Current CD Players and D/A Processors, New and Not So New, Multibit and One-Bit

By Peter Aczel, Editor and Publisher.

Inspired by David Rich's formidable treatise, your Editor tests a bumper crop of hardware on the lab bench, in the listening room, and some through the ABX Comparator (if you'll pardon the expression).

My favorite cliché, "the plot thickens," is quite safely applicable here, since just about every manufacturer capable of mounting a printed circuit board on a chassis has come up with CD playback hardware of some sort, more often of several sorts, and rival design philosophies are proliferating at all price levels, not just the high end. Armed with the technical insights provided by David Rich, I managed to keep my head above the water in the lab, but boy, there are more difficult choices in this sector of audio today than on the menu of a good Chinese restaurant. Let us, therefore, try to sort out the relevant issues and criteria. How they differ, how they don't.

All CD playback equipment currently or recently manufactured can be expected to have almost dead fiat frequency response, negligible de-emphasis error, stupendous stereo channel separation, virtually zero phase difference between channels, extremely low THD at reference level, insignificant wow and flutter, and nearly always noninverting impulse response. The elaborately presented curves for these measurements in the typical magazine review are mere gingerbread in my opinion (look, Ma, I have an Audio Precision!); my trusty Hewlett-Packard 3580A has a guaranteed amplitude accuracy of +0.3 dB and a visual resolution of about 0.1 dB, leaving me little or nothing to say about even smaller differences that are meaningless in any event.

At the same time, there are very real though rarely important differences in noise floor, dynamic range, 0 dB square wave clipping, RF output, possibly IM distortion and, most significantly, low-level gain linearity and monotonicity.

These are worth discussing, but here again I consider a 0.3 dB deviation from theoretical perfection, or a 0.3 dB superiority in device A versus device B, to be quite insignificant and not really what the enlightened audiophile needs to know.

What he needs to know, rather, is whether or not the unit is as well engineered-with regard to basic circuit concept, quality of parts, mechanical construction, control facilities, and ergonomics-as he has the right to expect for the money he is paying. Significant differences exist in those respects. What about the sound? I'll be coming to that shortly.

Low-level linearity: not so simple. When the deviation from theoretically perfect gain linearity with a dithered test signal at -70 dB, -80 dB, and -90 dB is small enough to be approaching the accuracy and resolution limits of my instrumentation (see above), I call the gain linearity essentially perfect, although it can happen that the spectrum of the signal still shows some harmonic blips above the "grass" of the noise floor. Usually, when the amplitude deviation is a fraction of a dB, no such blips are visible. Quite a few units turned out to be that good, even at -90 dB, but a number of those that showed some nonlinearity led me to a totally unexpected conclusion.

I now believe, very firmly, that trimmer potentiometers should be left out of designs using the J-grade and K grade DACs from Burr-Brown and Analog Devices. Those who use these DACs as is, exactly as they come from the factory, get essentially perfect linearity (e.g., Sony and PS Audio), whereas those who add the trim pots (e.g., Pioneer Elite and Theta) end up with far from negligible errors in actual production samples, correctable of course on a suit ably equipped lab bench but not by the consumer in his home. In fact, an untouched J-grade appears to be more linear than a typical trimmed--in K-grade. The lowest grades, on the other hand, should always be used with trim pots to bring their linearity up to a respectable par, but production tolerances are even sloppier in the lower-priced CD players, so that the end result is generally unpredictable.

The irony of it all is that the beautifully plotted low level linearity curves in all those highly detailed test reports are merely an indication of how carefully Norma tickled and sealed the trim pots on the production line, and how gently José handled the carton in the warehouse, but not of the inherent linearity of the design itself. They are QC curves, not engineering test curves. I have learned to take them cum grano salis. 1 am aware that Stanley Lipshitz and John Vanderkooy already flagged this trimmer pitfall in their March 1988 paper, but at the time they did their research the alternative of almost perfectly linear DACs right out of the package did not yet exist.

Double-blind, matched-level listening tests.

The point of any or all of the above is of course the obtainment of the best possible sound. I carefully listened at some length to every piece of equipment reviewed here, and a number of my associates also listened to most (but not all) of them. In a good many instances we had two of them level-matched within 0.1 to 0.15 dB of each other (meaning all four channels) and connected to the ABX Double-Blind Comparator. It would have been impossible, of course, to ABX each unit against each of the others; the permutations and combinations would have been staggering. We did enough double-blind listening, however, to come to a tentative conclusion that will not please the tweaks and cultists, or the major-brand lobbyists for that matter. There are simply no reliably identifiable differences in sound between any two units in this group, regardless of price, reputation or measured performance.

Those who can handle that without freaking out and showing me the door (as in "Get lost, Julian!") will want to know the details. The listening setup consisted of a pair of Quad ESL-63 USA Monitors driven by a Boulder S00AE power amplifier, which was fed from the balanced outputs of a Boulder MS preamplifier. In some of the listening tests a Velodyne ULD-15 Series II subwoofer was added to the Quads. The room was the one analyzed in Bill Rasnake's article in Issue No. 13 All of the participants in the tests were experienced audiophiles with no hearing impairments. The typical test between a given A and given B consisted of 16 trials, i.., 16 successive randomized X's, with unlimited time available for each X and backtracking/rechecking per mitted at all times. Some of the tests were stopped at 12 trials. The participants listened one by one, not in groups; the typical time they needed for 16 trials was about 60 to 75 minutes, some of which went into synchronizing the two identical discs (except when only one disc was needed to test a CD player straight through versus an outboard D/A processor). The music was quite varied-symphony orchestra, piano, soprano voice, string quartet, jazz, rock-but of course there was no way to include each listener's favorite test CD. Statistically, 12 right answers out of 16 and 10 out of 12 are needed for 95% confidence that no lucky guessing is involved. Nobody came even close to that; in fact nobody exceeded a fifty-fifty score by a statististically meaningful margin. And I must add that a Golden Ear who tells me that such and such "blows away" thus and so-*"night and day" and "not in the same league" are in a similar idiom-had better get 16 right out of 16 or I consider his credibility blown. For 12 out of 16, the words should be "maybe a little better" or "I can just barely hear it." Now for the qualifications and reservations. It is possible that there exists a piece of music that would have revealed small differences better than anything used in these tests. It is also possible that, currently used systems of A/D encoding being less than theoretically perfect, some future encoder will reveal such small differences regardless of the music used. Remember, some of these differences were measurable. Finally, it is possible that there are some amazing Golden Ears out there who would have scored higher in the tests than any of us. But, please, don't talk to me about tremendous differences in sound quality between CD players of current or recent manufacture because I'll laugh in your face. (And don't hassle me about the ABX method because I'll instantly agree to, say, switching by hand plugging and unplugging without relays, or any kind of time frame-such as one trial a day for 16 days-or any other method, as long as you match the levels and are listening to an unidentified sound when you give your answer. What I want the hasslers to explain to me is why every Golden Ear I or my associates have tested suddenly turns to tin when the levels are matched and the brand names are withheld. If you don't have an answer to that, please don't bore me with ecclesiastical arguments about side issues.)

Aragon D2A

Mondial Designs Limited, 2 Elm Street, Ardsley, NY 10502. D2A D/A converter, $995.00. Tested sample on loan from owner.

This is a gorgeous piece of equipment, somewhat handicapped by a wrongheaded decision regarding the analog output interface. The output stage is of the common emitter configuration, with a very high output impedance, unsuitable for driving a low-impedance volume control (as in a passive preamp or input-attenuated power amp) and also a poor match for high-capacitance interconnect cables.

A properly designed active preamp will wash out these in compatibilities-but what if you have, or want, one of those trendy passive preamps, or no preamp? The fully discrete analog section (by itself a noble idea) has the further small boo-boo that the differential pairs are biased by a resistor which causes the bias current to vary in the presence of a common-mode signal, resulting in increased distortion. A minor engineering simplism.

Other than that, the D2A is a most attractive buy. You take off the cover and you can see where the money went; the parts and construction are of near-military quality, and the digital circuitry is highly sophisticated, with no chintzy solutions apparent in the details. The digital filter is the very expensive and complex Sony CXD1144BP. I don't even quite understand how Mondial does it for $995. The DAC is the J grade of the 18-bit Burr-Brown PCMS58P, which is good enough in my book, but yes, there are trim pots, and no, they weren't perfectly adjusted in my sample. I measured a small amount of low-level nonlinearity that wouldn't have been there in my opinion with just the naked, factory-trimmed J grades (see above). On the other hand, the D2A is loaded with quality features, such as two coaxial and one optical digital inputs (no tweaky "optophobia" here!), a digital absolute-phase inversion switch (wow!), a pre-emphasis indicator light (an almost extinct but still relevant convenience), and more.

Summa summarum, this could have been the perfect D/A processor for the audiophile who knows value when he sees it, if only a few little engineering decisions had gone the other way. Even so, any owner of the Aragon D2A who is unaffected by those decisions can be justly proud of it. It's a good machine.

Carver TL-3220

Carver Corporation, P.O. Box 1237, Lynnwood, WA 98046. TL 3220 compact disc player with remote control, $529.00. Tested sample on loan from manufacturer.

Here we are at the bottom of the price range covered in this survey, meaning parts and construction typical of mid-priced made-in-Japan audio components, a few nice little Bob Carver touches, some inevitable engineering trade offs, the absence of certain features-you get the picture.

Nonetheless, amigos, the sound of the Carver TL-3220 was statistically indistinguishable in double-blind, matched-level listening from that of the $850 Pioneer Elite PD-71 (to name just one example), which is a thoroughly audiophile oriented product. Sorry about that.

This is also an 18-bit, 8 times oversampling design, but the DAC is the lowest-grade Burr-Brown PCM61P, which works best with a little trimming. The trim pots appeared to be reasonably well aligned, since the low-level gain linearity and harmonic distortion were quite acceptable though not outstanding. For reasons unknown, a sample and-hold circuit is included. Other eyebrow raisers are the very low +8 V supply rails in the analog stage, low-voltage op amps of unfamiliar designation, electrolytic capacitors in the output signal path-I could go on, but then I have no solid proof that the avoidance of such audiophile hang-ups has any audible effect.

One of the unique Bob Carver touches is the-you guessed it-Digital Time Lens, the flamboyantly named signal processor circuit designed to make early CDs sound more like LPs. It does that by softening the upper midrange and increasing front-to-back depth with some L - R tweaking. One thing is certain: when you press the DTL button, the Carver TL-3220 no longer sounds like the Pioneer or any other CD player. I have very little use for it, but it may conceivably be somebody else's main reason for buying the Carver. I do wish, however, that the DTL circuitry were by passed instead of merely deactivated when the button is in the out position. On the other hand, I rather like Bob's highly personal ergonomic layout of the front-panel control buttons, quite different from standard Akihabara issue.

My severest criticism of the TL-3220 is that it lacks a digital output, either coaxial or optical, and that neither the front panel nor the remote control has index search buttons.

A CD like the Richard Strauss Eine Alpensinfonie (Telarc CD-80211) has just one track but 22 indexes. The TL-3220 is incapable of selecting one of the latter; it can only be fast forwarded to the approximate location, and even that takes forever. Yeah, I know, Bob-that old Buddy Holly CD transfer you take with you everywhere doesn't have that problem.

Euphonic Technology MK II Signature

Euphonic Technology, 19 Danbury Road, Ridgefield, CT 06877.

Mark II Signature compact disc player with remote control, $1595.00. Tested sample updated from the ET650PX reviewed in Issue No. 11.

Michael Goldfield is one of the most highly endorsed Philips modifiers in the delirious little world of high-end audio. He does a beautiful job and then charges far too much, for the simple reason that you can't make a living charging a fair price for Philips mods. Therefore he absolutely needs a cult following-and he gets it. His mods just sound more "musical" than anything else you can buy, the true believers will tell you. (To paraphrase Samuel Johnson outrageously, musicality is the last refuge of a tweak.) Actually, the Mk II Signature differs from the 1987 vintage ET650PX reviewed in Issue No. 11 in only five ways that I can discern: the DAC is now the TDA1541A S1 "Golden Crown" chip, not the plain-vanilla TDA1541; the digital filter is similarly upgraded to the SAA7220P/B; the DAC power supplies are new; the headphones output is "disabled for sonic benefit" (tweak tweak hooray!); and the price is up $600. And for your $1595 you still get the antediluvian and relatively insubstantial Magnavox CDB650 chassis (reinforced with the Euphonic Technology DPS-1 stabilizer, to be sure) and the Motorola MC34082 analog output chip, wholesale cost $1.00. (Mike is very secretive about these chips, having obliterated all identification on them and refusing to reveal their provenance, but circumstantial evidence and educated guessing point insistently to the Motorola. "If this be error and upon me prov'd," blame it on the secrecy.) Now consider the Philips CD-80 reviewed below.

Same DAC. Same digital filter. Just as good, or better, power supply regulation. The greatly improved NE5534 de-compensated opamp in the analog stage (rather than the Magnavox's NE5532 which Mike disliked so much that he had to replace it with the Motorola). Plus a heavy-duty cast-alloy chassis with superior moving parts and better ergonomics.

All that for $799.95, barely half the price of the Mk II Sig nature. See what I mean about the Philips mod business? To tip the scales even more cruelly, the gain linearity at --90 dB in one channel of my Signature sample was off by more than 3/4 LSB, which is out of spec for the Golden Crown DAC, and the noise floor of the Signature in both channels was about 5 dB higher than that of the CD-80. The DAC glitch is probably just a QC slipup, but the noise is not; the Motorola chip can be assumed to be the culprit there.

None of this makes Michael Goldfield's handiwork less handsome, or the sound of his CD player less good than that of any other unit reviewed here. It's just that the realities of the industry are not on his side.

Harman/Kardon HD7600

Harman/Kardon Incorporated, a Harman International Company, 240 Crossways Park West, Woodbury, Long Island, NY 11797.

HD7600 compact disc player with remote control, $599.00. Tested sample on loan from manufacturer.

I should have reviewed this excellent CD player in the last issue-that's how old it is, with an updated Mark II version already in the pipeline-but then I decided to consolidate all CD playback-related material in this issue. (The same design also exists in a somewhat leaner $449.00 economy version, called the HD7500, which is identical except that it lacks digital outputs, index search buttons, and a few other minor control conveniences-almost forgivable at a list price $80 lower than that of the Carver above.) This "old" HD7600 represented my first encounter with any of the new 1-bit DAC architectures-in this case the Japanese MASH system-and I was duly impressed with the low-level linearity. Since then I have looked at other "bitstream" implementations, and in every one of them the nonlinearity was within the accuracy limits of my test setup.

Better than trim pots, right? As for the Harman/Kardon analog stages, they are the most elaborate to be seen in any CD player made in Japan, regardless of price, with fully discrete circuitry and total observance of the guidelines laid down by Matti Otala when he was with the company years ago.

Unfortunately, that approach is inherently more costly than the conventional one using inexpensive chips, necessitating inevitable compromises in the quality of parts and construction to keep the price of the HD7600 down. One wonders whether high-performance integrated op amps wouldn't have been a more appropriate choice in this price range. Of course, some of that Harman/Kardon personality would have been gone. In any case, I measured no anomalies worth mentioning in either the digital or the analog circuits.

Ergonomically I found the HD7600 to be excellent; the buttons are well-located and have a nice, positive feel, as does the disc drawer; the display is first-rate. The sound? Again, no different from that of any other unit in this group, as far as any of us could tell. At $599, however, this is an outstanding buy, and the $150 cheaper HD7500 version is a very serious bargain if you can live with its austerities. The Mark II versions have been announced at $699 and $529, respectively; at those price points they are somewhat less attractive and begin to have more competition, unless the improvements are greater than I'm currently aware of.

JVC XL-Z1010TN

JVC Company of America, division of US JVC Corp., 41 Slater Drive, Elmwood Park, NJ 07407. XL-Z1010TN compact disc player with remote control, $700.00. Tested sample on loan from manufacturer. ) JVC is also beginning to make the 1-bit DAC scene, so I don't predict a long life for this somewhat aging multi bit unit. What they call its "quadruple full-time linear 18-bit combination D/A converter" is actually the lowest-grade Burr-Brown 16-bit DAC, the PCMS56P, with external components added to handle the lowest 2 bits, bringing the count to 18. Something of a kluge. The low-level gain linearity I measured was essentially perfect in one channel and about 1/2 LSB off in the other channel (at 90 dB), so I can't complain too much. A sample-and-hold circuit is need ed with this DAC configuration, and there are other little not-quite-audiophilic touches throughout, such as an electrolytic capacitor in series with the output signal and the plebeian NES5532 op amps in the analog stage. I also saw a bit more RF in the output than I liked. On the other hand, the so-called K2 Interface, designed to remove jitter by re clocking the digital data before D/A conversion, is a state of-the art feature, made less impressive only by the fact that Sony does the same thing without making a fuss about it.

Don't misconstrue these critical observations as a general dis-recommendation of the JVC. If no other CD player were available to me, I would find it eminently satisfactory.

It has everything; it does everything; and it sounds as good as any of the others reviewed here. But in a circuit--for circuit, chip-for-chip, feature-for-feature shoot-out with the competition in its price range-not neglecting mechanical construction and controls/ergonomics-it is clearly out gunned. JVC has considerable sophistication in this area of electronics, and I fully expect them to come out with some thing more exciting in the very near future. They have already announced a "pulse edge modulation" 1-bit DAC that looks promising in their lower-priced line.

Meridian 208

Meridian America Inc., 14120-K Sullyfield Circle, Chantilly, VA 22021. Meridian 208 compact disc player and preamplifier, with 209 remote control, $2950.00. Tested sample on loan from USA distributor.

Yes, I know, the English gave us Shakespeare, New ton, the RAF fighter pilots of 1940, and the Beatles. But they drive on the left side of the road, serve lukewarm beer and hang their plumbing on the outside of the house so the water freezes in the winter. They're too damn impractical, and so is their Meridian 208. I still can't believe it costs al most $3000, even with the built-in rudimentary line-level preamp and Boothroyd Stuart pin-striped styling. (For pin stripe in four figures, I'll take Giorgio Armani.) Seriously, though, I had an off-putting experience as soon as I tried to put the battery into the remote control unit.

Everybody else's battery compartment has a sliding or snap on cover, but not Meridian's, chappies. Four Phillips-head screws keep it in place, torqued down by some Kentish lout with large hands, and the screw heads are butter soft so that the resistance to any counterclockwise turning will strip them. Unless you enjoy the sight of metal shavings shedding from your new $2950 toy, your heart will be filled with hatred by the time you have that silly, impractical cover off the battery compartment. A little intelligent planning could have saved a lot of aggravation here. And that's not all. The display of the 208 is of the earliest, minimalist Philips de sign, the same that Tandberg used to have, and the control buttons are an ergonomic fiasco. For example, moving to an index point is a three-step operation. Of course, inconvenience is the proof of high-end performance in some circles.

Well, what about that performance? Quite impeccable, I must admit. The Philips Bitstream 1-bit DAC architecture used results in just about perfect low-level linearity, probably more perfect than my measurement setup. Although the Philips SAA7321 chip is a stereo DAC, the 208 has two of them connected in a balanced configuration, a good idea made somewhat less remarkable by the fact that the Harman/Kardon HD7500 economy CD player at less than one sixth the price uses a similar arrangement. What's more, the latter gives you discrete analog circuitry whereas the 208 uses the NE5534 integrated op amp, the current Philips standard. On the other hand, the output of the 208 doesn't pass through an electrolytic capacitor like that of the HD7500 but is directly coupled with a DC servo. (Be thank ful for small favors.) Anyway, regardless of the strange mix ture of chintzy and quality touches on the circuit board, I could measure no imperfections worth mentioning in the electrical performance of the 208. As for mechanical performance, the disc transport is basically the same as in the top of-the-line Philips LHH1000-no complaint there-but the latter is a far more deluxe and better engineered package.

That leaves us with the $2950 question: What does the Meridian 208 have going for it at its price? The answer is-Martin Colloms! In the January 1990 issue of England's Hi-Fi News & Record Review, a few months before the 208's American debut, Mr. Colloms canonized it as the overall best-sounding CD player known to him. What can I say? It certainly sounds as good as any of the others re viewed here, but better? Not to my or my associates' ears.

Of course, Martin didn't use the ABX Double-Blind comparator, and I did. So the best I can say for the 208 is that I'll gladly use it in my system as long as (1) somebody else pays for it and (2) somebody else operates the buttons.

Onkyo Integra DX-7500

Onkyo U.S.A. Corporation, 200 Williams Drive, Ramsey, NJ 07446.

Integra DX-7500 compact disc player with remote control, $700.00.

Tested sample on loan from manufacturer: This is a very impressive player for the money, with a surprising number of quality features, although one of my routine tests tripped it up in a mysterious way. More about that in a moment. What I like about the DX-7500 is that it is very solidly built and generously engineered, with a high quality disc transport employing linear tracking (but, inexplicably, without a velocity-sensing feedback coil), control buttons with a positive feel and excellent ergonomic layout, dual transformers and opto-coupling to isolate the digital and analog blocks, coaxial and optical digital outputs, DC coupled analog output with servo, and a choice of several line-level output options, one of which (labeled "direct") al lows the signal to pass through only a single analog signal processing stage. Quite a serious piece of equipment.

The DAC is the J grade of the 18-bit Burr-Brown PCMS58P, with all four of the optional linearity adjustments included. The trim pots appeared to be more or less correctly adjusted in my sample, with low-level errors ranging from 1/4 to 1/2 LSB, including my measurement errors. I have seen slightly better J-grade performance, but only without the trim pots! An interesting though probably not very significant measurement showed the usual clipping of a 0 dB square wave by the digital filter to be symmetrical through the "direct" output but asymmetrical through the "fixed" output. Decisions, decisions.

The one thing I didn't like was the response to the high-frequency two-tone test (19 kHz at -6 dB plus 20 kHz at -6 dB, equivalent to a single tone at 0 dB). All players passed this test without any intermodulation products within the audio band, but the Onkyo showed intermittent distortion blips of the order of 40 dB (1 %) at constantly shifting frequencies (3.6 kHz was typical) and of short duration, impossible to pin down with any degree of accuracy. I have no idea what this was, certainly not garden-variety steady state IM. IT was ready to make the statement that nobody needs a better CD player than the Onkyo Integra DX-7500, but this anomaly stopped me. That doesn't mean that any other player beat it in the ABX comparisons; it held its own against all comers, but so did all comers against it.

Philips CD-80 Philips Consumer Electronics Company, One Philips Drive, PO. Box 14810, Knoxville, TN 37914-1810. CD-80 compact disc player with remote control, $799.95. Tested sample on loan from manufacturer.

From where I'm sitting, Philips appears to be headed for across-the-board 1-bit DAC architecture in their CD players, even though they originally developed the concept with portable and low-end models in minds. Thus the 16-bit CD-80, representing the highest evolution of the line in which the CD880 used to be the corresponding model, may very well be the last of the Mohicans; there seem to be no newer multibit models coming out of Hasselt, Belgium. In any case, I find the CD-80 to be an outstanding piece of equipment, with virtually no negative attributes.

The unusually heavy chassis is very similar in construction to that of the $4000 top-of-the-line LHH1000, and many of the electronic components are of unexpectedly high quality. The disc transport is not quite the same as in the LHH1000 but is still excellent. Special attention has been paid to routing the digital and analog signals away from each other. Fully discrete double-regulated power sup plies are another feature. The front-panel control layout is somewhat "creative" and takes a little getting used to, but you soon learn to like it. The remote control is conventional.

The chip complement includes, among others, the TDA1541A S1 "Golden Crown" DAC (which is designed without external trimming options), the SAA7220P/B digital filter, and the NE5534 de-compensated op amp, a combi nation also used in the LHH1000. The analog outputs are di rect-coupled with a DC servo and protected against failure of the servo. I found the worst-case low-level gain-linearity error (in the less good channel at -90 dB) to be of the order of 1/2 LSB, which is not quite as good as can be obtained with the best Burr-Browns but certainly good enough. The same can be said of the low-level harmonic distortion spectra; there are some tiny blips peeking out of the noise floor where there are none with the best Burr-Browns, but again nothing worth complaining about. Various high-frequency test signals produce the usual predictable small-amplitude beat tones above the audio range; that's the way Philips chooses to do the filtering and there's nothing really wrong with that, either. I would have liked, however, to see less RF coming out of the back end of my sample, although it didn't create any problems in my electronic environment.

The bottom line is that the CD-80 has made all those audiophile Philips mods overpriced and irrelevant. Philips took a good look and included in their package pretty much all of the goodies the modifiers had come up with, only with slicker execution and at a better price. I could live with this player, even if the future doesn't belong to 16-bit DACs.

Pioneer Elite PD-71

Pioneer Electronics ( USA) Inc., P.O. Box 1720, Long Beach, CA 90801. Elite PD-71 compact disc player with remote control, $850.00. Tested sample on loan from manufacturer.

This is another CD player I'm catching at the tail end of its natural life; by the time you read this it may have been phased out and replaced by the almost identical PD-73. The only difference is that the latter has the new 20-bit Burr Brown DAC, on which Pioneer has a temporary exclusive (at least as far as I know). The PD-71 uses the Burr-Brown PCMS58P-K, which is the top grade of the top 18-bit DAC in the line. You can assume that the PD-73 will perform similarly, or possibly even better if the jump from 18 to 20 bits is indeed meaningful, but only if the MSB trim pot in each channel is accurately adjusted for maximum DAC linearity.

Of the two samples of the PD-71 I had a chance to look at, one appeared to be trimmed in perfectly, the other not. Un fortunately, it was the latter that became my long-term lab sample; the first I had checked out on the fly while its owner waited. It would be meaningless to specify the errors in the poorly adjusted sample, as it would provide no information about any other sample, so let me just say this:

The Burr-Brown PCMS58P-K, with the optional external. bit-linearity trimming correctly fine-tuned, is the most nearly perfect 18-bit DAC on God's green earth, so the low level performance of your PD-71 (or, by extension, the up graded 20-bit PD-73) has nothing to do with engineering and is strictly dependent on the individual history of your unit, starting at the QC stage. That doesn't really help you, I know. It's fairly easy to make those adjustments on a properly equipped lab bench, but I'd be surprised to find a dealer able and willing to do it. The answer is, of course, to design the equipment without the trim pots.

The PD-71 has many other quality features in addition to the potentially best multibit DAC there is; in fact, it's more or less the Japanese opposite number of the Philips CD-80, each offering minor advantages over the other. The Pioneer is more deluxe in appearance, with one of the most elegant cabinets in the business; the Philips is much heavier, more rugged-looking, more technocratic/industrial in style.

Ergonomically the Pioneer is excellent and perhaps easier to like; I happen to prefer the Sony CDP-608ESD to either one. The Pioneer has an excellent linear-tracking disc trans port made with Sony components; there is some tenuous evidence that this transport tracks certain defective discs that the Philips has trouble with. The Pioneer appears to have slightly better RF suppression; it uses discrete push-pull power supply regulators (good); it operates all active op amp stages in the inverting mode to eliminate common-mode input signal distortion (good); unlike the Philips, it has no provision for headphones nor a volume-controlled output (high-end etiquette); it passes the analog signal through three gain stages and a non-polar electrolytic output capacitor (not so good-the Philips does it better); it also uses some op amps that aren't exactly state-of-the-art. Overall, the PD-71 is very conscientiously built and worth its price.

As I indicated in the Carver review above, the PD-71 didn't sound verifiably better or worse than the much lower priced Carver TL-3220, or any other CD player reviewed here, but that's an old refrain of this survey by now. Even so, I'd rather own the Pioneer as long as I get a chance to adjust those trim pots.

One more thing. The PD-71 is Precision Audio's cur rent favorite for their excellent D1 Analog mod (see Issue No. 12). The debut of the PD-73 presages heavy discounts on leftover PD-71's if you're interested in taking that route. PS Audio "Digital Link" PS Audio, 302 South 13th Street, Grover City, CA 93433. "Digital Link" outboard D/A converter, $799.00. Tested sample on loan from manufacturer.

Paul McGowan and Bob Odell of PS Audio are decidedly in the tweako camp. They believe in a lot of the audiophile voodoo I ridicule in these pages (the stuff that I can't hear and nobody can prove is hearable). At the same time, their products are superbly engineered and utterly sensible in terms of cost-effectiveness. As long as they make equipment like the Digital Link, they can go ahead and believe in the tooth fairy for all I care.

As a matter of fact, if an enlightened audio perfection ist made a wish list of D/A processor design elements and features requiring no extravagant expenditure, he would be describing something reasonably close to the Digital Link.

It's basically what the demanding but sane aficionado needs if he decides to take the outboard processor route.

The DAC around which the processor is built is the Burr-Brown PCM61P, which according to some maverick practitioners (but not Burr-Brown) is more linear than the PCMS58P and "sounds better." The J grade of the PCM61P was used in my sample; later production, according Paul McGowan, uses the K grade. Regardless of these distinctions, I measured essentially perfect low-level linearity in both channels of the Digital Link. The analog section consists of a single stage employing a state-of-the-art, high speed, complementary bipolar IC (Analog Devices AD847) in a rather unusual low-feedback configuration. A high current output buffer circuit is used in conjunction with the IC, and the output is direct-coupled with only an offset pot for DC cancellation. (No copycat, this Paul McGowan.) The current-to-voltage conversion circuit is passive, resulting in the relaxation of settling-time requirements for the op amp (good), greater voltage swing on the DAC output line (dangerous living distortion-wise), and a significantly decreased signal-to-noise ratio (not so good, but more about that in a moment). The power transformer is a bit on the chintzy side but is separated from the tiny main chassis by an "umbilical cord" in order to reduce hum levels; the Digital Link and the Aragon D2A were the only units in these tests with that feature. No jitter attenuation circuit is used in the SPDIF de coder, an economy I deem acceptable considering where the money was spent instead. On the other hand, I wish there were an optical input in addition to the coaxial one provided; fear of optical data transmission is a high-end neurosis I can't relate to. Physical construction is unimpressive; the crowded PC board floats inside the generic modem chassis and is kept from shorting to the chassis on the foil side by a thin piece of plastic.

My laboratory tests revealed no objectionable weak ness anywhere. Yes, the noise floor in the absence of a digitized signal is a whole order of magnitude (approximately 20 dB) higher than in the best Japanese CD players, but in the presence of a signal it is just about the same, rendering the issue academic. The maximum signal-to-noise ratio achievable on a CD with 16-bit A/D encoding is theoretically 98.1 dB, and the Digital Link accommodates that with a very healthy margin to spare. I must therefore approve of the audio-quality-oriented noise-floor trade-off. I was less happy about the amount of RF I saw pouring out of the back end of the unit, but I can't report any interference problems in my particular electronic environment (for whatever such a limited criterion is worth).

Bottom line: I left the Digital Link in my reference setup, driven by whatever transport happened to be handy.

No, not because it sounded better than any other unit re viewed here-as you already know, it didn't, and vice versa--but because it ought to have sounded better on the basis of its analog engineering and intelligent trade-offs. Let no one say I've stopped being a hi-fi nut.

Sony CDP-608SESD

Sony Corporation of America, Sony Drive, Park Ridge, NJ 07656.

CDP-608ESD compact disc player with remote control, $900.00.

Tested sample on loan from manufacturer.

When I received this outstanding unit for review, I made the mistake of saving it for this survey instead of squeezing it into Issue No. 14. Between Sony's propensity for constant model changes and this journal's propensity for delayed publication, that turned out to be a bad decision.

The 18-bit CDP-608ESD has now been replaced in the Sony line by the 1-bit CDP-X55ES, at the same price; in deed, their entire premium ES line now uses 1-bit DACs, of a newer generation than either Bitstream or MASH. Even 50, some dealers probably still have a CDP-608ESD or two left in their stockroom, and if the closeout discount is deep enough, grab it-it would be a very good value.

Frankly, I don't see how the new Sony 1-bit DAC can improve on the performance of the Burr-Brown PCM58P-J used in this superseded model-without MSB adjustment, I might add. I measured almost unbelievably perfect gain linearity all the way down to the lowest levels and saw no harmonic distortion blips peeking out of the noise floor at any level. The other star performer of the act is the Sony CXD1244 digital filter chip; here the design is one up on others by combining 8 times interpolation with noise shaping and digital de-emphasis. (The advantage of digital de emphasis is that it removes several passive components and a FET switch from the op amp summing junction; the disadvantage in comparison with analog de-emphasis is possibly increased noise and distortion at the player's output when playing a disc with emphasis.) Another advanced feature is that the digital data is reclocked before entering the DAC.

(JVC built its entire "K2 Interface" promotion around the same jitter-correcting technology.) The disc transport assem bly is Sony's high-quality G chassis, which combines a lightweight electromagnetic linear drive with the KSS151 three-beam optical block on a marble-like resin base. The decoder chip is the CXD1165, which was the dernier cri when the player was introduced. It's all pretty high-tech for a model going out of style and makes you wonder whether the switch to 1-bit DAC architecture is an engineering or a marketing decision.

The analog section, on the other hand, is not nearly as perfectionistic. The so-so NE5532 op amps are used as the active elements; the supply rails are +12 volts instead of the +15 volts specified by Signetics; the output signal passes through an electrolytic capacitor (albeit bypassed with a small film capacitor)-in other words, Japanese upper-mid fi audio circuitry. Not that it made an audible difference in double-blind comparisons at matched levels against various other players in this group; my objections are therefore somewhat theoretical.

Having said my piece on that, I must commend the CDP-608ESD for two things: the front-panel control layout and display, which were my ergonomic favorites among all the units reviewed here, and the total absence of RF at the output. Sony is the king of digital audio-if only they lavished equal care and talent on the analog part!

Sony D-555 "Discman"

Sony Corporation of America, Sony Drive, Park Ridge, NJ 07656.

D-555 "Discman" portable compact disc player, $450.00. Tested sample on loan from owner.

Does this yuppie toy, conceived for headphone listening on the way to the brokerage office or the sushi bar, belong in the company of the audiophile-caliber CD players reviewed here? I definitely think so. Even though its measured performance turned out to be somewhat inferior to that of any other unit in this survey, a quick ABX shoot-out between it and the $2950 Meridian 208 failed to reveal any reliably identifiable differences in sound. Admittedly, this test didn't go to the usual 16 successive double-blind trial runs but stopped about halfway. But even a sloppy non-blind comparison of the Discman with the Onkyo Integra DX 7500 was quite inconclusive. The Sony sounded maybe a little grittier and the Onkyo smoother to the listeners, who were quite happy that they didn't have to do any blind identifying. The visiting owner had to take the player back home with him, so I can't swear that a month's worth of comparisons wouldn't have established some clearer differences. At any rate, no other CD player, regardless of price, "blows away" the D-555 in sound quality. That much is certain.

The highly touted Digital Signal Processing (DSP) features of the Discman I found less impressive. The bass boost below 80 Hz (useful on cheap headphones), dynamic range compression (for car listening), "surround sound," and graphic equalization at five frequency positions-all of it digitally implemented-seem quite rudimentary; for ex ample, the so-called surround-sound processor appears to equate adjustable phasiness with an actual surround effect.

Of course, shoehorning even such rudimentary processing capability into that itty-bitty box is an achievement in itself, and that neat little LCD readout is a nice touch.

On the lab bench a number of little weaknesses be came apparent. The noise floor is only 90 dB below the 0 dB reference level, whether or not a digitized signal is present. The de-emphasis is not very accurate; it's off by as much as 1 dB at some frequencies and isn't right on the but ton at any frequency. The low-level linearity is simply not in the same league with the standard-sized players; in the less good channel I measured a full 1 LSB error at -80 dB, and at -90 dB there was total chaos in both channels. The resolution of the Discman is in effect somewhere between 14 and 15 bits-not a full 15 bits for sure-although the DAC is specced at 16 bits and paired with an 8 times interpolating digital filter. The digital circuitry even provides an optical output, but no coaxial. It should also be noted that the D-555 inverts the polarity of the input signal, a rare quirk these days. As for the disc drive and optical block, the quality seems good enough, but I was unable to play track 56 of the 99-track Philips "Audio Signals Disc 1" (SBC429); the damn thing kept muting for no discernible reason. Another possible cause for concern is the question of reliability and servicing; the owner of the D-555 I tested had had a terrible time with its predecessor, the D-T10; in fact, the D-555 was Sony's please-don't-bother-us-anymore free replacement for the hard-to-repair D-T10. Hm.

All in all, however, I must come out in favor of the Sony Discman. It's small, it's cute, it's not overpriced for what it offers, and it works. Its measurable shortcomings are almost certainly below the audible threshold, and its impact as audiophile costume jewelry is undeniable.

Theta DS Pre Basic

Theta Digital Corporation, 5330 Derry Avenue, Suite R, Agoura Hills, CA 91301. DS Pre Basic digital signal-processing preamplifier; $2400.00. Tested sample on loan from manufacturer.

Last in this survey, because of a vagary of the Roman alphabet, is the unit with the most elaborate digital circuitry.

The DS Pre Basic isn't actually a full-fledged preamplifier; it differs from a monolithic D/A processor only in that it has a digital tape loop, inputs for a single line-level analog source, fixed analog tape outputs in addition to the variable analog line outputs, a volume control, and a balance control.

It could be the control center for a simple CD/tuner/tape system, but that's it. The volume/balance controls involve no additional active stage. And yes, there's no optical input; it would spoil the high-end image, don't you see? (I don't.) Mike Moffat, the designer of Theta equipment, is yet another of those strange technologists who do everything knowledgeably and scientifically but talk voodoo to wide eyed audiophiles. (Do they think it's good for business, or do they with great sincerity manage to work themselves into a schizzy Jekyll and Hyde mind-set?) Mike Moffat's soft- ware-driven digital filter for the DS series, in effect a single purpose computer, is possibly the best-designed and most advanced in the business, at least as judged from his conversations with David Rich (no schematics and no computer code being available). At the same time, Mike claims to hear differences between printed circuit boards made of different materials and between DAC chips whose pins are made of different metals. Are these claims based on double blind comparisons at matched levels, Mike? Huh? (On the other hand, nobody held a gun to my head to make me g0 into high-end audio and take all this guff.) Other than the digital filter, which is implemented on a general-purpose DSP chip, the chip complement of the DS Pre Basic isn't proprietary but a little different nonetheless.

The 18-bit DAC is the AD1860N-K from Analog Devices, the K suffix indicating the highest grade. A trim pot in each channel adjusts the MSB. The op amp for the analog signal is the PMI OP42, a high-quality but no longer state-of-the art IC (a generation behind the AD847 that PS Audio uses, for example). The output is direct-coupled with a DC servo.

Construction and parts quality is very high (except perhaps for the use of that op amp), making the price tag palatable to the critical purchaser.

One design parameter that obviously matters a great deal to Mike is jitter. The SPDIF decoder includes three phase-locked loops to reduce jitter. The PLL circuits used are inexpensive CMOS devices (CD4046) rather than the more expensive crystal-controlled PLL circuits used in many Japanese decoders, which theoretically yield even lower peak jitter. Even so, Theta is the only company other than Mondial/Aragon to publish a peak jitter spec for the SPDIF decoder, namely 1 ns. Nice.

My lab-bench and in-use experience with the DS Pre Basic had its ups and downs. In the first sample they sent me, the left and right outputs were reversed and the MSB trim pots misadjusted. I proved to myself, however, that the latter could be adjusted for virtually perfect low-level linearity. A second sample, which looked more like a finalized production unit, had the left/right error straightened out, but the MSB adjustments were still way off, and the low-level linearity was poor until I again tried and succeeded tickling it into perfection. A few weeks later I sent the second unit back to Theta for a "basic capacitor upgrade" they had just then put into production. At the same time I insisted that they run the unit through QC again to bring it up to their highest standard MSB-wise. When it came back, everything looked textbook-perfect on the lab bench, with no anomalies or deviations worth mentioning. All right, one peculiarity, not a complaint: square waves at the 0 dB level are clipped more radically by the digital filter than in any other D/A processor I've looked at. No big deal. Also-and this has nothing to do with D/A conversion accuracy or audio fidelity-there's a lot of RF in the output, although a little less than before that latest mod. Still, it interfered to a slight degree with the performance of an FM tuner about three feet from the Theta. Little gurgles, hash, and birdies.

As for the sound of the DS Pre Basic--great! The fact that it's indistinguishable in ABX tests from the sound of any of the other units reviewed here doesn't make it less great. Indeed, on the basis of general engineering sophisti cation and palpable quality on the circuit board, this is argu ably the unit of choice in this survey, but those pesky MSB trim pots and the RFI give pause. My impression is that Mike Moffat has the ability to engineer a flawless piece of equipment; however, Theta as a manufacturing/marketing operation needs to get its act together a little more reassur ingly before I can be entirely satisfied. For openers, they could include an instruction booklet.

Recommendations

As the Germans say it thymingly, die Wahl ist eine Qual. The choice is agony. Trade-offs, trade-offs, nothing but trade-offs. My ideal CD player, or transport/processor, would have the nice feel, ergonomics, and quality control of the Sony CDP-608ESD... the digital filter of the Theta DS series ... the 20-bit Burr-Brown DAC of the new Pioneers (in the K grade but without MSB adjustments) ... the construction-quality-to-price ratio of the Aragon D2A and may be even its discrete analog circuitry (but with the addition of an output buffer)... I could go on but what's the use? It will never happen. Read David Rich's article, read my reviews, and decide what suits you best. When the unequivocally best choice arrives, I'll be less equivocal. Meanwhile (chuckle, chuckle) "they all sound the same"--and if you disagree with that, don't just vituperate but prove the contrary in a double-blind comparison at matched levels.

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[adapted from TAC 15, Spring through Winter 1990-91 ]

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