The Hi-Fi system
Features, gimmicks and sound quality
The ultimate quest at the upper end of the home audio market has always been for audio quality. For many decades, however, the performance of high-end hi-fi equipment has arguably been very close to 'perfection', leaving manufacturers few options to distinguish their products from the competition. Whilst most purists shun all but the bare necessities, many buyers have surely been wooed by the myriad extra 'features' introduced over the years in this competitive market. We start our tape-recorder section with a deck that boasts a rather unusual feature...
The Invert-O-Matic
Akai Invert-O-Matic
The Akai GXC-65D Invert-O-Matic cassette deck was an early form of auto-reverse deck which turned the cassette over to play the other side instead of turning the tape head. When the Compact Cassette specification was introduced as a dictation (speech only) medium in the mid 1960s, it was not intended for high performance applications. Due to limitations in the tape itself, a larger tape running at higher speed was necessary for high fidelity, and the open-reel recorder retained its supremacy for music recording. Over the next decade, improvements in tape formulation and tape head design lead to cassette performance that could rival many open-reel decks, and domestic 'hi-fi' cassette machines rapidly became the norm due to the great convenience and compactness of the format, and the opportunity of playing home-made recordings in the car and on the move in portable machines. As the cassette established itself as the worldwide standard for home recording, manufacturers started offering extra features on their decks, one of the most challenging of which was reversible operation, allowing both sides of the cassette to be played or recorded without the user having to remove the cassette and turn it over.
Tape path components and sensor
In a single-direction cassette deck, the three 'windows' in the end of the cassette shell are used by the deck to bring the erase head, record / play head, and the pinch roller / capstan combination into contact with the tape. These three components must be arranged in that order in the direction of tape travel and are normally laid out from left to right across the mechanism. To provide reverse operation using this layout without moving the cassette, the pinch roller / capstan and erase head would need to change places, which is difficult because the capstan is attached to a flywheel and bearing assembly and cannot readily be withdrawn from the cassette. Evidently an alternative layout was required for practical reversing machines. The problem was solved, in the case of playback-only decks (which have no erase head) by providing two capstans and pinch rollers, one in the left window running right-to-left and one in the right window running left-to-right. Only one pinch roller is engaged at a time, and the recording tracks on the appropriate 'side' of the tape are replayed by a stationary all-track playback head equipped with a double set of magnetic pickups capable of reading both side of the tape at once, avoiding the need to turn the head over. To provide a record facility however, the erase head must be squeezed into the middle window along with the record / play head, on a rotating turret that allows the two heads to swap over when the tape reverses, because the tape must always pass the erase head first. This arrangement forces the designer into some compromises regarding head structure and prohibits the use of separate record and playback heads. Furthermore, the accuracy of head positioning (which is crucial for good performance) can be impaired by the flip-over mechanism, making this arrangement undesirable for high-end decks.
Flipping a cassette
Akai, amongst others, introduced machines comprising a conventional single-direction tape transport and an auxiliary device to physically disengage the cassette, turn it over and re-engage it. The audio performance would therefore not be impaired by the constraints of reversible operation, a point emphasized in the Akai sales literature and manual. On the other hand, a complex mechanical arrangement was necessary to manoeuvre the cassette, and this complexity sometimes lead to a high breakdown rate. In the GXC-65D, the entire mechanism is driven by a single AC motor both for playing and manipulating the cassette. When the tape is running, its movement is sensed by an optical pickup (filament lamp and photocell) detecting the motion of a slotted wheel driven by the pinch roller. When the tape stops, the motion detector circuit operates a solenoid which engages the inverting mechanism main gearwheel with its drive pinion and trips a switch to temporarily boost the motor torque. As the gearwheel makes one complete revolution, its associated cams operate various pawls to propel the many parts of the inverting mechanism in sequence. There is no electrical control involved once the invert routine has begun; the timing is determined entirely by the arrangement of cams.
See the mechanism working in real time: Watch video: Invert-o-Matic flipping a cassette
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