes within it. Like a great tube preamp, the K-10 managed to sound beautiful and honest at the same time, though never cloying or ruthless. It resolved with grace, disappearing into the music it made better than any preamp I've heard.

Along with this, its sheer resolving power was evident but subordinate to its holistic approach to music-making. It was particularly useful at revealing the differences among source components. The reality of being a busy audio reviewer is that you are often listening to more than one product at a time -- not added to your system simultaneously, of course, but one after another, in order to determine what one can bring out in the other. Such was the case with the K-10 and, coincidentally, the K-01, a characteristically stalwart CD/SACD player that is Esoteric's top single-box source at this point in time. I have a great deal of experience with Esoteric digital gear, but that didn't prepare me for the K-01, which abounds with features that affect its sonic performance. The K-01's musical power -- a term I'll explain in my forthcoming review -- was never subordinate to the K-10's naturalness, and the sophisticated sound of the best SACDs extant, the Japanese SHM SACDs, was laid bare. In fact, that the K-10 possessed much of what makes those SHM SACDs special: a relaxed yet highly detailed view of the music, silky treble, adept communication of space, an inherent honesty, an elegant musical flow.

A sense of evenness permeated the K-10's sound from one frequency extreme to the other, the bass displaying the same delineation as the mids and treble. "Supreme coherence" my listening notes called it in the thrill of the moment of discovery. It was a trait that meshed especially well with analog. I had to send my Dynavector XV-1s back to Japan for a check-up, which led to my buying a Denon DV-103R to use as a backup. An Audio-Technica AT33EV had occupied that role, because it impressed me when it was mounted on the VPI Classic I reviewed over two years ago. More recently, mounted on my Tri-Planar tonearm and TW-Acustic Raven AC turntable, it sounded so mushy and blurred that I decided to give the Denon a go. Even before the '103R was completely optimized, it laid waste to the AT33EV, sounding faster and more open, yet harmonically rich and tonally sweet. While it didn't possess the airiness and sheer resolving power of my Dynavector, nor its bass definition and power, the '103R had no glaring flaws. There is an inherent effortlessness to analog that the K-10 also possesses, a free-flowing naturalness that, again, urged forgetting about the hardware.

How much you value the K-10 will depend on how much you value this sense of oblivion -- and the qualities responsible for it. I can imagine that some listeners will prefer a more forward, hard-charging sound, finding the K-10 to be too mannered. Those who fixate on the bass region may find the K-10's more integrated portrayal lacking in one way or another. Those who need a balance control, preferably on the unit's remote, will definitely want to look elsewhere. However, amidst the very best preamps I've heard, the K-10 fits right in, offering a little more of this in trade for a bit less of that (as they all do). It stands equal with units that are its price and performance peers -- and use tubes.

The limited-edition Audio Research Reference Anniversary ($25,000) inhabits the high ground in terms of sonic performance, its stature actually growing somewhat now that it's no longer available. Putting aside the obvious differences like its two-chassis configuration, vacuum-fluorescent display and remote control, wherever the Reference Anniversary excels sonically, the K-10 is not far behind. Contemporary Audio Research electronics -- amps as well as preamps -- always portray space with a side-to-side, front-to-back enormity that's both immediately impressive and addictive over the long term. Some will argue, I'm sure, that this is where tubes exert their greatest influence. While the K-10 doesn't sound as immediately big, the sense of space it conveys is still vast and, moreover, appropriate to the recording, even if it doesn't achieve quite the panoramic spread that the Reference Anniversary does. Likewise with the bass, which is a bona fide strength of the Reference Anniversary (and unusual for a tube preamp). The K-10 has nimble, well-defined lows that don't equal the sock of the Reference Anniversary's bass but never lack for weight and power.

Where the solid-state K-10 surprises -- to the point of stupefying -- is in the mids and treble, which are the domain of tubes. Its treble extension and refinement along with its midrange texture and dimensionality impart fine detail that, depending on the recording, equals or surpasses the Reference Anniversary, making for a presentation that's more sophisticated at the micro end of the dynamic scale, where low-level harmonics complete the musical picture. Small gestures -- breath through a woodwind, the pull of a finger on a string -- are more naturally rendered and intelligible. The K-10's resolution seems to come from a deeper place, where space is subordinate to the performers that occupy it.

Audio Research electronics also display very adept macrodynamic capabilities, scaling from soft to very loud dexterously and realistically. Perhaps because the K-10 doesn't sound as overtly big as the Reference Anniversary, it also doesn't put its dynamic foot forward first. It is as proficient at both ends of the dynamic scale, however, and ramps up and down gracefully -- as it does everything else.

Whether you would choose the Reference Anniversary over the K-10, or vice versa, may well come down more to the difference in features than sound. There is also the fact that the Reference Anniversary is discontinued, so buying secondhand is a requirement. Before the K-10 arrived, and knowing that it had no tubes, I wouldn't have expected that it would go toe-to-toe with the Audio Research preamp, but so it did.

The design of so much audio equipment, especially those products that occupy the uppermost strata in terms of price and performance, begins with an assumption about what technology will be used. This is natural, as designers come at their task with different belief systems in place, each dictating an approach before even the first part is chosen. This fact, along with his use of tubes in his K-70 amp, makes Robert Koch's design work for the K-10 preamp all the more curious. If anything, audio designers will use tubes in preamps and solid-state devices in amps, in order to make use of conventional advantages of each. Koch's approach was 180 degrees out of phase to "conventional"; his analysis of the product's purpose, from which the K-10's circuit grew, had making music at the very top.

It's hard to disagree with the outcome. Koch's K-10 bridges many audio chasms: between detail and coherence, vividness and ease, truth and beauty, solid state and tubes. This final one is not a matter of the K-10's parts, of course, but rather its performance, and that makes it all the more surprising. Tube electronics more often attain certain characteristics of solid state than the other way around, and when a solid-state preamp blurs its origins in a price range dominated by tubed competition, that's not just unusual but consequential.

Kevin Tellekamp wrote me about an intriguing hybrid amp, but it led to discovery of an extraordinary new solid-state preamp. My impression of the K-10? I loved it.

Price: $31,000.
Warranty: Two years parts and labor.

Robert Koda
1-9-4 Azusawa Itabashi Ku Tokyo 174-0051

Associated Equipment

Analog: TW-Acustic Raven AC turntable; Graham B-44 Phantom Series II Supreme and Tri-Planar Mk VII UII tonearms; Audio-Technica AT33EV, Denon DL-103R and Dynavector XV-1s (stereo and mono) cartridges; AudioQuest LeoPard and Nordost Odin phono cables; Allnic Audio H-3000V, Audio Research Reference Phono 2 SE and Lamm Industries LP2 Deluxe phono stages.

Digital: Audio Research Reference CD8 CD player, Ayre Acoustics DX-5 "A/V Engine," Esoteric K-01 CD/SACD player.

Preamplifiers: Audio Research Reference Anniversary, Convergent Audio Technology SL1 Legend, Lamm Industries LL1 Signature.

Power amplifiers: Atma-Sphere MA-2 Mk 3.1, Audio Research Reference 250 and Lamm Industries M1.2 Reference monoblocks.

Loudspeakers: Wilson Audio MAXX 3 and Alexandria XLF.

Interconnects: AudioQuest William E. Low Signature, Shunyata Research Zi-Tron Cobra.

Speaker cables: AudioQuest William E. Low Signature, Shunyata Research Zi-Tron Cobra.

Power conditioners: Essential Sound Products The Essence Reference, Shunyata Research Hydra Triton.

Power cords: Essential Sound Products The Essence Reference and MusicCord-Pro ES, Shunyata Research CX-series (various) and Zi-Tron Cobra.

Equipment rack and platforms: Silent Running Audio Craz² 8 equipment rack and Ohio Class XL Plus2 platforms (under Lamm M1.2 amps), Harmonic Resolution Systems M3 isolation bases.