Solid State Power Amp Reviews

Things didn't start off auspiciously. I'd been after Symphonic Line's Klaus Bunge for more than a year to send me the Kraft 400 Reference monoblocks. Finally he called. He said he was going to be in town for a few days, and he had with him a pair of what he described as his "traveling" Kraft 400s, which he proposed to leave with me (footnote 1).

Klaus showed up with the enormous amps encased in high-mileage cardboard domestic travel boxes so crisscrossed with packing tape they looked mummified. I eagerly poked around Klaus's Trooper for the cart I just knew he had to have with him. He didn't. When I queried the large, broad-shouldered one regarding this oversight, he admitted he hadn't brought one.

Two hunnerd'n'sixty pounds each! We managed to hump the amps into the elevator and up to our loft, but only just. It took me three days to straighten up fully again (please walk this way), and my arms seem to be a few inches longer. I'm positively simian now.

Death & the maiden
My advice to visiting manufacturers bearing heavy audio objects: bring a cart, or next time I keel! Kathleen and I listened to the German Giants for a few days, switched amps for a bit, then returned to the enormous, bad-Euroboy, sexy, cobalt-blue 400s. One channel was silent. I called Klaus, probed some under the hood with a voltmeter, and together we confirmed one of the amps was down for the count. Supine on the mat, so to speak. Kaput!

Of course. Give a reviewer your best piece, and it'll be sure to colorfully self-immolate. But "best piece"? I'm not so sure. This pair was a little scruffy and also sported what Klaus described as his "traveling top covers." The plates didn't fit very well and were a chore to screw down. In fact, a few of the retaining screws wouldn't seat at all, so the top plate resonated when thwapped. Not good.

I can appreciate that, at this price level, an importer can't spray amps around reviewers willy-nilly; but I knew I'd have to find some solution, which presented itself in the form of two Bright Star Little Rock 2s (in dark granite). Their hefty weight neatly damped and welded the top plates to the chassis, and their inherent EMF-rejecting capabilities may have sweetened the amps' overall presentation a touch. (They were placed a little forward on the top plates so as to rest over the transformer.) They definitely helped the sound.

I was also slightly Wienerschnitzled to learn I'd have to wait two weeks for a Symphonic Line–approved techie to visit us from Chicago to resurrect the duff amp. Klaus told me that, while he was at it, the output boards on both amps would be upgraded to the latest production spec, which included a new set of bipolar output devices ringed about the board, and which are an integral part of the assembly. And that meant, of course, that a further break-in period would be required! Kathleen and I asked ourselves just what Klaus had meant when he'd said "200 hours." Nawww...I thought of giving him 200 hours—to leave the country!

Resurrection
I contentedly returned to the Forsell Statement amplifier that I reviewed last June and my own Jadis JA 200s to drive the Avalon Ascents while we waited. Computer-whiz Karl Szczypta finally showed up at our door one Saturday, tool-kit and soldering station in hand. Karl, sitting cross-legged on our carpet, broke down the Kraft Kondominiums one at a time. Watching him remove the aluminum side panel cum heatsink and expose the amp to inspection from the side, I felt as if I was looking at a skyscraper under construction—all stainless-steel girders and giant nuts'n'bolts.

I've heard many showgoers exclaim, while gazing into this cavernous amp, that they just don't find that much in there! The main circuit board, a tiny thing (for short signal paths) measuring but 5.6" by 6", hangs like a limpet mine on the center of the smooth inside of the heatsink, with the output power devices arranged around it like spider legs. At the bottom of the amp (the ground floor?) and running the full length of the interior is the immense, suspended-for-isolation power-supply assembly. But "power supply" hardly does justice to this tall, Metropolis-like construction. Understand, the Kraft 400s are all power supply. The amps are immense but, at the same time, very simple. When you open up Forsell's The Statement amplifier, you're confronted by a maze of tightly packed boards and electronics. The Kraft 400s, on the other hand, are the antithesis—minimalism personified.

At the front is the horizontal 1200VA toroid transformer, and a great, heavy lump of a thing it is. Behind the black hole that is the transformer lurk four high-speed rectifiers, and eight 50,000µF electrolytic capacitors with a total capacitance of 400,000µF. The caps are linked along their top surfaces by three flat, aluminum "bridges" which give the power supply an extremely low impedance and further the 400's dynamic capabilities, according to designer Rolf Gemein. In addition to the two internal fuses and the single outside fuse is a special circuit which protects the loudspeakers. And you'd best pay attention to the bright yellow High Voltage sticker.

In addition to a bit of support circuitry are two user-replaceable, sand-filled fuses and a pair of large, bright LEDs at the back end of the bridge, these given the task of signaling the successful sluice of power to charge Cap City below. While Karl was working away, I glanced at the brief technical description Klaus had supplied me:

"Differential amplifier in the input section with constant current source and current monitoring. Class-A pre-driver stage with constant current source. Output stage biased with two class-A Emitters in a row, followed by NPN-PNP outputs with six pairs of Ring-Emitter bipolar Sanken power transistors of 20 amps, 50MHz each. All transistors highly selected and matched which are very stable and operate with a high level of linearity on virtually all demands. Extremely low local negative feedback of all stages. Separate power supplies for input and output stages. Rectifier assembled with ultrafast diodes. Pre-driver stage protected by a special circuit that limits current flow against short circuits." Hmmmm. (For a closer look at the mind behind the Kraft 400s, take a look at "The Heart of the Matter," wherein I interview designer Rolf Gemein.)

Back at the ranch, Karl exchanged the main board/output transistor assemblies for both amps—it took him the better part of a weekend—and found that an input transistor had failed on one of the boards. Ach du lieber! Amps resurrected, we began the break-in process. And, yes, it took all of 200 hours to lose the edge and grain, smooth out, and open up. Audio can be hell. (Don't laugh.)

A la recherche du temps perdu
I began serious listening with my CAT SL-1 Signature preamp. Analog front-end was the Forsell Air Force One with either the Clearaudio Insider, Symphonic Line RG-8, or vdH Grasshopper IV GLA. Digital was rendered with Forsell's D/A coupled with their Mk.II CD transport.

Unhappily, the Jadis JP-80MC (suffering from RF heebie-jeebies) and the J1/JS1 Drive/Processor combo had all been repossessed by then-importer Victor Goldstein for use at Hi-Fi '95. (I tried not answering the phone or the door, but he got in anyway!) As it transpired, Frank Garbie's Northstar Leading The Way, Inc. was named importer for Jadis products shortly after the Show.

During this transition, I requested loaners from the factory in France, and toward the end of the review period, boxes of French audio goodies began to arrive. Oh, man, it was like...Hanukkah in July! I bring you the lurid details so you'll understand that my reviewing system was very stable for the first half of the serious listening, as Kathleen and I came to know the voice of the Kraft 400s.

Consider, then, the description of the sound to be a mélange of impressions garnered from listening with both my recently (factory) retubed CAT SL-1 Signature and an early-arriving Jadis JP-80MC. Some updates to the CAT vs JP-80MC debate: Over time, the sound of both preamps has moved toward a unparalleled convergence of presentation. The CAT, in its more recent incarnations, sounds a touch more like the JP-80MC. The Jadis preamp sounds...a bit more like the CAT! I believe their mutual excellence has driven each into the other's arms.

While maintaining its neutrality, the newer CAT Signature displays a richer, fuller-sounding tonal palette that better complements and fleshes out its legendary imaging. It continues to out-preamp the JP-80MC in the bass, and (to this point in the break-in) it wins the edge-definition sweepstakes.

The JP-80MC, with its tauter bass, beautiful highs, and to-die-for midrange—coupled with its luscious, bloomy, 3-D palpability factor (the air is simply incredible)—may be said to justify its lofty price, tellement cher though it may be. (The phono stage is phase-inverting, so I'll have to see if the focus sharpens up when the phono leads are reversed. Forget about flipping the tri-wired Avalons!)

Interestingly, this JP-80MC—the first unit I've heard direct from the factory—is certainly more neutral than I've ever heard from a Jadis preamp to date. I understand from importer Garbie that unadulterated, "factory-fresh" Jadises will continue to be available, and I applaud him for his efforts in this direction. It occurs to me that I finally may be hearing a JP-80MC as its designer meant it to be voiced.

Cherchez le cable!
I started listening to the Kraft 400s with the AudioQuest Diamond interconnects and Dragon speaker cables I found so suitable with Forsell's The Statement. I also cycled through a few of the several families of cables and interconnects I keep handy. Joe DiPhillips of Discovery Cable visited one day, his Signature interconnect and speaker cable held in one hand, a Clearaudio Insider cupped in the other. (More on the Insider and how it relates to the Symphonic Line RG-8 and the vdH Grasshopper IV in due course.)

We hooked the bright red Signature throughout the system and were well pleased with the result. I've found that most cable break-ins run as follows: to begin, a brief glimpse of the cable's sound (if a bit grainy); then a destabilized, out-of-focus, and phasey period; then they slowly regain focus and "cohere" into their final sound. Regrettably, some take longer than others. Much longer.

So it was with the Synergistic Research cables and interconnects that Boy Racer and "I'll-give-your-system-the-cable-it-needs" Ted Denny installed shortly after the Signature's arrival. (Denny makes cables at several price points optimized for different types of gear.)

Ted set us up with two pairs of Resolution Reference speaker cable for the midrange and highs, and a run of Signature No.2 to run to the woofers of the Avalon Ascents. Ted's cables bring new meaning to the word "stiff"—even to a totally inured guy like me, who's accustomed to the SPROING of tri-wired XLO Signature.

The 5m runs to the amps were handcrafted Phase Two Mk.V shielded to 1GHz for RF-rich New Yawk, with another 5m pair of Resolution Reference interconnect on hand for tube amps. The digital cable Ted left us with in both RCA/RCA and BNC/BNC (for the Forsell) was the Digital Corridor No.2. Not a bad coax datalink for $150, but I soon reverted to my favored Kimber AGDL or the airy Marigo Apparition Reference.

The digital line-level was more Phase Two Mk.V, and Ted went for a 1.5m run of the top-of-the-line Resolution Reference for the phono. This unshielded cable caused a minor low-level hum with the CAT, but an Original Cable Jacket quieted things to a tolerable level, while the JP-80MC's higher gain smote the hum into the noise floor. When I cranked the spls with the CAT, I substituted a length of Diamond or my favored XLO Signature Phono Cable.

After these loooong–to–break-in cables loosened up, Kathleen and I decided they sounded so good with the Forsell/CAT/400 combo that they would remain as the reference cables for this review. (They also got on famously with the JP-80MC and other Jadis front-end naughty bits. More on the pregnant-with-possibilities Discovery Signature as I rotate them into several systems coming up for review. And more, too, about the four-chassis Jadis JP 200 dual-mono preamp (!) that eventually showed up at our door.)

I prefer to use the same family of cables and interconnects when reviewing rather than hodgepodge around. So we powered up with Ted's stiff but bendable (you vill obey!) Synergistic AC Master Couplers. They are, simply put, excellent. They were everywhere in the system save for the Kraft 400s, whose nonstandard locking 90° connectors required a custom length to reach our dual-quad 30A hospital-grade sockets. (Kathleen crawled between ceiling and roof pulling the heavy BX cable when we installed the sockets, along with dual-quad 20 amp service for the front-end. What can I say? J'adore ma femme!) Other connectors are being evaluated, but these unusual locking connectors are childproof, pointed out new-Dad Klaus.

Michael Griffin of Essential Sound Products (Tel: (810) 375-5093) made up a custom pair of The Essence power cords for the 400s, and also sent along a number of IEC power cords for the rest of the system. These made a significant improvement to the sound of the amps, and as I moved them into the rest of the system, I noted how well they performed. (The connectors are filled with a material that is said to stabilize their impedance characteristics!) More on these guys later.

Round up the usual suspects!
The rest of the room treatments and accessories were much as you may have read about in my "A Matter of Taste," in the June issue (Vol.18 No.6), with these additions: I've had excellent results with a Shakti Stone placed on the Forsell CD Transport's lid. (Yes, that is during play!) And I've discovered what I consider the hot setup for mounting a CAT (can the jokes, please!)—Shun Mook Ultra Diamond Resonators, the biggest ones, placed under the unit: two in front, at 5 and 7 o'clock; rear center, 6pm (do you know where your CAT is?); and a fourth Resonator on top, also at 6—pointy side up, of course. This ebony-ringed CAT is snugged into a Michael Green Signature ClampRack. Eventually I'm going to try to gently squeeze the JP-80MC, which now sits on a trio of Shun Mook Super Diamond Resonators, the power supply on Michael Green Audiopoints.

Class-A though they may be, I left the 400s turned on for most of their stay, shutting them down and removing their power cords only when one of last summer's many lightning storms lit up the skies. One night I awoke only after the storm was upon us (the lightning is particularly vivid through the skylight), and found both amps had cycled off! Con-Ed must have taken a real hit! Next morning they reset with no problem.

Which brings me neatly to their turn-on sensitivity, which is either a two-stage or a two-person affair. Depress the large square switch (what else?) and either wait about 15 seconds for the answering click of the internal relay, or step around (walk this way) to the front of the behemoth and have a look at the LED. If it doesn't work the first time (it didn't), give it another shot. Or if your Significant Other hasn't murdered you yet for dragging Sphinx-sized Wunderampen into the house, you can ask, "Is the LED lit brightly, cherie?" And hope he or she won't tell you where to put your light-emitting diode! I consider myself extremely lucky in these matters. Kathleen is the consummate audiobabe.

Setting the stage
So, what is the sound of one multi-kilobuck amp clapping? Once again, as with the yet more expensive Forsell Statement, we have to ask if the Kraft 400s do anything to justify that kind of a price tag. I mean, what could be so entirely special about a pair of amplifiers?

Everything. These are magnificent beasts.

As Peter Forsell has pointed out, what we hear from the speaker is, in essence, the electricity itself. In this sense, the Kraft 400s stand alone as the ultimate expression of purity in design when it comes to the power supply and short, simple signal paths. This paradoxical fusion of gargantuan and minimalist concepts would prove a futile gesture indeed if it didn't actually serve the music in some mighty special way. But it does—magically.

The foundation of their sound was the richly complex and textured, powerful, transparent, and huge soundstage the 400s hung about the speakers and the listening room. The ambient soundfield had an integrity that I had never before experienced. They developed a spread and layering of soundstage of perfect control—all musical elements absolutely stable. The classic descriptions of wide, deep, layered, and so on lose their meaning in this context. Put a CAT/Forsell combo or a JP-80MC and a JS1/J1 in front of the 400s, and the original acoustic is simply there before you. Cue up an Insider or the Symphonic Line RG-8 phono cartridge on The Forsell, and you are transported. There are no room boundaries to overcome, no sense of displacement of your listening room's acoustic. You're simply there.

And there was a lot of "there" there. The detail and transparency coupled with remarkably fast transients to form a terrific sense of body. Focus was superb, yet enough of the natural bloom of music remained to prevent the sharp-edged definition from seeming unnatural. Know that the Kraft 400s set up the deepest soundstage we've ever heard produced here—and did so without recessing the top end and distancing us from the pointy end of the music.

As you should expect at this price, when you light the afterburners and crank the preamp (one of Kathleen's favorite pastimes), not a trace of distortion, grain, or compression exists anywhere in the frequency spectrum—the sonics remain as pure and coherent as at moderate or even low volume levels. The more you turn them up, the more magnificent they sound.

And the 400s articulated this nuanced soundstage with apparent ease. But we all understand that effortlessness is never what it seems. It requires, in fact, the highest degree of effort to achieve—another paradox of life that somehow transfers so readily to the high-end experience.

The power & the glory
So, let's spin a disc, shall we? To begin, I chose Poulenc's Concerto for Organ, Strings, and Timpani in g (side A) and his Concert Champêtre for Harpsichord and Orchestra (side B). This lovely LP (Erato STU 70637) was recorded by the ORTF (French National Radio Orchestra) under Jean Martinon. The Organ Concerto features Marie-Claire Alain on the Gonzalez organ of Studio 104 at ORTF; as recorded, the organ sounded deep, resonant, and less "wet" and ambient than a typical church-housed instrument would be. One hears an enormously deep, incredibly wide, totally ambient soundstage augmented by stunningly powerful bass registers, a richly textured harmonic palette, and lovely highs.

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Footnote 1: As reviewed, the amplifiers were called Kraft 250s. As we went to press, however, importer Klaus Bunge asked that we refer to them as Kraft 400s.—John Atkinson