| Originally Posted by Sugano-san Headphone Amplifier Review: Lehmannaudio Black Cube Linear 
Silver face plate Introduction The initial reaction I had when I first listened to music with this amp using my HD-650s was “Wow!” I was – and continue to be – quite impressed with this solid state amp. I will attempt to describe below why this is so. Lehmannaudio, a German manufacturer that has built up a solid reputation with products like its phono stages Black Cube, Black Cube SE and Silver Cube, is a new sponsor of our forum, and I feel honored that I was given the opportunity to pen a brief review of this elegant little amp for head-fi. Norbert Lehmann (the gentleman on the left, with his son David) together with “co-engineer” Klaus Böhm (according to Norbert a “superb project supervisor, pcb-wizard and - last but not least - down to earth audiophile”) are the designers of this very attractive 2004 addition to Lehmannaudio's product line. 
Norbert and David Lehmann (linked from the Soundstage HighEnd 2004 report) Construction The Black Cube Linear measures only 280mm x 110mm x 44mm and weighs around 1.5kg. It looks very nice, and with these measurements anyone should be able to place it conveniently in the vicinity of the source of choice for headphone listening. Have a look at this picture for a better idea of the Black Cube Linear’s dimensions: 
Two Black Cube Linears (linked from the Soundstage HighEnd 2004 report) Its finish oozes class, what with the nice front plate (also available in black with a black volume knob and white lettering), the tight fit of the hex screws (flush with the surface) that hold it in place (see picture above for a shot of the amp without the front plate), the way in which the Neutrik headphone jacks are installed flush with the surface, the massive knob (no pun intended), the input and switches on the back, the DIP switches (more on those later) and explanatory legends on the amp’s underside (no picture available), the elegant and understated lettering and the smooth feel of the Alps blue pot. 
Back view The gold-plated and Teflon-isolated pair of RCAs on the left is the amp's signal input (input impedance is 47 kOhms), but the second pair is not a "loop through" or second input, it’s a veritable pre-out. And the coolest thing about it is that it is switchable, too. The line out is switched off when the left headphone out is used, but the right headphone out has no influence on the line out! All this and more is explained in detail in the excellent user manual that comes with the amp and in shorthand on a sticker on the underside of the amp’s chassis. Of course both headphone output jacks may be used together, and naturally this works best with two headphones with identical or at least similar electrical characteristics (Norbert provided the example of HD-650 and DT-880). I did not audition the Black Cube Linear in its capacity as a preamp, as I only use integrated amps at home, but from what I read in the available reviews it must be more than capable of serving as the centerpiece of a purist single-source hifi system. Norbert told me that two more versions of the Black Cube Linear shall soon be released, one with a USB input, and another one with XLR inputs capable of accepting balanced signals (the amplification and headphone outputs, however, will remain unbalanced). The latter version will not have a line out, though. The Black Cube Linear uses an opamp-based first amplification stage (I was told by the manufacturer that the chip is the OPA2134), followed by a discrete zero global feedback Class A output stage to amplify the incoming signals. Its shielded mains transformer sits in a compartment at the back of the chassis; the neatly-designed PCB sits in front. I did not open the unit I reviewed, as it was a loaner and not my personal property, so I copied the picture below and some others from Lehmannaudio’s website, which is available in English and in German. 
Inside view The Black Cube Linear has a switchable gain of 0, 10 and 20 dB. The DIP switches are located on the underside of the amp, accompanied by stickers that clearly explain the meaning of the different switch positions. This allows the user to adjust the amp to the sensitivity of the headphones used, the strength of the incoming signals and to any preferences as to the usable range of the volume pot. A gain of 0 dB is more than enough to drive my HD-650s without the need to turn up the volume to max, and with a gain of 20 dB, I am not likely to increase the volume beyond 11 o’clock or so. These gain switches represent just another of the practical and intelligent features of this amp. The Black Cube Linear has an output power of 200mW into 300 Ohms (e.g., Sennheiser) and of 400mW into 60 Ohms (e.g., Koss). That should be more than sufficient for anyone. Norbert told me that the Black Cube Linear is also capable of driving the extremely power-hungry AKG K-1000s (within reason). I would conclude that AKG K-501s, K-240 DFs or any other not-so-easy-to-drive headphones should present no problem whatsoever for this amp’s power reserves, either. For the record, the amp’s output impedance is a low 5 Ohms. Lehmannaudio provide a calculator on their website, which allows calculating the maximum available SPL based on the individual headphones’ specifications and the voltage of the input signal. The amp’s manual contains a table with the recommendations of maximum exposure to different levels of SPL, which are based on German workplace regulations. Neat! Sound The first thing you notice when putting on your headphones is nothing. No hiss, no hum, no other noise, just nothing at all. Quite impressive. The manufacturer quotes a signal to noise ratio of >95 dB at 0 dB gain. The first thing you notice when playing some music, and also the characteristic that caused my “Wow!” reaction mentioned above, is the amp’s treble energy. There’s just so much of it, but in an entirely benevolent way. This is not like an EQ’ed sound where the treble is obviously boosted, and there is no sibilance either. There is just an abundance of treble that results in a very transparent and highly resolved and dynamic sound. I contacted the manufacturer right away and asked about his views on “burn-in” and the like. Norbert recommended leaving the amp on for some days, with a signal (I set the input selector on my amp to “tuner”) and the volume turned up, but with the headphones disconnected, and that is what I did. Sure enough, the treble became better and better integrated into the amp’s sound as a whole, and it ceased to stand out in the way described above. However, both the amp’s transparency and its resolution remained in place, and if someone asked me to describe the Black Cube Linear’s characteristics very briefly, these two words would be on my short list. The third word would be “control”, since that is another thing that strikes you immediately when listening to this amp. Due to its power reserves, as described above, it firmly controls the headphones’ diaphragms, which does not only result in a very open, informative, detailed and expressive midrange but in particular in a bass that is ultra-tight, very variable, really deep, but at the same time never, ever overblown or boomy. This amp is definitely not for those bassheads who have no appreciation for the finer things in head-fi. There is no lack of bass, but more than anything else it is of a "gentlemanlike" quality. I could imagine that the Black Cube Linear goes together very well with the Grado PS-1s. These headphones, which have a rather pronounced bass, should be combined with an amplifier which does not have a pronounced or boomy, but instead a very controlled bass, and which supports these headphones’ clarity and treble reproduction. It would appear that the Black Cube Linear belongs to this sort of amp, and the reviewer of the German magazine image hifi had nothing but praise for the Linear/PS-1 combination. My fourth and fifth words to describe the Black Cube Linear would be “balance” and “civility”. There is nothing that really sticks out in this amp’s performance; it does everything with a stoic approach that makes long-term listening (if desired) a non-fatiguing experience. It is refined, not rowdy. From deepest bass to highest treble, you always perceive a balanced and civilized way of dealing with things, effortless and liquid. If there is one noticeable characteristic then it is the treble energy. Even after the “burn-in” the amp retains a slightly bright timbre, an excellent veil-removing trait for headphones like the HD-650s, which it really wakes up and brings to life. This characteristic has pros and cons. On the con side, I noticed that the Linear has a slight tendency to draw attention to flaws in the recording (e.g., the tape hiss on the “Dark Side of the Moon” CD) or to vinyl surface noise. On the pro side, this thing has a way of revealing the finest details and of creating "images" by precisely and accurately positioning voices and instruments within the soundstage that I have rarely experienced before. This is very impressive indeed, and I would say that this quality easily outweighs the other effects described above. I received the Black Cube Linear shortly after I sold my Grado PS-1s. In order to provide impressions with Grado-style headphones, I had to resort to the next best thing in my possession, i.e. a pair of Koss KSC-35s hooked up to the amp by means of a Grado extension cord. I can confirm that the sound was surprisingly good for these cheapo earclips, and I conclude that Grado owners should be very happy with this amp, too. In fact, due to the Linear’s dynamic, yet balanced and civilized character and the absence of any sibilance in the treble, it is hard for me to imagine a pair of headphones that would not sound good when driven by this amp. The manufacturer claims “now you can hear the ultra transparent sound and the explosive dynamics formerly known only from electrostatic headphones”, and so I compared the Linear/HD-650/Mobius combo to my Stax Omega II set (with the tube energizer 007t). Unsurprisingly, the Stax is the clear winner, with an overall fuller sound, a sweeter and more charming midrange, and even more fine detail combined with less tendency to expose hiss or surface noise. But then, the Linear driving the HD-650s is no slouch either. But what am I doing here? Am I criticising the Linear for not being a Stax? Surely not, this is most probably an expression of my personal bias in favor of tube amps, as I also preferred the HD-650s out of the RKV, which has clearly less of the qualities that make the Linear such a transparent and resolving amp, but simply sounds a little more believable to my ears. But then, the RKV is a completely different design, and a much more expensive one, too. So, what about the Linear's competitors in the same price bracket? The Linear's recommended retail price is EUR700 (US-$780 in the States), and as it happens that's just about the same as that of a Grado RA-1 (in Germany anyway, where its r.r.p. amounts to EUR 670 [approx. US-$880 at today's exchange rate!]). How does the Grado RA-1 compare to the Lehmann, then? The answer is: it doesn't! There is no aspect of the Grado amp that could in any way compete with the Lehmann's respective characteristics. In particular the Lehmann's sound, but also its appearance, its functionality, its materials and parts, its built-in PSU, etc., make it the clear and unambiguous winner of such a comparison. Amendment, December 3: I just noticed that the Grado RA-1's price was lowered to approx. EUR500, which equals approx. US-$665 at today's exchange rate. Conclusion The Lehmannaudio Black Cube Linear is an extremely well-built and thought-out headphone amp with an elegant design that distinguishes it clearly from the many DIY attempts so often (and rightfully) discussed on head-fi. Its sound is dynamic, balanced and very transparent with very well-controlled bass, detailed midrange and an ever so slight emphasis on the treble, which is never obtrusive due to the overall balanced and civilized nature of the sound. It is clearly a solid state amp, and does not attempt to imitate a “tubey” sound in any way. To me that’s a good thing, because the amp does not only have a recognizable character, but it also plays all the best cards that a solid state approach has to offer. If your budget is EUR700 or above, you must absolutely listen to this amp, even if you are prepared to spend more than that. If your budget is a little below that threshold, you should consider the Black Cube Linear anyway; you may well find that it could be worth the extra mile. Any road, the Black Cube Linear represents an important addition to the market for headphone amps, and I am grateful that I could try it out and summarize my findings for you. UPDATE AUGUST 2005 After some more months with the Lehmannaudio Black Cube Linear I would like to report the following: Its sound has developed further over time and become even more pleasant. My overwhelming listening impression nowadays is that of an integrated sonic spectrum where nothing really sticks out. This applies in particular to the ever so slight, but formerly noticeable emphasis on the treble, which has all but disappeared to be succeeded by a general feeling of linearity, transparency and balance. What has remained are the Black Cube Linear’s previously mentioned qualities, i.e., its powerful and dynamic sound, its excellent bass control, detailed midrange and its civilized, non-obtrusive way of going about things. In addition, I understand that the above-mentioned USB version of this amp is well underway, which – in its own right – should make another interesting addition to the headphone amp market. An XLR input version has been announced as well. There are some posts by Norbert (norbert:lehmann) in this forum providing more details. Moreover, mounting brackets with which the Linear may be fastened to the underside of a desktop or the like will become available soon. Computer-as-source users will be able to enjoy excellent headphone sound by mounting the USB verison of the amp underneath their desks and in the immediate vicinity of their computers, for shortest possible cable runs. Finally, Norbert told me that a small power amp with 20wpc housed in an enclosure the same size as that of the Black Cube Linear is also supposed to be released later this year. You can position it next to the Black Cube Linear under your desktop and drive conventional room speakers with it, e.g. your desktop speakers (or K-1000's for that matter). That equals DAC, headphone amp, preamp and power amp plus excellent sound in two elegant boxes. Lehmannaudio continues to be a manufacturer to keep on the radar screen, and to me the Black Cube Linear is certainly one of the most attractive offerings in the solid state-segment of the headphone amp market. |
| Originally Posted by akwok How does this amp compare to the RKV modded (and unmodded) when using HD650s? |
