Headphone Bliss: B.M.C. Audio amazes with PureDAC
by John Grandberg
What does it take to separate a piece of audio equipment from its similarly priced peers? Is it based purely on sound? Features? Looks? Or, ideally, a combination of all three? Us writers are always talking about this or that category being extremely competitive … but the reality is that nearly every category, at every price range, is jam-packed full of great options. Budget DACs? I can name half a dozen under $1k that I highly recommend. Headphone amps? There’s a really good one at every price level you can imagine. Monitor speakers? That category has been contentious for decades. What’s a company gotta do to really stand out? Is it even possible given the sheer volume of competition these days? Keep in mind, all these standouts exist in a sea of decent, mediocre, “also-ran” gear, to say nothing of the lesser products out there.
German firm B.M.C. Audio believes they can separate themselves from the pack. True to their name — Balanced Music Concept — the company aims to tick all three boxes in spectacular fashion. The name involves a bit of wordplay because B.M.C. has a strong preference for balanced circuit designs. See what they did there? Balanced? As in well-rounded? Versatile? I think you get the picture.
All puns aside, B.M.C. brings considerable resources to bear on their “budget” model. Selling for $1,790, the PureDAC is a far cry from being “cheap”, though in relation to its B.M.C. siblings it’s rather affordable. Their next most affordable model is the MCCI phono preamp at nearly $4K, and it goes up from there, reaching $16K for a pair of M2 monoblocks, or up to $40K for the Arcadia speakers. Check out Scot’s coverage of the B.M.C. room at CES 2013 for some good pics and video, and see the rest of the line at Aaudio Imports, the North American distributor who was kind enough to loan me a unit for several months.
Having already discussed the double-meaning of the “Balanced” in B.M.C., I feel justified in taking my linguistic analysis a bit further. I’ll go out on a limb here and say the “Pure” in PureDAC isn’t referring to functionality, but rather addresses sonic properties. When a DAC has multipurpose functionality such as a very high quality preamplification and headphone amplification on board, one can’t rightly call it a “pure” DAC anyway – at least not by the obvious meaning of the word. Let’s explore those extra features a bit before we delve into the “purity” aspect.
First off: Build quality. General aesthetic design. Good golly, this thing is nice!. I’ve owned quite a few DACs in my day – must have over half a dozen on hand at any given moment – and I’ll venture to say the PureDAC is in the absolute top percentile when it comes to fit and finish. It does not feel at all out of place sitting next to Esoteric and Chord gear, both companies being highly regarded for their design and build quality (and both units having considerably higher prices). If I had to guess purely on looks alone, with no prior knowledge of the device, I would have thought the PureDAC to be at least double the asking price. Seriously — take a look at the pics from the B.M.C. website and see if the PureDAC looks any less impressive than its more expensive siblings (hint: it doesn’t).
Next up: Features. The PureDAC has a lot of ’em. Inputs include the usual coaxial and Toslink, plus AES/EBU, all capped at 24-bit/96kHz due to B.M.C.’s choice of digital audio receiver. The focus here is decidedly USB which is about as bleeding-edge as one could hope for. It’s an asynchronous solution (based on the XMOS chipset) with PCM support up to 32-bit/384kHz, while also supporting DSD64 and DSD128. With a few wacky exceptions (DSD256, largely a marketing exercise at this point), that’s pretty much everything you could possibly want, and it makes the PureDAC about as future-proof as digital gets these days.
There are technically 5 outputs to be found here. The obvious are the RCA and XLR outputs on rear, plus the 1/4″ and 3-pin XLR headphone outputs on front. Less familiar is the “B.M.C. Link” on back which consists of dual Toslink optical outs. These would come in handy when pairing the PureDAC directly to a B.M.C. amplifier but are not utilized for any other purpose.
B.M.C. seems to like giving acronyms to their various technologies: at play here is DIGM, for Discrete Intelligent Gain Management. Instead of a pure digital volume control, DIGM makes use of digital control of the analog levels. This preserves resolution as no bits are thrown away. Using the PureDAC as a preamp, DIGM can’t quite cover the entire range, so the more traditional digital attenuation does kick in at very low levels. The advantage to B.M.C. Link is that it combines DIGM on the source with DIGM on the amp for a completely analog volume control structure. The proprietary Link connection also allows the amp to work in Current Injection mode; the gain stage is replaced by the PureDAC feeding current-mode output to a “virtually lossless” I/V converter in the amp. This gives it the theoretical advantage over more typical connections, but I wasn’t able to test it due to not having a B.M.C. amp handy. Dang!
Back to the front panel for a second — I really like how B.M.C. handles things in terms of usability. We get separate volume controls for line-out and headphone jacks, with both levels being prominently displayed in the big circular window. Unlike many headphone-friendly designs I’ve experienced, this thing has a large enough display to be clearly visible from across the room, and the included remote seals the deal. This is no preamp imposter, but is actually usable as such, provided one doesn’t require analog inputs. The only usability downside I can come up with – the remote is somewhat counter-intuitive, with headphone and line-out volume controls being on opposite sides compared to their actual locations on the front panel. To be fair, the remote itself is properly labeled, but I’d still prefer to have them match up. While I’m complaining, the volume resets itself to a low-level upon powering up the device, ostensibly for safety reasons. It doesn’t bother me but it might be a nuisance for some people who strictly use low-sensitivity headphones, since they’ll need to turn up the volume with every startup. Lastly, the front panel has no dimming function, which again may or may not be a problem for some folks.
Moving to the interior, the guts of the device: the DAC chip used here is an ESS Sabre ES9016 which is a bit rare to see. We more often get the flagship ES9018 DAC, which is part of the ESS “Reference” family. The ES9016 is one step down and is the sole member of the “Ultra” family (as you can see HERE). I asked B.M.C. main man Carlos Candeias to explain his relatively unusual choice, and he basically told me the following: the ES9016 is a newer chip, and as such achieves nearly identical performance for a lower price. Which is why he chose it. Makes sense to me. In addition, Carlos believes the DAC chip itself is only responsible for a fraction of the final sound. The ES9016 sounds great and has the features they wanted, so why use a more expensive part if it isn’t needed?
Carlos makes it a point to describe the PureDAC as being different. Specifically, when talking about his designs he says we must do away with the old concept of functional blocks: the preamp section, the DAC section, and the headphone amplifier. I’m going to quote him here so I don’t misrepresent his design philosophy. Take note – English is not his first language, but I think he does a fine job even with complex technical explanations.
The balanced headphone output is a non-feedback LEF (Load Effect Free) amplifier. This is a very special amplifier design which delivers voltage and current from separate sources, phase independent. LEF avoids distortion by keeping the voltage source from handling any current movement. A headphone with a strong drive may not require high power, but the phase shift is a challenge. Beyer’s T1 is an example as well as the Fostex top model. Those headphones benefit a lot from LEF and the “thinness” tendency of the T1 turns to an almost perfect balance with an impressive sound-stage.
The output impedance is just one milliohm, meaning essentially a zero-ohm drive.
The PureDAC actually doesn’t need a headphone amp for delivering that function. It is a DAPC digital / analog power converter. This is a unique B.M.C. design avoiding lots of extra stages and thus preserving sound quality. You surely will notice when listening closely.
Every top DAC has a current output which has to be converted and filtered from sampling noise. Almost everybody uses OPAMPs simulating a low input impedance by a feedback loop and doing the first filter pole in the loop. This is a bad idea and when you look at the open-loop of an OPAMP you can easily see that the OPAMP can’t handle squarewave sampling noise on such high frequencies. One of the most sensitive points for sound quality inside the whole DAC! Beside this a secondary filter pole is normally applied by another OPAMP stage. For a balanced DAC chip you need at least 4 OPAMPs per channel and within each OPAMP you have at least 2 gain stages + buffers.
B.M.C. uses it’s proprietery CI (Current Injection) circuit, which delivers a native low impedance potential to the DAC chip and absorbs and routes the original DAC current, converting it to voltage in a single stage. The filtering is quasi-passive and does not depend on the open-loop performance of OPAMPs.
The integration goes even further: Normally a volume control chip is applied to the fixed DAC output. In addition a preamp (or headphone amp) adds a gain and a driver stage. The PureDAC has a “Discrete Gain Management System” (DIGM) replacing the volume control with a lossless solution. It is integrated into the CI-current-to-voltage converter and makes the conversion factor variable. At maximum position the original CI stage already delivers up to 13V rms, so additional gain stages are not required. Whenever DIGM reduces the conversion factor the quality benefits, unlike standard volume controls which always downgrade the signal quality. DIGM is digitally controlled, but works fully on the analog domain.
Adding an LEF driver stage completes the signal path. In total we have 2 stages with very low THD, but no feedback loop! Compared to 4 OPAMPs + volume + gain stage + driver this is a remarkable difference!
The LEF headphone stage has 8A lateral MOSFETs for the current sources. For not frying headphones a current limiter is implemented. Due to the always constant load of the voltage source and the non-existing modulation of the driver stage input load, LEF amps never have a tendency for compression. You will also notice that the control ability is regardless of the listening level and it is hard to nail a sonic signature.
The rear XLR Line output is also an LEF drive, but with lower power and 22 Ohm output impedance.
The approach might sound complex because it is so different.
As you can see, there’s a lot of proprietary design at play here. But honestly I don’t really care if a company reinvents the wheel or just makes a textbook example that doesn’t do anything revolutionary – as long as it has the features I need, with good looks and (most importantly) great sound, I’ll be happy regardless. Still, it’s nice to see someone go their own direction.
A quick note on inputs: B.M.C. will tell you this device is focused around the USB input. And it’s true, the USB implementation is quite good. But – as is very often the case – the best sound I was able to extract from the device came when using my Audiophilleo 1 with PurePower battery PSU, converting USB to SPDIF. It may seem a bit old-fashioned — the PureDAC won’t handle DSD this way, and it actually tops out at 96kHz. Aside from those limitations, the coaxial input is actually quite good. I also tried a YBA Design WM202 as transport over coaxial and it too did a bang up job. The presentation became a little more relaxed but nothing drastic. The WM202 is a small but competent $1,100 CD player, so we aren’t talking megabuck transport requirements. Still, I suspect most folks will head straight for the USB jack, and those folks should find themselves satisfied.
Now, technical stuff aside, let’s get on to the sound: once again, this thing is impressive! I initially threw it in my speaker rig driving a Parasound Halo A21 directly (as in, no preamp) and the result was very pleasing. I heard the impossibly deep, rich bass impact that my Sjöfn HiFi ( the clue ) speakers are known for yet can only do when fed from a quality system. Midrange was very involving and only slightly on the sweet side; not a major coloration, just a hint of deviation from strict neutrality. A welcome hint in my opinion. Upper mids and highs were suitably sparkly and very clean — truly something special in the context of sub-$2k competitors. You’d be surprised how many others get this aspect wrong. I left things this way for a week and got quite a few hours of enjoyment out of the setup.
To get a feel for the PureDAC’s preamplification chops, I added a Cambridge Audio 840E to the system and set the B.M.C. to volume level 59 which is said to be “standard” output. With the 840E in play, things sounded generally similar but didn’t quite have the same “flow”. Vocals became more forward than I prefer, and I sensed a slight edginess and grain where none had existed before. The whole presentation — though definitely still enjoyable — took a step down in realism. Now, I realize the 840E is not a world-class preamp, but neither is it chopped liver. For the PureDAC to better a reasonably nice, dedicated preamp which sold for over $1k a few years back is quite an accomplishment. A lot of DACs these days claim preamp capabilities but this is one of the absolute best I’ve heard, and is truly viable if one desired a simplified configuration.
All this switching and comparison brought to my attention something which I had suspected right from the start – the PureDAC sounds better from the XLR outputs than the RCA jacks. This sort of thing is hard to nail down because you can never be sure which component is contributing to the change. Is it really the PureDAC, or is it the Cambridge pre, or the Parasound amp making the difference? After lots of boring A/B comparisons using several other amplifiers and headphone amps, I’m pretty confident in saying yes, it is the PureDAC. Which of course is something they had implied from the get go. The RCA output is still respectable but just doesn’t take full advantage of the PureDAC’s abilities, so keep that in mind when system planning. RCA is a great starting point, just don’t make it your final destination.
From there I migrated the device to the main headphone-based rig, where it would find a home for several months. Mixed and matched with all sorts of gear, the PureDAC never failed to please. It did a bang up job feeding really transparent headphone amps like the Auralic Taurus MKII and the Questyle CMA800R, and I have no problem recommending it for that sort of use. But the real kicker for me was how amazing the integrated headphone output sounded. Note how I used the singular word “output” even though the device has dual headphone jacks? Yeah, that was definitely on purpose.
Simply put — the single ended 1/4″ headphone output is not very good. Carlos Candeias explained that due to the balanced topography and unique design, some compromises were unavoidable, but he wanted to keep the 1/4″ jack for casual listeners. Which makes sense to me. But headphone geeks, listen up: you’re gonna want to go balanced here. Trust me. The 1/4″ jack has a 100 ohm output impedance and a built-in crossfeed feature which cannot be disabled. Most headphones will sound fairly different compared to their normal character. If all you ever use it for is background listening while you multi-task, then perhaps you won’t mind. Critical listeners? Yeah, you’ll want the balanced option in play.
Using that jack is a whole different ballgame. With over 1000mW on tap, plenty of voltage swing, and that excellent DIGM volume control, the balanced headphone out is exceptionally capable. In fact I had no problems using it exclusively, despite being accustomed to rather expensive dedicated headphone amps. I got unbelievably clean sound with an inky black background even when using very sensitive custom in-ear monitors from Westone, Noble Audio, Unique Melody, and JH Audio. This of course requires a balanced cable which is never a factory option with these types. The good news? Nearly all custom IEM makers use detachable cables for easy field repair, and balanced options can be had without spending a fortune (but you can certainly do so if you like). I get mine from Toxic Cables and I can think of at least 3 other good sources just off the top of my head.
I want to stay on this topic for a moment because it’s kind of a big deal. See, custom IEMs are often used on the go, and I enjoy mine straight from a quality DAP or even a smartphone in a pinch. But they have so much more potential than that. With the right system, my favorites like the Noble 8C and Westone ES5 rank just as high in my book as big headphones like Audeze LCD-2 or Sennheiser HD800. It doesn’t take a super gutsy amp to extract the most out of them, but it does require finesse, and the ability to work well at low volume levels — traits not necessarily easy to find in the current age of high-powered headphone amps. So perfect volume tracking and a black background are already big accomplishments, but these IEMs are also very revealing. Any grain, etch, flabby bass, or what have you, will be ruthlessly revealed by something like a JH13 FreqPhase. When everything is up to the task, the system really sings, and makes one rethink the need for bulky full-sized models. The PureDAC is one of the absolute best integrated DAC/headphone amp solutions I’ve yet experienced with IEMs, and I especially enjoy the distinct lack of grain or fuzz on the upper mids — a common problem with lesser systems.
On the other end of the spectrum, the PureDAC has enough juice to do justice to most of my demanding headphones. The Audeze LCD-2 and HiFiMAN HE-500 were startlingly dynamic, which tends to be a byproduct of planar magnetic designs anyway – but only when properly driven. Similarly, I got excellent results from the new Mr Speakers Alpha Dogs which are somewhat difficult to drive compared to most dynamic-driver counterparts. All of these models can easily accommodate a balanced cable so it’s not tough to get them playing nice with the PureDAC. I’ve had dedicated amps costing more than the PureDAC which couldn’t handle the spectrum of IEMs to planars, so again I’m pretty impressed. The only limitation — to some degree — is the notoriously difficult HiFiMAN HE-6, which sounds good but not great in this situation. Better to stick with the more affordable HE-500 sibling as it will outperform its bigger brother this time around.
The best way I can characterize the overall sound is with the word “pure”. It may sound like I’m taking the easy way out here, but there’s no avoiding it – the PureDAC excels at tonal accuracy, on a level that few others can match. This made itself known when comparing to a Bel Canto DAC 3.5VB, a rather nice device costing nearly $5k just a few years back. I fed both with my trusty Audiophilleo 1 with PurePower to avoid any source discrepancies. The Bel Canto was obviously a high-end DAC — it imaged exceptionally well, had very good resolution, and in some respects mildly outperformed the PureDAC (low-frequency response in particular was a bit more convincing). However …. The PureDAC just walked away from it in terms of sounding natural and organic. Timbre, the ability to discern one instrument from another even when both play at the same pitch and level, was simply no contest. I can count on one hand the number of DACs that so accurately capture the distinctions between James Taylor’s voice and that of his brother Livingston, or the unique sounds of each percussion instrument on the 24/96 release of “Conga Kings”, or the differences between world-class pianos from Fazioli (incredibly clear) and Bosendorfer (wonderfully rich and somewhat dark). You might even make the distinction between a Hamburg Steinway and his lesser counterpart from New York, but that would require an ear for piano which I sadly do not possess. But get me in my element with really good percussion recordings, and I can usually pick out Spizzichino cymbals from more pedestrian Zildjian or Sabian models. The Bel Canto did an adequate job here, yet in comparison seemed a little “mushy”, like the distinctions were blurred to some degree. The differences just weren’t as clear, despite the seemingly high-resolution of the device. I doubt one would notice this during casual listening… but with a very resolving transducer (Sennheiser HD800 or Stax SR-007 in my case) and proper amplification it becomes clear.
I noted a similar situation when it came to playing really complex, dense music with loads of instruments. The Bel Canto might be slightly better at reproducing tiny microdetails, but if falls behind when asked to do a large, busy symphony. Here the PureDAC excels, painting a wide open, clear musical landscape with everything having a distinct “space”. It’s really quite impressive. I’ve owned far more expensive DACs from MBL and Esoteric that couldn’t achieve this nearly as well as the PureDAC, so Carlos Candeias is really onto something here. In fact I would more likely place the PureDAC in the same category as those highly-regarded brands, rather than most others serving the sub-$2k market. It feels like a clear step up, in build and sound, from stalwarts like Benchmark DAC1 and Mytek Stereo192 – a model which uses the same ES9016 chip but sounds absolutely nothing alike. I can think of others in this price class which do the ultra-detailed thing, or the smooth/warm thing, and therefore may be preferable in some instances, but the PureDAC is a very strong all around performer that has almost universal appeal. Unless you need a particular coloration to “balance” out some shortcoming in your system (there’s that word again), the PureDAC is hard to beat.
The B.M.C. PureDAC leverages some unique architecture to arrive at killer performance for a not-very-stratospheric price. It has plenty of strong competition in the $2k and under category, but distinguishes itself with spectacular build quality, plenty of functionality, and — most importantly — very good sound. The chief accomplishment here is tonal accuracy which is virtually unmatched in my experience.
Apart from that, the PureDAC is no slouch in any particular area. The balanced headphone output is up there with the two or three best integrated headphone amps I’ve yet heard. Most times a built-in headphone amp is a compromise; perhaps useful in the short-term until the budget allows for a dedicated unit. Not so in this case — I happily gave up many thousands of dollars worth of high-end amps to use the PureDAC exclusively, and not once did I feel underprivileged.
This gets me excited because there’s a whole big world of people out there looking for a great DAC with the latest technology and features, but who may not be fully on board with headphone listening just yet. These types may be curious and yet not want to jump in with both feet by spending big money on a stand-alone amp. They can grab a PureDAC strictly for its DAC prowess and suddenly find themselves equipped with a top-quality headphone amp as part of the bargain. Then snag a HiFiMAN HE-500, or a Mr Speakers Alpha Dog, or some other excellent headphone that doesn’t cost an obscene amount — making sure to add a balanced cable — and they’d be all set to explore new audio horizons. I have to give major credit to Carlos Candeias and B.M.C. for pulling this off — well done!