Product review - B2 Bomber DAC

Review of Burl B2 Bomber DAC and ADC.

Wednesday, October 6th, 2010


This review originally appeared in abridged form and with other comments in Tape Op Magazine.

The notion that a piece of audio gear can achieve complete sonic transparency is a bit idealized, yet when it comes to converters we hear a lot about neutrality, accuracy and transparency. It’s true that many designers have stabilized digital components and minimized the amount of color imparted by analog signal paths to produce converters that are, relatively speaking, quite transparent. This near-neutrality is especially desirable in the digital-to-analog converters we rely on for accurate monitoring.

When we flip the equation, however, and consider analog-to-digital input, transparency isn’t always so desirable. From day one of digital recording to the present, there has been a collective lament over the loss of the sonic coloration that analog tape machines brought to recordings. Further, the coveted preamps, EQs, and compressors of the “analog era” were designed specifically to work with the sonic imprint of analog tape machines. As digital converters took over for analog tape decks, it was as if the final coats of varnish had been stripped away from our recordings. Making ADCs as transparent as possible is perhaps one of the biggest oversights of the past twenty years of pro audio gear design.

Only a few designers have aggressively addressed this issue. Dave Hill of Crane Song put out his brilliant HEDD 192 (Tape Op #26) that allows you to dial in varying amounts of second and third–order harmonics to an otherwise very neutral, high-quality ADC and DAC. Universal Audio put out their excellent Class-A 2192 (#39), which created “harmonic glue”, with op-amps that sound “like tubes” so that their device was like a “musical instrument” (quotes from their promotional video). Not insignificantly, Burl founder Rich Williams designed the UA 2192, laying down a strong foundation in his understanding of how to integrate Class-A analog circuitry with top-notch conversion. The HEDD and the UA 2192 are the only converters I’ve ever heard anyone really claim to love. These were huge steps forward, but these two designs put both ADCs and DACs in the same box. They hadn’t quite taken the disparate goals of the two realms of conversion to the logical conclusion — design two very different converters.

And that’s exactly what Burl Audio has done with their B2 Bomber DAC and ADC. With the B2 DAC, you get nearly transparent, yet very musical, conversion that is ideal for monitoring; and with the B2 ADC, you get the lush color and mojo of Class-A, transformer-based analog circuitry with a sound that is very reminiscent of analog tape decks. While these two converters meet very different goals, they function as a killer combination that makes recording to digital a musically satisfying analog trip and monitoring back to analog a listening experience you can trust and enjoy. These are the most exciting converters to hit the market in years, taking us into a new era in which digital recording may just have finally caught up with its analog ancestors.

Let’s start with the analog-to-digital trip. With the B2 ADC, you get a 1RU-height unit packed with Class-A circuits and a pair of custom input transformers (Burl BX1s). On the back, you’ve got the standard I/O: two AES outputs, an S/PDIF output, two word clock outs, one word clock in, and your balanced stereo analog inputs on XLR. On the front panel you’ve got great RMS/peak metering (much like Dorrough meters) with a peak reset button, sample-rate selection (44.1 to 192 kHz), internal or external clock source selector, dual-wire on-off switch and — my absolute favorite addition to any converter — a front panel input attenuator. That’s right, no more laying across a bunch of coiled snakes behind your rack with a tweaker while your pal tells you what’s happening on the meters. Beyond convenience, this attenuator is a key feature of the design intended to let you instantly change input headroom in order to hit the front end hotter or cooler, depending on how you want the converter to sound — just like any piece of analog gear.

I’ve used the Burl B2 ADC in all kinds of situations, and I’m completely floored by how good this thing sounds. One of the most stunning applications was running mixes off my Studer A80 1/2” 2-track through the B2 into Pro Tools at 96 kHz as final digital prints. Here I was comparing the B2 to my Cranesong HEDD, which I’ve relied on to convert analog mixes to digital for many years. I love my HEDD, but I have to admit that the Burl really has it up against the ropes. What blew my mind was how easy it was to listen to mixes converted by the B2. Things just chilled out in a really great way, but with no loss of detail. Cymbals were particularly smooth yet shimmery, and the whole stereo image was wider and a bit deeper than the Cranesong. It’s important to note that the center of the mix with the Burl was very focused, too, with a tight, punchy low end that brought out the best my Studer had to offer. To improve width and focus is no small feat for any piece of audio gear. In the end, comparing the HEDD and the Burl was like comparing a Ferrari and a Lamborghini — which version of completely awesome high-end performance do you prefer? It is absolutely a matter of taste at this level.

Tim Hatfield and Eric “Roscoe” Ambel turned me on to the A80/Burl combo at their Coyote Technical Services Recording Rig here in Brooklyn. Both of them rave about it. Tim put it this way, “I love what it does to my mixes. I usually got to tape first then play it back into the computer through the B2. When I do, the top opens up, the bottom gets tighter, and vocals seem more present. What else do you want? I bet Elvis would have used it.” Roscoe says, “After six months with this box, the simplest way I can describe the B2 is that it is a great piece of audio gear as opposed to another piece of computer gear. Emphasis on audio. It’s a real game changing box for tracking and mixing.”

Just as analog tape machines were designed to sound good in conjunction with the outputs of the mic preamps, compressors, and EQs feeding them, the Burl is specifically designed to play nice with what comes before it. The goal was not to simply reproduce what comes in but to contribute positive tonal character to the signal path the same way an analog tape deck does. This is what I think Roscoe means when he says it feels like a piece of audio gear and not computer gear.

I hadn’t totally realized it until writing this review, but I am almost afraid of many converters, usually thinking things like, “Don’t go into the red,” and “Be careful, or it’s going to ruin everything.” With the Burl, I relax and push the circuit as I like, using the attenuator as any other gain knob in my signal chain to drive circuits to achieve the desired sound. Don’t get me wrong; it’ll clip if you push too hard. But, like recording to tape, you can shape the sound to taste by pushing a little harder or easing off. Want a fatter snare sound? Push the front end of the B2 ADC and it rounds off the transients and adds a nice little extra punch as the transformers do their thing. Want a more dynamic and clear snare? Open up the headroom on the B2, back off on the preamp a bit, and the transients are all intact. With other converters we can manipulate sound in this way to a degree, but they weren’t really designed for it, and they didn’t have a front panel attenuator to help you do it right. With the Burl, “hitting the converter” in order to achieve a desired sound isn’t breaking the rules; it’s encouraged by design.

Another set of problems with digital recording that the Burl B2 ADC seems to have remedied is the degradation of smoothness, depth, and width. I know these are vague subjective terms, but they do describe what many agree are ongoing issues with digital systems.  Lack of smoothness — or graininess — is most apparent in cymbals and other high-frequency, shimmering sounds like acoustic guitars, tambourines, and the air on vocals. The B2 simply smoothes out high end content without muffling it in a way that is uncannily similar to the way I hear analog tape decks do the same thing. I don’t have to be nearly as careful with boosting high-end when using the B2, even on tightly placed drum overheads. Taking a 20 kHz shelf up 6 dB with an API 550A EQ into the Burl produced sparkling, open cymbals that weren’t at all harsh. Depth is most apparent when tracking anything with stronger ambient sounds. At Mavericks Studio in NYC (where I do most of my tracking) there is great pride in the deep, warm sound of the room. I was tracking The Cinematic Orchestra’s new record there and had a pair of Coles 4038s (Tape Op #15) high and wide above the kit, capturing a very open, roomy image that we compressed with a pair of Distressors (#32) in order to emphasize the room reflections. When I heard the Burl’s representation of that image, my pride just shot up. I could hear more of the room and more of the direct signal simultaneously, making for a far more engaging 3D image that let the emotional charge of the drumming come bursting through. As for width, it’s back to stereo images and full mixes for the full effect of the Burl’s panoramic sound stage. Somehow the Burl can make a fat-ass analog console sound a little wider, and even digital prints can pick up some extra width just hitting some analog gear and coming back in through the B2 ADC — something mastering engineers are really going to dig.

As effusive as I am here, it’s easy to imagine that I’ve simply gone off my rocker for Burl, caught up in a wave of enthusiasm. But check out what others in the field have to say and how they echo my sentiments about smoothness, depth and width.

Mastering guru Greg Calbi says, “The Burl B2 Bomber ADC has extremely clear and detailed low end without sacrificing clarity in the mids or highs.  Above and beyond that, with the Burl, I hear expanded front-to-back imaging — something  I try so hard to achieve in all of my mastering work.  The Burl is the perfect antidote for mixes which have been caught ‘in-the-box’ needing more clarity and warmth.”

And Tape Op contributor Joel Hamilton says, “The Burl B2 ADC made me excited about digital again. I mean that. No single piece of gear meant to interface directly with my Pro Tools HD rig has made me get excited — ever. Some have been able to overcome the ever-so-glorious “finally, it doesn’t ruin it” threshold we all know and love, but none of them have been a piece that really makes you feel like you have gotten something exciting. You know the feeling — you unpack the Chandler thingy, or the Sta-Level, or the EQP‑1R, or the Symetrix 501, and you can’t wait to use it on the mix you are working on right now. That’s how I felt when I had the demo unit for a few days. I really hated letting it go out the door, because it meant I had to do a whole record without that glorious sound on the two-track print back into Pro Tools!!!  When I was in the middle of producing/engineering something for Matisyahu and Dub Trio, I would just flip back and forth during the mix, from the 2-mix to the 2-track returns, and the Burl just does something so great. It’s my mix, but wider and more 3-D. There was a ton of low end happening, as it was a Dub/Reggae thing, and the Burl tightened it up a bit while losing none of the physicality I had going on. I also love the front-panel attenuator, the color, the build quality, the metering, and the fact that it has two real channels of real electronics hitting nice conversion. I am ready for the multichannel version of this. Really. I need at least 16 inputs of Burl. Thanks for making this piece of gear, Burl, I truly, truly mean that.”

If converters are the tape machines of our era, it’s my humble opinion that the Burl B2 ADC may be the Studer A80 two-track of our times. It’s a design that benefits from the accumulation of technical knowledge and user feedback that can only exist after a certain branch of technology has been subjected to the frustrations of trial-and-error for a couple of decades. If we’re still using 0s and 1s to capture audio in fifty years, I wouldn’t be surprised to find that some young engineer is bragging to her clients about having picked up a vintage Burl B2 ADC. “It’s a 2010, yo — check it out! This is the real deal from the good-old-days when digital just sang!”


Okay, time to start thinking in the opposite direction and take a look at the B2 Bomber DAC, the digital-to-analog complement to the B2 ADC. On the back, you have two AES inputs, an S/PDIF input, two word clock outputs, one word clock input, and two analog outputs. The front panel gives you knobs for choosing sample rate (up to 192 kHz), clock source, input source, the same great peak/RMS meters as the ADC has, and — once again — an attenuator that allows you to move the output quickly between –18 dBFS and –8 dBFS. Mixers and mastering engineers are really going to love that output attenuator for everything from accurate calibration in a mastering environment to being able to heat up or cool down a signal heading out to analog equipment. It’s very straightforward to operate.

I’m going to be very frank for a moment; I get nervous writing about monitoring equipment because people tend to take it very personally. Our very ability to do good work is implicitly questioned when our monitoring gear is being judged. It’s like questioning the accuracy of a doctor’s X-ray machine. You’re not just questioning the machine but the professional integrity of the person who chose to use that machine, and many people I know care a lot more about their engineer’s gear than their doctor’s. It’s a touchy subject, so I tend to tread lightly when discussing monitoring gear like DACs, and above a certain performance threshold, I consider the choice to be a matter to taste.

It’s a matter of taste because no two DACs sound exactly the same, even if they both brag about being sonically transparent. Every DAC is going to have an analog signal path, a clock, converters, and a power supply all laid into a design that will determine how it’s going to sound, no matter how much the sonic coloration is minimized by design. To some extent, we all imagine that an idealized, Platonic state of audio purity exists on our hard drives and tapes, but the fact is that if we want to hear those recordings we’re going to have to do it on a playback system that’s going to shape that sound in one way or another. That’s a fact we can’t get around.

One of the things I immediately like about Burl as a company is that they openly embrace that fact. Check out what the Burl literature says. “The B2 Bomber DAC delivers sonic purity and dynamics thus far unheard of. As a complement to the B2 ADC, the B2 DAC punches you in the chest with low end while the 3D spaciality and stereo spread give you amazing detail throughout the spectrum. Add to that a sweet tone that is easy on your ears, and you have a unit that you will instantly fall in love with.” Sweet tone? Easy on your ears? Falling in love? This is not the kind of language one usually finds when reading about a pro-audio DAC, yet Burl is claiming that they can do sonic purity and sweet tone at the same time. It’s an unconventional and gutsy claim more likely to be pitched at the home audiophile market.

Such a claim also runs against the grain of two established ways of thinking about pro-audio DACs: the notion that unpleasant monitoring is preferable because it forces the engineer work harder; and the notion that a DAC can and should be completely neutral. As I said, I’m really not here to argue philosophies; whatever works for you is the best monitoring situation. Yet, I think that by embracing the idea that a DAC will have to sound like something, Burl has liberated themselves to design a converter in which the seemingly contradictory goals of transparency and musicality can co-exist more overtly.

So what’s the approach? With the B2 DAC, Burl uses no transformers and no capacitors in a fully discrete, Class-A design loaded with their proprietary BOPA1 op-amps. The lack of capacitors and transformers minimizes the amount of color imparted by the analog signal path, while the op-amps offer up the “sweet tone” of the unit. It’s as if Burl has said, “Okay, we’re not going to load it up with analog mojo because it should be relatively transparent (bye bye transformers and caps), but if it has to sound a certain way, it might as well sound good (hello op-amp).” The goal of combining accuracy and musicality is directly reflected in the circuit itself. But is accuracy and musicality reflected in the sound? I asked two mastering engineers to spend time with the B2 DAC and get some of their impressions down in writing.

Jessica Thompson is the mastering engineer at The Magic Shop in SOHO here in NYC. She specializes in archival restoration, currently working her way through the Newport Folk and Jazz Festival archives, and she does plenty of modern mastering there, too. Her main converter has been an 8X192 AD/DA by Mytek, a company whose stated goals are transparency and staying as faithful to the original signal as possible. Here’s what Jessica had to say about the Burl B2:

“With the Mytek 8X192 paired with my ATC monitors and good room design, I always feel confident that what I’m hearing is unadorned. There’s no extra punch or sparkle — just straightforward, clean lines. Since I do a lot of audio restoration on historic recordings, I rely on the accuracy of my Mytek DAC and monitors to hear extreme details — tiny dropouts or a lick of distortion on a vocal. Compared to the Mytek, the Burl seems a little sweeter, less plain, but not necessarily less accurate. The upper-mids ring like crystal without any of the fuzziness I associate with lesser quality converters. The Mytek also has a lovely high end, but the Burl’s is especially clean and pretty. The highs zinged without sizzling, which I can imagine being beneficial during long days of mastering or mixing because there will be less ear fatigue. Via the Burl, the midrange pops forward with more dimension than via the Mytek, especially on mono recordings. Because they’re both excellent converters, it’s hard to determine whether the Burl is hyped or the Mytek is particularly flat in the mids. Mainly, it seemed like there was much more depth in the center and mids with the Burl, and that dimensional aspect gave the music a very lifelike feel, which is lovely for listening and helpful when trying to separate out instruments in a muddy or tight mono recording. On the other hand, the mids also led me to consider whether working off the Burl would make me ease up on pushing vocals or other center/mid info forward when needed. When you get used to listening to a particular DAC/monitor combo, you learn to work with its particularities; I’m not making masters with overly full or hyped mids because I’m working off the Mytek, which seems more flat or straight ahead in that area. Again, this is a tricky aesthetic quality to judge, because so much of it comes down to personal preference at this level.

“In terms of specific listening, I checked out some lush, but fairly minimalist tracks by Natalie Merchant I mastered for an iTunes exclusive release. (Natalie’s most recent album Leave Your Sleep was mixed here at The Magic Shop by owner Steve Rosenthal and engineer Eli Walker.) Via the Burl, it seems as though the instruments are swirling and filling the air in the background around her vocals, and I wound up listening to all eight songs because they sounded so beautiful. Next, I brought up a live, mono recording of Miles Davis from the Newport Jazz Festival in 1967. Even in mono there is bright, clear delineation of the instruments when monitoring through the Burl B2. The high hats zing gently in the background (they zing but do not sizzle) while the piano and bass play off each other in the foreground. Within the very centered mono signal there seems to be a depth and height that allows for separation. This is something I was searching for during mastering mono material, and it says something about the ability of the Burl to bring out dimensions in a recording.

“The meters on the Burl B2 match up nicely with my Dorroughs; they bounce in unison, which makes me think I can trust the metering on the Burl — a bonus feature for a DAC.”

Next the B2 DAC travelled uptown to the mastering room of Howie Weinberg at Masterdisc to spend time with Matthew Agoglia. Matt ran the Burl through its paces against their DCS DAC, which they clock off of an Antelope Audio 10M (Tape Op #68). Keep in mind that the DCS cost about $10,000 fifteen years ago and has been a standard in mastering studios for well over a decade. (Many of your favorite records from the CD era have likely been mastered on DCS converters.) On top of that, the Antelope system runs close to $8000. Considering that the Burl B2 DAC sells for $2500, Matthew’s feedback is particularly interesting. Here’s what he has to say:

“Overall, the Burl (whether clocked to the 10M or internally) has a more neutral, smooth and transparent character compared to our DCS. The DCS has a color in its midrange, a tightness in the bass, and a subtle crispness in the highs. We could say that the DCS is more curvy, sounding different in different areas of the frequency spectrum, while the Burl is very smooth and linear, sounding very similar throughout the frequency spectrum. In particular, the Burl’s low end was actually a bit more extended, with sub frequencies a bit clearer, while the DCS had a very pleasant low end focused around 80–120 Hz. The Burl also sounds a bit wider than the DCS.

“When clocking the DCS off the Antelope 10M, we get that larger-than-life sound that some describe as “hype” — not necessarily a bad thing in mastering because you don’t end up adding too much EQ or other processing to achieve your results. I wondered if I might be inclined to EQ/process more with the Burl handling my DAC duties because I’d want to hear more excitement. Note that when I clocked the Burl to the 10M, it definitely took on more of the excitement I heard with the DCS, bringing the two converters closer in sound.

“Please keep in mind that we are talking subtle differences here. When I performed a null test between the DCS and the Burl (both clocked to the Antelope 10M), they nulled to approximately –40 dBFS. Since DCS no longer makes the DAC I am using and will someday stop support for their legacy products all together, it’s nice to see a unit like the Burl coming to the market. The Burl at $2500 is a bargain!”

Jessica and Matthew’s comments highlight two key points. First, the Burl is a very capable DAC that can hold its own when some of the most discriminating folks compare it to some of the most revered converters. Second, the way any two experienced people think about monitoring comes down to a matter of what one is used to, how one approaches their work, and ultimately, philosophy and taste — none of which can be argued to any productive end. Note that Jessica felt the Burl had more hype or excitement in the midrange than her Mytek while Matt felt the Burl was less hyped in that area compared to his DCS. Jessica wondered if she’d do too little processing and Matt wondered if he’d do too much. We are in a seriously subjective territory and well within the realm of taste. But I’m not copping out and saying, “It’s all relative.” Instead, I’m noticing what’s similar in Matt and Jessica’s impressions and how they line up with my own; the Burl delivers a ton of sonic detail (transparency), and it’s very pleasant to listen to (musicality). Not only is the Burl keeping up with the competition, it’s meeting its stated design goals when submitted to critical listening tests.

In my own critical listening at The Farm (my mixing room in Brooklyn) I put Burl’s DAC up against my Crane Song HEDD, monitoring my Pro Tools HD system through my API “Mini-Legacy” console. Matching output levels between my HEDD and the Burl was easy using the front panel attenuator — click, click, done — and I can’t say enough about those attenuators. Sonically, the HEDD and Burl DACs are so similar that I can’t honestly say that the differences I heard are terribly significant. They’re not identical, of course, but they’re very, very close. Both converters are crystal clear, and there is no difference in the amount of information I was hearing. In terms of listening pleasure, my preference depended on what I was listening to. The Crane Song excels at delivering a strong, focused center image, so for mixes where the interest lies in the center, I liked the HEDD a little bit more. Conversely, the Burl presents a wider and somewhat smoother image, so for mixes where there are a lot of interesting things happening on the sides, the Burl was a little more enjoyable. I could go on about other subtle differences, but I think it’s more useful to note that, like Jessica and Matt, I wound up in the realm of subjective preference where I knew that I could do good work on either converter. Let’s just say again that the Burl B2 DAC is easily hanging with the big dogs.

Perhaps more interesting for me was spending time with the B2 ADC and B2 DAC working together as an integrated system while doing overdubs. The system sounds sonically integrated the way a tape deck does, as if the input cards (here the B2 ADC’s transformer-loaded input stages) and repro cards (here the B2 DAC’s op-amps) were working together to make up the singular analog sound of one machine. You’re within Burl’s sonic world the whole time, and it’s a beautiful world to be in. I loved using the DAC and ADC together and want to echo Joel Hamilton’s desire for a multi-channel version of both the ADC and DAC.

Before wrapping up, there are a couple other applications for the Burl that will interest a lot of readers. First of all, both the B2 ADC and the B2 DAC have really great clocks in them. Clocking the Pro Tools HD system at Mavericks to either one offered up a significant improvement in monitoring clarity. Similarly, at The Farm, I clock off the HEDD, and when I switched to the Burl’s internal clock, I retained the detail and depth that I get off the HEDD’s internal clock. In fact, when clocking those converters off of each other, their marginal differences narrowed even further. The Burl clocks are excellent.

The Burl converters are also a boon to any “prosumer” system. My colleague Mark Marshall, another Brooklyn engineer/producer, bought the B2 ADC to replace both the clock and the input side of his Pro Tools LE rig and was blown away by the improvement. For far less than he’d have paid to upgrade to HD, he’s tracking with  two channels of world class conversion and monitoring with way more accuracy due to the clock. I think a lot of people are going to find the B2 ADC, the B2 DAC, or both, to be great upgrades to all kinds of systems.

I’m pretty thrilled about Burl for its own sake, but also because I think these converters are going to seriously raise the bar for other manufacturers of digital recording gear. If we’re lucky, Burl has chimed in a new era of digital recording where we no longer merely tolerate — or worse, fear — our recording devices but actually revel in their sound.

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