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Found in the Attic: Technics RS-686DS Portable Cassette Recorder

Posted by Tom Vernon on Dec 30, 2015 1:42:00 PM

Technics RS-686DSThe last installment of Found in the Attic examined the Uher 4000 series of portable reel recorders, which were widely used by radio news departments before cassette recorders were common.

Continuing on this theme of portable sound equipment, we'll travel forward in time a few years to 1977. That's when the Technics RS-686DS cassette deck was released.

While our Uher was primarily used for recording voice material, the 686DS was all about the music. Recording live music in the field has always been a challenge. Before cassettes, everything was recorded on open reel tape. The sheer size of 10-inch reels of tape meant that packing small and light for a field recording wasn't an option.

Perhaps the most ambitious field recording of live music took place in the mid-1960s, when Nonesuch Records began recording ethnic music around the world, to be released as the Explorer Series. These records, which came out between 1967 and 1984, were the root of the world music genre. Contemporary photos show Ampex 350-series recorders and electronics in transit cases, along with mixers and related gear. The results were spectacular, but the cost of shipping Ampex recorders and recording engineers around the globe was beyond the budget of most organizations. Fortunately, the solution was well on its way.

The audio cassette format, introduced by Phillips in 1962, was originally intended for dictation machines. That made the audio quality somewhat worse than AM radio. Over the next two decades however, the technology made great strides. Precision 3-motor transports, better tape heads, Dolby noise reduction, high-bias tapes, auto-reverse transports and automatic switching of bias and equalization all contributed to cassette recording quality approaching that of open reel tapes. The stage was set for the manufacture of true high fidelity field recording cassette decks.

Early models of portable stereo cassette recorders basically entailed putting a handle on a large box. All resembled in both size and scale the cassette decks of the period. They were typically designed around the transports of the larger machines and were powered by AC and sometimes a large complement of D cells. Usually they had full-sized speakers too, only adding to the size and bulk. Despite these drawbacks, sales were brisk enough to convince manufacturers that there was a market for portable recorders, both for consumers and professional users.

And so the evolution began. Cases and internal components were ruggedized to survive rough handling and Inside the RS-686DSminor drops. Power consumption was reduced, and batteries went from D cells to C. Power for primo grade opamps was provided by DC-DC converters, a novelty at the time.

Cassettes themselves improved. The shells were made to precision tolerances, resulting in less tape resistance and fewer jams. Tape went from normal formula (Type I) to chrome (Type II) to dual-layer ferrichrome (Type III). Notches in the top of the cassette would automatically switch to the correct bias and equalization on newer machines.

As the tape and electronics were improving, so was the transport. Portable decks have some unique challenges, among them excessive wow and flutter, and erratic tape speed. Regular cassette decks overcome these issues with big flywheels and motors. That's not possible with portables. Not only is the extra bulk an issue, but rotating parts become erratic as the machine is moved or rotated. Just for fun, don't forget the adverse effects on the transport of changing temperature, tape friction and decreasing battery voltage as the machine is used.

Most portable deck transports got around these issues with some form of electronic regulation. Sensors (usually optical or magnetic) located on the small capstan flywheel measured its speed, which was applied as a feedback signal to the motor. The system could respond to even abrupt changes in speed.

Cassette use and recorder technology development reached its peak in the late 1980s. After that, it declined sharply, as compact discs became popular, first for pre-recorded music, later as a recording medium as blank CDs were available.

The 686 featured unbalanced line level ins and outs, as well as balanced mic inputs. It is powered by either an external 9-volt supply, car adapter, or six 'C' cells, which gave a recording time of about 4 hours. A monitor head enabled source-tape listening, and a standard quarter-inch phone jack was available for headphones. Two illuminated (momentary) VU meters are provided.

Operating controls are designed to be operated without looking. Rather than have a series of transport controls all in a row and the same size, the location and spacing is such that it can be operated by touch only. Other front-panel features include 20 dB mic attenuation, built-in limiter and low cut filter.

A unique feature of this machine is the 'end eye'. It's really an LED that begins to flash as the end of the tape approaches. The closer to the end, the quicker it flashes. The intent was to give users a heads up in dark locations. The circuit (at least on this machine) was a bit cranky to set up so it would work properly.

As with professional reel recorders, the electronics for the 686 were designed with removable boards for each function. Seven circuit cards were included: mic-playback EQ, line amp, two Dolby amps, headphone/meter amp, record EQ amp and monitor amp. It features all-metal construction, and the precise mechanical engineering one would expect from a high-end machine.

Old analog formats never really die, and there are web sites devoted to all types of analog audio recording. For those who want to maintain their 686 DS in tip-top condition, resources are available. Service manuals and a replacement belt kit (5 belts) are available from Vintage Electronics, whose motto is 'keeping 20th century audio equipment alive and well'.

What was the ultimate portable cassette deck? That depends on who you ask. Some say the Sony TC-D5 Pro, which was introduced in 1978, and remained in production for over 20 years. Others cast their vote in favor of the Marantz PMD 430. Featuring both Dolby and DBX noise reduction systems, some audiophiles thought the 430's sound was comparable to reel tape decks. DBX had the edge in virtually eliminating tape hiss, but DBX machines were less common than Dolby. The Sony WM-D6C Walkman was the concert bootlegger's dream machine. It was mTechnics RS-686DSanufactured from 1984-2002 It could record in Dolby B or C. The fact that a machine this size had Dolby C was amazing at the time, and only possible because Sony designed its own integrated circuits to perform all the functions.

The 686 is remembered as a great machine, but it was developed before automatic bias-EQ switching, Dolby C and few other features, and not in the same category as the aforementioned decks.

This particular 686 was being tossed by a public broadcaster in the early 90s, after a decade of hard use for live concert recordings. It came with the service manual, AC adapter and shoulder strap. Sadly, the carrying case was long gone. It was in working condition, though not sounding great. It was put back into shape with new caps, rubber and heads. After that, the 686 met original specs, and used briefly for live recordings.

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