What a month! Having just finished with the wild and wonderful E.A.R. V20 integrated, here I am savouring an equally radical new power amplifier from an Italian designer as revolutionary and iconoclastic as E.A.R.'s Tim de Paravicini. After all, GRAAF's Giovanni Mariani is one of but a handful of electronics wizards brave enough to carry on with output-transformerless circuitry - only he chose not to emulate the seemingly standard practice of making amps that are ugly, unreliable and built like something which looked like as if it had been fashioned in a Russian farm tool plant - circa 1946. Then again, Mariani
Aah, Modena! Home of Ferrari, Maserati, Lamborghini, balsamic vinegar and the world's finest cappuccino. It's important that you know of the locale if you're to appreciate why all GRAAF amplifiers transcend the hi-fi norm, and why the GM20 in particular transcends the GRAAF norm. Just as de Paravicini has excelled himself with the V20, so has Mariani entered a new phase of excellence. And, again like de Paravicini, he's managed to produce something totally out of the ordinary, yet completely in character with the amps of his which preceded it.
Yes, the GM20 is an OTL amplifier like the GM100 and GM200. Yes, it offers balanced operation. Yes, it's built to standards surpassed by no other valve amp maker on the planet, and matched only by the likes of Wavac or Nagra. Yes, it contains exclusively Italian parts wherever possible (and begs the need for a valve plant to open somewhere between the Alps and Sicily if GRAAF is to make it nearer to 100 percent). But this particular model uses a rather special tube, one which I don't believe has been used in OTLs before...
Mariani's first OTL/OCL(output transformerless/output capacitorless) amplifier using the circuit now adopted for the GM20 appeared over a decade ago. The benefits of this type of circuit are recognised by a specific breed of tube junkie and may be summarised as providing unrivalled transparency, speed and dynamics. That's because OTL/OCL designs are as close as it gets to direct injection of signal into speaker: the format avoids the need to couple the loudspeaker load by means of an output transformer. In the GM20, as with other OTLs, the output stages are directly coupled to their respective loads. And the output tube in this case is the Russian military workhorse, the 6C33C tube known for a bunch of 'nipples' on its top surface.
Like its predecessors, GM 20 uses a fully differential and balanced configuration (i.e. symmetrical) and is DC-coupled between each of its stages. This explains the low levels of hum by OTL standards, and the general immunity to noise, including noise generated by AC mains. To reassure those who have been (metaphorically speaking) singed by OTLs, great care has been taken to ensure the amplifier's stability throughout, Mariani's expressed goal being to make them 'practically immune to variations in the characteristics of the active components (thermal, static and dynamic) and maintaining their special character unaltered over time.' And if reassurance is needed, the GM200 I've been using for - what? five years? - still behaves as if it were hardly used.
GM20's power supply is made up of six separate sections, four for the output stages and two sections for the driver and gain stages. Two of the aforementioned 6C33C triodes are used per channels, configured to exploit the ability of these tubes to deliver high current with a low voltage power supply. Mariani believes that these Russki masterpieces represent an ideal choice for an OTL design precisely because of their military origins, which endow them with great ruggedness...in addition to superb quality.
Completing the valve complement is an input stage using two 6922 double triodes responsible for the voltage gain and operating as impedance 'adaptors'. The driver stages employ two triode-coupled EF184 pentodes, to take advantage from the differential circuit mentioned above and to work as phase splitters. This guarantees good driving ability for the output tube grids and helps to maintain perfect symmetry between the two signals.
Who knows? Maybe in his youth Mariani had an unpleasant experience with an OTL. Whatever the reason, he's gone out of his way to ensure that the user can treat the GM20 pretty much as if it were a 'normal' tube amp. The stabilising offset and bias circuits ensure completely trouble-free setting-up, and loudspeaker protection is guaranteed by a novel and sophisticated circuit which avoids the use of series relays or current limiters; the tubes themselves are naturally current-limiting. GRAAF has employed only a small amount of feedback - 6dB - to allow the GM20 to drive difficult loudspeaker loads without problems.
Read more about the GM20 on Page 2.
All this, of course, is secondary if you're of a certain type: the
GM20 is so damned cool-looking that even if you don't like tubes, let
alone OTLs, and you'll
dimensions of 350x215x440mm (WHD) is a look very much of the
now-familiar GRAAF school, but the shaping of the tube cage and the
over-sized transformer make it somehow more svelte - still brutal and
purposeful, but more 'styled'. As with every GRAAF product, the parts
quality will never embarrass you, there's a bold green light built into
the on/off button, the cage is plated in some exotic 'black chrome' and
the gloss-black paintwork was applied in the Ferrari restoration
facilities. (The latest batch, by the way, shared space with Sig.
Agnelli's personal Ferrari F40, the first-ever Lamborghini Countach and
the Dual Ghia which once belonged to Frank Sinatra...) Build quality is
faultless, and be prepared to hump 22kg whenever you need to move it.
Once you've unpacked the GM20, all you have to decide is whether to
use balanced (XLR) or single-ended operation; I opted for balanced
because it's so audibly superior, and I had both the Krell KRC-3 and a
choice of various GRAAF pre-amps to employ in balanced mode. While the
GM20 is rated at only 20W/ch RMS (I only had one to hand so I couldn't
try it as a 65W monoblock...), it doesn't behave like some gutless
S.E.T. wimp - provided you respect the recommended impedance of 8 or 16
ohms; 4-16 ohms is available when using it in the mono configuration.
With this in mind, I stuck to LS3/5As (which it loved), old Quad
ESLs (which it adored) and Quad ESL-63s, which it revered). LS3/5As
aside, I wasn't even remotely surprised at the success of the GM20/Quad
matings because both OTL practitioners I recall from the past - Croft
and New York Audio Labs - were Quad fanciers, and it was a romance
based on an almost uncanny compatibility. There's something about the
openness of the Quads and the transparency of OTLs which makes the two
blend like Lea-plus-Perrin, and there really isn't any need to consider
other designs. But that that didn't stop me from trying a range of
box-type designs like the Quad 77-10Ls, Apogee Monitors and even the
New Audio Frontiers transmission lines.
Quite clearly, OTLs offer an immediacy and an intimacy which can
only be present when the signal path is uncluttered and direct. That's
not to say that the sound can match the ghostly cleanliness of certain
transistor amps, and an ear to the speaker will uncover very low level
tube noises, but that's not the point: OTLs deliver speed and detail, a
level of 'snap' in the upper mid and treble transients and a neutrality
that almost disavows what the converted feel are valve virtues. Warmth
remains - that much is indisputable - but the sound isn't all rosy and
cuddly and blatantly euphonic. Rather, the sound of this particular OTL
is commanding and controlled, yet gentle and inviting.
Despite power limits which can easily be reached if you use hungry
speakers, the GM20 sounds big and powerful regardless of the actual
SPLs. It's as if the GM20 incorporates the world's first ideal,
automatic and dynamic 'loudness control'. Because so few amplifiers can
do this - thing 'big Krells', triple-figure Audio Research amps and the
like - it creates a mildly confusing state if you're in the habit of
mentally compensating for the sound of low playback levels. With the
GM20, you get the full works whether you're playing at 65dB or 95dB.
But what sold me on the GM20, beyond the gloriously life-like
midband, the trademark OTL clarity and detail, and the sheer scale of
the musical recreation is the sense of what I can only describe as
'presence'. In physical terms, it's an impression of the speakers
disappearing and of the music truly being in the room with the
listener. This, of course, is a key tenet of all sound reproduction:
recreating the original musical event. But the sound made by the GM20
possesses something else, a palpability which gives the performers more
substance and body than I've experience from any amplifier this side of
the Marantz Project T1, the ARC Reference 600 and the $80k Krells.
What makes this palpability so remarkable via the GRAAF is the
GM20's price tag: 2750. Merely as an objet d'art, the GM20 is worth
double that. Add to it a sound which matches some of the world's finest
in everything bar the elements related directly to a surfeit of power,
and you have a stereo amplifier so good that you want to shake the
judges of every award program in the hi-fi world, and make them worship
at the feet of Sig. Mariani.
Trouble is, he's too unassuming and too humble. Thank goodness that
this is one time a designer has chosen to use an amplifier to express
his alter ego rather than his empirical personality. The GM20 is too
damned good for the majority of the world's audiophiles. Period.