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Reviewer: Srajan Ebaen
Financial Interests: click here
Source: 2TB iMac 27" quad-core with 16GB of RAM (AIFF) running OSX 10.8.2 and PureMusic 1.94g in hybrid memory play with pre-allocated RAM, Audirvana 2.01 in direct/integer mode 1, Metrum Hex, SOtM dX-USB HD with Super-clock upgrade & mBPS-d2s, AURALiC Vega, Apple iPod Classic 160 AIFF-loaded, Cambridge Audio iD100, Pure i20, Pro-Ject Dock Box S Digital, RWA-modifed Astell&Kern AK100, Aqua Hifi La Voce 2 DAC
Headphone amps: Bakoon AMP-12R, Eximus DP1, Questyle CMA-800R [on loan]
Headphones: Audeze LCD-2 with ALO harness, Audeze LCD-XC [on loan], Oppo PM-1 [on review], Sennheiser HD800 with ALO harness
Powerline conditioning: Vibex Three 11R, Furutech eTP6
Equipment rack: Artesania Exoteryc double-wide three tier with optional glass shelf, Rajasthani hardwood rack for amps
Review component retail: €1'500 + VAT or $1'795


It's Bakoon not bacon. Just so the Japanese/Korean firm's triple-awarded HPA-21 headfi amp brought home the porcine stuff in a big way. For its $2'995 sticker it should have. Now the new smaller HPA-01 sibling clones its recipe to success but obviously downscales to hit the significantly lower $1'795 sticker. Soo In Chae: "The Satri input circuit of the HPA-21 is simplified. It is now fully integrated into the motherboard. The buffer stages changed from JFET to bipolar. The output stage is the same but its bias was lowered by about 50% due to parts changes and smaller heat sinks. Output power is 1 watt into 50 ohms."

Companies like Krell and darTZeel have promoted current-mode signal transfer between components to eliminate the usual losses from unpredictable cable interactions. Yet their actual speaker outputs are always voltage mode to match the requirements of modern multi-way speakers. Nelson Pass' FirstWatt F1 amp was the very rare exception to operate in transconductance mode all the way to the speaker terminals. Hence its primary intended loads were no-xover wideband speakers. Because most headphones mimic that breed with their single driver and no electrical filter, Bakoon's Akira Nagai—who for decades had worked in the current-mode domain with his patented Satri discrete op-amp—authored the HPA-21 whose primary output also is high-impedance current mode. Whilst Alden Zhao's Questyle Audio CMA-800R exploits current-mode gain between input and output as does his domestic competitor Audio g-d, their machines rely on conventional voltage-mode outputs. To this day that decisive difference made the HPA-21 unique. Until now. The HPA-01 exploits the very same concept and audible advantages.
This Munich 2014 photo shows the black HPA-01 atop the bigger HPA-21 and the eliminated BNC-carried current-mode inputs.
Because Bakoon still haven't introduced a digital source with current-mode outputs to match their costlier gear's inputs, the HPA-01 only gets one conventional voltage-mode input on RCA whose connected source sees 10KΩ. Two 6.3mm headphone ports offer both voltage and current outputs simultaneously. The very rare load that's not better driven from the current output can thus be run off the conventional port. That also makes for instant proof of concept when the majority of headphones sounds clearly better over the unconventional port. In signature Bakoon style frequency response again is an ultra-wide 10Hz-1MHz for speed and zero HF phase shift. Battery power for "deathly quiet operation" is again from eight Li-ion cells here good for about 10 hours of play before needing 6 hours of recharge to full or 4 hours to 80% capacity. At 16x22x3.3cm WxDxH and 2.5kg, the HPA-01 is compact and quite light. To control build costs with simplified parts inventories, the only available finish is black.

With its $5'995 AMP-12R stable mate my designated headphone driver on the night stand fronted by Aqua Hifi's La Voce 2 DAC, how would the newcomer battle this 15wpc speaker integrated whose 1/4" socket obviously isn't its primary app but which works so well into my Audeze LCD-2 that I've not felt the itch to change? If it was anything like the HPA-21, I expected a draw or minor advantage for the 12R in voltage mode and a victory for the HPA-01 in current mode. How about the CMA-800R when the Bakoon was used in voltage mode to level the playing field?