AMP-11R Review (6moons)

Our AMP-11R has been tested by Srajan Ebaen of 6moons, and was awarded the prestigious Blue Moon Award for its amazing quality and sound. Read the entire review with a fantastic background to the company, the technology and the sound. 6moons AMP-11R Review February 2010. Of moles and men. Maurizio 'El Gelato' Galati—my mole inside the Italian audio embassy—had news. His friend Giulio Salvioni had become importer for Bakoon. As globe-trotting hifi ambassador from mye arm chair, I'd come across this very esoteric underground line from designer Akira Nagai before. But only in passing via forum praise. Ther wasn't a single English review on the brand. A contraction of Baku (a supernatural creature from Japanese mythology associated with dreams) and Un (luck), Bakoon denotes lucky dreams. Their core SATRI circuit meanwhile is named after the Japanese satori for enlightenment. Highly suggestive stuff. Bakoon launched in Kumamoto Japan in 1991. As of 2009 they've been headquartered in Seoul, Korea. Was I interested in a tête à tête? Assolutamente. Galati promised to pass my interest to Salvioni.   No buffoon. Even a cursory glance at the amp's specs makes clear how this is no lemming design. There's bandwidth from 10Hz to 1 Megahertz and a S/N ratio of less than 50μV noise without feedback. And two analog BNC inputs called SATRI-Link which allow for low-impedance current-mode signal transfer between Bakoon gear. Eluding power corruption, there's an 8Ω rating of just 15 watts. Flipping a finger at mass for respect too, shipping weight is a mere 10.5kg. Equally middling are dimensions of 270 x 75 x 340mm WxHxD. With a DC offset of less than 1mV and exploded bandwidth, one assumes a DC-coupled ultra high-speed circuit. But that's just the beginning.  
Bakoon's SATRI is a proprietary current-mode integrated circuit whose gain factor is set by the ratio of input to output resistor; whose linearity requires no global feedback; whose S/N ratio remains constant regardless of gain; and whose operating point is fixed inside the chip to be unaffected by outside thermal conditions. The first SATRI-IC appeared in 1998 inside an epoxy molding. It used surface-mount dual transistors and carbon resistors. Two years later, its SMD dual transistors became standard audio transistors. By 2002, the chip resistors became 0.1% precision metal film units. The current V9.0 Mosfet generation dates back to 2007. It relies on a discrete current mirror, adds 12 transistors and expands the former 2-layer circuit board to four layers. This reduced distortion by a claimed 1:10 factor.
No baboon. The 14-pin SATRI Super Precision chip measures 14 x 30.5mm and can run on from ±3 to ±25 supply voltages. Voltage and bias currents are below 150mW. Input impedance is less than 10 ohms while output impedance is a colossal 100 mega ohms. Definitely not another lemming design! With the latest AMP 31, there's also a headphone socket, remote control and new industrial design to distract from pure hair shirt appeal. Forum chatter talked of SET-type purity. And there was excitement. Bakoon was finally available outside Japan. Visions of 47lab and FirstWatt perhaps?  
June 2012. For reasons I don't remember, that review never materialized. But some things are meant to be. Now I'd gotten a press release from Klutz Design's Michael Hollesen in Sweden. He had a spiffy new leather-covered headphone stand. Logging onto his site I spotted a link to Our Imports (Hifi). This led to Trenner and Friedl speakers and Bakoon Products Intl. The latter rang the bell. But I didn't recognize the AMP-11R displayed. Skipping to Bakoon's own website I realized why. The AMP 31 had been discontinued in December 2011. Obviously I'd not come across its replacement earlier. Perusing specs and glorious gutted pix, I noticed that the company still hadn't a single English review. Feeling cheeky or perhaps predatory—these days I barely keep up with review solicits and rarely do any soliciting myself—I asked Michael whether he'd be interested in supplying a review sample and thus end the English embargo.
He checked with Soo In at Bakoon Int'l. The response was "thrilled". We were on. Here was a product that on paper looked immaculately built, thoroughly unique and had a very interesting back story reinforced by a lengthy designer interview that hadn't been up two years ago. Now forget all about the AMP 31 above. It's been discontinued. Feast your eyes on its sleek two-box replacement: The AMP-11R and its matching external power supply are carved from Apple-approved solid aluminum stock. 10-watt power remains solidly on FirstWatt turf but 20dB of max gain make up. As a single-input integrated or amplifier with volume control there are conventional RCA voltage inputs and Bakoon's proprietary BNC current inputs aka SATRI-LINKs. A 100kΩ input impedance for the former and 3.68Ω for the latter paints the picture.
With RCK-11 custom rack
  Besides Cardas terminals there's also a 6.35mm headphone jack promising the perhaps ultimate headfi amp. Power consumption at idle is 10 watts, 50 watts at max. Dimensions remain suitably demure—a footprint of 195mm square, 40.5mm height—and weight is a combined 6.4kg. Not he-man but she-woman hifi. The gutted images show Ayre R-Series style construction. The photos above already hinted at the horizontal volume wheel if you paid attention.   Those studying up on Bakoon's website would quickly learn that the company has put out a steady stream of products since 1991. If 21 years later you hadn't heard of the brand until now, it's fully working testament to the owner's refusal of spending coin on silly marketing. He prefers to finance ongoing serious research instead. This led to the brand's silver bullet in the BPM-7120SP iteration shown as the central SATRI gain circuit which has since been upgraded to the EX version shown on the next page.
AMP-11R in black
As did Krell's C.A.S.T. interface, the SATRI-LINK relies on components equally outfitted. Current-mode signal transfer allows for 100-meter interconnects without any loss. Back in the real world of hobbyist home hifi—and given that Bakoon currently only makes a matching phono stage—you and me quickly forget about those BNC sockets and revert to our customary RCA plugs instead. Be sure though to set the selector switch to 'up' so you don't accidentally feed the SATRI-IC a direct voltage signal. [Triple audio show stack of EQA-11 & AMP-11R with Avantgarde Acoustic hornspeakers.]
An interesting claim for the SATRI circuit is the absence of any slew rate. The designer claims zero time delay or signal loss between input and output. Time in fact is his major obsession. It's led him to reject tubes and negative feedback. For that story do refer to his interview on the website. It makes for an interesting read. For yet more out-of-box thinking consider the mere existence of Bakoon's BPS-01 battery supply. It runs 4800mAh and 2400mAh Li-ion cells to output +5, +6, +9 or +12V (3 hours recharge for the first two values, two hours for the second two). Components like Apogee's Duet2, Lindemann's USB DAC and such can thus be flown solo without the usual tether from the power utility. A replacement BPS-02 is announced for July 2012.   Summing up, Bakoon crosses off a number of unusuals. While they had very practical 100-watt monos in the past [SHP-5516M at right], the present lineup was down to an exclusionary 10 watts. The DAC had disappeared. So had the AMP 31's remote control. And aside from the obvious SATRI circuit and quite radical marketing avoidance to remain below the radar, there was extremist circuitry packaged in highly stylized enclosures. Those two sides of a coin—audio circuit engineering and industrial design—often don't show up together particularly with small companies. Here Bakoon's Akira Nagai reminded me of Zanden's Kazutoshi Yamada. Both would ask why premium sound shouldn't coexist with visual elegance. This even extends to the company logo and clever tag line: For Ears and Years.
Socket identifiers are on the lower lip to face up for easier visibility
  I don't know about you but the longer this professional cynic of been there done that circled this wagon, the more he couldn't stop grinning. This was a badly needed breath of fresh air. Simultaneously it felt uncompromising to the core. A real find admittedly two decades late but hey, better than never.
Klutz Design system with Antelope Audio Zodiac Gold DAC and Trenner & Friedl Pharoah speakers.
  No wonder the industrial designers cum audiomaniacs at Sweden's Klutz Design took note and signed up for domestic distribution rights (which presently cover all of Europe save for Italy until other importers are added). What's more, the Klutzes only sell the Bakoon AMP-11R packaged with the matching miniature rack. It's so cool that giving you the option not to have it is not an option. Score another one for different and unusual. This included surprises. "The amp I'm sending you is the 'new' (from February) upgrade to 15 watts. I've asked Soo In to send me all the specifications if they differ in any areas other than output power. This upgrade includes not only new power modules [boards at left] but also the latest IC/SATRI EX circuit from Bakoon in Japan. It's a unit we've been demoing since April so it's well played/burned in." Who'd say no to a colossal power increase of 50%?   On the subject of Japan vs. Korea Bakoon maintains operations in either country—Michael provided the following: "Bakoon Japan is the progenitor of the SATRI circuit and focuses solely on the Japanese market. Bakoon Products Int'l in Korea is a JV (as far as I understand it) which develops products and sells them outside Japan. Bakoon Japan supplies the proprietary IC, product development is done jointly and the packaging and aesthetics are the sole work of Bakoon Int'l (Korea)." This explained the two sides of the coin.   Soo In Chae from Korea's Bakoon Int'l: "The SATRI circuits are the same but overall construction and parts choices between the two Bakoons—from small diodes to big transformers to power supply design like the battery supply (for our future converters and phono preamplifiers or already for existing products from other firms)—are all different. You could say that our products are more modernish inside and out than the Japanese equivalents. And yes, a DAC is in development. We plan to introduce it together with new high-power amplifiers. Hopefully this might be within the year." Soo In then relayed my remaining technical questions to designer Nagai-san in Japan.
Exicon 10N20/10P20 output transistors for one channel
Akira Nagai: "The AMP-11R has a single voltage gain stage. The SATRI-IC takes care of this since its gain level is determined by the ratio of input to output resistors (A=RL/L). Voltage signals from conventional sources incoming over RCA are converted to current by a Jfet buffer before entering the SATRI-IC (which is current input/current output). This input buffer converts impedance but adds zero gain. The push/pull class AB output stage is based on lateral Exicon Mosfets. Because those provide no additional voltage gain either, the ultra-wide bandwidth and low noise of the SATRI-IC are barely affected. This results in the very same high performance of our proprietary gain stage even at the binding posts past the output current buffer.
Headphone gain jumpers - medium as delivered* [pins 1+2=high, 2+3=medium, open=low]
* With Burson's DA-160 converter set to +6dB, HifiMan's notoriously inefficient 50Ω/83.5dB HE-6 planarmagnetic headphones with 3-meter Entreq leash already played louder on the AMP-11R's medium gain setting than I could tolerate. Standard 2V sources plus hi-gain mode will drive any commercially available headphone to all desired levels. For details I asked Soo In Chae: "Headphones use the same Mosfet output stage except that impedance gets converted by a set of high-quality resistors via the jumper settings. These resistors make the 6.3mm output impedance 33Ω (high), 56Ω (medium) and 89Ω (low gain). To calculate the gain level of the headphone output, use this simple formula: Ghd = Gsp x {Hdz / (Hdz+R)} wherein Ghd = headphone gain level, Gsp = speaker gain level (given as 20dB max), Hdz = headphone nominal impedance and R = headphone output impedance. For example, using the 'high-gain' setting with a 50Ω nominal headphone factors to 20dB x 50 / (50+33) = 12.05dB max. The power ratings are a bit more complicated. I'll just give you the final numbers for your requested nominal headphone impedance values using only the high-gain setting: 38Ω = 1.81 watts, 50Ω = 1.74 watts, 300Ω = 0.65 watts and 600Ω = 0.36 watts."
The stand's trays with receiver dimples are decoupled to provide lateral play for physical isolation
  "The outboard power supply contains a good amount of chokes. This means the circuit becomes a CLC filter to remove the AC noise of 50Hz/60Hz. You can expect all the other usual benefits as well such as separation of heat, vibration, magnetic fields etc. that may harm the main amplifying circuit's performance. The bandwidth of the SATRI-IC is determined by its bias current. The higher the bias current, the wider the bandwidth. Because the current signal is not limited by any other factors, there is no slew rate or need for negative feedback. Hence the signal is never returned to the input and suffers no time-domain degradation. "These factors result in the stability and performance of the SATRI circuit. The design goal of the AMP-11R was to provide the highest performance in a simple system. The removal of the remote controller and input switching circuit created more benefits toward this goal while sacrificing only a little convenience."   Use is as simple as connecting the 3-pin umbilical between both chassis; one standard power cord between power supply and wall; one standard RCA interconnect between main unit and source; speakers or headphones (inserting the latter auto mutes the main outputs); then flicking up the power mains on the left cheek of the main unit (the power supply is always on) and slowly opening the finely stepped volume wheel at the right corner. The tiny power LEDs beneath the fascia logos will glow orange for the black units, a classy white for the silver versions and nicely reflect off the mini rack's tiers. That's when one encounters the Bakoon sound for the first time. Would that bring home the bacon? On bacon and Bakoon, you certainly could fry the porcine stuff on it (but not on the power supply). Unlike gas stoves which go hot in a literal flash and instantly cut off, the AMP-11R is a modern full-contact burner. It takes time to heat up but stays so well after shutdown. Its class AB Mosfets direct-coupled to the monolithic chassis dissipate copiously. That's likely a function of compact form factor and perhaps also high class A bias prior to transition. Sonics are such hot stuff too that I doubt any experienced listener who'd recognize both status and rarity in the same breath would remain quiet, certainly not as deathly as the circuit itself.   I had suspicion of top-class excellence already in my night-stand headfi rig where the Bakoon made the first rounds whilst another assignment concluded in the downstairs system. That turned déjà vu when my FirstWatt SIT1 monos which had returned for a day of personal reset vacated the stands between the speakers. Amp stands duly piggybacked to host the singular but stacked AMP-11R in its own mini rack with integral ceramic ball bearings, I still could have supported four Bakoons on the HeartSong's slightly larger than standard surface. Don't let size fool you. The Bakoon is dead serious. Soo In's insistence that their showroom's Rockport Anka were fair game translated to my sealed Boenicke Audio B10. With dual opposed sidefiring 10-inch woofers loaded into a 12cm narrow wood enclosure, they're inefficient and current hungry. To appreciate one 11R highlight at max resolution simply requires a tweeter like the Raal ribbon with Audio Consulting transformer in my Aries Cerat Gladius. That's because Bakoon has one of the best top ends I've yet heard from transistors. But the bass-heavier mostly omni radiating Boenicke whose woofers reach well up into the midrange already crossed off maximally extricated depth dimension of each sonic event to produce very deep relief for holographic-type staging. Such specificity which chisels out the performers from the background to nearly render them freestanding rather than attached to sonic mass seems to mandate low phase shift/wide bandwidth. Very low self noise then also makes visible those subliminally embedded details of the recorded venue to cast space different from your own. On all those counts the Bakoon proved to be an ultra-resolution component. Without going into endless detail to make that point, I'll simply say that the only amp through my system which plays at that level is the Nelson Pass SIT1. Refer to its review for the long version.
Left column top to bottom: Esoteric UX1/APL Hifi NWO-M with Audiophilleo 2 | Trafomatic 101D | Bent Audio Tap X
Right column: 27" quad-core top-line iMac | Esoteric C-03 | Eximus DP1 | ModWright LS-100
  One unique feature of the SIT1 is its 2nd/3rd-order harmonic gear box compliments of that novel operating-point (bias) adjust. The Bakoon counters with something on the surface far more ordinary but in practice just as practical. The volume control. Precede the 11R with a superior preamp like Sasa Cokic's SM101Dn single-stage direct-heated triode line stage. It's a single-input amp after all. Now use Bakoon's horizontal volume wheel to assign percentages: this much preamp contribution, this much amp. Works splendidly. If you favor the peculiar elasticity I call waft & wane factor that seems intrinsic to direct-heated triodes, this maximizes it. Run your DHT preamp mostly or wide open, dial back the Bakoon a lot. Presto, more dominant valve flavor. However, Bakoon's circuit speed and lucidity are such that I'd personally be leery of preamps unless you had a similarly brilliant execution which will only contribute, not take away. Weighing down the 11R with ballast to drag along would really defeat the purpose. It's not a harmonically bleached sound by itself. The only thing it hasn't got—because transistors can't do it—is that tubular elasticity. Which can be injected if you fancy it but for just that will require a very special preamp indeed. My ModWright wasn't up for it.  
On not got, the only other item would have to be LF headroom. 15 hi-gain watts only go so far. I had zero complaints. But that's a townhouser speaking. Massive historical building walls notwithstanding, neighbors are on my mind. My hifi journey over the last four years has been about maximum satisfaction at lower to civilized levels (which I reckon must be true for many audiophiles). That means a very early curtain rise. Useful ingredients are minimalist crossovers, higher efficiencies and minimalist quick circuits to jointly come on song at low volumes. In the real world that's the most important quality a hifi must possess. Yet it's barely talked about. That's because most hifis aren't good at it at all. The Bakoon meanwhile excels. That's true resolution just as headphone listening had already indicated!
As with the SIT1, fanciers of premium SETs (there's a vast swath from mediocre to brilliant, most somewhere in the lower middle) should recognize the same type of electrifying immediacy. Naturally there are textural differences. Valves light up 'more reverb' by being more focused on the decay. Transistors go for the transients. Unlike much class D which acts overdamped particularly in the bass, the 11R is far less stiff if not as supple as an Emission Labs solid-plate 45. On microdynamic reflexes for lots of ripples atop plenty of small waves, the Bakoon once again matches a quality SET even though it's a push/pull class AB circuit. That needs to be put aside lest it predicts things like more amorphous mass and minor indistinctiveness which simply don't apply. Self noise here appears vanishingly low. Even on my 100dB Voxativ Ampeggio the Bakoon was inaudible. That's a major asset for low-level listening against suitably low ambient noise. If you enjoy entering the zone late at night while family members are already sleeping, the Bakoon makes for the perfect exploratory space pod. Back on treble and ribbons, the Bakoon is very pellucid and wonderfully adept at tintinnabulation which the dictionary tells us is the ringing or sound of bells. Metal molecules scintillating, upper piano keys tinkling, violin flageolet climbing the harmonic ladder, very short pan flute pipes overblown at max air speed to capture even higher overtones... these and similar events the R11 executes brilliantly without getting flashy about it. I think that nonchalance is the elimination of phase shift in the upper frequencies. While on personal thoughts, I think that the best of D/A converters and amplifiers have currently reached a type of impasse. Unless we get a technological breakthrough—speakers need this more than anything else—we seem to have hit the limits of the currently doable. In the low-wattage realm Nelson Pass' SIT1 and Akira Nagai 's AMP-11R strike me as being that and there. Curiously enough they have arrived by quite different means. Yet the path of either designer represents many decades of constant refinements and maturation. The chosen approach seems to matter far less than the right combination of vision (knowing where the peak is), talent (knowing how circuit/parts choices impact the sound) and stubbornness (constant improvements to claw up that mountain for a few more inches with each new iteration). The Bakoon is very lit up. That's prone to misinterpretation. Reading that most people's minds reach for the treble control and turn it all the way up. Not! This kind is lit up all over. Valve fans have their own word. Illumination. Having owned many valve amps, I relate completely. Yet this quite extensive experience also has me see a certain area of inside-out radiation which itself is surrounded by darkness. With the 11R there is no darkness. As such there's no radiation. Light shines from the outside in and leaves out nothing. That's not bright. It's simply fully unconcealed and exactly why it requires minimum SPL to hear everything.   The Bakoon AMP-11R is very advanced. If you're into Jonathan Ive, the Korean packaging looks like a million bucks. With lavish functionality for an amp—discrete voltage and current inputs, headphone output, outboard power supply, volume control, mini rack—it's starkly minimalist for an integrated (just one input, no remote control). Power is low but due to high circuit gain farther stretching than you'd think. Headphone drive in high-gain mode embraces all current designs including HifiMan's HE-6. Here it delivers the same superlative performance it brings to speakers. That makes it an ultimate and on expense an ulti(check)mate headfi amp. Of course driving speakers means this ultimate headfi amp comes completely free. Hey, time perhaps to strap on a pair?
with HifiMan HE-6, Entreq Konstantin 2012 cable and Klutz Design CansCan headphone stand
  The amp is preternaturally quiet for extreme resolution. Colossal bandwidth translates into utter absence of subliminal fuzziness because phase shift in the higher frequencies where all the harmonics occur is absent too (obviously that subject gets diluted by higher-order crossovers). That means very realistic convincing tone without artificial colorations. I can't comment on bass performance in the context of cruel speakers and high SPL. Common sense predicts obvious limits for any puny 15-watter. On my speakers bass was just right but didn't stand out as any particular specialty. That's because the performance impressed so strongly on a whole. If you've had good results with the kind of suchness a superior transformer attenuator can bring to the right party, migrate that quality wholesale on the Bakoon. If you've heard a top-class SET on perfectly matched speakers, ditto for the same communicative directness. Differences with valve amps remain but like FirstWatt's SIT1, the Bakoon comes as close as transistors can (and as would seem desirable to avoid their weaknesses of noise, current and bandwidth). Those with visions of Mosfet mist will need to clean their glasses. No such mist here. The only remaining question—to me—is how successfully the company will scale up their baby Bakoon's tremendous performance to the kind of watts the populace with inefficient low-impedance multiway speakers and a lust for high SPL needs. 100 of exactly these watts into 4 ohms would really throw a big rock into audiophilia's small pond. As is, the AMP-11R's diminutive dimensions and what in that context seems like a stiff tariff won't cause too many ripples. Never mind that present global distribution seems asleep behind the wheel. Which is very strange given Bakoon's 20 years in business - unless their stuff got this brilliant only recently. Either way it's here now and available for what on performance is a perfectly fair price. Had I not just acquired my silver pair of SIT1s; and had I not a perfectly presentable headfi system to can that justification too (damn!) - I'd be very sorely tempted to contact Korea for a silver unit. After 10 years on the job, recognizing true greatness isn't brain surgery. Even so it's still quite the wakeup call. Consider yourself called then. But are you awake? Over and out to sneak in a few more hours of listening before this 'as compact as possible, as high-end as possible' amp is due back...

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