Digital Do Main

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From Hi-Fi World - December 2009 issue


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Field of Dreams





Following in the footsteps of japan's legendary 1970s MOSFET amplifiers, Noel Keywood assesses the new Digital Do Main B-1a stereo power amp sporting special Field Effect Transistors...


Drawn by the eerie purple glow of a corona discharge, I went into a room at the Munich High End show earlier this year to see the Lansche Audio No3 loudspeakers. Seated in the gloom of this low lit room, however, I saw to my right a very unusual looking amplifier, the Digital Do Main B-1a you see pictured here. Beside was an earnest looking Japanese gentleman, Kazuhiko Nishi, eager to explain to me the inner workings of a radical amplifier that used custom made, large area audio power FETs (field effect transistors) able to give better sound quality than we get from today's general purpose industrial power transistors. With words like "silver vapour deposition", a "mirror image FET power supply" using the same devices, "gold plated heatsink contact areas" and other esoterica, the Digital Do Main B-1a sounded like one highly specialised solid-state design to me, potentially able to overcome all the ills that afflict the breed, I thought, and hoped...


2SK278B, 2SK78 and 2SJ78 low power

static induction transistors used in the B-1a.

Aware that the amplifier has been little seen in Europe or the UK, I beseeched our Japanese speaking editor to phone 'em in Hamamatsu and get one if he could. I don't know what he said in Japanese but it worked, and a B-1a was delivered through UK importer ABC Audio. Well, collected in fact, from the ABC room at Audio 09 Show a few weeks ago by myself. I was again nervous, as with the wonderful Ortofon Cadenza moving coil cartridges I nabbed at Munich,  that the B-1a might not make it back to Hi-Fi World towers if anyone found out about it at the Show, but I was lucky enough to make it home Sunday night with a single B-1a securely housed in a sturdy flight case, adorned with Japan Airlines stickers. Yes, this unit was straight from the factory and the rear panel carries a large 'SAMPLE' sticker.  It is also a 100V version so was accompanied by a step-down transformer, one of surprisingly small dimensions. It struck me immediately that this would affect bass quality, likely for the worse, something to bear in mind in this review.

Our review sample was a single stereo power amplifier. But this amplifier can be set to bridge mode to double power output, in which case it becomes a monoblock and two are needed, doubling available power for those that need more than 150 Watts per channel. With rear mounted input level controls for each channel, plus a big volume control in the centre of the front panel, a preamplifier isn't needed, so we did not use one, running a Stello DA-100 DAC straight in for CD purposes and an Eastern Electric Minimax phono stage for vinyl. Loudspeakers were our Spendor S8e benchmark references, chosen for a nicely damped, colouration-free midband.

Weighing 35kgs – and much more in its flight case – our B-1a wasn't going to be spirited away from me too easily I must admit and I had to get two security guards to carry it into a London guarded store. Although it has a compact fascia measuring 218mm wide and 176mm high, it is an enormous 550mm deep.  The front carries a power switch and a centrally placed volume control illuminated by a small escutcheon. A master power switch sits on the rear panel. This also carries loudspeaker sockets able to accept bare wires, 4mm plugs and spade terminals. Balanced XLR inputs and unbalanced phono inputs are provided, each channel having its own input level trim control able to reduce volume to zero. These can be used to lower sensitivity (although at 1.25V it isn't high) or adjust channel balance. The amplifier switches on and off silently.

At the heart of this amplifier lies something known as a Static Induction Transistor. Originally described by J. Nishizawa in Japan in 1975 it is in fact a Field Effect Transistor, with Drain, Source and Gate, as usual. Digital Do Main manufacture the 2SK77b high voltage / current output device used in their B-1a, as well as smaller signal devices. It seems that the Static Induction Transistor (SIT) is difficult to fabricate and its excellent properties are only really needed in high voltage transmitters, where it can replace valves, and audio amplifiers – not a sufficiently large market to sustain profitable manufacture. So the SIT has been in and out of use for a long time, never having quite managed to secure its future. Its voltage transfer characteristics are triode-like, it does not suffer thermal runaway and it is able to work up to 225 degrees C.

All of this looks very good, but mismatching between devices will affect crossover distortion, which still exists, so feedback remains necessary. And also, the sound of 'triodes' isn't really something easily determined, as the few main types in use (300B, 211 and 845) all sound quite different and, in my experience (I use a 300B at home and 845 at work, so I suppose I am Mr Triode!) is nothing like any solid-state amplifier I have ever heard, including this one. Since the current density and dielectric within thermionic triodes both differ radically from any solid-state device, and since the latter don't suffer secondary emission, saying they sound the same is like saying a Mini and Ferrari are the same because they both have round wheels.

Best to forget simple but misleading comparisons like this; the B-1a can justify its existence without it and there is a need for solid-state amplifiers built around custom designed, linear audio transistors I believe. This is why I was so excited to hear about the B-1a in the first place, and why in audio it is a radical amplifier: this is the only amplifier I know to have output transistors optimised for audio use. By way of contrast, any 300B or KT88 based valve amplifier enjoys dedicated audio valves inside – almost an unfair advantage!


FET amplifiers of various flavours I have heard came across as dry in delivery, almost prim and proper and very much of the solid-state breed. And, broadly speaking, the B-1a is in this mould, although it is obviously a highly refined hi-fi product of its time, by which I mean that attention to component quality all through gives it a sense of being consummately well preened for its purpose. FET amps of the 1970s were nothing like this, mainly because apart from their V-FETs, general component quality was poor, as with other amplifiers of the era, and this compromised both clarity and precision.

The most striking feature of the B-1a I felt was a sense of intense insight and detailing quite beyond the almost - by comparison - approximate sound stage set up by modern transistor amplifiers. Dry in nature and constrained in a way a valve amplifier is not, the B-1a was at the same time intensely insightful, bringing a spotlight onto vocals that revealed every little inflection and nuance of delivery, as well as all the production details within the recording that act to enhance a studio recorded performance.

Gabrielle's usually warm, dusky tones in 'People May Come' almost crackled at me as information in the midband and upper midband jumped from our Spendor S8e loudspeakers, projected forward in megaphonic fashion. Her own backing harmonies also leapt out and the smallest fades and echoes used to add depth and embellish the recording all became intensely etched and very obvious. The only reservation here came from a diminution of warmth and body, from a singer whose vocals rely these qualities


The 2sk77b output device, a vertically arranged static

induction transistor designed for audio.

Do you think Hugh Cornwell has a strong, deep but almost rasping voice as he heads The Stranglers? Well, the B-1a makes more of all the tiny details that make up his vocal delivery rather than standing back and presenting a singer whose delivery suits his idiom. In this the B-1a's sense of analysis can detach content from performance slightly, at least until you acclimatise to it. I would describe the B-1a as more academic than atmospheric in basic character, but that it can get so much out of a recording where others seem to struggle suggests it has a lot going for it; it's just this amplifier puts it all together differently.

The B-1a is astonishingly forthright and peers right into a performance, pulling it apart with cool precision. Grippingly concise, it places every fine detail into place in the acoustic picture with military precision and, by way of contrast, makes normal amplifiers sound quite vague, both spatially and temporally. Although that makes the B-1a impressive rather than romantic, its abilities are obviously quite beyond the current norm and there were some fascinating consequences.


A single B-1a can be set to bridge mode (single

channel) to double power. Channel level controls are provided,

as well as balanced and unbalanced inputs.

One feature that intrigued me was that its intensity and precision resulted in a conspicuously well ordered sound stage on which instruments seemed to have a more forceful locational presence than I have heard before, so a cymbal would ring from just there - a point in space no bigger than a 5p piece 3 metres distant! This seemed to be a function of both the drily wrought, forcefully projected nature of instruments, as well as vivid insight into their character that made them seemingly closer. There's no doubt also that great midband and upper midband presence helped toward this effect and here I suspect the step down transformer was not helping by lessening bass impact, reducing emphasis of low frequencies.

However, I have to say that the B-1a has the sort of tightly ordered delivery of a high feedback amplifier and its enormous damping factor was holding back even our usually quite loose sounding Spendor S8e loudspeakers. As expected, the more I turned up volume the better it all got, bass coming across as viciously tight and impactful, if dry as a bone.


A guard wheeling in the weighty B-1a in its flight case, after the Audio 09 show at

Whittlebury, where it was on display.

There was a small but obvious de-emphasis, as it were, of upper treble that at times made the delivery almost creamy smooth in balance – until that is my attention was yanked back to the blare of a trumpet, the crash of cymbals or an attention grabbing vocal delivery much closer to my ear than I am used to. Not only does this amplifier possess clinical precision, it really does see into music and dynamically support it across midband and treble.

As usual, the taut bass of a high damping factor amplifier is a mixed blessing, yet with the right loudspeakers - and Tannoys come to mind - having prominent and deep bass, an amplifier like this might be just the ticket. With the Royal Philharmonic playing Tchaikovsky's 'March Slave', for example, all the emphasis was on the upper registers, yet when the tubas took up the slow main theme it sounded suitably hearty and physical, razor-sharp timing bringing precision that didn't go amiss. Violins interjected repeatedly with precise timing, stabbing into the sound stage with attention grabbing force.


Whimsically comparing pianists John Ogden with Volodos after someone had insisted the latter was a great player (technically true... but I prefer John Ogden's more romantic style) I heard barely a trace of the piano's body. Although both recordings I listened to were themselves short on low end information from the piano, probably due to microphone positioning, this amplifier does nothing to tease out information from the lower end of the musical spectrum. Yet at the same time, strong plucked bass rolled along solidly to provide a cheeky support line behind Amy Winehouses's 'You Know I'm No Good', and kick drum had a nice tight thud to it. Both seemed to reach downward without constraint and here the B-1a benefitted from its all-direct coupled design I suspect, our measurements showing it reaches down to d.c.

Over a few weeks of use with a variety of loudspeakers the B-1a remained consistently impressive, being both concise and revealing to a degree that is the hallmark of true high end. This is a highly developed and specialised product, that's obvious when listening to it. It does, however, need appropriate matching loudspeakers and here life may get a little tricky. Princesound Prince II electrostatics may be one choice, having complementary insight and also a need for high power (well, voltage swing). Tannoys like the Definition Series DC8s or 10s would match character-wise, even though they don't need the power of the B-1a, unless you have a baronial hall full of merry souls to amuse perhaps. The B&W CM9s I review in this issue worked quite well, the B-1a's slow roll down in upper treble acting to damp their treble unit just a tad, whilst their nicely balanced bass of good quality strengthened upper bass from the amplifier a little.

Vinyl LP also proved a nice match, although I felt a need to step up from an Ortofon 2M Black to the moving coil Cadenza Bronze to gain transparency, then quality cuts like Mark Knopfler's 'Punish the Monkey', from the album 'Kill to Get Crimson', sounded wonderfully tidy and poised, guitar strings displaying a firm, cutting twang, hand drums having substance behind the outline of their sound. Knopfler's voice was starkly clear centre stage, gloriously fleshed out with fine detail, enunciation highly specific as a result.


The B-1a basic circuit topology, with phase splitting and gain from two differential pairs,

and one pair of N Channel 2SK77 output devices. The amplifier is all direct coupled.

Not shown here are protection circuits, servo circuits, power supply and suchlike.



Digital Do Main's claim that this is a unique amplifier from a company that believes its products can go down in (Japanese?) history as classics possessing assured value (it's all in the company's founding documents, and why Canon invested), I completely believe. The B-1a is quite an amazing amplifier based on the unique technology of the Static Induction Transistor, developed in Japan and little known or used elsewhere. Likened to the triode valve in operating characteristics, in the B-1a amplifier it finds a suitable home. So like the original Yamaha B1 V-FET amplifier, the Digital Do Main B-1a is a unique and advanced design that is flawless in what it does.


The Yamaha B-1 MOSFET amplifier from 1974, after which the Digital Do Main B-1a is named.

Our 100V factory sample from Japan I suspect does not fully represent what a final 240V model will sound like. Forgive me for pleading with our editor DP to phone Hamamatsu straight away to get a sample, but on this magazine we have a lot of respect for product from Japan. And what Dr Nishi told me at the High End Show in Munich, and what I read on the info CD he gave me, was enough to make reviewing this product a must. The B-1a is a very special amplifier and when UK samples arrive at importers ABC Audio, if you have the money and inclination it is worth a close audition. Their deep clarity and sense of ordered precision will I suspect make many rivals sound quite vague and win hearts.


verdict five globes

Unusual and highly advanced power amplifier using special FETs, the B-1a is wonderfully detailed and concise.


ABC Audio

+44(0) 20 8462 1379


- midrange insight and detail

- strong imaging

- beautifully built


- awkward proportions

- overly tight bass

- no remote volume


I wondered before testing this amplifier whether its FETs would display the usual wide bandwidth these devices are known for, or whether the designers would avoid working up to radio frequencies. Well, it looks like the latter, because frequency response of the B-1a starts to roll down above 10kHz no less - a very low limit. It  measured -0.3dB at 20kHz – not much of a drop but still unusually low as hi-fi amplifiers go and enough to ensure the B-1a will not sound sharp or bright. Measuring -3dB at 100kHz (our quoted upper limit of 55kHz is at -1dB) the B-1a exhibits a very slow roll off in high frequency output and - thankfully - a sane high frequency limit not out at radio frequencies.


Damping factor measured an extraordinarily high 100. This suggests substantial feedback is used, but the amplifier’s special FETs are very high bandwidth devices with good linearity, so it may not be as high as early Japanese V-FET amplifiers. In itself this has no implications for sound quality, but high damping factors (above 30 or thereabouts) can make for dry bass, except when underdamped (boomy) loudspeakers are used, in which case the extra control is beneficial.


Distortion levels were low in the midband but rose toward high frequencies, unlike early high feedback FET amplifiers of the 1970s. However, a worst case distortion figure of 0.02% at 1 W into 4 Ohms is low, so harshness will not be evident. The distortion spectrum shows extended harmonics and another analysis, not shown, revealed this was classic crossover distortion. At a low level however, this is not a problem.

The B-1a produces plenty of power, 160 Watts into 8 Ohms and 240 Watts into 4 Ohms. It ran cool on the test bench, in spite of having big heatsinks. Input sensitivity was 1.25V through both unbalanced phono socket inputs and balanced XLR inputs (at full volume). The volume controls did not affect frequency response and performance figures were identical through either input.

The B-1a turns in a good set of performance figures, free of weaknesses. Its peculiarly limited bandwidth and high damping factor suggest there is something different inside. NK

Power 160 Watts

Frequency response 1Hz-55kHz

Separation 97dB

Noise -116dB

Distortion 0.02%

Sensitivity 1.25V

Damping factor 100





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