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The Graaf GM 200 Amplifier and 13.5b Preamplifier

Find out why there are good reasons that Ferraris can only be made in Italy.


Francis Vale

More often than we care to honestly admit, you'll be sitting there at a live concert, when you start thinking about what you are going to have for dinner tomorrow night, why the check hasn't come in the mail, what did she really mean by that, damn I wish that guy two rows ahead would stop squirming around, and what time is it anyway. And so, one more pleasant, but otherwise unmemorable evening goes by. But every now and then, it happens at a concert that you suddenly go, hey! What was that? All the miscellaneous mental musings come to a screeching halt, and your brain abruptly lasers in on what's being performed. At a live performance, two things can usually do this. One is when a piece is being played with real human emotion, and not just by highly skillful rote. Indeed, the playing may not even be all that great. But the performers are so deep into it, so intensely searching for a much larger musical meaning, that the audience collectively catches its breath. Everyone anxiously hopes these courageous artists can pull it off, and that maybe, just maybe, they all get to travel to a special, not often visited place in the human soul. The other thought-stopper occurs when you go, hmm, just what is being so compellingly said up there? Now solidly hooked, you have to find out where this work's deeper, inner truth lies. So you and the performers join up in tight musical formation, and go flying off together. And if everyone gets lucky that day, conventional reality suddenly gives way to a transcendent, truthful rush, as this musical flight comes to its extraordinary end.

Such musical epiphanies are, unfortunately, much rarer still in your home playback system. But the fervent hope that highly charged experiences like these can be mechanically reproduced at will, is, perhaps, what drives the high end--And likely drives otherwise rational people to do extravagantly mad things. To wit, the stunningly excessive Graaf GM 200. This is a 200 watt per channel tube amplifier that doesn't use transformers, a rarefied design otherwise known as an OTL (output transformer-less.) This sixty-six pound stereo amplifier, like a Ferrari V-12 engine, is a drop dead gorgeous machine.



And like exotic supercars, it speaks of lunatic engineering demands, and blatant disregard for conventional norms. That Graaf amplifiers, like Ferraris, could only be made in Modena, Italy, thus seems patently obvious. Italians just have this special flair for making high speed charges against civilized sensibilities. Moreover, another Modena-based company which does custom fabrication for Bugatti also makes the GM200's glossy black lacquer metal chassis, and its gleaming nickel-plated tube cages. No wonder then, that this amplifier's striking appearance, meticulous fit, and fabulous finish easily evoke exoticar images. Conrad Johnson's and Audio Research's tube amplifiers look like big, lumbering farm tractors in comparison.

Since the GM200 is an OTL, of which there aren't many being made, let's dwell for a moment on the nitty gritty of tube amplifier transformers. These very costly, bulky, heavy devices are used because the output impedance of the tube's plate circuit, which can be as high as many thousands of ohms, must be matched up with a loudspeaker's 16, 8, or 4 ohm impedance (and everything above, below, and in between.) But transformers are no ohm-corrective cure-all, as the thorny issues of transformer core losses, self-capacitance, and leakage inductance, to name just a few, always raise their ugly heads. And all manner of clever engineering tricks have been employed to come up with transformers that can simultaneously supply both shimmering highs, and thunderous lows. But unfortunately, achieving either end of this frequency equation produces contradictory design goals. In addition, the more watts produced by a tube amp, the more difficult it is to make ever larger transformers which also don't clobber the high frequencies. Consequently, all kinds of transformer design compromises end up being made. It's no surprise, then, that some tube amplifier designers have asked themselves, why not just ditch those troublesome transformers altogether? Hence, the OTL amplifier, which, obviously, is not for the faint of heart designer, and is thus still rather rare. Regardless, the OTL has a long and distinguished history. For example, tube amplifiers based on the patented OTL circuits of Julius Futterman were produced from the 1950's though the 1980's by several companies. Currently, Fourier markets an improved device based on Futterman's expired OTL patents. A small number of other vendors, like Graaf, also produce tube amps using their own unique OTL designs.

The motto of Graaf (which stands for Gruppo Richerche Audio Alta Fidelta) is "Il Suono Fatto A Mano." Loosely translated, that's "precision-crated sound." To that aspiring end, Graaf's chief designer, Giovanni Mariani, has produced, quite unbelievably, a tube amplifier which will successfully work with even current crippling, 2 ohm loads. For example, the GM200 can drive the legendary Apogee Diva, a full range ribbon speaker infamous for taxing even the most powerful transistor amplifiers. This 200 watt gallery of glowing glass is thus offering you a real world tube alternative to the transistorized behemoths. That the GM200 is also an OTL design is just icing on the high current cake.

The stereo GM 200 is a dual mono design. To deliver the power-hungry goods, thirty-two, high current PL504 tubes, sixteen per bank, sit beneath those Modena-manufactured tube covers. And under each PL504 also sits a one ohm resistor which will blow (producing its own individual red warning light) should you do something stupid, like quickly switching the amp on and off before the protective relays audibly cluck-cluck their ready-to-go approval. The input stage is a 12BZ7, operating as a balanced Class A buffer separator. Eight more naked tubes brazenly sit at the unit's front. The 12BZ7 is followed by two 12AV7/5965 tubes, one per bank, which serve as the differential stage, and also act as a phase splitter. The voltage gain is provided by two pairs of EFL200 double pentodes. Finally, each stereo channel gets its own EM81 "power meter," whose vertical, green-colored, display rises up and down in filigreed synchronization with the amount of watts being delivered. In between the two imposing arrays of PL504s sit four large capacitors, and a massive toroidal power transformer. The latter is shared by both channels, and the power supply is made up of five separate stages, with two floating in respect to ground. At the unit's rear are both balanced (XLR), and RCA single ended inputs. Two pairs of solidly-crafted, gold plated multi-way binding posts from Esoteric Audio allow easy speaker bi-wiring via twin runs of cables. Finally, unlike other floorspace-robbing, high powered tube amps, the GM200 is densely compact, measuring just 17.5" (w) x 8.2" (h) x 16.3" (d), and easily fits on a standard shelf rack.

When you plug the GM200's detachable power cord into the wall socket, you better shut down any other wattage-hungry devices you may be sharing on the same circuit. In the high rise building that Francis and Gordana live in (the Prudential Center Apartments, just off Boston's Copley Square), there is no easy way to install a separate amplifier-only circuit, so the lights in their apartment would noticeably dim for a second or two when the GM200 was switched on. And on several occasions, a circuit breaker blew when a halogen light was blazing in all its 600 watt glory in another room. One look at the GM200 specs, and you can see why this was happening: This black beauty sucks up 800 watts at idle, and 1,600 watts at full music tilt. Maybe if they had two units working in vertically biamped mode, Francis and Gordana could have dimmed the lights in the big Prudential Tower, but Boston Edison would probably have sent a (S)watt team out hunting for them.

The GM200 was also getting roughed up by some tough guy city electrons. In pained response, it began making an extremely high pitched, barely audible squeal. So Francis got on the blower, and called David Salz at Wireworld in Fort Lauderdale, FL (954-962-2650). Two days later, some big, heavy set "Auror" power cords arrived, and were quickly plugged into the Graaf. Mama Mia! The Italian squealer was unceremoniously rubbed out. Not only did the GM200's overall noise floor drop precipitously, but the soundstage opened up even more, the bass became stronger and tauter, and so on right down the audiophile check list. The Aurora also scored great sonic results with the Meridian 508.20, and Copland CDA 277 CD players. At a mere $230 for a three meter run, the Aurora is a must have system addition. (Shorter lengths, at lower prices, are also available from Wireworld.)

An Aurora cord was also happily plugged into Graaf's 13.5b, a line level pre-amp. Like the GM200, the 13.5b (it has 13.5 dB of gain) is a sleek, all gloss black, design. The tube preamp uses two 2C51/5670 double triodes per channel in a differential configuration, with a third 2C51/5670 for the tape record outputs in a buffered configuration. These six glowing tubes are covered by a 5.5" wide, sharply angled, dark glass window, giving rise to thoughts of Sophia Loren's brilliant eyes hiding behind designer sunglasses. The 13.5b offers one set of balanced outputs and two pairs of RCA outputs, and six source inputs (one pair of balanced inputs and five RCA inputs.) The 13.5b features dual component selectors for listen/record, as well as a top of the line ALPS pot. The 13.5b's switch gear is also very high quality. The component selector knobs click into place with the solid assurance of a Ferrari shift gate.

So how does the $12,500 GM 200, with the $5,500 13.5b in tow, sound? In a word, glorioso! The GM200 does something truly special with music. In this review's beginning, we discussed how a full-on emotional commitment by the concert's performers, or their ability to speak to you in a new and compelling voice, can abruptly yank you away from life's mental tediums, and refocus your attention on something much higher. The GM200 delivers the same sudden shock to your psyche. This amplifier has a special way of reaching down into the soul of a work, and communicating what is vitally important. The GM200, in some uncanny way, is accurately deciding which details are truly important, and then uses all of its prodigious resources to fully convey the overarching musical message. With lesser components, this meta-meaning can get lost in the reproduced mix, suffer from over exaggerated details, or just be ignored.

For example, the magic that the GM200 worked on the Kronos Quartet's "Pieces of Afric" CD. [Elektra Nonesuch, 79275-2]. This CD features new works from composers of Morocco, Gambia, Zimbabwe. Sudan, and other African countries. One piece on this CD collection, "Escalay" (Nubian, for waterwheel) was composed by Hazma El Din, a Sudanese composer born in 1929. El Din plays the tar, a stringed instrument, as he performs his composition with the Kronos quartet, which itself is comprised of two violins, viola, and cello. Escalay relies heavily on plucked instrument strings to provide its rhythmical, and ultimately religious, intensity. Francis and Gordana had heard this piece many a time, via many other amplifiers. But what they had not really heard before was how a particular plucked cello string had been tuned so deliberately loose that it liberally slapped against the instrument's body, producing a kind of mechanical buzz. This unusual cello playing was so startlingly revealed by the GM200, that the first time they heard it, Francis and Gordana momentarily thought one of the drivers in the extraordinarily revealing Impulse Ta'us horn load speakers had come adrift. But they quickly realized that this was music they were hearing, vigorously resonating notes which had rich, complex harmonics, and subtly decaying overtones, beyond which the bowed tar, viola, and violins were soaring up and over. It was like the other instruments were being catapulted into a higher plane by that one plucked string. The GM200 instinctively knew the musical importance of this detail, and made it an integral, vital part of El Din's reproduced work. Escaly had suddenly been ratcheted up several levels of emotional meaning for the listener--all because of one buzzing string. As the great modern architect and furniture designer Ludwig Mies van der Rohe once said, "God is in the details."

The GM200 thoughtfully provides a wide, deep soundstage to lay out all of a work's parts for critical inspection. Moreover, perhaps due to its OTL design, instruments are projected into a truly 3D acoustic space. The bottom and upper octaves are also in abundant, transformerless evidence. No, its deepest lows aren't in the killer Krell category, but they still can boogie with the best of them. Moreover, the deeper textures are separately layered, and the bass notes are kept rhythmically distinct. Its topmost octaves are not totally tube antiseptic, but neither do they suffer from the usual over-coloration sins. And its massive, glowing glass ramparts put the GM200 more on the side of emotion rather than totally transistor cool. In short, it's like a born again transistor amplifier which has discovered its soul.

For all these reasons, the GM200 easily conveys music, intelligence, and human emotion. Like when Nat "King" Cole sings "When I fall in love," or "Stardust" [DCC Compact Classics GZS-1104]. With the GM200, you know the King is not talking about prepubescent puppy love. This is the real heartbreak deal. Cole's voice also has this ever so slight, gravely quality, which the GM200 instinctively "knows" is Nat's unique way of putting his heart on the musical line. With a lesser amp, this critical, emotional detail could end up being thrown against jagged, sonic rocks.

Furthermore, the Graaf could provide a density of tonal color, a solidity of musical line. These often elusive qualities became materially manifest on another great cello recording, Yo-Yo Ma playing Beethoven's Sonatas No. 1 in F Major, and No. 2 in G Minor. Emanuel Ax plays the piano/klavier [CBS Masterworks, MK37251]. The opening bars of the Sonata No. 1 introspectively loop around, until the main body of the work is finally released via a keyboard-driven escape. All the while, the GM200 delivers a keen emotional immediacy, along with a head bobbing sense of musical timing and rhythmic pace. The cello's complex palette of colors also come through in Cinerama spades. Furthermore, since there are no traffic trooper transformers slowing down this audio Ferrari, the GM200 is lightning quick. The sometimes subtle, often difficult piano transients passed on through in all their ivory cascading glory. (This amp's incredible speediness was further evidenced on El Din's "Escalay.") Because this work, as well as those on many other recordings, was reproduced with such physical completeness, one could deeply peer into its innermost musical structure.

Incredibly, despite (because of?) its amazing transparency, the GM200 can make you forget about the hiss and junk on many a poor recording. Instead, it says, Just listen! Like to Astor Piazzola, a legendary composer of the new tango, who also produced a must-have two volume CD set, called "La Historia del Tango." Volume 1 [Polydor 314-511638-2] has pieces from the "Old Guard" tango composers, and Vol. 2 [Polydor 314-511639-2] deals with the "Romantic Epic." Neither one of these recordings would be called audiophile quality, but they are quite passable. Regardless, Piazzola, as he conducts his orchestra, is obviously trying very hard to communicate something vitally, deeply important to him. The tango, after all, is the lifeblood and musical soul of his native Argentina. This sonically simpatico amplifier intuitively understands Piazzola's passion. The GM200 opens up your musical arteries, and injects the tango's overheated South American blood right in.

Brass is a GM200 specialty. There is a roundness, a fullness of gleaming alloy tones that cannot be denied. The air rushes out the brass bell mouth, and whips up the local atmosphere into an infectious, frothy "crema." On "Salute to Bunny," which features the Rusty Dedrick All-Stars [DCC, DJZ624], the GM200 pulls out all the stops. Dedrick's trumpet moves the air to an almost wine glass shattering pitch on "I can't get started."

This musically involving story stays much the same no matter what you feed into the Graaf. Or what the Graaf feeds. The amplifier was also used on full range Apogee Studio ribbons, perhaps the logical successor to the sadly departed Divas. The Studios, although much less punishing than the Divas, still want the current, and routinely drop down to three ohms. The GM200 didn't even break into a sweat. However for ultimate control and bass slam, you would probably want to vertically biamp the Studios with two GM200's. (Unfortunately, Francis and Gordana would have to bring in a portable nuclear power plant.) The GM200, despite its forest of tubes, is as bullet proof, and current capable as a big transistor job. Its muscular musicality conjures up all kinds of interesting systems pairing possibilities, like using it with those other very demanding Italians, the Sonus Faber Extremas. Electrostatics should also be an excellent partner for the GM200. In fact, the US importer, Sonic Signatures (415-456-1632), has even used the very power-fussy Martin Logan CLS IIz electrostats to demo the GM200 at the Winter CES. One final system matching note: It was amore when the Nordost Red Dawn flat wire cables and interconnects were plugged into the GM200 and 13.5b And when the system was upgraded to Nordost's top of the line SPM Reference series, these two Italians beauties did an ecstatic tarantella.

The GM200, like the most skillful of performers, or the most musically astute of conductors, is an emotional, intelligent vehicle for accurately communicating a work's inner intentions. It is also a true musical instrument, as it somehow manages to transcend its mechanical assemblage of glass, wires, and metal. Similar to the Tin Man of Oz, the GM200 is stirringly alive because it has a great musical heart.

The extraordinary GM200 amplifier, and its excellent compatriot, the 13.5b preamp, are far from inexpensive. But then again, the truth never comes cheap.


Specifications, Graaf GM 200 Stereo Amplifier

U.S. Importer: Sonic Signatures, 30 Villa Avenue, San Rafael, CA 94901 Tel 415 456 1632, Fax 415 453 3136

Type: Tube, Output Transformerless, Output Capacitorless

Power output, 200 watts + 200 watts

Output Impedance: 4 to 16 ohms

Input sensitivity, rated output: 850 mV

Input Impedance: 100 Kohms

Total Harmonic Distortion: <1%

I.M. Distortion: 1%

Signal/Noise Ration: 87dB, unweighted

Frequency response: 7 Hz to 350 KHz (-3dB)

Slew Rate: 123 V/u sec

Rise Time: 0.8 u sec.

Damping Factor: 12

Negative Feedback: 17.5 dB

Power Requirements: At rest, 800 W; at rated output, 1,600 W

Dimensions: 17.5" (w) x 8.2" (h) x 16.3" (d)

Weight: 66 pounds

Price: $12,500


Type: Tube, Line Level

Gain: 13.5 dB

Input Impedance: 47 Kohms

Maximum Output Voltage: 20 V RMS

Output impedance: 600 ohms

Total Harmonic Distortion: < 0.6%

Signal/Noise Ration: 100 dB A

Frequency Response: 7 Hz to 450 KHz (-3dB)

Slew Rate: 32 V/u sec.

Power Requirements: 35 W

Dimensions 16" (w) x 4" (h) x 12.6" D

Weight: 16.5 pounds

Price: $5,500


Associated Gear: Graaf GM200 Amplifier &13.5b Preamplifier review

Speakers: Impulse Ta'us, horn loaded, full range loud speaker; Apogee Studio, Full range ribbon arrays

Amp: Graaf GM 200, 200 watt, OTL tube amplifier

Preamp: Graaf GM13.5B line stage (tube)

Tuner: Rotel RH10 'Michi'

Digital: Meridian 508.20 CD player, Copland CDA 277 CD player

Analog: All Wilson Benesch, including turntable, ACT Two carbon fiber arm, Carbon cartridge, and Stage One Phono Preamp

Cables and interconnects: Nordost SPM speaker wires & interconnects, Nordost Red Dawn speaker wires and Interconnects

Equipment stand: Base rack, and Base Isolation equipment platforms

Tweaks: Black Diamond Racing: The Shelf, The Source, Cones Mk 3 & 4, and Those Things;

Copyright 1998, Francis Vale, All Rights Reserved

21st, The VXM Network, http://www.vxm.com

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