Carver SD/A-490t CD-player Review

The Carver SD/A-490t, a full-featured CD player, offers an unusual combination of the new and the old in audio technology. For example, it uses the latest in 1-bit MASH digital-to-analog (D/A) conversion, yet its analog output stages are vacuum tubes, a 6DJ8 double-triode amplifier for each channel. The advantages of 1-bit D/A conversion are well known, including excellent linearity at the lowest signal levels and a correspondingly wide dynamic range. According to Carver, the vacuum tubes give the player “the warm, melodious sound that is typical of tube technology.”

The SD/A-490t also incorporates Carver’s Soft EQ circuit (formerly called the Digital Time Lens). This switchable circuit slightly modifies the player’s frequency response and reduces the ratio between difference (L-R) and sum (L + R) signals in the program. Carver claims that the Soft EQ processing produces a more pleasing sound from many discs, especially early releases that were mastered by engineers accustomed to working with vinyl records.

The SD/A-490t can be programmed to play up to twenty-four tracks in any selected order or in a random order. A group of small buttons below the display window provides direct access to any track up to No. 21. A music calendar shows the numbers of the unplayed tracks (to a maximum of twenty). The display normally shows the current track and index numbers and the elapsed time on that track, but it can be switched to show remaining time on the track or disc. The display window also indicates when any of the SD/A-490t’s special features are being used.

Other features include repeat of the entire disc, any programmed track sequence, or any defined segment. A fader button smoothly lowers the playback level to zero in 2 to 10 seconds (the time is adjustable), then puts the player into pause mode. Touching the button again resumes playback from the point where it paused, with a smooth fade up to the original level setting. For efficient dubbing of CD’s, the SD/A-490t has an Edit feature to select the tracks that will fit optimally onto a C-46, C-54, C-60, or C-90 cassette. It can also be set for any other desired time span, and you can do some things with it that you can’t with similar features in other players. For example, you can specify some tracks you want on the tape and let the SD/A-490t figure out the best way to fill the rest of the cassette.

The transport controls are at the right of the display window. The pause/stop button selects those modes on successive operations (pressing the play button restores normal operation), and the pairs of scan and skip buttons operate conventionally, with a faster speed when a button is held down.

At the right of the panel is a large level knob that affects the variable analog outputs on the rear apron and at the headphone jack. To the left are a large, square power button and a small stand by button with a red LED. Engaging the latter control keeps the heaters of the output tubes energized constantly at a reduced voltage in order to provide a fast turn-on after the main power switch is activated (otherwise a warm-up of perhaps 30 seconds is required before a disc can be played).

The infrared remote control furnished with the SD/A-490t duplicates all of its front-panel functions except for power switching, drawer open/close, Edit/Time Fade, and Time Set. The player’s rear apron has, in addition to the variable-level outputs, conventional fixed-level analog output jacks and both coaxial and optical digital outputs.

The Carver SD/A-490t measures 19 inches wide, 12-1/2 inches deep, and 3-3/4 inches high. Finished in black, it weighs 9 pounds. The front panel is fitted with sturdy handles. Price: $700.

Lab Tests

The SD/A-490t’s maximum open-circuit output (from a 0-dB-level, 1,000-Hz test track) was 2.55 volts, somewhat higher than the standard CD player output of 2 volts. The player produced excellent volume levels with medium-impedance AKG K340 headphones. The maximum variable output was identical to the fixed output. Interchannel phase shift was very low in the midrange but reached about 20 degrees at 20 Hz, 16 degrees at 20,000 Hz, and 8 degrees at 10,000 Hz. Channel separation was 90 dB at 100 Hz, 97 dB at 1,000 Hz, 87 dB at 10,000 Hz, and 78 dB at 20,000 Hz, and channel imbalance was less than 0.01 dB. The A-weighted signal-to-noise ratio (S/N) was 106.3 dB, and the dynamic range was approximately 95 dB.

The player’s frequency response was flat within ±0.05 dB from 20 to 7,000 Hz, rising to a maximum of + 0.2 dB at 16,000 Hz before dropping off above 20,000 Hz. With Soft EQ activated, the output rose below 600 Hz and fell above that frequency. The low-frequency portion leveled off at about +1.2 dB below 200 Hz, and the high frequencies were down 1 dB above 2,000 Hz.

Carver’s specifications for the SD/A-490t include total harmonic distortion (THD) of 0.5 percent at 1,000 Hz. Although this is considerably higher than the 0.002- to 0.003-percent ratings typical of conventional CD players, it is still negligible from a listening standpoint. Our measurements showed THD of 0.1 percent at 0 dB, decreasing to 0.01 percent at —20 dB and 0.006 percent at — 30 dB. As we have come to expect of players using 1-bit D/A converters, the SD/A-490t’s low-level linearity was superb, with an error of only 0.2 dB at — 90 dB.

The heaters of the 6DJ8 tubes are operated from a DC supply to minimize hum and noise. The heater voltage was 5.7 volts, somewhat lower than the tubes’ rated 6.3 volts, presumably also in order to reduce the noise contributed by a vacuum-tube stage. In the standby mode, the voltage was further reduced to 4.6 volts. The plate voltage of the tubes (each was used as a direct-coupled amplifier and cathode-follower) was less than 62 volts.

The SD/A-490t was fairly insensitive to impact, requiring a firm slap on the top or sides to cause momentary mistracking. Its error correction was satisfactory though not exceptional. It played the 1,000-micrometer defects of the Pierre Verany #2 test disc with only a slight mistracking, but it definitely mistracked at 1,250 micrometers. The laser pickup’s slewing time was average, requiring 3 seconds to go from Track 1 to Track 15 of the Philips TS3 test disc.

Comments

In normal operation and listening, the Carver SD/A-490t was everything we would expect from a top-quality CD player. Although its measurements did not push the state of the art (already at “overkill” levels in many respects) to new limits, it was not deficient in any significant way.

Two features of this distinctive player merit special comment. The Soft EQ circuit is supposed to reduce the harshness of some CD’s. (In our experience, harsh-sounding discs have been mostly very early releases.) Being switchable, the function’s effect is easy to assess. With most discs we tried, it was negligible, but a few were noticeably improved, with a slight softening of their “edginess" and a more mellow quality. On the other hand, really good recordings could just as easily have their brilliance and definition diminished by Soft EQ processing, so it’s good that the feature is switchable.

The second special aspect of the SD/A-490t is its use of vacuum-tube output stages. One obvious and measurable result is a nearly hundredfold increase in distortion at maximum output level. Such distortion is typical of vacuum-tube amplifiers without heavy negative feedback, but in practice it means nothing, and the distortion we measured from the SD/A-490t was totally inaudible (being limited to low-order harmonics).

A more pertinent question concerns the audible benefits of tubes. It is largely a matter of faith: If you believe that vacuum tubes have some magical quality, you may hear it. I do not and did not. On the other hand, the tube stages had no flaws that I could hear or measure. Their DC heater supply and low operating voltages reduce their contribution to the player’s output quality to a slight measured distortion at maximum level; there was no audible noise or hum.

The bottom line is that the Carver SD/A-490t is a very good CD player with a full complement of features that also happens to use vacuum tubes in its output circuits.

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