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Positive Feedback ISSUE47
Drive II and the Tube DAC IISE
as reviewed by Marshall Nack
When I set up the DRIVE II and the companion TUBE-DAC IISE from Accustic Arts, a red light on the back of the transport lit up. Red lights are never a good thing. According to the manual, it was an AC Polarity Indicator. If it lights, polarity is inverted. The manual instructed me to push the adjacent button to reverse it. The light dimmed, but didn't go out. This occurred with both Accustic Arts components plugged into my TARA Labs IDAT power conditioner.
When I disconnected both from the IDAT and plugged them into the wall via an Ensemble power strip, the light went out. Hmmm, I wondered, what does that say about my TARA conditioner?
I've never seen a Polarity Indicator on a transport before. Likewise the DRIVE II's Integrated Mains Filter. This feature came in handy, as it gave me the option of power conditioning without using the "red light" TARA IDAT unit. However, it wasn't as if the AA front-end needed any conditioning at all.
Plugged into the Ensemble power strip without any conditioning, I had a definite impression of less "improvements" being made, of less "goosing" of the signal. It was fast and focused and, interestingly, there was no appreciable increase in noise—noise being what conditioners principally address.
This speaks quite commendably about AA's power supply and circuit designs. It also reinforced the impression I got when I reviewed their Preamp I - Mk 3 a short time ago. That component was keenly sensitive to the power messenger. Accustic Arts pays more attention to the power line than most companies.
But I was catching a chill and the AA's laser-like focus was bothering me. Contrary thinking mandated I should try engaging the DRIVE II's built-in conditioning. As expected, it became smoother, warmer and less forward. Still, in my solid-state system, I wanted more flesh on those bones and even more warmth, although some listeners really liked the direct and honest quality heard from going straight into the wall. "Direct and honest" would keep cropping up in my listening notes.
I wanted the sound to be more like the way my reference mbl 1521A transport and 1511F DAC front-end does it. I knew I could get there largely by swapping to more synergistic wires, but what I didn't care to know about were the other insights into the mbl's presentation that the AA made apparent.
In a quick A/B, you'd probably say the mbl "sounds more musical." What does that mean? In pondering this question, I experienced another of those "ah-ha!" insights.
During the course of reviewing the McIntosh Mc501 monoblocks, it became obvious that transients in my current setup had lost their snap. As the amps were the only variable in play, I was able to trace back that persistent softness to my reference mbl 8011 AM amps. Now, guess what? Thanks to the AA, I'm hearing the same thing in the mbl digital front-end.
Remember how digital sounded back when it was first introduced? Like chalk on a blackboard. (Even today, the thought of it makes me wince.) Twenty-five years later, we're into the second (or third) generation of these products and designers have addressed those digital nasties. Typically, they opted to voice their products to sound more like analog or tubes. So, now we have the answer to why my mbl front-end "sounds more musical."
It has a degree of softening applied. Its sharpness has been moderated and its edges have been smoothed over. It has a round sound. And it has the same scooping transients and lingering tails as the mbl 8011 amps. One effect of this is that instruments make their entrance without "breaking" the silence.
I have to believe the voicing is done deliberately to address the problems of the medium. But at what cost?
Too high a cost for the designers at Accustic Arts. This respected German high-end manufacturer doesn't buy into the softening strategy. And for their top-of-the-line digital product, they reject most of the other common solutions, too. Instead, they came up with their own approach, and in the process, they created a front-end that doesn't sound like all the rest. I'll cover some of this when we get to the Technical Discussion below; more is available on their website. But solve the digital nasties they did all right—I can vouch for that.
Let's start with speed. The AA front-end is fast as blazes. Its transient has a beautiful shape. It doesn't soften the onslaught. It also has excellent coherence. My mbl front-end doesn't approach its speed and sounds comparatively sluggish. I tell ya, I didn't need to know about this. But enough on the mbl front-end—let's get back to the AA.
Most often, when we talk about the leading edge we have the treble frequencies in mind. Our ears are keenly sensitive to timing aberrations in this band. This might sound silly, but did you know that a piano, for example, has the ability to produce low frequency notes with sharp attack? The closer you get to the instrument, the more pronounced this becomes as you're getting more direct sound, less hall reinforcement and decay. Certainly this is what the microphones register, since they are typically placed in the near field.
The AA is the first digital front-end I've heard that handles sharp low-frequency transients.
The Tail End
It's the same at the notes' tail. From a close orchestra seat, the tail of the note doesn't hang around like it does in the balcony. And the closer you get to the stage, the shorter it becomes. On occasion I've heard languorous decays through the AA, as when the piano's sustain pedal is intentionally engaged, but I've never heard truly short ones from the mbl. The AA places you in the tenth row in terms of decay.
Even more exciting is what's happening in the sustain—there's actually resolution there! Digital playback never does this. Typically, it gives you a homogeneous and textureless span of time. With my mbl, for example, you get a beautiful tone, but it is smooth and glossy (again "musical," like old-fashioned tubes). Analog always gives you little variations of tone or timbre or texture. This goes a mighty long way towards establishing analog's vaunted credibility—it is one of the major feathers in its cap. The AA has this quality. (But it still doesn't sound like good analog. Analog brings other things to the table.)
In terms of timbre, the AA combo is complete, but because it is so focused, it doesn't sound rich or robust. "Which one did you say has the tubes?" you might ask. The DAC II is a hybrid employing a pair of 12AX7 tubes, but it is not the one that sounds "tubey." So no it doesn't make timbres beautiful or lush. However, it succeeds in no small way in nailing the distinctive harmonic clusters of each instrument.
Neutrality, Benefits of
The AA combo is a very neutral front-end. Neutrality means, among other things, you don't hear the same-old, same-old all the time. Let's start with the Richard Strauss Sonata for Cello, with Johannes Moser (hanssler Classics 93.207), a young cellist I would recommend keeping an eye on. From his very first CD, he's been garnering awards left and right. On this recording of the Strauss sonata there's no imaging to speak of. Both instruments are bunched up in center stage. Perspective is approximately what you might hear from mid-hall seats. Decay is modest.
Contrast that with Johannes Moser doing the Saint-Saëns Cello Concerto No. 1 (hanssler Classics 93.222). I was tipped off to this CD by a short review I read on www.allmusic.com. The performance is excellent; the sound is demonstration quality. The orchestra doesn't have a lot to do in these concertos. Sections come in and out, occupying appropriate stage locations, which sometimes stretch clear across the width of my room. Imaging is quite discrete with no overlap. The perspective on this CD is close, approximately from tenth row orchestra seats, and it is a bit dry. I refer to it often to get a baseline.
Demonstration sound of an entirely different order can also be found on the RCA SACD reissue of the Richard Strauss Symphonia Domestica (RCA 88697-08282-2). Here the aural space literally explodes, pushing up and out in all directions, bearing no resemblance to the two previous CDs (or any hall I've ever been in). The reissue impresses in a hyped-up way.
The point is that you're not put into the same space all the time. Just a curious aside, but a lot of guys judge their music software by how well the new CD measures up to their most impressive one, impressive being defined as having the widest, deepest stage and dynamic range, among other things. Well, there are other things in life. There are tons of compositions in the repertory that are scored piano over long stretches.
Macro dynamics are exceptional. I had not met my mbl Noble front-end's match… until now. The AA's dynamics are on par. You can tell they're out of the ordinary because I've been spending inordinate time with the likes of Rimsky-Korsakov. While he is known principally for Sheherazade, there's much more to explore (admittedly, much of it is reminiscent of, and not as good as, that classical war horse). I have a four-disc set of his orchestral works (BIS-CD-1667/68) and I put one disc in each front-end. It makes for easy comparisons.
An interesting point—the AA's treble is wholly unrestrained, yet it almost never sounds harsh. How do they do that? As this is a well-known problem area for digital, some kind of band-aid must be in place. It sounds as if a degree of sweetening has been applied to the top end. This is the only frequency band with such a treatment that I can detect.
Just for the record, in case you're getting the impression the AA's honesty comes bundled in an analytical envelope, you do have to choose ancillaries carefully. But pair it with synergistic wires and gear leaning to the musical side and it produces correctly-sized images with good body and quite satisfying weight. Tonal balance comes in a bit lighter than the mbl.
Also, please understand that my task is to highlight differences in the two front-ends. While the AA compares favorably or equally to my mbl Noble Line front-end throughout this copy, it's not as if it renders the mbl unlistenable. When I come home and put on the mbl, I'm quite content. It's only when I do A/Bs in quick succession that my grumbling begins and I stay with the AA for the rest of the session.
Design and Features
The DRIVE II and DAC II belong to Accustic Arts' reference line. They share cosmetics with the AA Preamp I Mk3 I reviewed a few months ago. All three exude the same quality, attention to detail and build quality. This is well-made stuff.
Basic functionality is provided on the front panel controls of the DRIVE II. Additional functions are accessed via the matching aluminum remote. Everything operates with a silky, quality feel, except the CD drawer cover mechanism.
The top-loading DRIVE II sports a solid aluminum chassis of substantial weight—40 lbs. To operate, you slide back the drawer cover (which weighs 3.5 lbs on its own) and place the CD on the spindle of the CD-Pro2LF die-cast metal CD holder. Then stabilize it with the magnetic puck and close the cover. The drawer cover rails give the unit a sporty appearance, but the sliding action of the drawer cover has the feel of the flywheel on an inexpensive analog tuner, the ones you have to push, unlike the ones that glide.
The well known and highly regarded CD-Pro2LF is mechanically decoupled by steel springs and rubber bumpers, forming its own subchassis. Special attention is paid to the power supply, which has approximately 61,000 uF of capacitance available. Other nice features are the built-in conditioning and the Polarity Indicator.
In the TUBE-DAC II, the common solution of using oversampling was rejected in favor of something quite original. Oversampling typically generates a degree of high frequency noise. The higher the sampling rate, the more noise is generated. This necessitates the introduction of filters to clean it up, which bring their own set of issues. AA developed a new algorithm.
Instead, AA uses 26 "multiplying processors" working in parallel on the incoming signal. The arithmetic mean value of these 26 processors is computed and that is the bit stream sent forward. No noise is generated, no filters are needed, and more precision is the claimed result. The newly computed bit stream is also boosted to 32 bits. Moreover, left and right channels are separated at this point to become dual-mono—two 32-bit streams are generated from the original 16-bit one. From here forward, left and right are processed separately, requiring two DA converter chips, etc.
TUBE-DAC IISE Ref
The Tube DAC II I'm using is the Special Edition. The 12AX7 tubes in the SE version are military grade and are matched after 200 hours of burn-in. The SE version also has gold-plated tube and fuse holders and closer tolerances for parts and pcb boards. The SE costs $500 more.
I'm happy to report the coronation of a new bits and bytes king. The Accustic Arts DRIVE II and the companion TUBE-DAC IISE comprise a major contender in digital front-ends. At its price point, it is the best I've come across.
Accustic Arts opted not to follow the pack and pursued an original route to solving the digital nasties. For one thing, in their reference level product, they didn't buy into oversampling. For another, the DAC II may be a hybrid employing a pair of 12AX7 tubes, but it is not "tubey" sounding. And the trump card is they don't buy into the softening cover-up most designers use. Consequently, their top-of-the-line digital front-end does not sound like the rest of them.
The AA equals or betters my reference mbl 1521A transport (MSRP $10,950) and 1511F DAC (MSRP $10,650) in every grade on the audio report card, but the difference is not huge. It is only when I do direct A / Bs that I start to grumble. Then I'm forced to swap to the AA for the rest of the session.
While the Accustic Arts DRIVE II and TUBE-DAC IISE still doesn't sound like good analog, it brings you closer to the truth than any comparably priced digital front-end. Marshall Nack
North American Importer