Whilst the final AMP-51R has four switchable inputs (2 x standard voltage-mode RCA, 2 x high-Ω current-mode BNC called SatriLink) and remote volume, it is no ordinary integrated but an amplifier with precision variable gain. That's not the same thing. It's not hair splitting either but conceptually more advanced and elegant.


If you weren't aware of Bakoon, they at first were a purely Japanese underground brand of inventor Akira Nagai. They subsequently expanded to exports to move above ground for the rest of us. This growth materialized when Soo In Chae of South Korea formed Bakoon International, contributed modernized cosmetics, circuit refinements, took over production of the global (non-Japanese) models and expanded the internal design team.


The 2-year+ gestation cycle of the AMP-51R was partially predicated upon insistence to marry circuit Zen to chassis Zen. They could have just used a macho case with visible heat sinks to avoid many headaches. Instead Soo In with his background in nano metrology was adamant. The design would be as compact and elegant as humanly possible. Another hold-up was the challenge to maintain the now discontinued AMP-12R's sonic purity. Scaling up its petite but superb 15wpc to a full 100 without sacrifices turned out a lot more difficult than expected. Yet Bakoon knew that to escape the perception trap of a fringe 'transistor SET' fit only for widebanders and horns, three-digit watts were key.

[At left, Bakoon's first exhibit at the Munich HighEnd show in 2013 with the AMP-12R and loudspeakers by Swiss/UK brand soundkaos.]


Of course team Bakoon appreciate that not everyone needs 100 watts; or their special future/retro display. The forthcoming AMP-41 will thus shrink to 40wpc, pack into a simpler case sans display or 'R' level circuit extremes but demand less than half, $8'500, whilst about tripling the 12R's power. As a flagship showcase for Akira Nagai's most advanced Satri circuit however, the AMP-51R wears the crown. With it, Bakoon hope to make a splash in the top sector of no-compromise hifi electronics. Specs supportive of such ambitions are <1mV noise at full gain, <1mV DC offset drift, 10Hz-500kHz bandwidth, three power transformers, 26/32dB max gain in stereo/mono, 700w max consumption and 30kg of mass all fitted into 42.5x46 x11.4cm WxDxH.


[Below we see the latest-gen purple Satri module with its many miniature transistors; the MCU-controlled 'volume control'; the power supply; and a pre-production unit in gun-metal grey.]


With my review loaner provided by Martin Gateley of soundkaos, I learnt that he considers not just the Satri IC but SatriLink intrinsic to the magic. Until I had my DAC-21 loaner, I'd never yet been empowered to exploit our AMP-12R's current-mode outputs.

Custom Plitron toroidal transformer.

As soon as I leashed up the DAC-21/AMP-12R in BNC fashion, Final's brilliant flagship Sonorous X headphones in the amp's ¼" port, I began to think likewise. The quality present already over the standard RCA connection deepened in a remarkable way. I was eager to transfer my initial headfi experiment to the main listening room. Gratifyingly, my DAC-21 loaner was authorized to stick around long enough to facilitate an all-Bakoon chain with the AMP-51R flagship powering various resident and loaner speakers in SatriLink mode. Bavroom.
 


"The small blue Talema transformer in front is dedicated to MPU and AC voltage detection and covers AC voltages from 95 to 253VAC. We developed a method to detect the incoming AC and change the transformer's secondary tabs in real time during play. This makes the power supply's regulated output voltage extremely stable despite AC fluctuations or sudden drops due to current load. We believe nobody else does this due to the complexity involved. The other blue Talema in front of the 36 caps is for the low-voltage circuits such as the Satri-IC and input buffers. The single pairs of output Mosfets—one per channel—mount to the bottom panel almost beneath the main PCB. The entire base works as primary heat sink, with two additional 'heat pipes' situated directly beneath those power transistors. These finned pipes float above the shelf as they're a bit shorter than the three isolation footers for better air flow [red arrow]. The shiny copper bars and side panels transfer remaining heat to the top panel. This becomes the second thermal dissipation area. With this 'clam shell' concept, the entire case operates as a heat sink. Low-impedance power delivery is ~160/200wpc into 4/2Ω stereo and ~350 watts into 4Ω mono. In bridge mode we don't specify 2Ω as that would run more than 350 watts continuous. The constant current source for the output stage bias insures that the Mosfets are always on. A similar concept was called 'super class A' or 'class AA' back when Sony and Technics tried to come up with new ideas. Our circuit improves bias stability of the power transistors to a whole new level."
 

Attendees of the Seoul hifi show March 3rd-5th had their own SatriLink op in room #317B where the DAC-21/AMP-51R duet sang with speakers by Sven Boenicke. In this photo, those keen of eye will even make out the AMP-41 with the big volume knob on top of the left rack though they won't spot its plastic remote.


The overlays at the bottom show how Keng Koe shrunk the AMP-51R's MCU-controlled attenuator. Barely bigger than an Alps pot, Bakoon have already created a tiny housing for this miniature PCB. Dubbed the ATT-01M, this digitally controlled super compact precision attenuator will become an eventual upgrade for the HPA-21 as well as suitable products from the Bakoon Japan range. This is but one example for how lengthy development work on their flagship spawned modular trickle-down tech for the smaller models.


On the appointed day, the van driver slid open his side door to reveal a sizeable flight case. Martin Gateley had customized it to fit his luxury property. It makes regular appearances in various of his soundkaos show exhibits to quickly trash regular cardboard. I warned our nice chap to watch his back. He looked a bit surprised. Once he began heaving the thing onto terra firma, he nodded gamely. "Whatever's in there is certainly well made," he offered. "What is it?" When I said stereo amp, his eyes ballooned. He doesn't know audiophilia from a donkey. Ireland isn't that kind of country.