CD Player/Transport Reviews

"In the fields of observation, chance favors only the mind that is prepared."

When Louis Pasteur uttered these words more than a hundred years ago, he must have speculated that they would apply equally well to future circumstances as to the events of his day. What he couldn't anticipate, however, was the technology to which his insight now seems so appropriate.

Finding himself by "chance" without a CD transport at home one night, Theta Digital designer Mike Moffat (footnote 1) borrowed a videodisc player from his video system and hooked its digital audio output to a digital processor.

His "observation" was that it sounded better than the high-end CD transport he had been using. Being a designer of D/A converters and having a "prepared mind," he began looking into the mechanics of videodisc players to find out why they might sound better than his high-end CD transport.

The result of this fortuitous confluence—the "favor"—is the Theta Data transport reviewed here. After listening to different videodisc players and studying how they work, Mike became convinced that they were inherently superior to the CD-only machines used in high-end systems. Theta then picked the best-sounding videodisc player they could find, a Philips CDV-400, developed a data-clocking circuit to further increase its sonic performance, and put it all in a solid chassis with the Theta nameplate on the front panel—all for $2400 retail. And it plays videodiscs too.

Intrigued?

So was I.

Technical description
Huge. That's the only way to describe the Data. At 5½" high, 19" wide, and 17½" deep, the Data is imposing next to any equipment. Moreover, the chassis is nearly as high as the front panel, making its volume about three times that of the Esoteric P-2 transport. If I thought the chassis was big, I was in for an even bigger surprise when I opened the drawer. Being a videodisc player, the Data has a 12" drawer made to accommodate 12" and 8" videodiscs as well as CDs.

The Data is as slow as it is big. It takes a full 17½ seconds to load a CD and begin playing. In addition, its track access time is much slower than CD-only machines, taking nearly four seconds to search for a selected track.

The Data is based on a Philips CDV-400, a so-called "combination" player that accepts a variety of optical disc formats. Consequently, the Data can be hooked up to a TV or video monitor and play videodiscs just like a normal videodisc player. One difference, however, is that unlike most videodisc players, the Data has no built-in D/A converter for the digital audio soundtracks encoded on nearly all videodiscs. The videodisc's analog audio tracks appear at the analog audio output jacks, but to hear the digital tracks, an outboard D/A converter must be connected to the coaxial digital output.

The rear panel holds a variety of output connectors. In addition to the standard digital audio coaxial RCA output for connection to a digital processor, the Data provides video outputs in normal, RF, and S-Video formats. An antenna input, looped to the antenna output, is also provided. This allows your TV to get the antenna signal or the videodisc RF signal without switching. A pair of analog audio outputs allows connection to an amplifier for listening to a videodisc's analog audio tracks.

Most of the Data's controls are found on the remote control, not on the front panel. The remote is generous in features, including all the usual amenities plus a mode display option, random play, and index search. The front-panel display shows what kind of disc has been inserted, whether the videodisc has digital audio tracks, track number, and elapsed time. The remote is covered by 42 buttons of identical size and shape, making the Data more difficult to control than many CD players and transports. In addition, the remote's videodisc-related functions interfere with the Data's primary role—as a high-end CD transport.

But what makes the Data different from a normal videodisc player is the addition of a small printed circuit board attached to the rear panel near the digital output jack. This circuit reclocks the data with a crystal oscillator, reportedly lowering jitter in the digital datastream appearing at the digital output. This reclocking circuit also includes an output line driver, specifically designed for driving 75 ohm coaxial cables used to connect digital processors. A small output transformer completes this reclocking/output driver circuit. The final output appears on a high-quality RCA jack. For an additional $400, Theta offers an AT&T fiber optical output in addition to the coaxial jack.

The front panel is ¼" machined aluminum and the chassis is bent steel. A spike that threads into the bottom rear of the unit is supplied, presumably supporting the chassis weight. Theta claims better sonics with the spike installed, and recommends its use. Build quality is good, but the Data's look and feel are decidedly utilitarian rather than the elegant.

Why a videodisc player?
Before getting to the musical impressions, a little background on videodiscs may shed some light on why a videodisc player may be inherently superior to a CD-only transport. Looking at the Data as a CD-only machine, it is clearly over-engineered; the design requirements for a videodisc player are far more rigorous than for a CD player. Here's why.

A CD spins at a constant linear velocity (CLV) of between 1.2 and 1.4m/s (meters per second—the linear velocity is chosen according to program length). As the laser head moves toward the end (outside) of a disc during normal play, the disc rotation gradually slows down to maintain a constant data speed as seen by the laser. A CD player's rotational speed thus varies from about 200rpm (outside) to about 500rpm (inside). The player's focus servo system that keeps the laser at the precise distance from the disc is designed for these speeds. Similarly, the CD transport's other circuits and mechanisms—tracking servo, rotational servo, and drive mechanism—are all designed around a lightweight disc that spins to give a constant linear data velocity of 1.4m/s.

A videodisc player, however, has a much more difficult job. For starters, a 12" videodisc weighs 200 grams, about 11 times more than a CD's 18gm. The rotational drive must be strong enough to accommodate this additional mass. On top of that, a CLV videodisc (also called "extended play," with 60 minutes per side) spins with a Constant Linear Velocity of 11.4m/s, about 10 times greater than a CD's linear velocity (the videodisc's larger diameter, however, means than the actual rotational speed is less than ten times faster). In addition, the videodisc player's rotational drive must also respond to rapid changes in playback radius when searching different areas of a CLV videodisc. Scanning from an outside disc area to an inside disc area means the player must accelerate the heavy disc quickly to very high speeds. The combination of the videodisc's faster rotational speed, much greater mass, and the fact that much of that mass is far away from the rotational axis when compared to CD, means the inertial energy is vastly greater than that of a 4¾", 18gm CD.

Further taxing the player, a Constant Angular Velocity (CAV) videodisc (30 minutes per side) spins at 1800rpm regardless of its playback radius. This means that at the outer edges, the disc is traveling at over 60 miles per hour (28m/s) in relation to the laser (over 20 times faster than a CD). Remember, the laser pickup must maintain a constant distance from the disc to stay in focus, putting enormous demands on the focus servo electronics and mechanism at these high speeds (footnote 2).

When playing a comparatively featherweight CD at snail-like speeds, a videodisc player is operating far below its design parameters. Consequently, there theoretically will be less servo interaction with the power supply, and the focus and rotational drive systems will maintain a greater precision. Playing a CD in a videodisc player is like shipping a phono cartridge in a freight truck.

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Footnote 1: Now with Schiit Audio.—Ed.

Footnote 2: The lens is attached to a voice-coil–like structure suspended in a magnetic field. The focus error signal is amplified, driving the voice-coil/lens in the correct direction to maintain focus.