Nakamichi had several models in this 6xx range, starting from 660ZX and ending with famous 682ZX. Produced at the end of 70’s. these models were pretty expensive with price tag range from 995 to 1.800 USD.
Unlike other cassette deck manufacturers, this companz didn’t make his 6xx line in the way that 682ZX is the best in every aspect and that option/quality goes down as we are moving towards less expensive models.
All of them use famous second generation Nakamichi transport and other same or similar parts. But Nakamichi 680ZX was unique in many ways.
Starting from the design point this one looks unordinary: just take a short look and you will feel that we are talking about serious recording machine. Transport buttons are metal with engraved symbols, almost indestructible. Other commands are well made: Dolby B (no C here), tape/source switch and others which usually need cleaning after many years of use. Tiny plastic covers on these switches tend to loose their grip because glue is getting to old, so be careful not to loose them. Cassette compartment is lightened with nice green bulb and shines gently in the dark, producing feeling like not many non-Nakamichi decks can. Of course, this light bulb can be replaced with more modern diffuse LED lighting, if You wish, which looks pretty in the other way.
This model – Nakamichi 680ZX is specific in the way it has two running speeds: standard 4.76 cm/s and the other which is half of it, around 2.4 cm/s or 15/16 ips. By using slow speed you should be able to record high frequencies up 15 kHz, which is pretty good. I actually measured top end around 16 kHz on normal and chrome tapes using one of mine 680ZXs (-3 dB, ref. point 1 kHz, -20 dB signal). From this point of view it is pretty strange that Japanese company decided to make such an excuse regarding speed – maybe the were thinking about some specialized professional use or so. I can’t imagine an audiophile who would give 1.550 USD (around 2.920 DEM in June 1979.) to record using slow speed with decreased response and higher wow&flutter, resulting in less wide soundstage, less details etc. Maybe it would justify just recording from some FM radio stations…
Nakamichi 680ZX also has RAMM – Random Access Music Memory which is complicated name for track search, in case You want to move, say, three tracks forward or reverse. It also supports cue and review during which the used can hear output sounds in high or low speed mode, which is more used by professionals.
Nakamichi 680ZX has manual level calibration system. It is based on 400 Hz oscillator an 6 trimmers accessible from the front panel. The actual goal is to get VU/Peak meters get to the mark point for both channels. There are additional six trimmers designed for half speed level calibration. It is important to say that this calibration is not just a straightforward task: when activated it requires several seconds to adjust recording head in respect to playback head. Nakamichi claimed that this is very important because many so called sandwich heads have not been perfectly aligned during the manufacturing process.
So, Nakamichi calls this an Auto Azimuth Alignment system: it uses the same 400 Hz tone as level calibration does. It consists of motor with pulley which turns simple mechanism and changes the angle of the record head. The electronic part of Auto Azimuth Alignment system is made on relatively small PCB with phase comparator and motor driver. Start of level calibration activates Auto Azimuth Alignment system and play bulb (no LEDs on 680ZX) begins to flash until the process is finished in several seconds. Than the user adjusts recording level.
It is interesting that Nakamichi 680ZX doesn’t use any kind of specialized microcontroller for it’s pretty sophisticated functions. Everything is organized around TTL logic circuits, so it would be easy to find many parts even nowadays. On the other side this “logic” PCB is rather large. I must admit that I have never seen any failure on this PCB.
While this may be enough for most of us, the star of the show are fluorescent VU/Peak meters. Packed in steel box, they consist of two PCBs which drive vacuum tube display. Nakamichi 680ZX can work in peak hold mode or VU mode which shows peak values at the same time. These peak meters are very fast and implemented in such a way that one segment runs in front of VU bar, showing actual peak value. Ingeniously, these are one of the best cassette deck indicators I have ever met.
Although 680ZX is so nice, there is one thing to prove that You can’t have everything: there is no user adjustable bias. It can be accessed only when you remove the deck’s cover. I would like to have one speed machine with variable bias rather than two speed with no trimmers for bias on the front panel.
Transport used in Nakamichi 680ZX is classic second generation Nakamichi type. It has three panels with base made of aliminium sheets and plastic connecting parts between them. Nakamichi claimed that, after extensive research, this principle was found as the best one for fighting against transport-born vibrations. It also uses closed loop dual capstan diffuse resonant system with capstans slightly different in diameter so they could resonate at different frequencies. The whole system is belt driven and there is another motor used for reels.
This mechanism has been used, more or less, on many other decks from the same generation (480, 580, 582, to mention just a few) and later (LX3 and 5) and also Dragon, ZX9 with addition of direct driven capstan motor. Comparing Nakamichi 2nd generation transport with, say, Studer/Revox beast gives you feel that they have totally different concept: Germans made it of metal, steel and metal in case you forgot. Japanese used aluminium and plastic. Nakamichi transport looks like toy but works well. Studer will probably last much more, but again most Nakamichi 2nd generation transports can work for decades without any servicing.
But, let’s get back to 680ZX: after many years of use, plastic connecting parts molded on the aluminium plates tend to get little cracks which, fortunately doesn’t affect the system. I usually fill these cracks with small amount of cyanoacrylate glue. Motors are usually pretty durable and most of the problems is related with grease getting too old on pulley shaft or rollers. This kind of mechanism also uses idler reel drive of the highest quality. In many cases it can work literally for decades and decades – I’ve seen some original Nakamichi idlers still working after 30 years, with almost no slipping at all!
When you decide to replace the reel idler, you will have to disassemble most of the transport, Nakamichi engineers didn’t try to make this easier. It will take some spring and glue removal and in this case it is the best to completely clean and lubricate the whole transport. However, it is interesting that both capstans are not balanced after manufacture process. Since there are the same type of them in Nakamichi 480 and they have traces of post balance process, I think that 680ZX and similar capstans were made with greater precision.
The sound
Nakamichi 680ZX keeps the true Nakamichi spirit: elegant and transparent, gentle and strong at the same time. When You put some other very good deck to compare with it, for example Sony TC-K990ES, NAD6300, JVC TD-V1010 or Technics RS-B100 then you can feel the difference which describes very good to outstanding machine. No tone makes 680ZX sweat under it’s dark metal skin. No music makes it try hard – everything is just a game for it and he is a very old player with great experience. Bass notes are strong and high frequency extremes give the answer why Nakamichi never implemented HX Pro system – they simply didn’t need it. Three dimensional stage is perfect and timbre and rhythm are perfect. Listener can actually feel the air around single instruments. I can’t say that Nakamichi decks sound neutral – I have never met neutral Nakamichi. On the other side it gives the soul to the music, completely different comparing it with many other decks who suffer cassette format restrictions. So, I can say that 680ZX doesn’t just reproduce music – it plays it in front of the listener. It makes it softer and more listenable even if it is produced in different way. In the end, it can make you sleep singing it’s sweet lullaby.
After having several Nakamichi decks, from cheap ones to some pretty expensive units, I must admit that every time I get surprised when listening to 680ZX and the rest from this series: their looks is specific and different from the others, their transport is also different but they don’t have so complicated electronics with exotic parts etc. But they sound so good, and this is the miracle and magic of Nakamichi decks. I must note that I am not a Nakamichi fan, I also like Revox, TEAC, Sony and other specific decks from different manufacturers. But I will tell You about them some other time.
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