Interview with Robert Koch of Robert Koda Takumi K-10 preamplifier

What drive you to create Takumi K-10?
My customers! After hearing or buying the K-70 power amplifier, there was a strong request for a Robert Koda pre-amp so I really had to put my thinking cap on to come out with something
that would be substantial in terms of musical performance and impress this very demanding audience.

Did you use some of the technology from K-70?
Yes, while far from identical, one technology does inspire the next. One great point about pre-amplifiers in general is that one is freed from being overly concerned about overall efficiency or power output so ones design choices expand quite a bit.

What is exactly ITC gain stage?
It is a gain stage that has an inherent ability to self cancel much of the distortion. It is also very resilient to the imperfections that all power supplies ultimately have.

One half of the amplifier follows the other half but the current transfer works in inverse. That is to say the total transconductance stabilizes so distortion is reduced.

There are other perhaps more important electrical benefits of our ITC circuit but I would prefer to keep a closed hand on that.

It's surprising, that you didn't use any tubes in preamplifier. Why?
Yes many folk were surprised,especially knowing my background. The purpose of the K-10 is to serve the music rather than serving the technology.

It is quite easy to build a good sounding tube pre-amplifier. The audio scene is full of them! But good sound was not enough for me. I wanted something that would be spectacular in performance and so I had to seek out alternative methods to get above current limits.

Why all copper chassis?
Electrically and mechanically for a pre-amplifier, copper is ideal if price is not the primary concern.
Copper is much more effective at screening from the electro-magnetic fields that surround us. The massively improved thermal conductivity is also a plus and copper is much less prone to vibration. Perhaps I will use aluminium for a less expensive model.

You were directly involved with famous Kondo M-1000 preamplifier. What would you say is the difference between K-10 and M-1000?
They are so completely different that it would be very difficult to draw any similarities. Interestingly however, I have noted that there can be more than one path to the audio perfection we crave for. This seems to be more true on power amplifiers though.

What have you changed from going solo with Robert Koda from the in house philosophy of Kondo?
Just about everything. Two remaining similarities though are that we both place audio perfection as our goal and we both place internal building technique / reliability very highly indeed. I'm talking about viewing a product as a creation not a box with a dollar sign next to it.

You certainly had an insight into the mind and approach of Kondo San and Audio Note Japan technology. Was this a good ground for pursuing your own venture?
Sure, there is no substitute for experience. Sharing a common quest made Kondo the place to be!
Don't get me wrong though, some days were very frustrating. Designers like Kondo tend to have their own very tight bundle of ideas about how things should be done. Sometimes change becomes very difficult then.

What do you feel, that you gained there?
Patience, consistency and to be thourogh. I also learned a lot about the impact materials can have on sound.

Solid state vs tubes in ultimate preamplifier?
I have never found a solid state pre-amp that I actually liked! There were plenty of outstanding tube pre-amps though and they easy to design.

When I started the design process of the K-10 I tried several tube and several transistor options. Tube options tend to soon give a good sound but ultimately show some bottle-necking tendencies. It just so happens the ITC circuit concept manages to play down the poor aspects of transistor behavior and build up upon their strong points.

The result is something that no longer sounds like a transistor. It is the basis of that circuit that enabled me to create the K-10 knowing that I had finally surpassed the vacuum tube.

Is this the same point to point and litz wiring as with Takumi K-70?
There is plenty of point to point wiring. If one would to dissect the K-10s innards one would find the audio signal is in effect free of the printed circuit board. Its a very labor intensive thing, doing point to point nicely but there are instances were it is the best approach if sound quality is ones goal.

Why the name K-10?
Well the K-10 uses ten transistors. Also its a bit of a homage to an old Kondo model the M-10. But I wouldn't read to much into the name...

What was the first responses from the owners?
One very memorable response was "An answer to my prayers". Another described it as soul catching. The response has been quite overwhelming.

Are they strictly owners of your power amplifier?
Not at all. You know, the K-70 owing to its physical presence is not perfect for everyone. I saw one owner had a huge pair of Halcro power amps with his K-10. Indeed the K-10 was never voiced to only match with a K-70. It is very much a universal pre-amp.

This is you state of the art preamplifier?
Yes. Over the years I will no doubt learn more though and perhaps some day find a way to build a successor.

Where is the line between high-end and super or ultra high-end audio?
For me its about soul. Much of today's high end is just about high price and a glamorous external finish. Ultra high end is the place where pre-conceptions have no place. It is the cutting edge for those who's interest is one of sound and its road toward rewarding music listening.

What would an music lover and audiophile gain with ownership of K-10?
Now this is a very good question. Much greater insight and enjoyment of their music collection. Tracks the were one skipped over might suddenly make sense and take on a new meaning. Its a very exciting time and one may not find enough hours in a day!

What did you learn and changed with K-10 from experience with K-70?
Well, in order to keep shelf requirements down, I really wanted to come up with something that would only occupy one box, but without compromise to sound quality. Indecently this made the use of vacuum tube less attractive. I have also come to realize that if tubes are used, placing them inside the chassis is the best place. Sad that it because concealed tubes don't really "feel" like tubes.

Do you plan to introduce also a phono stage any soon?
Soon? I'm not so sure. I have been working on a phono stage for some time and many customers have asked me for a phono stage. If and when it can be done properly, I will be happy to release a phono stage. There is however little point in releasing something unless it has real value so I don't want to release a phono stage just to fill a market gap.

Do you use ALPS top of the line volume potentiometer? If so is it special?
No I use what is known as an L-Pad attenuator. Its rather expensive but its as close to invisible as one can get provided the surrounding circuitry matches.

No remote controls?
Firstly, including a remote control requires some logic, micro processor and accompanying clock oscillator plus the extra support power supply. All these things are moving us away from our goal. For input selection then, relays or even worse, a solid state switch becomes necessary. This is what I call "un-necessary complication".

And for what? If you going to change the source, you almost definitely going to need to get up to place the record on the platter or whatever. If you always need to adjust the volume by half a dB or something then perhaps the sound is just not good. That is un-natural behavior.

Can you elaborate on the DC reactor power supply? What is so special about it?
DC reactor AKA pure choke input supplies do some things very well. They also place much less stress on the quality of your AC supply and while not as important for a pre-amplifier, they also extend the life of power supply capacitors etc.

Some claim esoteric frequency response but your specs show "only" 20Hz to 20KHz?
Ahh, but look carefully at the performance specification. Its within a very tight tolerance, plus / minus 0.03dB not the typical 3dB! These kind of measurements are of questionable importance in any event. They are however nice to show off.

We can find ground connection on the back side. Why is that?
There is spurious interplay of a very complex nature when you hook more than one audio component together, especially if they use AC power. Grounding becomes more critical to get the best out of a system and so sometimes a ground terminal is useful. There are even certain brands that make very exotic ground management systems but they cant be used if the component does not have an accessible ground terminal.

Text: Matej Isak
Mono & Stereo, July 2011
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