Sie sind hier : Startseite →  Hifi Magazine + Zeitschriften→  (32) US "off duty"→  US off duty - 1973-intro→  off-duty-1973-07 - Tape Technics

"off duty" 1970 - 1997 - eine Werbezeitung für's US Militär

Die in diesem amerikanischen (Freizeit-) Shopping-Magazin angeprie- senen Produkte waren auschließlich amerikanischen und kanadischen Militärangehörigen ausserhalb der USA zugänglich - also zu kaufen - vor allem zu ganz ungewöhnlich (verblüffend) niedrigen US $ Military-Preisen. Zu der einführenden "off duty" Seite geht es hier lang.

.

Wie vergleiche ich Magnetbänder ? Die sehen alle gleich aus.

Hier gibt der Autor einen Einblick, wie man einem amerikanischen Interessenten diese komplexe Materie rüber bringt, so einfach wie möglich.

.

They Only Look Alike

Our examination of cassette mechanics - Off Duty / Europe / July 1973 By THOM PRINGLE
.

CHOOSING THE RIGHT CASSETTE

CHOOSING THE RIGHT CASSETTE for your recorder can be a confusing task with so many types of tapes, cassette designs and new features on the market today.

Certainly, the tape itself is of major importance not only as far as its oxide is concerned but the degree of care with which it is manufactured is of utmost importance, too.

There are many firms which make a practice of buying up old computer tapes and manufacturers' seconds which are then sliced, spliced and sold as "high-quality" tapes at suspiciously low prices.

  • Anmerkung : So etwas kam bei uns in Deutschland West nicht vor. Es war per Gesetz verboten, den Kunden zu täuschen und es wurde sehr teuer. Die Hongkong Chinesen versuchte es, wurden aber vom Zoll abgewürgt undhatten recht schenll aufgegebn, in die EU zu exportieren.

.

Hier nur "first-line" manufacturers

We are happy to say that all the firms represented in our tape SHOPPER in this issue are all first-line, responsible manufacturers who take a great deal of pride in their products and usually back up their products with a valid guarantee, too.

The matter of choosing a particular oxide as your standard, however, can be tremendously frustrating. Every day, manufacturers bring out new types of oxides - each with a subtle difference which may or may not benefit you. Of course, the claims made for these oxides sound pretty good and if you listen to all the claims, you won't know what to believe.

Ein neues "super-oxide" ist nicht immer vorteilhaft

The fact is, a new super-oxide can actually give worse performance than the old "plain" oxide you may now be using. This results from the fact that there must exist a marriage between your tape recorder and the tape you use.

We're not talking strictly about the special chromium-dioxide tapes, but the special ferrite tapes, too. Even though some claim to work on any machine with optimum efficiency - no adjustments required - this may not be true.

Every tape requires special amounts of modulation, bias and equalization in order to deliver its optimum performance and this is where the difficulty begins.

Very few audiophiles or repairmen have the equipment or qualifications to adjust a tape recorder so it gives absolute optimum freedom from distortion, signal-to-noise ratio and frequency response with a particular type of tape.

Nevertheless, the best way to set up your recording would be to choose a particular type and brand of tape (which you could only hope would be manu-facturered for several years to come) and have your tape recorder tuned by a qualified person for that specific tape.

Or, you might try "compearing" - listening to several kinds of tape on which you have recorded and let your ears be the judge - but this is pretty difficult.

Kaufen und hoffen, der beste Weg ?

Finally, and this is the method used by just about everybody, simply buy a reputable brand and type of tape, stick with it and hope for the best.

Certainly, however, there must be something you can look at to help you in choosing a cassette, and there is "Cassette mechanics".
.

"Cassette mechanics"

How is the cassette shell put together? How well is it put together? How long is it likely to run without jamming?

There are dozens of parameters applying to cassette mechanics which can be examined - each of which can and does have a definite effect on the performance and sound of your recordings.

OFF DUTY asked the major suppliers of cassette tapes to the military market to provide samples of their cassettes for a non-performance evaluation of cassette mechanics.

We inspected the cassettes according to a list of features we feel are important and for which, in some cases, we have definite preferences.

Wir haben ein paar sehr gute Cassetten gefunden

Did we find any cassettes that were particularly outstanding or any that were below par? Yes.

Some cassettes, we feel, offered features that placed them far above most cassettes as far as cassette mechanics are concerned.

On the other hand, we were surprised to find a couple of brands which have remarkable deficiencies by our standards. All of this indicates to us that careful consideration of cassette mechanics by the user can make an important difference!

Of course, you may place less emphasis on some aspects of cassette mechanics than we do, so we will explain the features we looked for, as well as our recommendations and a review of each brand's mechanical features, then let you decide for yourself, depending on which brand names may be available at your local outlet.

Shell Design. (das Gehäuse-Konzept)

Exploded view of a symmetrical cassette.

As shown in our exploded view of a standard cassette, the shell consists of a top and bottom half which are fastened together to form a complete unit with integral tape guides and structural support points.

The tape, hubs, head assembly, rollers and lubrication elements are separate components which are placed into the shell to complete the unit. It would seem that once a mold has been designed to precision standards, there can be no appreciable variance in production and that all shells will be identical. Such is not the case.
.

Symmetry.

Some manufacturers have found that making both the top and bottom halves of the shell almost symmetrical limits the design flexibility allowed for the various internal components. In addition, the symmetrical design seems to sacrifice meticulous design and assembly to gain production efficiency.

We definitely recommend asymmetrical shell designs since most cassettes we examined which had asymmetrical designs appeared to be more carefully engineered and had better controlled tolerances.

  • Anmerkung : Das ist leider ganz großer Unsinn, wie uns der Test-Ingenieur von "AGFA Kassetten Technik Köln" (unser "Mr. Macrolon") verraten hatte. AGFA hatte nämlich (nach anfänglichem Markterfolg) aus dubiosem Sparzwang, der aber gar keiner war, ein fundemantales Eigentor geschossen. Bei der Montage von asymmetrischen Kassetten (-Schalen) könne man wieder ein paar Montage- "Sekunden" einsparen und das bei 10 Millionen Stück wäre toll, wegen des Bonus am Jahresende für die Produktionsleiter oder Starverkäufer.
  • Es stellt sich nämlich ziemlich schnell heraus, daß bei geringster Erwärmung aus der Normaltemperatur (wir reden noch nicht mal von der Sonneneinstrahlung im Auto-Recorder), der Lagertemperatur im Wohnzimmerschrank, sich das Gehäuse ganz leicht asymetrisch verzog (sich wölbte) und die Kassette bzw. das Band klemmte mit erheblichem Jaulen - ganz fatal bei weit über 10 Millionen auf der ganzen Welt. Das war der Anfang vom Ende der AGFA CC-Kassetten - obwohl AGFA das bessere Bandmaterial hatte als die BASF und auch viel besser als die ganzen Amerikaner. Es hatte AGFA nichts mehr geholfen. Die Japaner übernahmen den Markt vollständig.

.

Closing method.

Two methods for closing cassette shells are being used - screws (Schrauben) and welding (verschweißen oder verkleben). The main difference is that you can easily open one (the screw-type) and you can't easily open the other (welded).

There are some other drawbacks but they have been designed out of most cassettes. Some manufacturers have now started using both types depending on the kind of tape in the cassette.

We do not like welded cassette shells. Too many times we have had something happen to a valuable recording which made it necessary for us to open a cassette shell and make repairs - you can imagine the problems in cracking open a welded shell. You can probably also imagine the problems involved in putting the shell back into operating condition!

However, in a screw-type shell we want five screws, not four! The extra screw installed near the head assembly is vital in maintaining proper positioning of the tape guide elements. You would do well, by the way, to purchase a small screwdriver of whatever kind is necessary to fit the cassettes you settle on. The screws are quite small and you'll probably have trouble finding an appropriate screwdriver at the last minute.
.

Windows.

Large windows in the side of a cassette are great. Cassette mechanics are far from perfect and it's nice to be able to see what is going on inside a cassette - especially when it seems to be malfunctioning.

The normal size for the windows is about 1/4" x 3/4". Anything this big or bigger we like - anything smaller seems hard to work with but this is certainly not a crucial point.

Seam precision.

One big problem with cassette shells is the joining of the two halves, especially at the front where the tape comes into contact with the seam (der Schweißnaht).

It is not unknown for the tape to slip through the seam and actually start spilling out into the recorder mechanism or bind in some manner. This problem can be eliminated if the seam is exceptionally tight. If you choose an asymmetrical cassette shell, you will usually find that the front seam is offset to either the top or bottom and this will help a great deal in preventing the tape from slipping out, if the seam is closed tightly.

The latest answer to this problem, however, is the mortised front seam (a type of tongue-and-groove configuration) which comes as near to eliminating the problem completely as anything we've seen.

The old center seam units should still be individually inspected to make sure that seam mating is complete.

On some of the cassette brands we received for inspection, the seams were so incompletely mated that we could actually slide the tip of a table knife between the halves with no effort. Tape slipped through quite easily, of course.

What's best? If the seams on your cassettes are completely mated, then there is no problem. If you don't want to be bothered with checking on things like that, choose mortised seams first, then off-center seams and, finally, center seams.

Slip sheets.

Lying horizontally above and below the tape spools in cassettes are two sheets which are designed to reduce friction that may be generated between the cassette shell and the spools of tape. The trend is to make these sheets of synthetic material and to coat them with a special dry lubricating compound.

We think these types of slip sheets are somewhat better than others we have encountered although polished or waxed paper sheets presented no visible difficulties. Plain acetate sheets, however, became statically charged and actually clung to the spooled tape.
.

Head assemblies.

The business end of things is where the head of the recorder comes into contact with the tape. Here is where the tape must make contact with the head in an absolutely prescribed manner and position if good performance is to be obtained.

Shields.

Two shield designs were represented in the cassettes we inspected, standard plates and the new "bathtub" shields. The plate is simply a straight, rectangular piece of metal dropped into a slot
in the back of the cassette's head well, while the bathtub shield is a five-sided shell which actually lines the sides of the head well. Although we rather liked the bathtub shields from a professional standpoint, we could find no outstanding reasons why the average audiophile should consider the bathtub shield better than the standard plate.
.

Pressure pads.

Two basic types of pressure pads are being used in cassettes, the standard leaf-spring mount and the newer direct-mount pads. The pads on the old standard types are tiny in comparison with the new pads - 3x5mm versus 6x8mm - and are mounted on thin strips of metal which run horizontally behind the tape across the mouth of the head well. The direct-mount pads, on the other hand, are mounted on a rectangular piece of springy foam which is, in turn, glued to the shield directly behind it.
.

The direct-mount pressure pads

With some reservations, we favor the larger direct-mount pressure pads. The standard pads are designed to be dropped into a molded slot in the shell and have an excessive amount of play, both vertically and horizontally. Because of this, and the small size of the pads, the tape often flipped up over the edge of the pad during our tests which made the cassette unusable until the condition was corrected. The one exception among the standard-pad users was Agfa which secures the ends of the leaf spring in the sides of its bathtub shield - a technique that gives considerable stability to the assembly and represents a definite improvement, in our opinion.
.
The larger direct-mount pads, however, are very stable, cover more area and have the additional advantage of being able to apply equal pressure at all points on the face of a curved head. This can be quite important when multiple function heads are used in a recorder.

The fact that these pads are so big can, though, be a serious drawback. If you happen to have a recorder that uses a head with protruding horizontal guides on the top and bottom of the head, do not use cassettes with large direct-mount pads.

Normally, these horizontal guides are spaced 6mm apart and will catch a large pad at the top and bottom in such a way as to prevent the pad from making good, intimate contact with the tape and head. If you are already using some of these cassettes with a machine of the type mentioned, you can cut about 1 mm from the top and bottom of the pad with a pair of cutters and the pad will fit the head with no problem.
.

Cases.

The cassettes available today are contained in a variety of cases - some provided as standard equipment and some available by special request. Submitted to us, along with the cassettes, were four different kinds of cases.

Standard.

This is the type of case normally used with cassettes and consists of two halves which hinge together and snap closed. We think it is still the best all-around cassette case on the market. It has built-in hub locks, plenty of index space (indexes can be easily changed) and affords a fair amount of protection to the cassette. Our biggest complaint about these cases is that many of them fell open too easily -even with gentle handling.
.

Sony Handy Holder.

This is one of the most ingenious cases we've seen and is absolutely the best case for people who want to carry cassettes in their pockets. It is ultra-thin (no thicker than the cassette itself) and contains built-in hub locks. Its biggest drawback is that it doesn't give a cassette as much protection from dirt as other case designs.

BASF library pack.

For people who want the best protection for their cassettes, this case is definitely recommended. We won't say this case is indestructible, but we placed one of these units with a cassette inside on the floor and jumped up and down on it. Case and cassette both came through unscathed and the cassette played perfectly.

The drawbacks to this case include its exceptionally large size, poor labeling system and absence of built-in hub locks. (Trying to keep track of those little inserts supplied as hub locks just doesn't work!)

Memorex case.

This is a beautiful case with precision molding and a most professional appearance. It has serious drawbacks, though, including no built-in hub locks and poor labeling provisions.

We consider the absence of built-in hub locks in a case to be fairly serious. We found that without these locks, a few flicks of the wrist throws enough tape loops in a cassette to make an initial fast-forward or fast-rewind operation in a recorder quite risky.
.

Conclusion

These, then, are some of the things you can consider when deciding on your next cassette purchase. Consult our accompanying chart and give most emphasis to those things which seem most important to you.

.

Things we especially liked . . .

.

  • - The special head-cleaner leader on Maxell cassettes. This leader is impregnated with a chemical which helps remove deposits on the head of your recorder as it passes over the head at the beginning or end of play.
  • - The pressure-pad mounts on Ampex, Agfa and Memorex cassettes. All were held precisely in place - Ampex and Memorex use direct mounting methods while Agfa's leaf-spring mount is solidly held by the sides of a bathtub shield.
  • - The dynamic tape-handling elements in the BASF cassettes. These consist of two channeled tusks which ride on the outside of each spool of tape and guide the tape onto or from the spool, and, on the larger 120-size cassettes, a spring tension brake which controls spool movement. In one of the few dynamic tests we made, the BASF cassettes spooled very cleanly - even during fast forward or rewind - a definite help in eliminating tape feathering. We did not have time to make endurance tests but experienced no mechanical difficulties with these cassettes during our tests.
  • - The exceptional attention to detail in the manufacture of the Memorex shell and case. Even though we might not have designed these elements to include the same features, we found the precision and thought put into them by Memorex to be outstanding.
  • - The clear see-through shell material used by Sony for its cassettes. Especially useful to see inside when problems develop with welded cassettes.

.
Off Duty / Europe / July 1973 By THOM PRINGLE
.

- Werbung Dezent -
Zurück zur Startseite © 2007/2021 - Deutsches Hifi-Museum - Copyright by Dipl. Ing. Gert Redlich Wiesbaden - DSGVO - Privatsphäre - Zum Telefon der Redaktion - Zum Flohmarkt
Bitte einfach nur lächeln: Diese Seiten sind garantiert RDE / IPW zertifiziert und für Leser von 5 bis 108 Jahren freigegeben - kostenlos natürlich.

Privatsphäre : Auf unseren Seiten werden keine Informationen an google, twitter, facebook oder andere US-Konzerne weitergegeben.