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Reviewer: Srajan Ebaen
Financial Interests: click here
Source: APL HiFi NWO 3.0-GO; Ancient Audio Lektor Prime; Raysonic Audio CD-168
Preamp/Integrated: Supratek Cabernet Dual; ModWright LS-36.5 with PS 36.5; Wyetech Labs Jade; Almarro A318B; Melody I2A3; APL Hifi UA-S1; Woo Audio Model 5; Raysonic Audio SE-20 MkII [on review[; Trafomatic Experience One [on loan]

Amp: 2 x Audiosector Patek SE; 2 x First Watt F4; Yamamoto A-08s; Fi 2A3 monos
Speakers: Zu Audio Definition Pro; DeVore Fidelity Nines; WLM Grand Viola Monitor with Duo 12; Rethm Saadhana; Zu Presence [on review]

Cables: Ocellia Silver Signature loom; Crystal Cable Ultra loom; Zanden Audio proprietary I²S cable; Crystal Cable Reference power cords; double cryo'd Acrolink with Furutech UK plug between wall and transformer; Stealth Audio Indra and Meta Carbon
Stands: 2 x Grand Prix Audio Monaco Modular 4-tier
Powerline conditioning: 2 x Walker Audio Velocitor S fed from custom AudioSector 1.5KV Plitron step-down transformer with balanced power output option; Furutech RTP-6 on 240V line feed
Sundry accessories: GPA Formula Carbon/Kevlar shelf for transport; GPA Apex footers underneath stand, DAC and amp; Walker Audio Vivid CD cleaner; Walker Audio Reference HDLs; Furutech RD-2 CD demagnetizer; Nanotech Nespa Pro; Acoustic System Resonators and front wall sugar cube matrix
Room size: 16' w x 21' d x 9' h in short-wall setup, with openly adjoining 15' x 35' living room

Review Component Retail: ¥680,000 - 780,000 depending on tubes supplied

When Shigeki-San of Yamamoto Sound Craft announces a flagship amplifier, connoisseurs of low-power SETs are nearly prepped to get on their feet for a standing ovation. While the secret has leaked out only over the last 5 years, handcrafted wares from the house of Yamamoto have developed an enviable underground reputation since the Internet first facilitated sales outside their native Japan. Being subsidized as it were by Yamamoto's own machine shop for whatever custom parts Shigeki-San might spec out for his esoteric audio division, these vacuum tube electronics -- plus vintage driver speakers, accessories, vinyl bits and general parts also available to OEMs (Teflon tube sockets with tight-grip gold contacts, precision bias meters and such) -- are about as custom as regular production goods can get.

On paper, the new A-09S seems little more than another traditional 8wpc 300B stereo amplifier with tube rectification via 5U4G EML mesh plate. But instead of the ubiquitous 6SN7 driver, there are ultra wide-bandwidth noctal NOS C3m from Germany's 1960s telephony supplies. Though self-biased, the amp includes two bias current meters to confirm proper valve operation. Being able to supply up to 2A of filament current, the A-09S is compatible with most 300Bs on the market without any user adjustments. This includes the traditional 1.2A Western Electrics, KR 300B Balloons, Valve Arts, Electro-Harmonix and TJs as well as the hotter biased Emission Labs (1.3 - 1.5A from the Mesh to the XLS versions) all the way to the 1.8A KR 300B-XLS and the EML 320B-XLS at 1.95A.

As is de rigeur for any Yamamoto amp, the transformers are in-house issue and, uncommonly, all of the toroid type, albeit in slit form for the 30-ohm choke coils and output transformer. The main polypropylene supply capacitors are encased in Ebony housings and potted with epoxy resin to kill foil resonances. Turned Ebony also shows up for the footers which hold aloft the trademark resin-impregnated Shashi Cherry deck which looks fantastic and adopts Bakelike-type properties from the vacuum injection treatment.

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Input impedance is 200K, bandwidth 15 to 22,000Hz -3dB, gain 27dB, DC filament heating via Schottky diodes.

Each 300B couples to its own output transformer. After the quick popularity of Yamamoto's newer A-011 2A3 'integrated' [below], an equivalent direct-drive version with integral attenuator is presently under development also for the A-09S.

On the uncommon driver tubes, Yamamoto's European importer and owner of Emission Labs JAC Music has some useful information: "These were low-noise audio tubes made by Valvo* and Siemens exclusively for the German post. They were not for sale to other customers. They were used in audio repeater amplifiers for long distances. If there is one enemy of long distance calls, it's signal loss and noise. So what they needed was high amplification and low noise.

Sidebar I: For the technically curious, JAC Music's PDFs on original C3m data sheets are available here: 1 2 3
"Since amplification and low noise are no friends of each other, such tubes were hard to find. In the end, the German post defined their own tube specifications and let the tube factories compete for good quality. That worked out perfectly. These German post tubes were first designed in the heads of the amplifier engineers who finally wanted something without compromise. The engineers simply asked what performance parameters their ideal tube had to have and then let the tube factories try to fabricate it.

Valvo operated out of Valvo Haus at Burchardt Str. 19 in Hamburg, the Siemens & Halske Aktiengesellschaft was in the Wernerwerk für Bauelemente, Berlin

"The wish list included highest amplification; lowest noise; lowest microphonic effects; higher lifetime than other commercial tubes; metal shielding; had to be a pentode but work perfectly when triode connected and then exhibit real triode curves; supply complete data sheets, leaving out no data; had to optionally come with individual serial numbers on each tube." From these original data sheets, one learns that the operating specs for the C3m are a heater voltage of 20V, heater current of 125mA, anode current of 16mA, mutual conductance of 6.5mA/V, equivalent noise resistance of 1200 ohms and hum voltage of 10uV RMS. The tube was encased in a metal cover but Yamamoto runs it for better sonics and cosmetics with the shield and metal base removed. Having assumed Japanese distribution for Emission Labs*, Yamamoto outfits the stock A09-S with EML rectifier and output tubes unless a customer requests differently. This close working relationship between Yamamoto Sound Craft and Emission Labs promises many interesting future collaborations. The forthcoming A06-2 to run EML's new current-production AD1 will be merely the first. While transistors and switching amps make up the ruling class today, an underground movement of perennial malcontents is committed to the old ways. These people continue to offer interesting alternatives to the mainstream. In the process, some endangered valve species even enjoy a second coming (KR Audio's reissue of the PX 4, PX 25 and Marconi R as well as the recent Chinese relaunch of the infamous EL156 pentode are other quick examples).

* The Emission Labs trademark is held by Jac van de Walle. EML-branded tubes are manufactured by former AVVT personnel under exclusive license to Jac.

In the driver's seat
As speakers and amplifiers hog all the attention at trade show demos, so do output tubes completely overshadow their drivers. Hence it's as common to hear generalized remarks about 300Bs -- insert favorite valve -- as it is to hear showgoer comments on "great amp in that room" without a second thought that it's always a complete system plus room one hears - and that a driver tube seasons the sound of the output tube to a greater extent than consumers might appreciate. For example, when Jim Hagerman of Hawaiian Hagtech brand recently experimented with a push/pull 2A3 amp's drivers, "I tried out a 6E5P (was using a 7788 as driver before). Well, knock my socks off! The amp went from 6 watts to 8 watts! Distortion dropped a tad but mostly it was more signal swing [original post on]".

While it's perhaps possible to generate a bit more than the expected power from a given output tube, the main reason why valve audiomaniacs chase exotic driver tubes is to find the perfect fusion of sonics (which naturally includes technical parameters like distortion, noise, gain, output impedance and current delivery). Next time we find ourselves instinctively reacting to any particular mention of a valved amp, we might inspect our presumptions by asking what drivers such an amp employs before we categorically
Sidebar II: "Shuguang, Valve Art, TJ, Full Music, Sophia Electric. All I knew for certain was that 300Bs thus branded originated in China. From which factory though? And who were the makers and who were the rebadgers? Similar confusion -- to the less than fully informed at least -- reigns in Eastern Europe between AVVT, EAT, EML and KR. When KR and Vaic split, AVVT rose, then collapsed, to be just partially resurrected by EAT with a handful of tube types. EML is produced under exclusive license by former AVVT personnel as we learned from Jac van de Walle. What else might one learn about the present-day Czech-based 300B makers?" - for that and a 2-page pictorial factory tour of KR Audio by Marja & Henk, on how tubes are made, continue.
slot its expected sonics into a tidy shoebox. It would likely be incorrect to think a driver tube more important than the output tube. Yet it's equal folly to underestimate the potential an unfamiliar driver tube might have on the performance of a well-known power tube. This closes the circle of the earlier remark on " just another 8wpc 300B SET". Never mind that Shigeki Yamamoto has never been in the business of cloning what others are up to; his driver choices alone demonstrate
original thinking. The custom design and manufacture of most the auxiliary parts around his unique triptychs of rectifier, driver and power tubes then merely underscore how this man marches to his own drummer. (My A-08S for example uses the mushroom 717A drivers and an 80 rectifier to make its 45s sing). If I have any casual expectation about the A-09S, it's that it will be anything but another single-ended 300B amp in the usual mold. As they say, time would tell...
Sidebar III: "The subject of appropriate driver tubes for direct-heated power triodes is quite esoteric to most consumers. Investigating it just cursorily presents immediate reasons however why 'famous' tubes like 300Bs may sound anything but famously in certain implementations. From Lynn Olson's Nutshell Hifi pages, we learn that "vacuum tubes are good at doing different things. A driver is not at all the same application as an input tube, which is really a preamp-style voltage amplifier and input buffer. Driver tubes have to confront the shock of power-tube grid current whenever the amp clips - which happens more often than people think. They also have to deliver a massive voltage swing to the power tube grids which is more than two or three times the swing required by pentodes, combined with a heavy capacitive load..." continue.