May 2001

Kore-eda Model 2658B Monoblock Amplifiers

Review by Steven R. Rochlin
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  As many of you know from reading my previous reviews that i got hot and bothered by new products (see Archives section for previous reviews). Tube, solid-state, atom regenerators... If it is said to reproduce music and seems interesting, hopefully it will appear within my humble abode for review. Here we have a very interesting piece of Japanese exotica (my fave type... and Italian goodies too). The Kore-eda Model 2658B is a powerful 16 watt monoblock employing two Western Electric 300B output tubes in a classic Williamson-type design.

Beautifully constructed and weighing in at a hefty 40 lbs or so, they seemed to exude that classic showing off of the tubes with no-frills, work for a lifetime and easy to maintain aura. Even the Gold Hammer color seems to hark back to days gone by before polished chrome or gloss black made their way into high-end products. Priced at $16,000 a pair in Gold Hammer ($17,500 a pair if you prefer stainless steel finish), what is it with these exotic amplifiers that makes me so eager to review them? After all, they have no real following, no "legendary" status and no underground movement and club.

It is within the initial discovery that one finds true opportunity.

Call it being bored to death from reviewing yet another (add popular manufacture name here) product. After many years of reviewing it is the predictability of things that can make us all grow tired of something. Ok, i admit to being guilty of reading a popular audiophile magazine and yawning when seeing review of (insert popular manufacture name here) and it reads just like the now outdated product from last year. As G-d as my witness, never shall these ears be subjected to the never-ending reviews of monotonous "new and improved" versions of the same thing three times in a row. Sure a proper follow up of a next generation may be in order, but not three times. They say bad things happens in threes... and four is unpleasant luck number in Asia.

Here we have a Japanese artesian carefully discovering when he feels is a top-range product after many years of research and development. Mr. Shigeharu Kore-eda has been in love with the 300B operating in single-ended triode mode and has crafted them for well over years!  Encounters with the Western Electric WE86 and WE42 then opened up enormous possibilities of a new 300B push-pull circuitry for him. As i said above, the basic circuit topology is based on the typical Williamson 
circuitry, though there are many refinements of the circuit structure within the Kore-eda Model 2658B monoblock amplifier. This includes the using of very high quality parts. To quote Shigeharu Kore-eda, "You have to throw in the highest quality parts possible without hesitation. The word 'economical' is the ultimate taboo on designing 300B push-pull."

Outer beauty fades over time...
Inner beauty flourishes everyday.

The Kore-eda Model 2658B is of the choke input variety. The choke is made by the highly respected Tamura Corporation. Fairly normal for audio exotica, sure, though then comes a power transformer custom made by Noguchi. Add to its uniqueness is an output transformer (fixed inductance type) is custom made by Hirata Electronics. Of course it takes more than just a choke and some transformers to make fully complete audio exotica.

The 300B cathode bias resister is a Dale NHG50 while the resisters in the signal lines (i say "line" as all parts are technically in the signal's "path") are RN type by Tokyo Kouon Denpa and IRC. According to Shigeharu Kore-eda, the Model 2658B is designed to eliminate the hum balance of the 300B tube's filament and pulls out the cathode current directly from the center tap of the transformer winding. By connecting the winding center parallel with 10 mF condenser, all the signals except the extreme low end receive an in-phase feedback. The cathode bias resistor works parallel on all frequencies with exception to the very low end (which has no bypassing condenser). Being connected at the center by 10 mF condenser, the two 1k ohm bias resistor works as one 500 ohm resistor.

Hirata Electronics made output transformer is a fixed inductance type with a 45% Permaloy-core that can handle large amounts of unbalanced DC. Negative feedback is approximately 7dB. Phase-inversion circuitry is P-K sprit type while the power transformer and choke are completely sealed. The Block-type electrolytic capacitor is a custom made 500V type by Mallory while all others are Atom by Sprague. To quote an e-mail received by the Kore-eda representative "Every part in 2658B has been chosen after extensive experiments without any cost considerations." Tube compliment per monoblock includes two Western Electric 300B, two RCA 5692 (6SN7) for input, P-K sprit and driver stage while a single 5U4GB is employed for rectification duties.

If the doors of perception were cleansed,
everything would appear to a man as it is,
infinite.
-- William Blake

One installed, the Kore-eda amplifier were singing before only a few hours. Fortunately the units received for review had made the rounds at the recent CES and had quite a few hours on them. First impressions include clean, tight bass and speed of initial attack. As many will claim, going from pure single tube, zero feedback design to one using multiple output tubes and some negative feedback will yield such results. Keeping expectations low so as to not allow for any preconceived notions to creep in, i sat down for a long listening session after a week's time of the usual tweaking and fine tuning.

There is no doubt that 16 watts per channel with my various loudspeakers is more than adequate. KEF 104/2 (tweaked), silver wired Audio Note Level 2, Royal Reference 3A MM De Capo and of course my beloved Avantgarde Acoustic Duos... Settling on the Audio Note Level 2 (design based on early Snell loudspeakers), this seemed to be the best match for overall natural harmonics, loudspeaker sensitivity to achieve good volume levels, and also frequency extention. Using the Avantgardes would be cheating of sorts as the lowermost frequencies are aided by a built-in solid-state amplifier. Preamplifier included the excellent conrad-johnson Premier 17LS while vinyl duties went to my trusted VOYD with silver-wired Audio Note tonearm and Clearaudio Insider Reference (wood body) cartridge and the 47 Labs 4712 MC phono stage. Cables include Nirvana and Kimber Select. (Humor) As an environmentally conscious dude, no CDs were used nor harmed during this review.

In much wisdom is much grief;
and he that increaseth Knowledge
increaseth grief.
-- Ecclesiastes

Cutting to the chase here at this 11^th hour writing of the review (it has been a very busy month), the Kore-eda Model 2658B has incredibly solid bass with extremely good imagine capabilities. The amplifiers themselves were virtually dead quiet. This is a good thing when you use super high sensitivity loudspeakers. Thiels and the like with their lowish sensitivity allows lower quality amplification to hide in my humble opinion whereas 95 dB/w/m and above loudspeaker will lay it all out in front of you. This is why those of us who love horns and more efficient loudspeakers also tend to choose only the best gear. (As i begin to sing) "Nowhere to run to baby, nowhere to hide". Note: Avoiding discussing those truly nasty designed loudspeakers whose impedance goes down to an inexcusably low three ohms... or lower.

While the midrange of the Model 2658B may not be as delicious as that offered by my fave Wavelength Audio Cardinal, it is not far behind. The advantages is higher wattage while using some negative feedback tends to provide a more condensed, solid image... yet at the expense of some bloom (that some may consider a euphonic fattening of the image). Alas, there is no free lunch here as the very solid images seem to also keep the front soundstage width between the loudspeakers and never going much past. Ok, so having images going far beyond the right of the right loudspeaker, and left of the left, is something that probably 95% of audiophiles may never experience so this may be moot in any event.

As for the upper frequencies, they appeared to be delicate and glorious as one would most certainly expect from a 300B amplifier. Especially one that employs the Western Electric 300B output tube. In fact to my ears in my system, the music's harmonics seemed to be quite good and could be said to more accurately portray the music versus adding rose-colored glasses. We must call a spade a spade here folks. Some single-ended zero feedback amplifier do indeed add a rosy portrayal of the music. While not inherently lending itself to accuracy, it can make for highly enjoyable listening. The Kore-eda monoblocks do not sugar coat the music, instead they offer an extremely fine microscope into the glories of authentic music reproduction which is very compelling.

All things considered these amplifiers still walks on the wild side of glorious tubes yet with a good dose of non-euphonic musical accuracy. Those of you with less than 92 dB/w/m loudspeakers who are looking for the grandeur of tubes will not be disappointed as this amplifier brings with it the legacy of the Western Electric 300B (two per channel no less!). In fact with my Audio Note Level 2 loudspeaker setup (and briefly with the Avantgarde Duos) seemed to provide no end to achieving thunderous volume levels. The Kore-eda Model 2658B would most certainly be on my short list when looking for more than eight watts and less colored amplification needs.

One sees great things from the valley
Only small things from the peak
--G.K. Chesterton

As i started this review by admiring the ability to review lesser known items in this world of audio exotica. The Kore-eda Model 2658B begs to question how such a well balanced, sturdily built unit will find its way into other's home for audition. My hopes are in being a music lover with the ability to share in those rare opportunities this industry allows us to have. It is no secret that you can easily walk down to your local specialty audio store and buy a (add popular manufacture name here). What about all those small manufactures and gifted artisans? Are we to ignore their efforts in the vain of commercialism and ease of availability? i think not!

The Model 2658B monoblock amplifier begs to question just how far a music lover will go to enjoy the music. Of course the internet has opened up vast opportunities for in-home audition of gear since it can easily be shipped directly to one's doorstep. Since this unit is sold directly through the American distributor, music lovers also benefit from there being no grey market and a single source for repairs and service. Add to that additional savings through less retail markup (read: lower pricing) and even audio exotica is a bit less painful on the wallet.

Specifications

Output Power: 16 watts

Input Sensitivity: 0.5 Volts

Residual Noise: Below 2 mV (at 8 ohm)

Tube Compliment: Two Western Electric 300B
                          Two RCA 5692 (6SN7)
                          One 5U4GB

Loudspeaker Taps: 8 ohm and 16 ohm (standard)
                           4 ohm and 6 ohm (optional)

Colors: Available in Gold Hammer and
           polished stainless steel finish

Retail Price: $16,000 a pair in Gold Hammer
                  $17,500 a pair in stainless steel finish

Company Information

Sakura Systems
2 Rocky Mt. Road
Jefferson, MA 01522

Voice/Fax : (508) 829-3426
E-mail sakurastms@aol.com
Website www.sakurasystems.com