Given that few people will defend tube/transistor hybrids, how do you go about satisfying the valve-oriented consumer who wants his or her amp to have everything under one cage? And without simply adding to the buttonry?
One of the last of the new-ish Italian companies I'm exposing to you this year, GRAAF
(Gruppo Ricerche Audio Alta Fidelta) has as its slogan "Il Suono Fatto A Mano", which I think translates into 'Hand-Made Sound' -- about as cool a way of saying 'Lunatic purism' as I can imagine. Additional Resources
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It's a monomaniacal vision, a sense of purpose usually associated only with such wonderful Japanese crackpot outfits as Air Tight and Audio Note. Designer Giovanni Mariani looked to one of the oldest, most awkward of purist configurations, output transformerless design (OTL), and yanked it into the present by incorporating all of the best audiophilic developments since the days of the great Julius Futterman.
GRAAF's philosophy consists mainly of excessive, train-spotterish attention to detail and a disregard for component cost. The sense of no-compromise and "Fatto A Mano" is everywhere, from the use of a real glass cover instead of perspex over the pre-amp tubes to the decoupled feet underneath every chassis. But plenty of ultra-conservative manufacturers operate using cost-no-object criteria.
GRAAF's persona is a happy blend of luxo-finish prestige and salivating audio dementia, because GRAAF produces a fully-balanced OTL amplifier which will drive 2 ohm loads without self-immolating. It leaks no strange substances when the chassis turns hot. It has enough safety circuitry to satisfy the Danes. It's the most wayward of hi-fi cult topologies ever offered but now forced to behave like, like, like a super-secure tranny amp! It's one of those blissful contradictions, an exoticar that's easy to drive or a computer that's user-friendly. That it comes from Italy says plenty about why the further development of high-end audio is probably going to be Latinate instead of American or British.
To be specific, GRAAF is based in Modena, the heart of the country's supercar industry. It's no accident that the GRAAF metalwork comes from the same factory as that which produces parts for the new Bugatti. Neither is it an accident that GRAAF is truly performance-oriented like its automotive neighbours. The GM 200 amplifier isn't just fully balanced and OTL and capable of driving something with a lower impedance than that of an LS3/5A: it pumps out a very useable, very real 200W/channel. And you're all hip enough to know that an OTL amp delivering 200W into sub-4 ohm impedances must be sporting a lot of tubes. And it does.
Each channel of this dual-mono amp's power is derived from sixteen PL504s, chosen for their ability to supply high current.
The rest of the circuit is all-valve and tranny-free, including an input stage using a 12BZ7 working as a balanced Class A buffer separator, followed by a 12AV7/5965 differential stage. This section of the circuit was design for good linearity and immunity to noise from the AC line; it also acts as a phase splitter. Voltage gain is provided by a pair of EFL200 double pentodes.
GRAAF's insistence on an all-tube circuit in which the signal handling, offset, bias control and stabilisation are pure tube, with no solid-state components present, extends even to the power meters. They're separate EM81 'magic eyes' for each channel, which glow green and illuminate according to the amount of power the amp is delivering. If you've not been keeping count, the valve tally runs to 42.
Not that you'll have to worry about tube failures, because this unit has been designed with dependability in mind...even when being manhandled by a reviewer. Switch-on, for example is accompanied by a silent period of a minute or so, during which three or four relay clicks indicate that all systems are stable and ready to rock. Beneath each of the PL504s is a 1ohm resistor (cost from Tandy: 3p) which will be taken out before the valves; this might happen, for example, should you not show patience by switching on and off too rapidly. (This demand for restraint is not an inordinate request.
The most modern of all late 20th Century appliances, the home computer, also needs to rest for a minute or two between switch-on-switch-off sequences unless you want to trash your hard-drive.) The only current limiting in the GM 200 is the intrinsic behaviour of tubes to act as current limiters, so audible clipping rather than shut-downs say when it's time to back off a bit.
When you first lift the GM 200 out of its wooden crate, you know it's all business. The unit weighs just under 30kg, even though the chassis measures a compact 445x415x210mm (WDH). Visually, it's 'cleaned-up lab chic', the mirror image layout placing two rows of eight tubes on each side, running from the back to the front. Flanking the centrally-positioned blue on/off button are the EM81s, the EFL200s and the 12AV7s. Above the rows of output tubes are black nickel-finished cages which, when removed, reveal chrome 'barrier' rods reminiscent of the old Radford handles.
Inbetween the banks of tubes are large capacitors and a massive toroidal transformer, the only shared component beside the chassis. All of these parts are made in Italy, to GRAAF specification.
The rear panel contains the XLR-type balanced inputs (there's no unbalanced alternative), beautiful gold-plated Esoteric Audio multi-way binding posts, a mains fuse holder and an IEC mains socket. Removal of the bottom plate reveals the milspec mother board, secondary boards and the balancing-act 12BZ7 tubes. Fit and finish are absolutely flawless, as befits an amplifier retailing for around £6400 back home. (If that's all too frightening, there's a half-power version, the GM 100, for less £3600.)
To drive the GM 200, GRAAF supplied one of its two line-level pre-amps, the GM 13.5B, either model selling for £3200. The one not supplied is the single-ended version, which sports a superior resistor ladder volume control. The GM 13.5B is the fully-balanced version and it contains a more compact but top-of-the-line ALPS pot because the other wouldn't fit; a future model will incorporate both balanced operation and the 'killer' volume control.
Continue reading about the GM 200 on Page 2.