Control Systems & PLC's

Pushbutton Switches

Cassette deck

History

Origins

A typical portable desktop cassette recorder from RadioShack.

The concept of a tape deck that used tape reels permanently housed in a removable cartridge, as opposed to individual reels and tape that needed to be threaded by hand, dates from the early 1950s. Various manufacturers attempted to commercialize this concept but a major difficulty was getting sufficient playback time with the low-performance tapes of the time, though by the early 1960s, tape formulations had improved enough to make the concept viable.

The "compact cassette" (a Philips trademark) was introduced by the Philips Corporation in 1963 and marketed in 1965 as a device purely intended for portable speech-only dictation machines. There was never any intention that it be a replacement for reel-to-reel recorders. The tape width was nominally 18 inch (actually 0.15 inch, 3.81 mm) and tape speed was 1.875 inches (4.76 cm) per second, giving a decidedly non Hi-Fi frequency response and quite high noise levels.

Early recorders were typically hand-held battery-powered devices with built-in microphones and recording automatic gain control, intended for dictation and journalists. However, by the mid 1970s, both tape and recorder quality had improved to the point where a cassette deck with manual level controls and VU meters became a standard component of home high fidelity systems. Eventually the reel-to-reel recorder was completely displaced, in part because of the usage constraints presented by their large size, expense, and the inconvenience of threading and rewinding the tape reels, while cassettes are more portable and can be stopped and immediately removed in the middle of playback without rewinding. Cassettes became extremely popular for automotive and other portable music applications. Although prerecorded cassettes were widely available, many users would dub songs from their vinyl record or cassette collections to make a custom mixtape.

In 1971, the Advent Corporation combined Dolby B-type tape-hiss-noise reduction system with chromium dioxide tape to create the Advent Model 201, the first high-fidelity cassette deck. Dolby B boosts treble levels well above the noise level, and reduces them on playback, while CrO2 used different bias and equalization settings to do much the same, and these technologies extended frequency response into high fidelity range beyond 15 kHz for the first time. This deck was based on a top-loading mechanism by Wollensak, a division of 3M, which was commonly used in audio/visual applications. It featured an unusual single VU meter which could be switched between or for both channels, and lever-operated controls, similar to those used on reel-to-reel mechanisms.

Typical Teac top loading stereo cassette deck from mid 1970s

Most other manufacturers adopted a standard top-loading format with piano key controls, dual VU meters, and slider level controls. There was a variety of configurations leading to the next standard format in the late 1970s, which settled on front-loading (see main picture) with cassette well on one side, dual VU meters on the other, and later a dual-cassette format with meters in the middle. Mechanical controls were replaced with electronic pushbuttons controlling solenoid mechanical actuators, though low cost models would retain mechanical controls. Some models could search and count gaps between songs. Cassette players pioneered the modern set of control buttons: play, pause, stop, record, and "locking" fast forward and rewind (which when depressed momentarily would remain depressed until stopped.)

Widespread use

Cassette decks soon came into widespread use and were designed variously for professional applications, home audio systems, and for mobile use in cars, as well as portable recorders. From the mid 1970s to the late 1990s the cassette deck was the preferred music source for the automobile. Like an 8-track cartridge, it was relatively insensitive to vehicle motion, but it had reduced tape flutter, as well as the obvious advantages of smaller physical size and fast forward/rewind capability. A major boost to the cassette's popularity came with the release of the Sony Walkman "personal" cassette player in 1979, designed specifically as a headphone-only ultra-compact "wearable" music source. Although the vast majority of such players eventually sold were not Sony products, the name "Walkman" has become synonymous with this type of device.

Performance improvements

Cassette decks reached their pinnacle of performance and complexity by the mid 1980s. Cassette decks from companies such as Nakamichi, Revox, and Tandberg incorporated advanced features such as multiple tape heads and dual capstan drive with separate reel motors. Auto-reversing decks became popular and were standard on factory installed automobile decks.

Three-head technology uses separate heads for recording and playback. This enables hearing playback during the recording. Also, it allows different record and playback head gaps to be used, which is important for the highest fidelity, as a narrower head gap is optimal for playback than for recording, and so the head gap width of any dual-purpose single record / playback head must necessarily be a compromise. A three-head system was common on reel-to-reel decks, but it was more difficult to implement for cassettes, which do not provide separate openings for record and playback heads. A cassette has one opening designed for the erase head, a center opening for the record / play head, and a third opening for the tape drive capstan. Some models squeezed a monitor head into the capstan area, and others combined separate record and playback gaps into a single headshell.

Cassette decks sold by Harman Kardon and Japanese companies such as Aiwa, Akai, Denon, Pioneer, Sony, Teac, Technics and Yamaha were also common, with each company offering models of very high quality. The best units could record and play the full audible spectrum from 20 Hz to 20 kHz with wow and flutter less than 0.05% and very low noise.

A very good live cassette recording could rival the sound of an average commercial CD, though the quality of pre-recorded cassettes was usually lower than could be achieved in a high quality home recording. Cassettes remain popular for audio-visual applications. Some CD recorders incorporate a cassette well to allow both formats for recording meetings, church sermons and books on tape.

The Dolby noise reduction system was key to realizing low noise performance on slow, narrow, cassette tapes. It works by boosting high frequencies on recording and then restoring them, also lowering the constant high frequency noises. Enhanced versions included C (in 1980) and S types, though the B system is the only standard supported on most high fidelity automobile decks. Some decks incorporated microprocessor programs to adjust tape bias automatically. Bang & Olufsen developed the HX Pro headroom extension system in conjunction with Dolby Laboratories in 1982. This was used in many higher-end decks. Chromium dioxide was the first tape formulation for extended high frequency response, but it required a special bias and equalization and switch (referred to as Type II). Later decks incorporated coded holes in the shell to autodetect the tape type. TDK and Maxell adapted cobalt-doped ferric formulations to mimic CrO2, which was thought to quickly wear out heads. Sony briefly tried FerriChrome which claimed to combine the best of both (Type III); some people, however, stated that the reverse was true because the Cr top layer seemed to wear off quickly, reducing this type to Fe in practice. Most decks today produce the best response with metal tapes which require yet another setting (Type IV) for recording, though they will also play back at the II setting on other machines.

In later years, an "auto reverse" feature appeared that allowed the deck to play (or, in some cases, record) on both sides of the cassette without the operator having to manually remove, flip, and re-insert the cassette. In early auto-reverse machines, and most inexpensive machines to this day, this uses a dual-direction head that can play all four tracks; only two at a time are connected to the electronics. The transport in these decks also has two capstans and pinch rollers, one set used for each direction.

It is difficult, however, to align a dual-direction head correctly for both directions. In some more expensive machines the "Auto Reverse" mechanism operates by disengaging the head and then flipping it around and re-engaging it, with alignment screws available for both positions. In one machine Nakamichi addressed the issue with a mechanism that physically removed the cassette from the transport, flipped it over, and re-inserted it.

Noise reduction and fidelity

A variety of noise reduction and other schemes are used to increase fidelity, with Dolby B being almost universal for both prerecorded tapes and home recording. Dolby B was designed to address the high-frequency hiss inherent in cassette tapes, and along with improvements in tape formulation it helped the cassette win acceptances as a high-fidelity medium. At the same time, Dolby B provided acceptable performance when played back on decks that lacked Dolby circuitry, meaning there was little reason not to use it if it was available.

The main alternative to Dolby was the dbx noise reduction system, which achieved a high signal-to-noise ratio, but was essentially unlistenable when played back on decks that lacked the dbx decoding circuitry. Philips developed an alternative noise reduction system known as Dynamic Noise Limiter (DNL) which did not require the tapes to be processed during recording; this was also the basis of DNR noise reduction.

Dolby later introduced Dolby C and Dolby S noise reduction, which achieved higher levels of noise reduction; Dolby C became common on high-fidelity decks, but Dolby S, released when cassette sales had begun to decline, never achieved widespread use. It was only licensed for use on higher end tape decks that included dual motors, triple heads, and other refinements.

Dolby HX Pro headroom extension provided better high-frequency response by adjusting the inaudible tape bias during the recording of strong high-frequency sounds, which had a bias effect of their own. Developed by Bang & Olufsen, it did not require a decoder to play back. Since B&O held patent rights and required paying license fees, many other manufacturers refrained from using it too.

Other refinements to improve cassette performance included Tandberg's DYNEQ, Toshiba's ADRES and Telefunken's Hi-Com, and on some high-end decks, automatic recording bias, fine pitch adjustment and (sometimes) head azimuth adjustment like the Tandberg TCD 320.

By the late 1980s, thanks to such improvements in the electronics, the tape material and manufacturing techniques, as well as dramatic improvements to the precision of the cassette shell, tape heads and transport mechanics, sound fidelity on equipment from the top manufacturers far surpassed the levels originally expected of the medium. On suitable audio equipment, cassettes could produce a very pleasant listening experience. The best home decks could achieve 20 Hz-20 kHz frequency response with wow and flutter below 0.05%, and 70 dB of signal-to-noise ratio using Dolby C, up to 80 dB of signal-to-noise ratio using Dolby S, and 90 dB with dbx. Many casual listeners could not tell the difference between cassette and compact disc.

From the early 1980s, the fidelity of prerecorded cassettes began to improve dramatically. Whereas Dolby B was already in widespread use in the 1970s, prerecorded cassettes were duplicated onto poor quality tape stock at high speed and did not compare in fidelity to LPs. However, systems such as XDR, along with the adoption of higher-grade tape (such as chromium dioxide, but typically recorded in such a way as to play back at the normal 120 s eq position), and the frequent use of Dolby HX Pro, meant that cassettes became a viable high-fidelity option, one that was more portable and required less maintenance than records. In addition, cover art, which had generally previously been restricted to a single image of the LP cover along with a minimum of text, began to be tailored to cassettes as well, with fold-out lyric sheets or librettos and fold-out sleeves becoming commonplace.

Some companies, such as Mobile Fidelity, produced audiophile cassettes in the 1980s, which were recorded on high-grade tape and duplicated on premium equipment in real time from a digital master. Unlike audiophile LPs, which continue to attract a following, these became moot after the Compact Disc became widespread.

In-car entertainment systems

A key element of the cassette's success was its use in in-car entertainment systems, where the small size of the tape was significantly more convenient than the competing 8-track cartridge system. Cassette players in cars and for home use were often integrated with a radio receiver, and the term "casseiver" was occasionally used for combination units for home use. In-car cassette players were the first to adopt automatic reverse ("auto-reverse") of the tape direction at each end, allowing a cassette to be played endlessly without manual intervention. Home cassette decks soon added the feature.

Cassette tape adaptors have been developed which allow newer media players to be played through existing cassette decks, in particular those in cars which generally do not have input jacks. These units do not suffer from reception problems from FM transmitter based system to play back media players through the FM radio.

Maintenance

Cassette equipment needs regular maintenance, as cassette tape is a magnetic medium which is in physical contact with the tape head and other metallic parts of the recorder/player mechanism. Without such maintenance, the high frequency response of the cassette equipment will suffer.

One problem occurs when iron oxide (or similar) particles from the tape itself become lodged in the playback head. As a result, the tape heads will require occasional cleaning to remove such particles. The metal capstan and the rubber pinch roller can become coated with these particles, leading them to pull the tape less precisely over the head; this in turn leads to misalignment of the tape over the head azimuth, producing noticeably unclear high tones, just as if the head itself were out of alignment.

The heads and other metallic components in the tape path (such as spindles and capstans) may become magnetized with use, and require degaussing.

Isopropyl alcohol and ethyl alcohol are both suitable head-cleaning fluids. (Rubbing alcohol may contain oil which is not suitable.) Head cleaning fluid is a relatively expensive way to buy isopropyl alcohol.

Decline in popularity

Analog cassette deck sales were expected to decline rapidly with the advent of the compact disc and other digital recording technologies such as digital audio tape (DAT), MiniDisc, and the CD-R recorder drives. Philips responded with the digital compact cassette, a system which was backward-compatible with existing analog cassette recordings for playback, but it failed to garner a significant market share and was withdrawn. One reason proposed for the lack of acceptance of digital recording formats such as DAT was a fear by content providers that the ability to make very high quality copies would hurt sales of copyrighted recordings.

The rapid transition was not realized and CDs and cassettes successfully co-existed for nearly 20 years. A contributing factor may have been the inability of early CD players to reliably read discs with surface damage and offer anti-skipping features for applications where external vibration would be present, such as automotive and recreation environments. Early CD playback equipment also tended to be expensive compared to cassette equipment of similar quality and did not offer recording capability. Many home and portable entertainment systems supported both formats and commonly allowed the CD playback to be recorded on cassette tape. The rise of inexpensive all-solid-state portable digital music systems based on MP3, AAC and similar formats finally saw the eventual decline of the domestic cassette deck. Tascam, Marantz, Yamaha, Teac, Denon, Sony, and JVC are among the companies still manufacturing cassette decks in relatively small quantities for professional and niche market use. By the late 1990s, automobiles were offered with entertainment systems that played both cassettes and CDs. By the end of the late 2000s, very few autos were offered with cassette decks. As radios became tightly integrated into dashboards, many autos lacked even standard openings that would accept aftermarket cassette player installations.

Despite the decline in the production of cassette decks, these products are still valued by some. Many blind and elderly people find the newest digital technologies very difficult to use compared to the cassette format. Cassette tapes are not vulnerable to scratching from handling, and play from where they were last stopped.

Some audiophiles believe that the technology of the highest quality cassette decks, due to their analog nature, provides sound recordings superior to current digital technology, such as CD-R and DAT. However, cassette decks are not considered by most people today to be either the most versatile or highest fidelity sound recording devices available, as even very inexpensive CD or digital audio players can reproduce a wide frequency range with no speed variations. Many current budget-oriented cassette decks lack a tape selector to set proper bias and equalization settings to take best advantage of the extended high end of Type II [High Bias] and Type IV [Metal Bias] tapes.

See also

Tape deck

Nakamichi and Revox. These corporate pages contains links to external sites relevant to cassette decks.

high end audio. This page contains links to high-end audio companies, including companies formerly producing "high-end" audio gear such as cassette decks.

Notes

^ Advent cassette decks

^ Circuit and description of DNL URL accessed August 25, 2006

External links

Pictures of Cassette Decks A Japanese language page, but containing pictures of historic cassette decks.

Audio Asylum Tape Trail A discussion forum of interest to those involved in cassette technology.

Vintage Cassette Decks - A collection of Vintage cassette decks of all brands.

Categories: Recorders | Audio players | 1963 introductions
About the Author

I am an expert from China Crafts Suppliers, usually analyzes all kind of industries situation, such as vhf wireless microphones , dual vhf wireless microphone.

Is there a 2-circuit N.O. Pushbutton available anywhere?

I need an industrial electrical switch that has 2 positions (I'm thinking push-pull), which closes momentarily when pushed on one circuit and then closes momentarily on a second circuit when pulled. Anyone have any ideas? I've searched far and wide to no avail.

Does it have to be a push/pull type switch? The problem with this style of switch is that it looks very similar to a typical Emergency Stop (E-Stop) switch. I would avoid using it for the plain fact that you don't want other switches that LOOK like E-Stops that aren't really E-Stops.

I would suggest a 3 position, momentary switch. In the 'rest' or center position, the switch is off. You can toggle the switch to the left to close one set of contacts. Toggling the switch to the right closes the second set of contacts.

Allen-Bradley: http://raise.rockwellautomation.com/catalog/_0_17_1_3.asp?

However if you REALLY must use the push/pull switch, Allen-Bradley sells a '3-Position Push-Pull Units, Non-Illuminated' switch. You can search their site for the specifics.

Hope this helps.

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