Nakamichi 680ZX

Name: Nakamichi 680ZX
Brand: Nakamichi

A lubrication-free deck that plays a C-90 at half speed with response flat to 15 kHz. The period press could barely believe it.

Overview

The Nakamichi 680ZX was strange because it would halve the tape speed. It ran at 15/16 ips instead of the standard 1-7/8 ips, so a cassette held twice the music, and it did this without the dull, rolled-off top end that half-speed operation usually brings. Reviewers of the day could not get past it. Nakamichi's own advertising, running in HiFi-Stereo (February 1981, p.31), High Fidelity (February 1981, p.83), and Audio (February 1981, p.35), quoted reviewers finding the response almost perfectly flat out to 15 kHz and noting that few cassette decks could match that figure at regular speed, much less at half-speed. They judged the half-speed results comparable to the very best full-speed decks and called the standard-speed performance simply superb. One reviewer admitted to eyeing a collection of fractured acts after fitting an entire Carmen onto a single C-90.

The service documentation lays out the two speeds plainly. The standard 1-7/8 ips setting is calibrated at a 3 kHz test tape, and the half-speed 15/16 ips setting is calibrated separately at the same 3 kHz reference. Two speed-calibration trimmers, VR407 and VR408, sit on the Speed Cal. P.C.B. for exactly that purpose. The deck needed its own calibration hardware for each speed, so half-speed was built as a full operating mode and not tacked on.

The 680ZX also carried Auto Azimuth Alignment, which Nakamichi's own advertising billed as the most advanced and sophisticated innovation in cassette-recorder technology, launching a new era in high-fidelity recording. HiFi-Stereo (April 1980, p.41) ran that claim under the banner "The dawn of a new recording era." The mechanism is real, and the manual is candid about its complexity. An azimuth motor, an azimuth alignment wire, a slide lever, and a trimmer on the Auto Azimuth P.C.B. all have to be brought into agreement. The setup procedure involves shorting capacitor C903 with a jumper wire, then aligning the record head height gear and azimuth screw against a Reference SX tape while watching for maximum output on both channels. It is not a feature you service casually.

The front panel is built for people who calibrated rather than guessed. Below the meters sit twelve screwdriver adjustments, two groups of six, one group for each tape speed, each group with left- and right-channel trims. Modern Recording (April 1980, p.76) counted them and noted they sit alongside a vertical row of switches for tape bias, tape EQ, Dolby with a multiplex filter setting, metering display, optional timer, tape/source monitoring, and power. The tape switch offers EX, SX, and ZX positions. The EQ switch toggles between 120 µs and 70 µs. A fluorescent level display handles metering, with a separate Cal. position on the display switch used during alignment. There is a pitch control, a tape start memory switch, a tape counter, and a timer switch.

Around back, the deck has input and output jacks, a DC output jack, a remote control socket, and a voltage selector. Watch that selector if you shop across borders. The manual describes it as installed for other versions of the 680ZX and capable of selecting either 120 V or 220-240 V. A North American unit and a European unit are not the same machine underneath the cover, and the service literature treats them as separate versions.

Modern Recording (April 1980, p.79) described the whole exercise as a demonstration that high levels of both audio and mechanical performance could be achieved at half the tape speed of the existing format. Lowest distortion, best signal-to-noise, and maximum headroom were the trade-offs the engineers had to juggle. The magazine called the 680ZX not only a great piece of audio equipment but something of an historic event, and compared its significance to the fabled Model 1000 deck.

The manual says more about living with one, and it is more useful. Nakamichi describes the N-680ZX as a lubrication-free cassette deck except when parts are replaced, and then specifies exactly what goes where. LAUNA #100 goes on the capstan shaft, pressure roller shaft, and thrust cap. FLOIL GB-TS-1, made by Kanto Chemicals in Japan, goes on the reel hub shaft and the thrust portion of the capstan shaft. Silicon Oil #3000CST goes on the air damper piston, with an explicit warning that over-lubricating the damper can clog the 0.2 mm hole at the end of the cylinder and defeat the damper action entirely.

The mechanical adjustments are just as specific. Head base stroke is set differently in play mode and in cue mode, using a Stroke Check Gauge M-9047 and, for the record head, a Record Head Mounting Gauge M-9048. Record and playback head tilt is checked with a Tilt Check Gauge M-9039 and a set of beacons that light when each head sits correctly. Erase head height, tilt, and azimuth are set with an EH Tilt Check Gauge M-9040 and three beacons. The manual warns that excessive turning of one screw will extinguish the others, so the adjustments interact. Thrust screws get a warning of their own: over-tightening damages the flywheel assemblies. Once set, the screws are backed off half a turn, locked with a nut, and sealed with lock-tight paint.

Cam timing is calibrated against voltages at the sliding contact of VR405 — 3.0 V in stop mode, 1.7 V lower in fast wind, -2.8 V in pause, 2.6 V lower again in playback, with separate targets for the reel motor start and mute release points. There is a "PY" mark on the cam that has to come to the pointer, and an "S" mark for stop. Control motor driver offset is set with VR402 and VR403 on the Logic P.C.B., and the manual notes the two interact, so the procedure has to be repeated two or three times before both positions land accurately. None of this is exotic for a high-end Nakamichi of the period, but it is a reminder that the 680ZX rewards a technician who reads.