Nakamichi 660ZX

A discrete-head cassette deck with an Auto Azimuth Alignment system that Nakamichi billed as a new era of high-fidelity recording. The service manual reads like a warning label.

Overview

The 660ZX was Nakamichi's attempt to end the fiddliest ritual in cassette recording. Its headline feature, Auto Azimuth Alignment, was billed in the company's own advertising as "undoubtedly the most advanced and sophisticated innovation in cassette-recorder technology," a system that "launches a new era in high-fidelity recording." The same campaign copy ran in HiFi-Stereo (February 1980, p.13), High Fidelity (February 1980, p.19), and Audio (February 1980, p.59), so Nakamichi pushed it hard. Marketing copy is not a verdict, but it shows what the deck was for: automatic correction of record-head azimuth, so the alignment between record and playback heads stayed optimal without the owner touching a screwdriver.

What the surviving documentation makes clear is that the 660ZX is a machine built around a motorized alignment mechanism, and that the rest of the deck — the cam-driven transport logic, the head-height and stroke adjustments, the back-tension setting — exists in service of keeping that mechanism honest. The owner's manual lists the front panel as a fairly complete control set: a pitch control, a tape start memory switch, a RAMM display, peak level meters, record calibration controls, a three-position tape switch (EX/SX/ZX), an EQ switch for 120 µs and 70 µs, a Dolby NR/MPX filter switch, an Auto A/Tone switch, and a timer switch. There is a see-through cassette holder cover, a headphone jack, and a rear-panel voltage selector that lets the deck run on either 120 V or 220–240 V — a useful detail for anyone buying a unit that may have crossed an ocean.

Auto Azimuth Alignment and the Service Reality

The Auto Azimuth system is the reason the 660ZX exists, and the service manual treats it as the most delicate thing on the chassis. Setting record-head azimuth is not a matter of turning a screw until it sounds right. The procedure calls for a VTVM connected to the Playback Eq. Amp outputs, a Reference SX tape (Nakamichi part DA09025A), the EQ switch set to 70 µs and the tape switch to SX, and the Auto A/Tone switch in the Cal. position. From there the technician turns the record-head height gear until both channels peak, feeds a 15 kHz tone at −20 dB, and turns the azimuth screw for maximum output. Then the whole sequence is repeated once or twice. The manual is also explicit that the azimuth alignment wire must be pulled off the motor assembly by hand, the slide lever left undisturbed, and capacitor C903 on the Auto Azimuth PC board shorted with a jumper before any of this begins. When the work is done, VR901 on that same board is adjusted so the azimuth motor stops rotating.

That is a lot of procedure for one adjustment, and it explains why technicians know the 660ZX as a deck you do not hand to a beginner. The verification step gives it away. After alignment, the manual tells the tech to record a 400 Hz tone to the same portion of both sides of a tape, immerse the tape in magnetized developing solution, and inspect the recorded tracks to confirm the record head is tracking across the center with a gap of 0.55 to 0.75 mm, typically 0.65 mm. Nakamichi expected whoever serviced this deck to develop tape.

Transport, Back Tension, and the Cam Logic

The 660ZX is described in its own manual as "an adjustment-free Model," which reads differently once you've seen the adjustment section. Back tension is only specified for units with serial numbers A30704141 and greater. Earlier decks used a different arrangement. On the later units, the procedure requires a Tension Arm Adjustment Cassette (DA09056A) and a Back Tension Gauge (DA09055A). The target is a torque reading of 6 to 10 g-cm, with a recommended working range of 7 to 9 g-cm, achieved by moving the installation point of the back tension spring. If the reading is off, the manual says to bend the back tension arm with pliers until the gap between the cassette holding spring and the arm is 0.5 mm, without bending the pointed end. A separate caution says the reel hub assembly should be replaced rather than repaired if take-up torque drifts, because weak or excessive take-up torque causes tape travel problems that no amount of guide adjustment will fix.

The transport logic runs off a control motor and cam. The manual devotes pages to keeping the cam's stop, play, fast-forward, pause, record, and cue positions aligned with their marks on the mechanism chassis. The reference voltages at the cam control volume VR405 are given as typical values - 3.0 V in stop, −2.8 V in pause, −5.4 V in play, 4.1 V in record. The fine adjustment is made by changing fixed resistors on the logic board: R461 for stop, R462 for fast wind, R445 for pause, R443 for play, R601 for record. The manual notes that adjusting R461 throws off the fast-wind reference, so the fast-wind value has to be rechecked afterward. It is an interlocking chain of adjustments, and a properly sorted 660ZX feels like a different machine from a tired one.

The Head and Alignment Gauges

Nakamichi's service documentation for this deck assumes a bench full of proprietary tooling. The recommended instrument list includes the Tilt Check Gauge M-9039 (DA09039A), the EH Stroke Check Gauges M-9042 and M-9051, the Stroke Check Gauge M-9047, the Record Head Mounting Gauge M-9048, and the 15 kHz Azimuth Tape DA09004A, alongside standard gear like an audio generator covering 20 Hz to 200 kHz, an AC millivolt meter with dB scales, a distortion meter, and a speed and wow/flutter meter. The manual even specifies which stroke gauge applies to which serial number range: M-9042 for decks from A30701001 to A30702750, and M-9051 for A30702751 and up. A deck that requires you to know its serial number before you can buy the right gauge is a deck with a paper trail, and the 660ZX has one.

Head height and azimuth alignment on the playback side follow a more conventional path. A 1 kHz track alignment tape (DA09007A) goes in, and the height gear is turned until both channels read minimum. Then a 15 kHz azimuth tape goes in, and the azimuth screw is turned for maximum output, repeated once or twice. The tilt adjustment uses the beacon-equipped M-9039 gauge, which lights "Upper" and "Lower" indicators as the height screw is turned. The goal is to have all four beacons - playback upper and lower, record upper and lower - illuminating after the gauge is pushed in and released. The gauge must not contact the pad lifter.

Ownership and Maintenance Notes

The fact sheet carries no pricing, production figures, or independent bench measurements for the 660ZX, so its market value and measured performance are not documented here. The manual does establish the maintenance profile. The deck is full of interacting adjustments. Cam timing affects mute and bias-oscillation release points, which are set by observing signals at the Q418 and Q417 collectors and trimming R483, R484, and R488. The record switch linkage has to be positioned so the switch sits on the play side before the spring holder is tightened, then checked for roughly a 1 mm gap in record-pause. Tape speed is trimmed at VR407 on the speed calibration board against a 3 kHz speed and wow/flutter tape (DA09006A). Counterclockwise slows the motor and clockwise speeds it up. None of this is unusual for a high-end Nakamichi of the period, but a 660ZX without service history should be treated as a project until proven otherwise.

The appeal is specific. It is a Nakamichi that does automatically what almost no other cassette deck does, and it does it with a mechanism you can still adjust, measure, and verify with gauges that occasionally turn up on the used market. The catch is just as specific. Don't buy one untested, and don't service one without the manual open on the bench.