Bakoon HPA-21: The Current Amp

Disclaimer: The review sample of the Bakoon HPA-21 was sent to us by Audionext.de, with the help of Soundconsult.nl and Mr. Soo In Chae, Managing Director of Bakoon Products International. The sample has been sent back to Audionext in Germany in the meantime.

Probably a whole lot of our readers have never heard of Bakoon, even though Mike reviewed the Japanese version of one of their amps not so long ago. Bakoon Products International is a South Korean company that was founded in 2009 in Seoul.  It was derived from Bakoon Products Co. Ltd that was established in 1991 in Japan and till 2009 the company’s products were selling only in Asian territories. Bakoon Products International was founded to broaden the horizon for promoting products outside Asia. Their latest creation is the HPA-21 Headphone Amp and I discovered it when visiting Canjam in Essen last September.

The Unit

Packaging has never been our thing and while the –I will shock you right away – 2.995€ amp comes in a nice box with a fancy bag, there’s nothing special to report for this price class. They could have done something extra special, I even expected it maybe, but personally I don’t really care as you’ll probably never use the box again, right?

The unit itself looks great and that actually was the first thing that attracted me at the meet. I find the design gorgeous. Simple but great and I wouldn’t mind having this in my living room at all as build quality is extremely good and the materials used are top notch. It has a small footprint measuring only 195mm x 237.5mm x 55mm but you’ll be surprised picking it up as it weighs an impressive 4.5 kilograms.

The back of the unit is not that special. There’s the power connector, a pair of RCA inputs and a pair of Satri (BNC) inputs. There is no balanced input and I can understand it’s technically not needed with the Satri inputs but a lot of people will have a balanced out and not a Satri connector and expect balanced anyway at this price level but ok, let’s forget about this for now. On the front there are two regular headphone “outs”: one using the voltage circuit and one the current output. There’s a switch to select what input to use and a gain switch for the current circuit. Oh and the extremely smooth to turn, perfectly balanced and dead quiet volume control of course.

As the previous paragraph mentions, the HPA-21 amp is based on the Satri-principle and it isn’t designed like the usual solid state amps are. Power output of the HPA-21 is 1W (50Ohm, 1kHz) but if you’re interested in the technical aspects of a Satri design, click here or do a search on Google or Wikipedia and read all about it. We don’t want to get too technical in this review. The Japanese Bakoon HDA-5210mk3 that Mike reviewed also had a Voltage and Satri/Current circuit.

Besides this mysterious Satri design, another big feature is the internal battery. It is said that the best or better, cleanest sound is achieved when using batteries and not a power grid. The HPA-21 has an internal battery that charges 80% in four hours (6 for a full charge) and lasts you six and a half hours. Unfortunately the battery does not charge when playing, of course surprising me in the middle of a session. A battery also means it will die over time and Bakoon guarantees 500 recharge cycles for the battery to reach 80% lifetime capacity. The 2 battery packs are replaceable though from what I read on the web. Another big advantage of the Bakoon HPA-21 is it only needs 10 minutes of “warm-up” before being optionally functional. Eat that, tube amps ;-).

 

The sound

While the HPA-21 does have 2 outputs I’m not sure you can use them both at the same time. I quickly tried but sound quality decreased immediately, so it was a one minute experiment.

Don’t let the 1W output number fool you, the HPA-21 is incredibly strong and loud. The voltage out is the loudest and with a high impedance headphone you can only turn the volume dial for a few millimeters. The current out on low gain is much better and more normal to listen to. Not only is the voltage output very loud, it also sounds very aggressive. I couldn’t really get to liking it with any of my headphones because of the Current out / Satri circuit being so good. I wouldn’t call the voltage out bad but compared to the current out or other solid state amps like the Violectric V200, it just isn’t up to the same level. With the Bakoon HPA-21 the current out is what it is all about. The best sound quality is achieved when using low gain (isn’t that mostly always the case?) and high gain was only “needed” with the HE-500.

Is the current output really that good to make you forget about the lesser voltage out? Yes is certainly is! The HPA-21 (current out) has the blackest background ever and the sound stage is very good but not the widest ever. It is extremely clear and very detailed (lots of lovely micro details at this level) in a good way. I’ll for sure miss these micro details as none of my other amps achieve this level. The HPA-21 is a very musical amplifier that doesn’t overanalyze, while you get a lot of details and micro details the focus always is on the musicality and it is not over-analytic or dry because of that. Some people don’t find this amplifier musical but I really can’t agree with that because it surely is (I mostly used Jan Meier’s Daccord DAC as source). Left-right separation and 3 dimensionality aspects are truly excellent. Every single note has a lot of timbre and you get a deep sound stage with a lot of layers. The HPA-21 has an airy laid-back sound where there’s a lot of space between the instruments. The amp never distorts at any volume and the more you listen to the Bakoon, the better it gets.

Bass, mids and highs are not influenced or boosted by the amp, it doesn’t really color the sound to my ears. Yet at the same time it doesn’t sound like another solid state amp either, in a good way. Don’t get me wrong you can clearly hear you’re listening to a very good solid state amplifier and not a tube amp but it has this laid back sound with a touch of smoothness. It is a fast sounding amp with great attack that’s very easy on the ear.

The result is a very linear sound from bass to highs and nothing really stands out. Bass has a good kick, is extended and has the right amount of body while being very tight and detailed. Same more or less goes for the (micro) detailed and layered mids where you won’t miss anything. If I have to make one remark I could say the treble extension could be even further/better, but that would be me nitpicking.

I’m very impressed with its sound to say the least: detail and timbre are very impressive. I kept getting goose bumps all the time and after all these years this amp still revealed some micro details I hadn’t heard before in Leonard Cohen’s recordings for example.

 

Headphones

I mostly used the HE-500, LCD-2 and HD650 (and T90) with the HPA-21. Most people in the market for one of these amps will be using headphones of this level and -with all due respect- not a Beyerdynamic COP for example, so the focus is on these headphones.

The Current out is definitely the way to go when using all these headphones. Smoother, less aggressive and relaxed sound with gorgeous detailed and layered deep bass. Good soundstage.

The Hifiman HE-500 was best with the high gain setting but you could also use the lower gain one. With the LCD-2 it was the other way around: low gain is best but high gain is doable. To me it is clear this amplifier was especially made for orthodynamic headphones, it makes them sound their absolute best. Also the HPA-21 wouldn’t have any problem powering the most power hungry cans like the HE-6, although I didn’t have one at the time to test it out.

Beyerdynamic’s T90 high impedance headphone however is not suited for the current output. At the same time the Voltage out makes it too aggressive sounding, missing body mostly giving it a thinner sound. Something the T90 doesn’t need. It needs a warmer amp with good body like the V200 and especially tubes. The voltage out is very loud and very aggressive and I’m not really a fan of this combination.

On the other hand the Bakoon sounded extraordinary with another high impedance headphone, the Sennheiser HD650. You can only use the volume dial ever so slightly but you get an excellent sound as it by nature is a darker sounding headphone. Both outputs can be used, and depending on if you want a slightly smoother sound or not you can switch outputs but watch out with the volume dial or you will blast the drivers back to the Sennheiser factory in Ireland. A really wonderful combo and I’m sure I have never heard my favorite HD650 to sound this good with a solid state amp! Mike has told you a lot of times the HD650 scales up very well, this amp proves his point (again).

 

A Gem

So is there really nothing bad to report? Yes and no.

Yes, because it is very good with a selected number of headphones but not with all. Plus, the voltage output while being good isn’t as good as the current out. And then there’s the loudness, be careful with the volume dial.

No, as the sound truly is exceptional and beautiful. Get the setup right and you will constantly be in audio  heaven, I can give you that. Audeze didn’t partner up with Bakoon and this amplifier for their LCD headphones for nothing, it is incredible. I will for sure miss this level of sound reproduction. Music just has so much feeling it’s hard to express.

So here’s the weird thing. Would I turn in my Violectric V200? No, I wouldn’t. The Bakoon is extremely good with the planars and the HD650 and probably a bunch of other headphones too but the V200 is just good with a whole lot more. Sound quality wise the Bakoon is quite ahead of the V200 but as a reviewer I need an amp that does all the headphones. Then again, if you just need an incredibly good amp for your orthos, don’t look any further. Get it immediately and you’ll be sold for life. You’ll be amazed how it makes your headphones sound. I promise you that.

Together with ALO’s Studio Six and the Leben CS300XS (which are both tube amps), the Bakoon HPA-21 using the Satri out is the best sounding amplifier I’ve ever listened to using the Audez’e LCDs. The Bakoon HPA-21 is available for 2.995€/$2.995 directly from Bakoon International or through their dealer network, like Audionext and Soundconsult.nl

EDIT: After I published the review, Mr. Soo In Chae sent me this info:

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 HPA-21’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.
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.

 

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Lieven is living in Europe and he's the leader of the gang. He's running Headfonia as a side project next to his full time day job in Digital Marketing & Consultancy. He's a big fan of tube amps and custom inear monitors and has published hundreds of product reviews over the years.

25 Comments

  • Reply November 16, 2013

    John123John

    All I got from that was “Where’s the Leben Review?!”

    jk great review. Lol I honestly didn’t notice the functions (seems pretty interesting) on the HPA21 but I was more interested in the headphones at the time. Though as you said before, there is a reason Audeze pairs the headphones with this specific amplifier.

    I kind of hate that there isn’t alot of possible movement on the dial, as with many headphone amplifiers. I guess that’s what current and voltage outs and impedance switches are for. Could you clarify something technical for me: Does that mean regular headphone amplifiers are neither voltage or current outs but like regulars outs? I hope the meaning is clear though my explanation is terrible.

    • Reply November 16, 2013

      Mike

      When I did the Japanese Bakoon review, I also couldn’t get a clear explanation on what Current and Voltage out means.
      Regular headphone outs, and all headphone outs that work should have both voltage and current element.

      • Reply November 16, 2013

        L.

        I’ll post technical stuff later sent to my by Bakoon this morning

  • Reply November 16, 2013

    MassiveTurboLag

    It’s probably for the best that you didn’t try it with the COP. I highly doubt it has the muscle to drive them anyway.

    • Reply November 16, 2013

      L.

      Barely probably

  • Reply November 16, 2013

    L.

    Bakoon also wonders if I didn’t receive a High Gain Demo version in stead of the “normal” version because of the Voltage out being so loud, it’s under investigation

  • Reply November 17, 2013

    Dave

    It’s a big shame that author didn’t have a chance in trying HPA-21 with HD 800. I don’t think there’s another amp out there that can do the same magic with those Senns. Look, I’m aware that you might not have HD 800 on hand and that’s fully understood. But HPA-21 is considered as the best one for HD 800, no matter the price. Audio-Gd Phoenix, that was claimed to be nice combo with HD 800, compared to Bakoon HPA-21 sounds, well, couple classes below.

    • Reply November 17, 2013

      L.

      If everyone else is saying the Bakoon is the best for the HD800, I’m glad I didn’t use it, would have been too easy.

      But seeing how well it performed with the HD650, I can very well believe there’s magic with the HD800 too. there certainly was with the LCDs

      • Reply November 18, 2013

        Dave

        You don’t know what you’ve missed :E

        But cool, I understand. Two major things with that setup is excellent smoothness and, finally, bass. Best lows in HD 800 so far, at least for me.

        Anyway, thank you for answering. Take care.

        • Reply November 18, 2013

          L.

          Thanks, you too. enjoy the amp!

        • Reply June 9, 2014

          STARSTERN

          ok will take your word about the HPA- 21

          but in order to put leverage to what you are saying ,

          will need to know whether ,you ever compared it to a cavalli gold /or to a masskobo 394 / or rkv mark II / or to HPA -21 japanese version http://www.head-fi.org/t/64905

          and in top all of these the HPA-21 you talk about still shines out above them to drive well the hd800 in all respects >?

  • Reply November 22, 2013

    STARSTERN

    am I better off in terms of sound quality ‘to get a amp and to get a dac rather then a combo amp/dac ??

    CEntrance Inc. DACport LX
    which amp/cac would meet that quality dac ?

    • Reply November 22, 2013

      Mike

      Usually if the DAC has a built in amp, you’ll get better value than getting a separate amp. If you don’t have a particular target for the kind of an amp you want, go for the one with a built in amp. One day when you know what sort of an amp you need, then get a separate amp.

      • Reply November 22, 2013

        L.

        True, but imho separate components are better, and more expensive

    • Reply November 22, 2013

      dalethorn

      My feeling is you should check your actual options for sound quality if separates – make sure the DAC and amp are a good match and are of equal quality. Also consider cabling, and whether that could compromise the sound. High quality (and short!) interconnects are important. When it comes to the combo DAC/amps, there’s a lot to choose from.

  • Reply December 10, 2013

    STARSTERN

    are you in any schedule to view the new generation amp by bakoon

    http://www.head-fi.org/t/649056/lightbox/post/10051149/id/991600

    • Reply December 10, 2013

      L.

      Maybe Mike can get these Japanese versions. The HPA-21 is Korean Bakoon.

    • Reply December 10, 2013

      Mike

      Not at the moment.

  • Reply December 27, 2013

    bmichels

    Have you tested the HPA-21 with the TH-900 ? Is it also a VERY-Good match ? Better than with the TU-05 🙂

    • Reply December 27, 2013

      L.

      no I haven’t. 2 different reviewers 😉
      You live in Brussels right? we should get together for coffee one day

    • Reply September 17, 2014

      Andy Q

      I find that if you pair that combo with a dark DAC, the whole sound is far too bassy. I ended up selling my TH900 because all my DACs at the time made the combo too bassy to bear. This is coming from an ex-basshead.

  • Reply March 30, 2014

    bertrand

    Thank for your previous answer.
    Also could you tell me if you tested the HPA-21 with the AlphaD0G. An AlphaDog distributor told me that the synergy was not that good… ! 🙁

    • Reply March 30, 2014

      L.

      I don’t have the amp anymore. I would be inclined to believe your dealer though

    • Reply March 30, 2014

      dalethorn

      Out of curiosity, what did the dealer recommend for the Alpha Dog?

    • Reply September 17, 2014

      Andy Q

      I got that combo (alpha + bakoon), tried it out and I concur. Bear in mind that this is to my tastes. I found the voltage out to add much needed kick to the bass but the treble was hard and harsh. The current out smoothed the treble but bass was too soft. Couldn’t find a nice balance.
      Put my T1s back on (current out) and it sounded much better. I sold the Alpha Dogs the very next day.
      A surprising thing is how good Voltage Out sounds with some IEMs (eg. RE-400). I had no idea a humble RE-400 could sound THAT good until I plugged it into the Bakoon’s Voltage Out. Soundstage, bass, separation. The works. TWFK based IEMs may sound too harsh. My customs did.

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