HPA-21 Review (6moons)

• reviewer: Srajan Ebaen & Wojciech Pacula • bedside headfi system: source - Apple iPod 160GB Classic, Pure i20, Burson Conductor - headphone amplifier - Bakoon AMP-11R - headphones - ALO Audio-rewired Audez'e LCD-2 and Beyerdynamic T5p - cables - Western Electric & Crystal • secondary system: source - NuForce Edition Oppo BD93, Sony Bravia TV - preamp - TruLife Audio Athena -amplifier - FirstWatt SIT2 or F5 - speakers - Boenicke Audio B10 - cables - Zu Event - headphone amplifier - Eximus DP1 - headphones - HifiMan HE6 or HE-500, ALO Audio-rewired Sennheiser HD800 • review component retail: $2.995
final rendering
As I'd put it in my Year 2012 Retrospective, my ongoing search for headfi, perfection had hit the amplification mother lode with Bakoon's AMP-11R. At $4.995 with a gorgeously machined mini metal rack, strapping this two-box class AB amplifier of 15wpc to my Audez'e LCD-2 seems overkill. Until you hear it. Whilst the law of diminishing returns kicks in heavy past Burson's $1.850 Conductor—we're well on the limpid side of twice the price, twice the performance—the Bakoon at the time was my ultimate headphone amp. But it's a lot more. Driving speakers copasetic with its power rating has it perform on the rarefied level of Nelson Pass' FirstWatt SIT1/SIT2. Via its voltage-mode inputs. To hear the full Monty will require using Akira Nagai's current-mode inputs. They will enjoy matching outputs in Bakoon's forthcoming DAC of course but just then featured exclusively on Bakoon's EQA-11R phono stage. Late in 2012, Soo In Chae of Bakoon Korea had told me about a forthcoming 50wpc stereo amp and 200-watt monster monos and another surprise that would hit even sooner: a dedicated headphone amp. "More and more people love the AMP-11R as headphone amp. We thus wanted a more affordable model superior even to the 11R for this specific purpose. With an output impedance close to 2.5MΩ, expect up to 1/10th the headphone distortion with the HPA-21's current-mode output. We believe this will be a true game changer. It's a larger one-box solution with internal battery power supply derived from our EQA-11R." With Polish contributor Wojciech equally smitten with the Bakoon integrated on speakers and headphones alike to bestow upon it his rare Red Fingerprint award, anticipation within our ranks over a new Bakoon anything was high.
Whilst Krell and darTZeel exploit current-mode transmission between components as Bakoon does, at the final barrier between amp and speakers they all must return to voltage drive to accommodate our regular multi-way hifi speakers with their reactive crossovers. The lone commercial exception I'm aware of is the FirstWatt F1 from Nelson Pass. Quoting from the F1 concept brief, "... in a power current source, an input voltage causes the amplifier to deliver a proportionaloutput current. Of course this same sort of thing would occur with an ordinary amplifier driving a pure resistance but a loudspeaker circuit is not purely resistive. It possesses numerous reactive elements, some due to inductance and capacitance in the electrical circuit, some from the reaction to motion of the voice coil in a complex mechanical system.
From the review: AMP 11-R and outboard power supply in black
"Fed by a voltage amplifier, the current through the driver's voice coil is not directly or instantly proportional to the input to the amplifier. Ordinarily loudspeakers are designed around this assumption but the 'pistonic model' of loudspeaker design assumes that the acoustic output mirrors the acceleration of the voice coil/cone assembly over a specific range. This is reflected by the current through the voice coil. The most precise way to develop that specific current is with a current-source amplifier. Such an amplifier ignores the impedances in series with the circuit, the resistance and inductance of the wire and voice coil and the back electromotive force (EMF) produced by the cone motion. Most speakers are designed around voltage sources but there are a few instances where a current source can be used to advantage. One of the best is the category of full-range high-efficiency drivers."
HPA-21 power supply board which sits above the following amplification board on standoffs, open space for the batteries.
That was our cue for today. Once you ask yourself what other loudspeaker is of high efficiency and uses just one driver, you arrive at headphones. Bakoon's HPA-21 thus can apply Akira Nagai's favored current-mode concept directly to the transducers. And since all standard over/around-the-ear headphones use but one driver, the HPA-21 has broader appeal for headfi than the F1 had for loudspeakers where only a very small percentage conforms to its concept.
As my review of the BPS-02 reported, Bakoon already had a clever supply solution which power-cycles two batteries for uninterruptible operation by charging one whilst playing the other. Would the HPA-21's rail voltages—likely higher than the 5V or 6V the BPS-02 puts out—allow for the same? And just how would its single-chassis casing be styled? Soo In had let slip that it wouldn't revisit the AMP-11R's form factor but grow in size yet sport the same exacting industrial design and finish standards.
Two HPA-21 amplification boards populated with parts
The same boards prior to parts population
"The Pass explanation does apply to headphonesand our HPA-21 just as suggested yet with 'phones, current-mode amplification has another big advantage. Most headphone drive units show an almost flat impedance across the audio spectrum to result in more stability and better response. Our battery supply for it doesn't incorporate the BPS-02 but EQA-11R circuit. That runs a dual-voltage supply on higher-voltage batteries just as you predicted. Here we use four cells in series to generate 16.8V. That's what Samsung SDI recommends as the max reliable working limit for their batteries. "This battery control circuit is as complex as the BPS-02's. Once again in the analog domain it must control the likely dissimilar behavior of two batteries simultaneously. To make this circuit non-stop would require a total of four Li-ion batteries plus the complex power-cycling control circuit of the BPS-02. This overreaches on size and budget for how we've targeted the HPA-21. This we shall save for the later DAC and another source model. [Akira Nagai's bench in Japan at right.]
HPA-21 passing a 100kHz sine wave
"During our HPA-21 prototyping we already achieved up to 7 hours of playtime despite its rich class A bias. This we consider sufficient for headphone listening. The automated recharging process cuts off during playback but starts as soon as the power switch is depressed. On finish we will consider a silver option but keeping stock in two colors can be difficult for distributors and dealers alike. We must first solicit their feedback.
First silver prototype case
"Our planned roll-out of 2013 products will be the HPA-21 in the 2 Series; the 50wpc AMP-51 and DAC-51 in the 5 Series; and finally the 200-watt AMP-91 monos in the 9 Series. Each series will feature a different industrial design yet share the same company identity as indicated by the HPA-21 above which incorporates key elements from the 1 and 3 Series (hence 2 Series). We will most likely apply the same idea for all new models. "One exception could be the AMP-91. This will be a cost-no-object design outside and in. For example it will have 8 power transistors, 16 drive transistors and more than 200 micro transistors for calibration and bias per channel. Hence we are planning on an equally impressive aesthetic and mechanical design to match this very ambitious circuit. "The AMP-91 will be very important for us and represent a monumental effort to sum up all of Nagai-San's circuit development history whilst introducing new circuits which over time will affect our future products along the way."
World premiere at the Highend Mässan 2013 Stockholm. Swedish importer Klutz Design and Soo In Chae both share my admiration for how well Bakoon and Audez'e combine.
Headphone amp from Bakoon Japan
Designer Akira Nagai on the HPA-21: "Speaker and headphone drivers produce sound by emitting vibration caused by electrical current flowing through a magnetic voice coil. Here the drive force of the voice coil F can be represented by this formula: F = I x B (force = current x magnetic field). As we see, the driving force is generated by current, not voltage. However, when driven by a voltage source with an impedance of Z, we use Ohm’s Law and substitute the above formula with this: I = E/Z (current = voltage/impedance) and F = E/Z x B. "When driven by a voltage source, now impedance affects the driving force. The value of Z is comprised of voice coil reactance, capacitance, DC resistance and contact resistance all of which exhibit non-linear behavior to cause distortion errors in the driving force.
"As the HPA-21 drives headphones with current, impedance doesn't factor into the equation. We can expect far lower distortion. Such has been studied by Dr. Yoshiaki Muda of the Department of Electrical Technology at the Nara University of Education in his 1996 paper Transient and frequency response of the moving-coil loudspeaker current-drive and voltage-drive method*. During his experiment he found that when a speaker was driven from a current source, he could achieve up to 1/10th its distortion. The HPA21's current output achieves the exact same behavior. The major drawback of current drive for loudspeakers is that whilst there are continuous impedance changes across all audio frequencies, the current-driving force remains fixed. Therefore the unit’s impedance curve becomes the frequency response of the driver. Because of this it is not appropriate to use current drive for most loudspeakers whose impedance varies too greatly.
Mechanical rendering
The abstract of this paper states that the "frequency response of the moving-coil loudspeaker in the current-drive and voltage-drive methods has been investigated. It is shown that for current drive the low cut-off frequency is f0=(k/m)1/2π and the high-frequency response is limited only by the cut-off frequency fA of the acoustic impedance of air. In voltage drive the frequency response is far more complicated. It has another high-frequency cut-off at ωRL=R/L along with fA where R and L are the voice-coil resistance and inductance respectively. For voltage drive when R increases, ωRL increases but Q decreases; when Bl increases, efficiency increases but Q decreases. In current drive the reduction of pistonic radius increases the HF cut-off frequency but any reduction of pistonic radius doesn't necessarily improve the HF response for voltage drive."
This first sample of the power supply PCB had a few mistakes to show some resistors and a capacitor above the PCB which final production corrected.
"Back to headphones, using a single driver of mostly constant impedance, we can safely adopt current drive with great results both on the bench and at the ear. The HPA-21 offers 6.3mm voltage and current outputs which may be used simultaneously. Then their current signal level becomes the same. Therefore even when driving a headphone with greater impedance variation, connecting it to the voltage output results in a variation of the output current (high impedance = less current). Due to this one can expect to automatically compensate the output level of the current-output socket when running two headphones at once.
Amplification board showing the four output devices per channel bolted directly to the undercarriage as monolithic casing heatsink and the two SATRI EX current-mode gain modules.
"Damping factor with a headphone amplifier is of less significance especially in current-drive mode. The formula for calculating damping factor is D=R/Z (damping factor = resistance of headphone/amp's output impedance). Since the HPA-21’s voltage output is about 1Ω, a 10Ω headphone encounters a damping factor of 10 whilst a 100Ω headphone sees 100. As we see the damping factor varied by a factor of 10. The HPA21’s current output is about 2.5MΩ. This renders damping factor effectively zero. Now the music signal itself becomes the drive current and it is unaffected by any other variables to generate much higher and more precise output drive."
Soo In: "We started production this third week of March. We redesigned the power supply board by meticulously studying all PCB patterns and planes to create an even lower noise floor. It's surprising how performance became even better than it had been at the Stockholm show. This took us a while but I'm very pleased with the outcome. Above is the final PCB from actual production. You'll notice quite a difference from the prior version. To the right are the final mother boards for the gain circuit. The other review unit out of two besides yours is currently in the USA with one of the organizers for the NYC headfi meet. He finds it excellent with the Fostex TH900 too and prefers this combo over the LCD-3. (The unit will go to Tyll at Inner Fidelity after the meet.) I've not yet heard the TH900 but like Denon 'phones based on Fostex drivers. Perhaps you'll have a chance to hear the Fostex TH900?"
final production
With the current-mode BNC-terminated Satri-Link connection even 100-meter long interconnects are claimed to suffer no signal loss. This overshadows usual advantages of balanced-line transmission, hence no balanced inputs. The absence of remote control reflects firm headfi focus where no wand is required. The lack of line-level outputs underscores once more that the HPA-21 was never meant to double as preamp and is a very narrowly focused extreme machine.
Soo In specified a fine Tokyo Ko-On Denpa 2CP Series 10kΩ attenuator with a resistive ladder circuit. He enjoyed not having to worry about internal EMI from a motor controller IC. Bakoon's advanced bias circuit is said to create thermal readiness in 10 minutes. This lays to rest concerns over wasting battery power for lengthy warm-up calisthenics.
With my first headphone on the desktop—Beyerdynamic's sealed 102dB/32Ω T5p—even at full left the machine still leaked sound. The next few millimeters on the volume control betrayed imbalance before both channels locked in. Then things got too bleeding loud a bare crack beyond. Low-gain current mode delayed this by a few more millimeters. Yet useful range with the Wyred4Sound mINT's fixed output was intolerably narrow. This couldn't be true. I wondered about the chosen taper. To see whether I'd chanced across an utter fluke, a pair of Sennheiser HD-800 off AURALiC's Vega were next. Those reacted just the same.
Soo In Chae: "I can see why this would be an issue. Your T5P seems to be the most sensitive headphone I've ever seen due to its low impedance and high sensitivity. I understand why they call it portable. As you already know, the Satri circuit takes a full 2V input signal and and controls gain in the output section. This is one reason why it's better than conventional designs which reduce gain at the beginning to sacrifice signal purity. But with our circuit, gain could be too high for headphones like yours. Please listen to the HPA-21 with your LCD-2 first. In the meantime I'll discuss with Nagai-san if there might be a fix for high-sensitivity headphones. Our Satri circuit determines gain by the ratio of input resistor at the voltage/current conversion just prior to the Satri IC to the output resistor at the volume pot right after the IC.
"The pot's resistance at minimum is small but it's still 2-3Ω. That's why there's leakage even at the lowest level. This is not audible with less sensitive headphones or speakers in the case of the AMP-11R. But it's there and you can hear it with highly sensitive headphones like your T5P. I wonder how many high-end users will use the HPA-21 with such headphones. If this is the case, we'd need to think about a design change. Otherwise the current gain level seems appropriate especially since you can adjust the output gain on the current output. And this we could easily change by simply switching the current output's gain-setting resistors. The voltage output gain level would still require a design change if at present it's too high." The likeliest fix for high-efficiency cans and/or high-output sources—4V outputs after all are quite common—will be to reduce lo-gain's amplification factor. My question was whether the attenuator's current taper might not still come on too quick across its first quadrant. This could be addressed with a 5kΩ pot. Here Soo In cited 8 to 10-week lead times for TKD to make this an option for the next production run. The gain resistors for lo-gain current mode could be changed right away.
Swapping in my favorite Audez'e from the nightstand rig hit true mute at the left stop in lo-gain current mode though hi-gain and voltage mode still leaked. But now the taper was more gradual and channel tracking perfect in all modes. The white power LED of my silver loaner confirmed a precharged battery. An hour later a red light appeared beneath the central toggle. This probably warned of impending power loss. True enough, a bit later the white light extinguished. Time for a full charge with the included SMPS wart and its figure-8 two-prong power input. Without listen-while-you-charge function, when the power goes out, it's lights out and concert over.
The four thin cork wavers mirror what goes for footers beneath the AMP-11R too. It suggests that like the latter's RCK-11, a proper decoupling undercarriage could be in the works. If a DAC-21 is planned to complete a current-mode Satri-Link'd headfi system—hello please!—one expects a similarly styled two-tier stand.Time to take the measure on sonics. Retreating upstairs into my dedicated headfi rig—160GB AIFF-loaded iPod Classic, Pure digital dock, Burson Conductor as DAC, Bakoon AMP-11R as headphone amp, Audez'e LCD-2—the superiority of current drive was plain. It was hard fact, not marketing fiction. The effects were super resolution and ultra clarity. This manifested as heightened simultaneity of intelligible detail. That's a mouthful. It means that by a simple act of attention, the tiniest feathered cymbal tick was as completely drawn out in its harmonic halo surrounding a clear physical action as were the forward-mixed main instruments and everything between. To illustrate, let's go into the kitchen. Cooking a stew we expect our individual ingredients to blend. This 'mushification' gives up the discrete separation of flavors we began with. We end up with a new group flavor. Perhaps it retains some layering which allows a professional chef to identify everything (or most) of what's in our stew. But in general it's a changed thing of considerable complexity.
This was very different. Very fine brush work on a cymbal's edge so minuscule compared to the louder bass runs and various other instruments was perfectly unchanged; just as though it'd been cooked (recorded) separately all by itself. This was true for each and every detail (microphone). By simply shifting attention, I could zero in and drill down on what each had captured as though in isolation and as a single track in the sound booth. All the ingredients were still neatly laid out like on a TV chef's kitchen counter. I could inspect each in all its complexity of harmonic shifts, string/wood components, air/finger pressure modulations surrounded by finger slides, key clacks or other giveaways. It didn't matter how far down the mix anything was, how subdued it was versus louder foreground stuff. It all was one massively paralleled event of discrete overlaid slides. I could decide which to inspect or whether to look through the entire stack at once.
In 'holistic' listening mode this was richer, fuller, denser and more colorful. In 'analytical' mode it was the ability to lock down on the tiniest item and see it clearly, then follow it unwavering and constant no matter what happened around it. Analytical mode on everything at once relies on a quasi-meditative state. Your mind can't get stuck to anything or you'll be out of the flow in that moment and as such out of the oneness that sees/hear everything. Should you be capable of such fugue vision, the HPA-21's astonishing degree of resolution supports it ideally.Bakoon would tell us that the cause was significantly lower distortion. That's about less interference. What's there as recorded substance is undisturbed, laid bare and made obvious. Easy. That's true and not manipulated resolution. With photography true resolution begins with a superior lens, proper lighting and a tripod. Manipulated resolution is corrective. It happens in Photoshop. It's artificial and routinely creates pixilation, unnatural saturation, color shifts and more. The HPA-21's higher current-mode resolution didn't sound like a trick, after-the-fact correction or enhancement. It sounded like a byproduct of less interference. Some disturbance or filter had been removed. And that made what was recorded sound better because I heard more of it. Despite the wordy abstractions, this was a simple outcome of lower distortion = higher resolution = better sound. And it begged a question. Why had Bakoon even bothered with their voltage output when current drive was so clearly superior? Was it as proof by contrast? Or perhaps not all headphones respond similarly well to current drive? Time to play musical chairs.
But first more background on 30-year old Soo In Chae. "My college major was in industrial engineering. My last job was at one of the most advanced inspection equipment manufacturers in the nano tech sector. We customized and developed products to meet client specifications. I sold one to a well-known German company which cost over €1.000.000. This had a lot of engineering challenges which I as product manager had to overcome with some of the very best engineers. During this time I learnt how to make a good product and how to collaborate with top personnel. This affected Bakoon Products International where I again work with possibly the best engineers to create something perfect or at least superior to the usual high-end hifi products. About four years ago I quit my last job. I was about to pursue a Ph.D in the U.S. Then I was fortunate to meet Nagai-san (I still was a customer) whom I considered to be the top audio/electrical engineer in the field. After I got to know him, I realized that I could become part of Bakoon. He felt the same and so I started my company."Along the way I found and was introduced to top engineers and suppliers with whom I now collaborate. We do not simply 'repackage' Nagai-San's Japanese products. Each time we release a new model, its circuit is more advanced than the original's. The HPA-21 vs. HDA-5210MK3 for example had the HPA-21's current output completely redesigned to perform better. Sometimes I do this also by upgrading parts. But I'm no electrical engineer. I don't get into too much electrical engineering myself. I understand enough to discuss with Nagai-san how to improve things. Then we have a Korean master engineer who develops measuring/inspection systems for Samsung factories all around the world. He develops or customizes auxiliary circuits to my needs. With him we successfully designed the perfect battery power supply for example."
My currently favorite speaker in Soo In's system. soundkaos and Bakoon would co exhibit at Munich HighEnd 2013.
A few days after my email about the gain, he had this: "I just wanted to update you that we made a quick fix which has lowered the low-gain level of the current output. With my Grado SR225 for example—not the most sensitive design but quite so at 98dB/32Ω—my 'normal' listening level with a standard 2V source now is around 12:00 to 1:00. This falls into the gradual range of the Tokyo Ko On and I believe clears your concern about the T5P or similarly sensitive 'phones. The fix was applied to all units we sent off today and I hope we've met more customer demands/situations with it."
For a personal overview on whether current mode was categorically better, I burnt through all the cans on hand. Curious whether the delta of difference would vary with load, I at first thought to qualify it with percentile numbers. But it turned out that things weren't quite as straightforward. Because the 4V AURALiC Vega sports 32-bit volume control, I trimmed up to 20dB of signal to expand the TKD's taper where needed. Source was my usual quad-core iMac with Audirvana 1.4.6 in integer mode 1 set to 352.8kHz upsampling. The Vega's clock was set to 'exact' and the digital filter to '4'.
Except for one all my cans preferred current mode. Even so the degree of advantage wasn't the same. Neither was the improvement always total. This latter qualification of overall better yet slightly worse in one aspect applied mostly to the HE500 and HE6 HifiMan planars. Their bass got looser. Especially with the HE6 this could approach bloated and a bit boomy. Of all my headphones I thought Fang Bian's most expensive to be the iffiest in current mode and not just on bass. To explain, let me paraphrase the key sonic difference. In voltage mode all surface textures of the musical action were matte. In current drive they grew shiny or outright glossy. Don't think artificial Las Vegas glitz. Think current Apple displays. They sit behind polished glass. Earlier computers used plastic. The latest-gen displays have keener contrast, stronger colors, blacker blacks and greater depth. That's current drive.
In my AMP-11R review, I'd characterized a lesser version of this effect as "lit up all over. Valve fans have their own word. Illumination. Having owned many valve amps, I relate. Yet this quite extensive experience also has me see a certain area of inside-out radiation which valves surround with darkness. And there is no darkness with the 11R. 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." I'd also said that "...fanciers of premium SETs—there's a vast swath from mediocre to brilliant, most somewhere in the lower middle—should relate to the 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. In the treble 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 it's undeniably the case that being lit up all over makes for an unusually informative truly exploded treble—and current drive in the HPA-21 is an even higher octave thereof or like turbo boost over the AMP-11R—there's no brightness per se. That's because this shiny very direct quality encompasses the entire audible range. It's consistent, not specific. I simply find the HE6 quite bright already to distinctly prefer the cheaper more efficient HE500. Here current mode especially at high volumes became too glossy then. And for me that crossed the line into hyper intense. Now paler mellower voltage drive didn't seem boring but welcome and more natural. This was the one exception to the general rule that current mode always beat out voltage drive - playing the HE6 at very high levels.
In my collection the headphones which underwent the smallest sonic makeover from current drive were the AKG K-702 recabled by ALO Audio. They sounded excellent either way. Meanwhile the ALO-cabled Beyerdynamic T1 and T5p truly maximized current mode as though they were the concept's poster children for a flashy campaign. The Sennheiser HD-800 also ALO-cabled showed less overall gains but in particular their bass improved. The ALO'd Audez'e LCD-2 also favored current drive but once more to a smaller degree than the Beyers. What surprised me with my favorite planars was how their well-known massively hung bass didn't get sloppy or overblown.
Answering my own question of why Bakoon even bothered with voltage drive, it's proof of concept and a built-in voicing option. Even though its colors are actually more muted, conventional voltage mode feels warmer. That illusion of warmth derives from reduced contrast. Current drive is more driven, taut, crystalline and ballsy as though transducer control had measurably improved. In those terms one could think of current mode as the day-time adrenaline option. That would make voltage mode the night-time comfort gear. Listening at very low levels makes current mode absolutely preferable. Its distortion is lower to increase magnification power and directness. You hear more with less.
Listening at very high levels and particularly to overcooked sizzly Pop makes voltage drive more forgiving and thus benign. In current mode headphones with a built-in forward treble balance will seem even more imbalanced. 1MHz bandwidth creates rise times and phase linearity that leave nowhere to hide. All of this goes places tube amps couldn't even dream of. Lest previous semi parallels to valves conjured up a sense of likeness, the HPA-21 in overdrive sounds nothing like tubes! To wrap up the question, having both modes isn't just a case of going beyond traditional voltage mode limitations by contrast. There will be loads, moods and music which make conventional drive preferable for various reasons even when preferable really doesn't mean better per se.
At $2.000 less than the fabulous AMP-11R but with novel current drive, headphones score appreciably higher with the HPA-21. In my personal hierarchy which is obviously limited by exposure, this parks the 21 atop the two-box 11R. That sat slightly above the Burson Conductor which sat atop the Eximus DP1. Illustrious company. Where the 21 adds usage over the others is with its built-in batteries. Connect Astell & Kern's iPod-crushing AK100 mini (preferably with Vinnie Rossi's mod to eliminate the stock 22Ω output resistors) and take your audio show on the balcony for some T&A. That'll be tunes 'n' air, preferably with rays.
In my ongoing 32Ω audio coverage, I've routinely said that the best way to participate at the very top of the high-end game is with headfi. Eliminate the room for more linear predictable performance. Shrink speakers to tweeters in housings, amps to a fistful of watts. This compresses budget by a factor of 10. Nullify neighbors and schedules. Anything goes anytime! To approach the HPA-21 driven from a Vega-caliber source would cost very big the other way. To equal it without professional room tuning is impossible. The closest I'd come would be with the same DAC, then adding €10.700 for the Nagra Jazz, €10.000 for the FirstWatt SIT1, €20.000 for the soundkaos speakers, €5.000 for the Zu Submission, another €5.000+ for cables, cords and power conditioning and another €5.000 for acoustic resonators+. And still the headfi rig's linearity and hence fidelity would be superior.
With all my talk of lower distortion, higher res and grippier drive, you'd be forgiven for wondering about sensory overload. From a sonic wallpaper perspective that abuses music as noise fill, absolutely! This is about hearing everything and in full color. That's very intense. Participation isn't desired. No polite invitation. It's demanded. At sonic gun point. Density of raw data packed into expanded space between your ears; maximized extension toward the frequency extremes; how direct, crystalline and unavoidably unmistakable all of it becomes... it all puts a fat lie to propaganda. There's nothing wrong with good old 16/44.1 Redbook. Once you hear the HPA-21 with a top can like the Audez'e LCD-2—I didn't have opportunity to sample the Fostex TH-900—you forget that greener grass on the hi-rezervation with its endless remasters of yesteryear's tunes. The Bakoon HPA-21 creates renewed appreciation for the 'ordinary' music we already own on ordinary shiny discs. It's a statement-level proposition at the very top of this game but for a fair price. Now let's see what Polish contributor Wojciech Pacuła had to say.
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When I returned from the Munich HighEnd 2013 show where Bakoon had made a splash enlarged by soundkaos' resourceful Martin Gateley who built them a wonderful temporary exhibit on the open ground floor, Klutz Design's first Swedish buyer of the HPA-21 had published his forum review. In it he compared the Bakoon to his Bryston BHA-1. He concluded that the latter would have to be relegated to those rare occasions when he forgets to recharge the HPA-21. Seeing how the Bryston is a well-known quantity, that was a useful data point. HPA-21 = end-of-the-road headfi amp.
Outside the soundkaos/Bakoon room in Munich with three LCD-3/HPA-21 listening stations
Prior to the show Trafomatic Audio's Sasa Cokic and compadre Mica Despotovich had announced themselves for a brief visit to Switzerland to deliver a custom phono stage to a client. We thus spent one afternoon in Villeneuve. Sasa's fave cans are the Sennheiser HD800. Hooked up to the HPA-21, I asked him which mode he preferred. Sasa favored voltage drive. To him it was more 'musical'. To my ears it's fuzzier, softer and gentler. But perhaps that's closer to the tube sound Sasa works with every day. The point is, folks could respond to what I view as the advantages of current-mode effect in different ways. Having both options really is a great idea.
Here's what Polish contributor Wojciech Pacuła has to say on the subject. The HPA-21 is the result of the incredible popularity of the AMP-11R used as headphone amp. Although its 6.3mm port would seem nothing but a convenience addition to its speaker outputs, many users including this writer began to treat this integrated amplifier as a very serious headphone amp. In this the machine wasn't alone. The Leben CS-300 integrated had gained similar popularity for headfi use before. My custom version of the Leben in fact had been my long-term reference headphone amp. Now I listened to the HPA-21 for almost four weeks non-stop. With the usual breaks to sleep, work and family life, I otherwise sat around wearing headphones even whilst writing. During these four weeks a few things in my system changed. With each change I became more and more convinced that the HPA-21 was one of the very best if not the ultimate headphone amp I knew regardless of price, technology or country of origin. At a single aural glance this Korean clearly showed each single change I made in my system.
If you remember my original review of the AMP-11R, you'll know that I found it to combine unheard-of purity with outstanding resolution which together threw open a window of unbelievable width. It was a stunning accomplishment. Now I revisited this effect by connecting my headphones to the HPA-21's voltage output. I thought that relaxing its requirements for the output section over the AMP-11R by not having to drive speakers whilst increasing the stability of its supply voltage with batteries had pushed things even further. Although this improvement wasn't large, I had an even clearer insight into the signal. This was one of the cleanest least colored sounds I'd ever heard from headphones.
All others including my beloved tubed Leben seemed tinted, voiced and somehow manipulated by comparison. And here I'm not talking about failed competitors but the very best of the crop like the Leben CS300 XS, the SPL Phonitor 2730, the Tonstudiotechnik Funk LAP-2.V3, the Ear Stream Sonic Pearl or the Phasemation EPA-007. Only the last one would come close on selectivity. The saturated Leben perhaps communicates better and has superior across-the-band fullness and a very natural bass. Yet none—and here I repeat, none of them—approached the Bakoon's current mode.
I listened to all my headfi amps on hand over a proper period, with various CDs, headphones, sources and cables. When I finally had to describe what I heard and returned to my Leben, I discovered in it something new which by contrast became even more addictive. After a few days back in its power, I felt ashamed that I had doubted it even for a moment. That said the Korean Bakoon HPA-21 became the first machine I listened to after which I had no need to return to the Leben. My custom version of the CS-300XS remains a wonderful piece of audio engineering. It's my beloved trinket with a ¼” hole if you will. I won't ever give it away.
Except that with the Bakoon I no longer had any need to analyze what I heard. This is probably a transitional state until I encounter something even better to change my mind and discover weaknesses in the Bakoon. At the moment however I don't see any. There of course have to be. There's no absolute sound. I still remember how the Siltech cables dethroned my Acrolink interconnects which I'd thought to be perfect. I'm painfully aware that the same thing will one day happen to me with the HPA-21 when I shall be amazed that I didn't hear it sooner.
But like the black slave said to Maximus, not yet. Right now I don't feel the need to analyze anything. With the Sennheiser HD800 this amp was supremely natural. It was of course also most differentiated, selective and resolved but none of these traits 'popped out' to vie for attention. The main achievement for me was the perfect balance between resolution and selectivity. The first quality is essentially infinite. The more the better. There's no such thing as too much resolution, too much differentiation. It simply becomes a partial virtue in the absence of proper tone but nonetheless remains the driving force to hear the natural and normal aural cues that resemble what we hear live.
How resolution portrays the difference between very small subdued sounds becomes selectivity. This ability to separate closely spaced or overlaid sounds is often confused with detail but is really an action whose measure must maintain proper balance. One can go overboard with excess selectivity. That destroys the illusion of live performers and leaves in its wake merely cheesy hifi. Here the Bakoon achieved a very rare balance. Its selectivity was very high but the various sounds didn't convince on their mere strength of isolated separation. In turn resolution was so unique that it felt smooth and silky despite the enormous wealth of raw information and detail it laid bare. Together these two factors produced far greater insight than any other machine to transcend the efforts of analysis and make it all easefully obvious instead.Despite its high selectivity—which in the wrong hands could have gone the wrong way—the HPA-21 was a joy with any CD no matter its pressing or mastering quality. They all were musically digestible. I heard a lot of previously unheard elements. But the real key to success wasn't the raw data extraction but the perfect harmony of color, space, imaging, solidity and tangibility. For a long time I listened to older recordings, particularly voices recorded in large churches. With their long decay times it's easy to miss things yet the HPA-21 brought them all to the surface. Whilst some recordings were more pleasing than others, none became unlistenable for their greater truth. When I ultimately decided that I'd rather not listen to some of these oldies it never was about the sound but rather the quality of the music.
The same was true with electronica and Rock, even the new releases of Daft Punk and OMD. I compared the Japanese CD version of Random Access Memories to its Naim 24/96 FLAC counterpart and clearly preferred the CD. Earlier Naim 24/96 or 24/192 versions had always had more detail but the stock box versions the better color saturation and palpability. Hence I preferred listening to the discs. The Bakoon showed these differences as though in passing. Dead obvious without making a fuss. This was a different quality because usually hifi emphasizes such differences and has us stop to notice them. The Bakoon just walked on by.Conclusion. My above comments focused primarily on the HD800. The reason was simple. This combination wasremarkable. I'm fully aware of the relative strengths and weaknesses of this German top model but its assets are far more important to me. The HPA-21 had me rediscover them all and even discover new ones. The amp played well with all the cans in my collection but the higher their impedance the better. My least favorite combo was the beyerdynamic DT-770 Pro 32Ω Limited Edition. A completely separate chapter were the planar HifiMan HE-6. I'm aware that many Bakoon users love the HPA-21 with the Audez'e planars. Here I can only say that after the Phasemation EPA-007 in balanced mode, the HPA-21 was only the second amp with which Fang Bian's top headphones finally sounded right. One day I'll come back to the Bakoon and the HE-6. For now I'll simply say that they were even more accurate and defined than the Sennheiser HD800. Their perspective was different too. Voices and instruments were closer to involve less of the recorded acoustic environment. The bass didn't extend as low either but had excellent definition. The Korean amp simply killed me with the HD800. I had never heard them as good safe perhaps with the Leben. Yet in this juxtaposition the Japanese was clearly colored and at times I had to switch in its 'bass boost' tone control to compensate for the lack of a given recording. The Bakoon never required any such compensation however. I never felt a lack of anything. I thus was most impressed. I'd never heard the Sennheisers this perfect before.
Wrap. With Wojciech's 2nd opinion confirming my own findings albeit with different comparators and listening biases to further expand context, an award really was the only logical conclusion. Wojciech felt the same and granted his own Red Fingerprint award for his Polish pages. Now it felt a bit silly to issue two awards. I originally suggested to simply consider his as shared between our two publications and quipped that perhaps that turned it into a blue fingerprint. Wojciech loved the idea. Obviously this distinction is going to be pretty rare. Both of our magazines will have to review the same item andindependently reach for an award. For now this one's the very first of its kind. Congratulations Akira Nagai and Soo-In Chae!

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