A tale of two Sonys

What do hi-fi designers actually do nowadays? Some would say “not a lot”, as technical refinements all too often seem reduced to devising new software applications to run on platforms whose architecture was laid down twenty or so years ago. Electronically, hi-fi has been largely stagnant since the end of last century. Contrast this to the boom years that started in the mid nineteen sixties, when the Japanese joined the game seriously. The period ended in the mid eighties when the rising value of the Yen made it too expensive to carry on competing at this level. Factories churned out gear which the public lapped up in quantity, volume sales lead to big development budgets and large ranges of models. There really was something for everyone…

Take for example two of Sony’s less well known models, a pair of receivers from the beginning of the two great decades of hi-fi. From the seventies there’s the STR-6055 and from the eighties the STR-S5L. Both are their period’s answer to the same problem, both are AM/FM receivers with about 40 watts of output with connections for a turntable, a tape recorder and a couple of extra line sources, one connected at the back and one at the front in both cases. Both have tone controls, multiple loudspeaker outputs and headphone sockets, all things that have quietly disappeared from modern equipment. Both are also much the same size and much the same colour, although their styling details leave no question as to which decade each was from.

Starting with the STR-6055, the generic looks hide what would have been a pretty high-tech product. For a start, the power amplifier is DC-coupled to the loudspeakers, something that in 1971 (when this model was designed) was only just becoming practical for models of this type. DC coupling allows the power of the amplifier to be effective right down to zero Hertz, curing once and for all the bass ‘flab’ that is usually a feature of transformer- and capacitor-coupled amplifiers. Another bit of cutting-edge technology can be found in the tuner section, where the image of the received station that the circuit ‘sees’ is defined by precision-made ceramic filters, not the manually aligned transformers used previously. Sony sold this model as mid-range but the more expensive ones only added a few more knobs and a bit more power.

The STR-S5L is very much a product of the era immediately before the launch of Compact Disc. Eighties modernity required no big knobs sticking out, no rotary controls, lots of displays and plenty of writing and legends – and this design has all these things. The key feature here is digital tuning; instead of the mechanical pointer that the STR-6055 has the STR-S5L has a numerical read-out and automatic station search. These things were both possible from the mid seventies onwards but it took cheap microprocessor chips to make them a practical proposition on a consumer product. Even so, digital tuning was still far from ubiquitous at this stage and would have straight away put the STR-S5L into the upper levels of its market sector. Computer technology wasn’t quite at the stage where station naming was possible within the software so Sony used its familiar method of interchangeable labels to mark the station buttons, originally a large sheet would have been supplied and the user simply inserted the ones that were relevant. Quaint as it seems, this technique was used on some pretty serious models, the range topping ST-J88 and the ST-P7J tuners to name but two.

Another compromise of this ‘semi digital’ era is the volume control, which has an up/down rocker and a linear scale. Behind the façade though is a conventional rotary volume control driven by a motor, which also moves a coloured ribbon in front of a lamp to show the setting. These days such setups are used to keep the control systems separate from the signal path and thus to keep any interaction to a minimum, but in the early nineteen eighties it was the cost of digitally controlled attenuators that made this electro-mechanical solution desirable. One of the advantages of a user interface that works completely by push buttons is that a comprehensive remote control system becomes a realistic possibility. The STR-S5L doesn’t include one directly but it does have data connections to allow it to function with an external timer/control unit and handset.

Technically the STR-S5L follows the STR-6055 with a DC-coupled power amplifier and a tuner that includes ceramic filters. Cheaper units of this type would have used an ‘amplifier on a chip’ as the output stage but the STR-S5L retains a setup of discrete transistors, despite the extra bulk and component count. The circuit used includes Sony’s Legato Linear system, which like most power amplifier refinements of this period is concerned with setting and stabilising the operating conditions of the output stage. It has no controls or indicators; it’s just ‘there’. Build quality throughout is immaculate, construction and materials are first rate.

Two models, ten years between them, how do they compare? Trying the amplifiers first using a line level source (CD) two very different characters are revealed. The STR-6055 has a surprisingly delicate sound, the bass is dry and the treble a little on the bright side. This isn’t to say that it is harsh; the treble lift merely serves to illuminate any mid band detail that is present in the recording. Focus is pin-sharp at all frequencies, vocals are full of texture and percussion is never diffuse. This all comes a quite a surprise as much of the middle range equipment from this era can sound pretty turgid with modern sources and loudspeakers, Sony must have been very confident in the abilities of the partnering equipment. Power is not really an issue; this receiver will play loudly with ease and never seems power-limited, although inevitably the sound does begin to break up at very high levels. This sort of performance tends to suit the more serious listener who has partnering equipment that is complemented by the revealing nature of the amplifier.

The STR-S5L is quite different. One of the extra features offered is a choice of three preset sound modes, each of which give a slightly different take on the ‘loudness’ theme. They can be disabled in favour of the traditional treble and bass controls, but even with these set to neutral it still sounds like the system is still making its mark. The sound has more pronounced bass than the STR-6055 does and the midrange is recessed in comparison, giving the impression of power and richness. In audio terms it is the essence of showroom appeal, many buyers associate this characteristic with being better in some otherwise intangible way. Under critical conditions the bass can get in the way; although plump it doesn’t seem to carry much information and can tend towards being ‘one note’ in nature. Treble is bright and clean, ready for the new digital future, but the slightly recessed midrange means that the music’s texture takes some searching to find. What is impressive is the way that the power is delivered, the amplifier sounds muscular at all volume settings and appears to be able to keep the loudspeakers under tight control.

Tuner-wise, both give very similar results. Although an outdoor aerial is required for either to give their best, both give basic reception of local stations with a metre or so of wire pushed into the antenna terminal. The manual tuning of the STR-6055 is complicated by the fact that the AFC system can’t be turned off and that the tuning meter shows balance rather than signal strength. This makes it simple to verify the correct point of tune but gives no indication of which of a choice of frequencies gives the strongest signal, a subjective assessment of background noise is the only way to do that.

Tuning the STR-S5L is as easy as could be; automatic search gives perfect tuning of each station in turn. Two levels of sensitivity are offered, basically ‘strong’ or ‘all’ broadcasts. AFC is applied automatically as soon as a station is found and the frequency display is pleasingly accurate. An alternative method is offered in the manual mode, which uses a small rotary knob located in the concealed part of the front panel. Pushing the knob once engages manual mode, where upon the tuner operates without AFC and is locked instead to its own quartz crystal reference. This is useful in the more congested parts of the waveband or for tuning into a weak signal which is in close proximity to a much stronger unwanted one. Both give clean results free of excessive noise and spurious whistles, although the STR-S5L gives more consistent FM stereo results over a range of levels of signal strength. This is due no doubt due to the use of a phase-locked loop stereo decoder, a distinct improvement over the regenerative type that the STR-6055 has.

These two receivers represent carefully market researched answers to what the hi-fi buying public wanted during their respective eras. The STR-6055 turns in a surprisingly good performance that would not disappoint an audiophile user used to high calibre equipment. Sony’s STR-S5L on the other hand would delight the casual listener who wants versatile facilities and plenty of power from an attractive, well engineered package. Both are clearly built to last; even with a combined age of over seventy years they are still fresh and full of life. TJ

One comment

  1. Ed

    The STR-S5L you show is a 50 watt .05% distortion unit from 81-82. You showed the UK model as the LW band (350Khz and below) seemed to be a british fad and had died in the states. There is the S5 plain model (one of which I just restored) that only has AM and FM capabilities. and there is a dual voltage european model – the -S5S which has a 3rd tuner a short wave band (around SW1 IIRC)

    These models look to be a direct competitor to the new-at-the-time pioneer SX-single series, aka the SX-4 thru SX-9 otherwise known as the ‘Champagne Series’ The pioneers were a direct repackaging of the amps from the flouroscan series (SX-3×00) and adding a digital tuner but I do not know if these were a direct follow-on to a linear tuner machine from sony.

    Very hard to work on due to the compaction and the early computer controls. everything is a delicate CMOS circuit and to make it more fun, only the flame proof resistors are on top of the boards, standing off. all the regular resistors are SMD devices soldered underneath.

    These make a ton of heat and must breath and the idle current setting is critical. err on the side of lower.

    There is at least 1 mistake on the main board screen printing regarding the polarity of the volume display ‘film mask’ motor capacitors AND more critical, the values at 10v on a circuit deemed 11v from the power supply. They should be uprated.

    Other than this weirdness, it is a fine adult machine inside and is more obscure than the SX-singles – yet are good machines. finicky public.

    There is a service manual for the -S5L online, its usable even for my -S5 if I ignore the english line voltage portion and there are still service manuals on ebay for each variant.

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