OTHER TECH

The Original Review, April 1983
The Dragon is the first Nakamichi cassette deck to be given a name rather than a model number, and if the intent was to suggest an awe-inspiring creation, the technological innovations it embodies make “Dragon” a wonderfully apt designation. It is the company 's first recorder to feature auto-reverse playback and the first from any manufacturer with continuous automatic playback-head azimuth alignment.

The Dragon 's record and playback heads are made of Crystalloy, and they are entirely separate units whose gap widths (3.5 and 0.6 micrometers, respectively) are optimized for their different functions. The three-head design also permits immediate comparisons between the incoming signal and the recorded result. The near and far edges of the head faces are slotted so that no “wear groove” can develop during their life time, and the playback head is fitted with a lifter that pushes the cassette 's pressure pad out of the way when the heads engage the tape. Removing the influence of the pressure pad eliminates a potent source of scrape noise but requires an unusually precise dual-capstan drive system.

All these head-design features have been incorporated in Nakamichi decks for several years, though the use of a four-track playback head (two tracks for each direction of tape travel) is new. Overall, however, the Dragon 's playback-head design is utterly unique in our experience and sets an example we hope other manufacturers will emulate. Understanding this tape head and the NAAC (Nakamichi Auto Azimuth Correction) mechanism that goes with it requires a little explanation.

Ideally, all tape heads, whether for recording or playback, should be aligned so that their head gaps (where the magnetic action takes place) are exactly perpendicular to the axis of the tape. The recording and playback gaps are then parallel to each other. When this condition is not met there is an “azimuth error,” the result of which is a loss in high-frequency response. In the cassette format, an azimuth error of only a quarter of one degree, while having no measurable effect at I kHz, causes a 14.6-dB loss at 15 kHz and a 25.5-dB loss at 17 kHz, so its seriousness is obvious.

Even if a deck 's head gaps are perfectly aligned, cassette shells are notoriously imperfect; they all physically skew the tape to some degree, creating azimuth errors. This skewing is not consistent from one cassette to the next and, indeed, even varies somewhat as the tape plays through a single side. The most obvious skew-induced azimuth errors, however, tend to be between the two sides of the same cassette. No matter how carefully you align the playback head for one side, there is likely to be an appreciable treble loss on the other. To minimize skew-induced azimuth error in cassettes recorded and played back on the same deck, a number of Nakamichi (and some other) decks have for some years provided either manual or automatic recording-head azimuth adjustments, so that no matter how the playback head is aligned, the recording head will lay down a matching track. But this system, though effective, requires recording a test signal and thus cannot help with prerecorded tapes. And the cassette shells used by tape duplicators tend to be far worse in all respects than those you get with a premium blank tape.

The Nakamichi solution, embodied in the Dragon, starts by splitting the inside tracks of the playback head (which provide right-channel signals for each direction) into two electrically separate halves with their own playback gaps. Instead of only one gap “scanning” the 0.021-inch-wide right-channel tracks as on a conventional tape deck, there are two. As long as the playback head and the tape are correctly aligned, with no relative azimuth error, the output from these two gaps will be identical. But if the playback head is at all tilted relative to the recorded track, the signal on the tape will arrive at one of them before the other. This creates a phase difference between the two gaps, which is amplified within the Dragon and used to control a motor that pushes or pulls a flexible stainless-steel band inside the deck. This band, in turn, drives a mechanism that adjusts the head azimuth so as to eliminate the phase error and thereby match the playback head 's azimuth with that of the tape. The correction process is continuous during the recording or playback of a cassette. (Only the inside tracks are used in this process since the signals from the outside, left-channel tracks can be too unreliable due to tape damage.)

The construction of such a head and the automatic servomechanism that goes with it is an engineering tour de force, although, like all good engineering solutions, it is elegantly simple in concept. The playback head simply automatically adjusts its azimuth to compensate for any error it finds, whether it stems from the recording head next to it or from one in a tape duplicator 's plant, from a shift in tape direction or from cassette-shell imperfections or tape-path variations during the playing of a cassette.

If less dramatic than the automatic azimuth adjustment, the drive system in the Dragon is no less sophisticated. There are two direct-drive motors with a unique, constant-torque design in a closed-loop, dual-capstan arrangement. Constant tape tension is achieved by a 0.2 per cent speed differential between the supply and the take-up capstan motors, which are governed by a quartz-referenced phase-locked-loop circuit. The intent is to lower wow and flutter almost to the vanishing point-and our measurements indicate that the attempt is spectacularly successful.

Cassettes are inserted, openings downward, into the familiar cassette-well-door slides. When the door is closed a momentary drive pulse is supplied to take up any slack in the tape winding. The well is accessible for head cleaning and is illuminated, though label visibility is poor. Transport controls are arranged somewhat like rows of shingles on a roof, making for easy operation. A motor replaces the conventional solenoids to activate the various modes, resulting in smoother, quieter operation. In the fast-winding modes a CUE button slows the tape to about a third of its normal fast-wind speed and brings the heads close enough to it to pick up the program material faintly. Depressing one of the fast-winding controls a second time while cueing slows the tape still further and permits you to jockey the tape back and forth to find the beginning of a recorded selection. The memory-rewind feature backs the tape a counter unit or so beyond the 0000 indication on the LED readout, then advances it to the selected spot. All transport controls have indicator LEDs, and additional tape-direction indicators are provided on the cassette-well door. (The latter flash as the NAAC system corrects a large error.)