NAKAMICHI: 680 dual-speed cassette deck – test review

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Howard Popeck writes:

Launched in 1980, the maker’s claims were, on the face of it, outrageous; “True high-fidelity performance at half-speed”.

Although cassette recording and play-back technology were, through outstanding engineering, approaching the theoretical limits of what could be achieved, and enthusiasm for the medium was probably at its peak, true audiophiles rarely accepted that cassette technology really could achieve high-fidelity. After all, neither Linn nor Naim built cassette decks, ergo the technology had little credibility, in the UK at least.

Clearly then, to claim audiophile quality at a mere 15/16-ips was, in the eyes of the ‘flat-earther’ either heresy, or lunacy, or both. Having said this though, Nakamichi cassette decks had at that point long enjoyed a reputation for high performance and technological innovation and their other products, such as the strange but technically brilliant Dragon D1000 turntable and the extraordinary tiny monitor speakers were attracting favourable comments. So maybe, just maybe, they were on to something.

So I bought one. I still use it to this day. It has standard speed too and yes, I rarely use it on half-speed – but that’s really not the point. An extraordinary machine, a joy to use and yet very rare. In fact, absurdly rare. Can you think of another company that ever released a half-speed cassette deck? More on this later.

The front-loading 680ZX uses 4 d.c motors in its transport system. The capstan motor is controlled by a phase-locked loop (PLL). During playback, tape speed can be varied by plus or minus 6 per cent.

One motor drives a unique (at that time) “Automatic Azimuth Alignment” feature that fine tunes the vertical alignment of the record head in order to compensate for manufacturing-tolerance differences in cassette housings that could result in high frequency losses. This is particularly important for 15/16-ips operation since obtaining a response to 15,000 Hz at that speed is equivalent in difficulty to extending the normal-speed frequency response to 30 kHz; in neither case can even the slightest azimuth error be tolerated.

The motorised azimuth adjustment is pushbutton-activated and takes only 3 to 4 seconds to complete its action. The Crystalloy record and playback heads are separate, each with its own set of alignment adjustments, but they were so miniaturised that both fit into the cassette-shell opening originally intended for a single tape head. The playback head gap is less than 24 millionths of an inch.

The fluorescent level display covers the range from –40 to + 10 dB. The level indicators can be switched between a peak-reading mode (with a peak-hold function), a VU mode (which reads average levels but is constantly accompanied by the higher, peak-reading, function as well), or a calibrated mode (used to adjust the record sensitivity of different tapes to match a built-in Dolby B level tone).

Finished in camera-quality black that still looks good in my room after 23 years of use, the 680ZX comes with standard rack-mounting adapters and stands just under 6 inches high.

I am deeply impressed with the Nakamichi 680ZX. At standard speed it was and remains capable of faithfully and accurately recording the output from my Trio KT917 FM tuner (also 1980 vintage and, no, not for sale). Imaging and space on replay are not as clearly defined as you’d hear from a live BBC Radio 3 recording, but in terms of speed stability and tone, well to my admittedly ageing ears, it’s spot on. And I’ve achieved equally impressive results using my Nu-Vista 3D-CD and my GyroDec/Breuer combination as sources. But of course you’d expect this from any upmarket Nakamichi machine. So what about half-speed?

But first, why half-speed. For people who taped long musical works, the maximum of 45 minutes a side was a serious limitation of the cassette format; half-speed taping, with 90 minutes a side, virtually eliminated the problem. Incidentally, Nakamichi eventually offered an alternative and equally brilliant solution in the RX505 machine – but that’s another story.

Also, it was argued, that doubling the available use of a given cassette made it much more feasible to send twice the money to by metal-particle tapes. So I did. Only on the most demanding material played at high volumes through the best equipment I owned could I hear a slight, very slight degradation at half speed although the need for Dolby was more obvious. A slight compression in the dynamics, and that’s about it. Mind you, this was long before support tables such as the Mana ones came along. Maybe, just maybe I’ll try the comparison while the 680 is supported that way.

And the rarity? Well it was very strongly rumoured (leaked, I wonder) that Phillips who held the licencing rights to all cassette technology (it was, after all, their invention) envisaged that if this caught on, sales of blank cassette tapes would be severely diluted, potentially even halved. And so, it is rumoured, they put pressure on Nakamichi and the 680ZX had a very limited production run. Maybe other makers who were either engaged in half-speed research of their own and/or were in negotiations with Nakamichi, were frightened off?

As I write this there are a couple of 680ZXs on ebay at low asking prices. But they are US spec. I’ve only once seen a UK spec for sale. Parts may now be hard to come by and yes, it could be argued today that this machine represents the apogee of slide-rule technology in the era of programmable calculators. But to me that’s crass. Does a Fuji FinePix S2 digital image adequately replace a Canaletto painting? Of course not. The brilliance of the engineering and the boldness of the innovation really do reinforce Nakamichi’s then pre-eminence in state-of-the-art hi-fi and justify the 680ZX as a true audio classic.

A great resouce for Nakamichi FAQ can be found HERE

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