Sony set out its stall as a high end cassette deck manufacturer as far back as 1974 with the TC-177SD. A top loading, dual-capstan, three-head design, it was one of the most sophisticated machines around at the time, and presaged some excellent recorders which cemented the brand’s rising reputation. By 1979 however, times were changing and rivals from Akai, Aiwa, JVC and Pioneer were advancing apace. Then, the sudden arrival of metal tape changed everything. Able to carry higher recording levels, it required heads capable of producing more magnetic energy. It duly forced a completely new generation of cassette decks into being…
Metal tape – along with IEC standardisation of all recording media – caused a fundamental rethink for all cassette deck manufacturers. Suddenly, Sony’s excellent Ferrite & Ferrite head – which had been a fitment in all its top machines throughout the seventies – was obsolete because it wasn’t able to record on metal tapes properly. Out went the big TC-229SD, TC-K7 and TC-K8B – to be replaced with a range of slimmer models based around a range of common parts. An interesting bridge between the past and the future, this range was both the last gasp of the old, nineteen seventies way of making cassette decks, and the new era of metal tape-capable machines.
Sony’s new 1980 cassette deck range started with the TC-K35 and K45, both of which shared mechanical piano key-type transports and a smaller case – alongside F&F heads with no metal capability. The high end range started with the TC-K55, which wasn’t initially metal compatible but was soon upgraded to the MK II guise which was. The K55 had a larger case with full microprocessor sequenced logic control. It sported moving coil VU meters with six peak indicators; opting for the slightly more expensive TC-K61 changed these for high resolution LED Peak Programme Meter types and added a level control for the headphone socket.
The Sony TC-K65 came fitted with an Automatic Music Sensor (AMS) system similar to that of the previous TC-K60, whilst the TC-K71 went seriously upmarket with a dual capstan drive and three heads. Top of the range though was the TC-K81, which like the TC-K71 had two capstans and three heads but added the facility for the user to adjust the bias and recording current for all tape types with reference to a built-in calibration system. Despite being just over twice the price of the basic TC-K55 MK II (£316 in 1980), this was the model which appears to have sold in the largest numbers.
The whole range had a pleasingly sleek, modern look with a large and almost square cassette viewing window and small, flush keys to operate the deck functions. Despite the difference in head types and the number of capstans the basic transports used were all essentially the same; all employed a miniature version of Sony’s BSL (Brushless and SlotLess) direct drive turntable motor to drive the flywheel via a ground flat rubber belt. The same motor could also be found in the PS-X800 Biotracer turntable, which used two of them in its arm servo. All could also be used with the RM-50 wired remote control, or the RM-80 infra-red alternative. The key to metal tape compatibility was Sony’s new S&F head, which used a Sendust core set into a Ferrite guard block to give the best qualities of both materials. The TC-K81 alone had a diecast front panel whose slightly roughened surface gave it a luxurious, exclusive feel. The rest had a sheet of aluminium clipped over a plastic frame, par for the course for Japanese decks of this era.
For the TC-K71 and TC-K81 two completely separate heads were used for recording and playback, although they were small enough to allow both to be inserted through the normal aperture in the cassette housing. They were constructed using the ‘dual suspension’ principle, which allowed the alignment of one in respect to the other to be accurately adjusted in the factory and then sealed. This eliminated a problem of the TC-177SD, Sony’s first three-head cassette deck, some of which were obliged to have a user adjustment for record head azimuth.
The TC-K81’s excellent calibration system allowed the owner, armed with only basic technical knowledge, to optimise the deck to almost any cassette and therefore make near perfect recordings. The system made use of the deck’s LED metering, although it was also possible to tune the setting by ear alone using the source / monitor switch. Bias and equalisation were set independently so the owner was free to experiment with different settings of each, an extra low bias setting was offered for ferric tapes of the most basic type so that the full treble range could still be obtained. An indication of the superb head design of the TC-K81 can be gained by looking at the PPM level meter. The Japanese typically place the Dolby level reference (an absolute signal magnitude which is obtained by playing back a calibrated reference tape) at around +3dB on the scale, higher than the maximum recommended recording level. On the TC-K81 however it is found at just over -2dB, meaning that the machine will easily record up to (and beyond) this point without significant distortion. In fact, recordings can be made to peak at nearly +4dB with no obvious degradation if a decent quality tape is used (e.g. TDK SA).
Despite its technical excellence, the TC-K81 in retrospect feels more like the final generation of nineteen seventies cassette decks rather than a trendsetter for the eighties. Logic transport controls aside, the use of mechanical switching for all the other functions precluded automation to any useful extent. The mechanical tape counter and the absence of Dolby C date the design too, decks like Aiwa’s AD-F770 and AD-F990 showed the way forward just a few years later. Sony’s own TC-FX1010 would soon demonstrate what was possible with the latest computer controlled signal processing techniques, although the popularity of this model was limited by its quirky appearance and high price.
Many IEC compatible cassette decks feature a clean, bright sound for pre-recorded tape replay and the TC-K81 is no exception. Nineteen seventies machines often sound dull (especially when the noise reduction system is used) when playing anything other than their own recordings, but the TC-K81 clearly has a carefully resolved EQ circuit built to the latest specification. This, combined with a stable tape transport, gives excellent performance which takes a good turntable and record pressing to match it. If only pre-recorded cassettes had been more consistently accurate in the way they were produced…
Recording quality is exceptional; once the three little knobs have been correctly set it really is difficult to tell the source and the off-tape signal apart. There is a difference of course, but it’s only noticeable in the harsh A/B environment that flicking the switch over creates. Were one to leave the room when the change was made it is highly unlikely that the difference between the source and the recording could be perceived, it really is that good. The changes that one does notice are a slight brightening of the treble (an unusual effect for a cassette deck) and sometimes a slight shift in the centre point of the stereo image, due possibly to tiny but unavoidable differences in head-to-tape contact across the width of the head. Compare this though to the differences in sound that occur in the process of mastering, pressing and playing an LP and you realise what an amazing machine the TC-K81 is. It is an excellent way of making high quality archive recordings of irreplaceable analogue originals or to create physical copies of material only otherwise only available on radio broadcasts or streaming services.
There are still plenty of good examples of the TC-K81 to be found. Most will need a new set of belts by now as the tension is critical for the dual capstan system to work correctly. The S&F heads are almost as wear resistant as the previous F&F type so it is unusual to encounter a worn pair. The ferrite erase head is fragile and can become chipped if mishandled, check that it is still smooth and shiny across its entire surface. The BSL motor had no sliding contacts to wear out and is therefore durable; mechanical noise tends to come from a lack of lubrication elsewhere in the deck. A more serious potential problem is that the plastic bracket which locates the bottom of the head bridge can break off the main base of the deck, making accurate alignment impossible to achieve. This is difficult to repair properly so check this area carefully.
If no deck functions can be selected at all despite even though the BSL motor can be heard running the chances are that a small bell-crank connected with the eject mechanism at the side of the deck has seized. Cleaning and re-lubrication isn’t that difficult, but the deck has to be removed from the chassis to do it properly. TC-K81s originally came with the calibration controls centred for Sony’s own tapes which were slightly different at this time from the IEC norm. Internal adjustments allowed them to be reset to a more conventional alternative, modern TDK AR and SA work well, for example.
After many years of languishing in local ‘free ads’ papers for £30, prices for the whole range are now on the rise. They’re now very variable, with plenty of £50 bargains to be had, but some more optimistic souls are asking £300 for the range-topping TC-K81 on eBay. In a way, it has been underpriced for too long, but the current ‘cassette revival’ has spurred a number of more entrepreneurial types to overprice it. There are surprisingly large numbers of this range still on sale, so don’t pay too much – even for a fine example. Indeed, it’s a testament to both its popularity at the time and the enduring engineering quality that so many are still around now. TJ