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Frederic Beudot
Financial Interests: click here
Digital Source: Esoteric X-03SE
Analog Source: Acoustic Solid Classic Wood, AS WTB211, Grado Reference Sonata 1, Denon DL103, Clearaudio Nano,Nagra BPS [in for review], Ray Samuels Audio F117 [in for review]
Preamplifier: Wyred 4 Sound STP SE
Amplifier: Genesis Reference 360, McIntosh MA2275, Yamamoto A08s, First Watt F5
Speakers: FJ OMs, Rogers LS 3/5a, Zu Essence
Cables: Zu Varial, Zu Libtec, ASI Liveline interconnects & speaker cables [in for review]
Power Cords: Zu Mother, ASI Liveline power [in for review]
Powerline conditioning: Isotek Nova [on loan]
Sundry accessories: Isolpads under electronics, ASI resonators and sugar cubes, ASI HeartSong racks
Room size: 21' x 13’ x 7.5'
Review component retail: $4,995

I have never owned or reviewed a SET. Yet ownership of the high-efficiency Zu Essence has thrown wide open the door to exploring a breed I’ve always enjoyed and admired at shows and demos but never sampled at home. My first encounter with a single-ended triode amplifier was a shock that directly birthed my love of audio. This was with an Audio Note Ongaku close to 20 years ago. Its memory persists whereas hundreds of other auditions since have faded away. That seems telling.

When speaking of direct-heated triodes, the first one to mind is likely the 300B often called the Queen of triodes. It’s a tube that delivers a large helping of the ‘deep magic’, a blend a spaciousness, midrange intensity and treble sweetness that makes SETs so enticing to those who heed their charms.

The fact that triodes achieve their magic through non-linear and more or less heavy-handed even-order THD is a fact admirers gladly accept while detractors call it a fundamental design flaw. I have no desire to try and reconcile both perspectives. Our editor’s dive into a variety of 300B tubes and amplifier designs proved that the more modern representatives of the family are transcending some of the traditional limitations while maintaining the desirable qualities. In many ways the Bravo 3.1 monoblocks by JAS under review today strike a similar more modern balance.

The 300B, 2A3 and 45 all have their own flavor but one characteristic they share to varying degrees besides the deep triode sound is pitiful low output power when implemented as single-valve single ended. While it is possible to successfully parallel or push-pull those tubes to increase power and control, to purists it’s not quite the same mostly because added circuit complexity is regarded as deleterious to signal and phase integrity.

Not everybody can accommodate the often huge speakers necessary to reach >100dB/W/m sensitivity where micro-power triodes begin to shine. The 300B and its usual 8 watts are a little more friendly but few wide-bandwidth speakers with 92 to 95dB sensitivity exhibit the flat and high impedance behavior that makes for a happy triode marriage (thankfully such designs have become more readily available in recent years with Zu, John Blue, WLM and Coincident Speaker Technology just a few of the more reasonably priced options – Quest for Sound's horns also fit the category though the larger model is not quite as interior design friendly).

Of course more powerful triodes exist to support less efficient speaker designs. The most common are the 211 and 845 whose implementation is complicated by the high plate voltage required. My recent auditions of various such designs led me to believe that there is no such thing as a good and cheap 845 or 211 amplifier. The only exception I know is one of our Blue Moon recipients from a few years ago, the Consonance Cyber 211 (though $5,000/pr isn’t exactly pocket change).

At the other end of the triode power spectrum one finds the NAT Magma and its 160 watts from a  single 450TH tube or Wavac, TruLife Audio and Win Analog 833-based designs delivering 100 to 150 watts per side. Those very exclusive designs will cost you very dearly to bring some level of triode character to lower efficiency speakers. That’s a reflection on how complex those designs are, how dangerous their rail voltages are and how expensive and complex their output transformers become to match tubes with very high internal resistances to much lower speaker impedances.

That said, there is another triode of smaller frame, more reasonable cost and great qualities which occupies a sweeter spot on power, control and linearity but which few have exploited thus far. I speak of the 805 at the heart of the Bravo 3.1 monos. While for years already the 805 has been Wavac's star tube for their mid-power designs, that endorsement was insufficient to move this solid radio triode out of the relative anonymity it remains shrouded in. A quick online search revealed 805 designs by Wavac (for those of deep wallets), Ming-Da (slim wallets but no US distribution, audition or service), Antique Sound Labs, Audio Space and JAS. That's all I could find, four Chinese and one Japanese maker. Contrast that to hundreds of 300B amplifiers on the market. It shows just how under-represented the 805 really is.

Most 805 circuit implementations I found are variations on—or plain copies of—the circuit developed by Nobu Shishido and published in Japan a few years before his death in 1998 using a pentode driver to deliver around 40wpc. There’s precious little online information on this tube which is believed to be the ancestor of the more powerful 813.

Nevertheless one unique feature of the 805 according to The Virtual National Valve Museum is an anode milled from a block of graphite. It’s the bright white tungsten filament you’ll notice during listening sessions in the dark. A number of manufacturers like JAS seem to prefer a triode driver and both JAS models adopt it. They also depart from Shishido's design by using a more complex shunt-regulated power supply.

JAS, a Chinese manufacturer imported to the US by NAT Distribution, should not be complete news o our readers. Srajan reviewed the 6C33C-based Bravo 2.3 integrated, Paul Candy the Audio Array 2.1 integrated which also boasts a pair of 805 triodes driven by 300Bs instead of 2A3s. Paul's review of the Array 2.1 is a great read and introduction to 805 tubes and my listening observations mirror his pretty much to the word yet with an added emphasis on dimensionality and spaciousness - not surprising when talking about monaural amplifiers.

The Bravo 3.1 can be used as power or one-input integrated amplifier with passive attenuators. Neither the distributor nor I recommend this second mode. The sound thins out considerably and loses some of its charm, even turning hard at times (resolution does improve further so those after ultra detail should remember it).

After running my Esoteric X03SE CD player into the variable inputs of the monoblocks for a few days, I was convinced that this was not how I wanted to listen to these amps. I reinserted the Wyred4Sound STP-SE preamplifier ahead of the Bravos using their direct input. That's how I did most of my listening. I also alternated between my usual Zu cables, ASI LiveLine cables and JAS' own silver interconnects and power cords. Those differences are covered in more details in the sidebar to the right.

Before turning to my listening notes, it's important to remember that the Bravos use 2A3 triodes to drive the 805s. This probably explains why the 3.1 monos only develop 32 watts (THD level at max output is not provided, 1% is reached at 8 watts) versus the 45 watts in the Array 2.1 whose drivers are 300Bs. It also explains the character of this amplifier, in many ways close to a 2A3 with boosted drive.

The Bravo 3.1 consume about 350 watts in idle per side to make 32 watts. The difference is released as heat. This x 10 ratio is fairly standard for SETs (class A) and not really noticeable when dealing with a 2wpc amplifier. Yet the Bravos did heat up my listening room like a regular space heater. They come with tube cages, mandatory with children or pets who could get close. Six tubes per amplifier get extremely hot up close.

The pair I received had been running for months as Quest For Sound's demo pair. Break-in was no issue and upon delivery it just took a few hours to warm up before the amps came on song. Speaking of warm-up, the amplifiers will reach 90% of their potential within 30 minutes but take a solid hour for the sound to blossom to full intensity (prior to that the midrange can sound a little glassy and congested).

I also must point out that all listening was done with the amps sitting on Isolpads instead of directly on the floor. Listening shortly without the pads confirmed the usual improvement in transient precision and better image focusing typical with those pads so I saw no reason not to use them full time.

The very first thing I noticed with the Bravo 3.1s driving the Zu Essence was the immensity of the soundstage both in width and in depth as well as the precision of the layering within that stage. I know this triode effect but it works on me time and again. I had heard it with the monos driving the SoundQuest SQH-12 a few months ago and I was hearing it again but even more magnified in my own room. Depending on the setup, I am used to hearing a very wide stage from the Essence but depth had been more elusive. With the Bravos compared to the almost thrice priced Genesis GR360 class D amp, depth utterly changed scale. Not that the Genesis renders a flat soundstage but it remains behind the speakers. There is no sense of the curved disposition of a symphonic orchestra on stage for example. The Bravos differed in that they expanded the stage behind the speakers—beyond the front wall even—but when appropriate, also projected up to a third of the stage in front of the speakers.
I typically review gear with my reference set of Zu cables (Varial, Mother, Libtec). I know them and they have been a constant for the past 3 years when about everything else has changed in my system. Yet I also know they do not cotton to every piece of equipment. Since JAS also manufactures cables that I assumed would mate well with their gear, I requested a pair of power cords and interconnects in case I was faced with major incompatibilities.

I should not have worried. Unlike the Esoteric A03 amplifier, the JAS Bravo 3.1 seems reasonably easy to please. I started with a pair of Isotek Premium power cords (despite that name it’s actually their entry level) with good success but overall the sound was a little too thin and lacked in bass grunt - the typical sonic signature I have learnt to expect from those cables. Moving up to Zu Boks added resolution and a little more bass power but retained some leanness that was more pronounced than desirable. A pair of Zu Mother addressed this beautifully by adding intensity in the midrange (especially its lower band) and bass depth.

In comparison with the Zu Mother, the JAS Zion P1-S AC power cord had slightly less bass weight and resolution in the lower midrange but only marginally so and without any impact on the sonic qualities of the amplifiers. These were overall very minor differences that will matter only when fine-tuning the tonal balance of a system to the nth degree. The good news? Those copper/high-grade silver double shielded cables cost $389/ 2m while the same length Zu Mother sells for $624. When one needs to buy two cords for mono amps, things add up quickly. Although on the JAS Bravos I found the Zu Mother just a smidge more refined in the midrange and a tad more articulate while weightier in the bass, considering the price difference a pair of Zion P1-S is a no-brainer.

JAS also proposes a very high-quality silver interconnect called the Zion S3. Each S3 is made of 6 conductors shielded in pairs and twisted. Each conductor comprises 30 strands of 6N continuous cast silver. The single-ended cables I received were terminated with platinum-plated silver connectors, Neutrik's finest. That’s to say that the Zion S-3 are as well constructed and designed as they come for $549/pair (you won't find many pure silver cables in this price range).

Let it be said upfront that I am not a silver cable man. I own a pair of Slinkylinks interconnects to help rebalance components that are a little too endowed in the upper bass—the Slinkylinks do not suffer from upper midrange harshness but certainly have the extreme bass leanness of the breed—but my affection for silver cables stops there. For once the JAS Zion S3 interconnects did show me a different sonic signature than what I expect from silver cables. Their bass prowess was excellent if not quite as deep as the Zu Varial or ASI Liveline and with a level of resolution there approaching the LiveLine cables and exceeding the Varial.

The differences actually were far more profound in the midrange - drier for the Zion S3, warmer and wetter for the Varial, dead-on neutral and extremely resolved for the LiveLines which also won in the imaging department. The only area where the Zion S3 fell significantly behind the two more expensive cables was during low-level listening. Both Varial and LiveLine managed to maintain resolution, timbre and dynamics at much reduced power levels versus the Zion S3. Like for the power cords, the Zion S3 may not be the ultimate choice but considering its price, the small omissions are certainly not dramatic and the S3 proved a very worthy partner to the Bravo 3.1 monoblocks at a 30% to 50% lower sticker than what I compared it to.

That was particularly obvious on well-recorded symphonic orchestras. The first violins were now located in front of the speakers to the left. Overall the Genesis puts more distance between you and the performance. Hall effects also were very faithfully reproduced, transporting me to the original venue. The very interesting element about the Bravos was that this effect wasn't systematic. A recording without captured ambiance like 2L's DeUSYNLIGE, organ arrangements that lack depth or hall sound (it pains me to write this as I admire 2L's work but even the best can flunk on occasion and Joel and I will just have to disagree on the qualities of this disc)... it sounded as flat, cold and lifeless through the Bravos as it does through the Genesis. The Bravo monos clearly do not artifice ambiance with some editorialized artifacts but they certainly enhance and magnify what's on a disc.