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Product Review
 

Kora Galaxy Reference Two-Channel Tube Power Amplifier

April, 2003

Jason Victor Serinus

 

Click on the photo above to see a larger version.

Specifications:

Class A Triode Stereo Power Block
Rated Power:  2 x 50w (3 > 12 ohms)
Consumption: 200 watts max.
Mains supply: 230V/50Hz (Europe); 115V (USA)
THD: < 0.3% @ 1 watt
S/N: 100 dB
Inputs: 2 x RCA (1V RMS / 47 k ohms)
Outputs: 2 x RCA Unbalanced) and 2 x AES/EBU
     XLR Balanced
Size:  448 x 452 x 150mm
Weight: 21 kg
Tubes: 8 Sovtek 6AS76 Triodes; 4 Sovtek EL84M, and
     2 Jan Philips (or Sovtek) 6922
MSRP: $4,150 USA

Kora E.C. 8 bis rue Claude Perrault, 31000 Toulouse, France

http://www.kora.net

Introduction

In the course of hunting down promising equipment for review, I spent an afternoon with Joe Cutrufelli, proprietor of JC Audio in Vallejo, California  (http://www.jcaudio.com). After I expressed my dissatisfaction with much of the triode amplification I had heard in show settings, save for the ultra-expensive LAMM gear and less expensive offerings from ART Audio, Joe told me that the Kora Galaxy triode amp was a step above most of what I had auditioned. On his recommendation, I contacted Kora for a review sample of the Galaxy Reference.

I have since spent three extended periods auditioning the Galaxy. My first listening experience took place when my Bruce Moore Companion III preamp was equipped with its original shunt attenuators, resistors, and capacitors, and my Talon Khorus X speakers had not been upgraded to their current state. The amp to which I compared the Kora Galaxy was the Bruce Moore Dual 70, which lists for roughly the same price. Both units were auditioned using RCA-terminated Nordost Valhalla interconnects between preamp and amp.

After my initial listening sessions, I questioned whether the Jan Philips 6922 tubes that came with the Galaxy Reference were making the best case for its presentation. I have tried these tubes in both my preamp and amp on numerous occasions, and have consistently experienced that, despite their fine midrange, they truncate high and low frequencies. After sharing my reservations with Joe Cutrufelli, I drove the amp to his place and switched to Sovtek 6922s. For an explanation of what adjustments were necessary to make this switch, see “Set-Up” below. All subsequent auditioning occurred with the Sovtek 6922s in place.

While we were together, Joe told me that, in his opinion, I would experience a 20% increase in bass response from the amp if I listened in balanced mode. Since the Bruce Moore preamp cannot accept balanced (AES/EBU) interconnects, I set about securing the appropriate equipment to make auditioning in balanced mode possible.

The second listening sessions occurred after the Companion III preamp’s shunt attenuators had been upgraded to series attenuators, affording better sound. I was also able to audition the Kora Galaxy in balanced mode via the loan of an Atma-Sphere MLS-1 preamp and Acoustic Zen Silver Reference balanced interconnects. During this period, I also upgraded my amp to a hand-wired Bruce Moore Dual 100 that lists for $6,000. Finally, I secured Telefunken 12AU7 tubes for use in both the Bruce Moore and Atma-Sphere preamps.

My final listening sessions, after which this review was written, took place many months later, in the spring of 2003. A thorough revision of the Khorus X speaker, including installation of a completely new crossover, different wiring, different braiding configuration for the wiring, changes to the woofer cone and compartment, and modification to the supertweeter, left me confident of my conclusions. This major upgrade completely opened up the sound, making it far more detailed, transparent, three-dimensional, and lifelike.

With each upgrade, I was able to hear further into the sound. Regardless of these major improvements, however, my opinion of the Kora Galaxy remained relatively constant throughout the upgrade process.

Set-Up

The Galaxy arrived chez Serinus after it had been fully checked out and declared in 100% working order. The bias of each tube receptacle had been pre-adjusted for a specific tube, and that included in the shipping carton was a drawing of the tube layout, identifying each socket by a number that matched numbers penned onto the tube boxes, so it is important to note the prescribed position of each tube before inserting them, since they will fit in several sockets.

When my initial audition proved less than satisfying, I brought the amp to Joe’s place so we could switch from Jan Phillips to Sovtek 6922s. This was no simple task. In order to rebias the Galaxy, one must open it up, replace whatever tubes one wishes to replace, turn it on and warm it up until everything stabilizes, carefully measure voltages across certain resistors via a voltmeter, and adjust the bias by turning screws a little bit at a time.

While there is no way to adjust the bias of driver tubes (6922s), replacing them affects the bias of the EL84s. Adjusting the bias of the EL84s in turn slightly affects the overall bias of the quadrant, necessitating rebalancing of the eight 6AS76 triode power tubes. These power tubes are biased in pairs, with the biasing of one pair affecting the biasing of the total quadrant. For utmost accuracy, since rebiasing each tube affects the bias of all others tubes in the quadrant, those who wish to end up with optimal biasing will wish to allow the tubes to restabilize after initial adjustment and then repeat the process, starting with the EL84s. This process, which takes a decent amount of time, is not explained in the literature which accompanies the amp. 

Some audiophiles and engineers may enjoy all this fiddling with the tubes and bias. For me, the simplicity of rebiasing the Bruce Moore amps, accomplished by turning external surface mount screws while consulting a built-in meter mounted in full view on the chassis, makes the Kora biasing process seem positively medieval. It’s certainly not a process that those with shaky hands, poor eyesight, or fears of accidental electrocution would wish to engage in. P.S. - I fear electrocution.

Kora writes the following in its manual [bold and italics theirs]: “The tubes supplied… have been tested, matched and biased in our workshops. They are guaranteed for 900 days after purchase and under proper usage. They do not need re-biasing except in the unlikely case that the tubes need to be changed for some reason. Well, this does happen! If this is the case, please contact your dealer who will be happy to supply and re-bias new tubes for you…” To which I would add a word to the wise: Purchase this amp from a local dealer, rather than by mail order or on the web, if you want to avoid possibly undertaking the biasing process yourself.

The voltage in my apartment changes from morning to night. Although voltage to most of my components is stabilized via the P600 Power Plant, I plug my amp directly into the wall via an Ultimate Outlet. Thus the bias of tubes changes throughout the day (along with the normal changes that occur as the tubes age), as well as between weekdays and weekend. According to Joe Cutrufelli, this small change in bias affects the “flavor” of the presentation, but does not dramatically alter the sonic signature.

Apples and Oranges

In most reviews I have read, reviewers simply list a host of interconnects, power cords, speakers and the like, that they tried with the component under consideration. Other than saying that such and such amp sounded much better with Brand X interconnect than with Brand Y, and reminding readers that “component matching” is essential, they rarely discuss how differences in component configurations affect their ultimate conclusions.

In a perfect world, I would have used the same model preamp and interconnects in balanced and unbalanced modes. This, however, was not possible. Rather, my evaluations in unbalanced mode employed the Bruce Moore Companion III preamp connected to the Kora via RCA-terminated Nordost Valhalla interconnects, while balanced mode evaluation called upon the Atma-Sphere MLS-1 preamp connected via balanced Acoustic Zen Silver Reference interconnects.

The Atma-Sphere is a more expensive unit than the Bruce Moore, but the Valhallas cost far more than the Acoustic Zens. How possible is it to determine how these differences in configuration affected the sound I heard? Without engaging in hours upon hours of testing, all I can say for certain is that the expensive Atma-Sphere preamp is highly rated, quite transparent, and very neutral. The Bruce Moore, while different in price and design, is a fine unit; in its Deluxe Version, long overdue, it will hopefully give the Atma-Sphere a run for its money. As for the interconnects, in a brief A/B comparison of Acoustic Zen Silver Reference and Nordost Valhalla conducted at Joe’s, I felt that while the Acoustic Zens lacked the body and low extension of the Nordosts, they were quite transparent and open on top. Putting this all together, I feel relatively confident that my conclusions about this amp - certainly about its top extension - are valid.

Listening

Liquid, liquid, liquid. A beautiful, unimpeded flow of sound, an ease of production, and a marvelous sense of transparency are the features of this amp that struck me the most. Whether listening in unbalanced or balanced mode, I experienced an unimpeded flow of sound, bordering on the elegant.

Listening to music through the Kora Galaxy Reference is a lovely experience. It doesn’t jolt you, startle you, grab you by whatever; sound naturally flows through the room, like water in a gentle stream.

This does not mean that detail is lacking. A case in point is Matthias Goerne’s brilliant, albeit artistically controversial recording of Schubert’s great song cycle, Die Schöne Müllerin. I have commented elsewhere that Universal has done a lousy job of capturing the elemental combination of Goerne’s voice and Eric Schneider’s modern piano. Goerne sounds almost as if he’s in a tunnel, with an unnaturally huge amount of reverberation around his voice that lends it an artificially metallic, somewhat harsh sheen and obscures detail. The disc offers anything but the acoustic and beauty of tone I encountered when I heard Matthias Goerne perform live on three different occasions.

The Kora/Atma-Sphere combination certainly doesn’t hide this sonic defect; rather, the recording’s deficiencies struck me as even more disturbing than when I listened to the disc using the Companion III preamp equipped with shunt attenuators and less than top-of-the-line resistors and capacitors.

What the Kora Galaxy Reference offers in spades is midrange. The center of Goerne’s voice or the piano’s strings; the beautiful warm sonority of strings, winds and percussion on the superb Reference Recordings disc of Rachmaninoff’s Symphonic Dances; the beautiful liquidity of soprano Arleen Auger’s voice on her great Delos Love Songs recital, all come through beautifully.

On the other hand, what I missed the most was sheer weight and sense of instruments - a visceral sense of bulk to the sound - and extension at frequency extremes. The lack of weight, of course, is in part a result of an amp rated at only 50W, which provides less heft, slam, and forte swell than one rated at 100W. But the issue of frequency extremes is another matter entirely.

A case in point. One of my favorite “pop” cuts for evaluation purposes is “Blues No More” from Terry Evans’ JVC-XRCD, Puttin’ It Down. I am accustomed to hearing huge contrasts in timbre between snare drums, electric guitar, trombone, cymbals, and Evans’ voice. The cymbals are soft in the beginning, but when the drums are thwacked hard, I expect to sit up and taking notice. And when Ry Cooder begins to twang his guitar, there’s a characteristic spice to the sound that I continually look forward to.

Such was not my experience with the Kora Galaxy Reference. Its presentation was quite mellow. The highs did not shine; neither did the bass pound. There was a uniformity to the sound, ideal for listening without intruding on the space of one’s partner or neighbors, but certainly farther from the real thing than I’m used to hearing. My Bruce Moore amp may fatten the sound a bit, but the Kora Galaxy errs in the opposite direction.

I had a similar listening experience playing mezzo Susan Graham’s recent Erato release of French operetta arias, or the Grammy and Golden Ear award winning Sony recording of Brahms and Stravinsky Violin Concertos by Hilary Hahn. The lack of bass slam or deep extension was a minor issue; far more crucial was the lack of a leading edge to the tone, and an overall greyness to the sound. Even as I write this, with the Bruce Moore equipment reinstalled, I return to Graham’s recording and play the first cut, Moïses Simons’ “C’est ça la vie, c’est ça l’amour” from Toi c’est moi and hear a range of instrumental color, a luscious roundness, and a life to the voice that are lacking through the Galaxy Reference. The midrange at which the Galaxy Reference excels is certainly there, albeit presented with less liquidity and transparency. But this is a tradeoff that I am glad to accept.

My experience would have been quite different if I had bright speakers, bright interconnects or speaker cables or power cables, or digital equipment that lent a harsh, digital edge to the sound. Some horn speakers and Lowthers frequently employed with triode equipment might thus prove a superior match with the Galaxy Reference, providing they can handle 50W of power. But for this music lover, who has gone to great lengths to assemble a system that makes it a pleasure to engage in extended, concentrated listening without fatigue, the Galaxy Reference did not prove an ideal amplifier.

Conclusions

At a recent Master Class I attended, the great soprano Elly Ameling, now retired, attempted to explain the nuances of interpreting French art song by referring to the difference between French sadness and German sadness. I cannot pretend to accurately paraphrase her comments, but she implied something to the effect that the sadness one encounters in Debussy and Fauré is far more contained, far less of an open outpouring of pain and angst, than what one encounters in Schubert and Schumann.

Such an analogy might equally apply to the Kora Galaxy Reference. The Kora is by all means a refined product, capable of producing an extremely elegant, flowing line. It doesn’t confront you with its feelings, or knock you over with sentiment. Cultured, poised, perhaps a bit guarded of its secrets, it’s the antithesis of a walk down the streets of New York  or an evening with The Boss. With the right equipment, the right music, or in the right listening situation, the Kora should prove a fine match.



- Jason Victor Serinus -

Related to the article above, we recommend the following:

High Fidelity

Nature of Equipment Reviews
Accuracy, Distortion, and the Audiophile

What we Hear

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