Deze pagina is nog niet in het Engels beschikbaar.
If you would like to help translate this site please click here.
At present most of GRN's recorded messages are distributed on Compact Cassette. Almost always these recorded cassettes are produced using Cassette Duplicators. In order that our product is of the highest practical quality, it is necessary that duplicators be kept in good order and those who use them understand the appropriate ways of looking after and using these machines. Throughout GRN many different makes and models of duplicator are in use, and information about each is found in the Manufacturer's Operating Instructions and Service Manual. Unfortunately, not all GRN Facilities have these Manuals, and in many cases the information is given in a way that may be understandable only to a technically trained person. This document is intended to be a general guide for the training and guidance of non-technical users of duplicators.
Because of the many makes and models of duplicators in use, this document can only give general advice. Most cassette duplicators are designed to be used by non-technical people. However, to get the best performance and longest life from a duplicator, some knowledge of the basic principles of the technology is helpful. If anyone experiences difficulty with the following basic explanation of the technology, or how it applies to a particular machine, please seek help and further explanation from a member of the GRN Technical Team. Contact GRN Australia with your questions.
Cassette duplicating machines need to be mechanically strong to give consistent quality and performance. The cheapest units are unlikely to be satisfactory, and until a list of recommended machines is available, the advice of the GRN Technical Team should be sought. The machines from the lower end of the price range are likely to prove a bad deal in the end, because of the difficulty of servicing and the shortness of their working life.
Very few "technicians" offering to service electronic equipment in the commercial market have experience of Cassette Duplicators. It is important that before allowing any person to service a duplicator, members of GRN should seek the advice of the GRN Technical Team.
At the present time duplicated cassettes are made on both mono and stereo cassette copiers. When purchasing a new copier, a GRN Facility should consider whether to get a mono or stereo copier. Factors to consider include: the difference in cost, the format of the playback machines available in the market place which are typically used by the target audience, and what necessity there may be to reproduce stereo programs. Stereo copies can be played on mono machines quite satisfactorily.
[Note 1: The purchase of a stereo copier in 2002 would have increased the purchase price by between 30% and 40% compared to a mono copier, with an increase in cost for replacement heads of 10% to 15%. Setting head height is a little more critical for a stereo machine.]
The most basic configuration consists of two cassette mechanisms, a "Master" and one "Slave", and there are machines of this sort in use in GRN. The most common configuration has four cassette mechanisms, a "Master" and three "Slaves". These are often part of a modular system that can be expanded by connecting other modules that consist entirely of Slaves. The "Master" deck is equipped only as a replay machine, and the "Slaves" are equipped only to record. Duplicators usually operate at a nominal eight times (8X), or sixteen times (16X) speed. At 8X, the tape runs at 15"/sec and a C60 cassette takes 3 minutes 45 seconds (3:45) to copy. At 16X, the tape runs at 30"/sec and a C60 cassette takes 1:52 to copy. However, a machine may run at only 5/6 of its nominal speed in some countries.
[Note 2: The reason why some duplicators run at 5/6 of the rated speed is as follows - if the motor is designed for a 60 Hz mains frequency (made, say in the U.S.) it will run slow by that fraction when run from 50 Hz (say, in Australia). This is not necessarily a serious problem, most are still satisfactory, and in some cases alternative 60 or 50 Hz motors may be available, but it needs to be borne in mind. Similarly, a duplicator with motors designed for use with 50 Hz mains frequency, it will run at 6/5 of the rated speed if operated from 60 Hz mains.]
Because duplicators operate at higher speeds than normal recorders and players, their components are operating at the limits of the technology. This applies to the magnetic properties of the heads, the electrical performance of the electronics, and the mechanical performance of the mechanism. The higher the speed (e.g., "16X" versus "8X") the closer to the limits at which the duplicator is operating, and this usually means there is a trade-off between speed of duplicating and performance.
The materials most affected by magnetism are those containing iron although some other materials also show magnetic properties. When a magnetic material is exposed to a magnetic field it becomes "magnetised", that is, it retains a magnetic field. Generally speaking, the harder it is to magnetise a magnetic material, the better it retains that magnetism. The easier it is to magnetize a material, the easier it is to later remove the magnetism. Magnetic fields can be removed or reduced by a number of means including heating and mechanical shock (hammering), but for our purposes, they are "Erased" by the application of a strong alternating magnetic field which is then reduced to zero. This alternating field cycles the magnetisation of the material being de-magnetised (erased) from one polarity through zero to the other polarity in gradually reducing amounts until the amplitude of the magnetic field falls to zero and the material is left with zero magnetism.
The heads used in Duplicators must be made of materials that are easily magnetised in order to perform their function, and this makes them vulnerable to being inadvertently magnetised by a "stray" magnetic field. An important part of using a Duplicator is the regular demagnetising of the heads and other components in the tape path.
[Note 3: Even leaving a duplicator in one position for a long time will result in the earth's natural magnetic field doing this to some extent.]
Because the recorded layer of cassette tape is magnetic, it is affected by any magnetic fields it encounters, not only the magnetic field which properly maintained duplicators produce at their erase and record heads. A slave head will fail to properly record a cassette if it has become magnetised. A Copy Master can be partially or wholly erased by a stray magnetic field, and this could be produced by a faulty head or some other faulty component in a duplicator, or by accidentally putting the Copy Master into a Slave module. Most cassette duplicators ignore the record protect holes in the cassette, so they will erase a Copy Master if it is placed in the wrong module. Copy Masters or copied cassettes can be damaged by a field produced by other parts of the duplicator, such as the steel frame of a pinch roller, if that part has become magnetised.
[Note 4: It should be noted that a powerful magnet is a necessary part of a loudspeaker. Care must be taken to keep loudspeakers, or any equipment containing a loudspeaker, away from tapes and from tape duplicators.]
Cassettes use "magnetic tape", i.e., a plastic tape that is coated with fine magnetic particles, held in a binder. The particles, and hence the tape, can be magnetised. Binders are not perfect, and some of the magnetic particles become lost to the tape and deposited on heads and other parts of the duplicator. Unfortunately, these particles are chemically very similar to rust, and need to be removed before they cause rusting or other forms of corrosion. They are also slightly abrasive, and this leads to wear as the tape is moved over the heads, the tape guides, etc.
Tape recorder and player heads consist of a "ring" of easily magnetised material with a "gap" at right angles to the direction of tape travel, and with a coil of copper wire wound on the ring.
"Record heads" turn an electrical signal into a corresponding magnetic field across the gap that magnetises the tape as it passes. This leaves a varying pattern of magnetism on the tape which is a copy of the electrical signal, which in turn was a copy of the air pressure of the original sound.
[Note 5: To be pedantic, it is an "analog" of the electrical signal, which is an "analog" of the sound pressure of the sound.]
When a recorded tape passes the gap of a "Replay Head" the pattern of magnetisation on the tape generates a corresponding electrical signal in the coil of the head. Ultimately, when the tape is played, the replay head (often called a "play head") of the player turns this signal back into a sound.
It is possible to use the same head to both record and replay, and most consumer type cassette recorders do this. But for optimum performance, "Professional" recorders usually have separate record and play heads so that each head can be optimised for its particular role. Duplicators operate at the limits of the technology because of the higher tape speeds used, and so the play head of the Master deck and the record heads of the Slaves are always different.
Many duplicators include "erase" facilities on the slave decks, but not all do so. Erase heads operate by applying a constant amplitude, high level signal to the tape as it passes. Because the tape initially experiences it as a very strong signal, which decreases as each magnetic particle moves away from the head, it effectively erases the tape.
[Note 7: All tapes which are to be used for copying should be bulk erased before use!]
Because the duplicator moves the tape at several times the normal speed, this raises the frequency range of the recording by the same factor. For example, consider a Copy Master recorded with sound having a range of 40 Hz to 10 kHz. In a duplicator operating at 8X speed, the signal circuits have to handle a range of 320 Hz to 80 kHz. In the case of a duplicator operating at 16X, the frequency range is 640 Hz to 160 kHz! Designing heads and circuitry for this frequency range can be a serious challenge!
[Note 8: Heads used in recorders are usually made of special alloys of iron, but these alloys may not be the most suitable for recording the high frequencies found in duplicators. For this reason some modern duplicators can optionally be fitted with "ferrite" heads. Ferrites are synthetic ceramics, and have a higher upper frequency limit compared to "ferric" (iron alloy) heads. Ferrites are usually more expensive, but last longer because the surface over which the tape passes is harder. Therefore, where competent technicians are only available to visit at long intervals, the higher cost is justified as head wear seriously limits the performance of the duplicator.]
A high frequency component called "bias" is added to the signal applied to the record head in all recorders, including duplicators. The bias is necessary to obtain a linear recording, but cannot be heard in the completed recording. The bias frequency has to be at a frequency several times higher than the highest signal frequency to be recorded, and this adds to the difficulties of designing suitable recording circuits. Also, the amount of bias has a pronounced effect on the frequency range, noise level and amount of distortion of the recorded signal. Therefore it must be accurately adjusted, but this is usually done by an experienced technician when servicing the equipment. The optimum amount of bias depends on the type of tape being used, so preferably it should be adjusted to get best performance with one type/brand of tape, and then only that type/brand of tape be used to make copies.
All tape recorders and players require the tape to move past the heads at a constant, precise speed and duplicators are no exception. Originally, this was achieved by driving capstans using "synchronous" motors which by their design rotate at a speed locked to the mains frequency. This is a simple system, but has the disadvantage that the mains frequency is different in different parts of the world. More recently, duplicators have used motors which run at an electronically stabilised speed. These can operate from mains of any frequency.
All the duplicators presently used in GRN have conventional mechanical layouts, in which tape is drawn past the heads by a pinch (pressure) roller, which presses the tape against a rotating capstan. Some means is needed to provide control of the supply and take-up spindles, and usually this needs to provide at least rewind facilities. This is usually done by one of a number of possible arrangements of rubber belts, slipping clutches, gear wheels, etc. Means must be provided to sense the end of tape (recording completed). Many duplicators also provide automatic rewind. Older duplicators will usually control the operation of the various functions by simple electrical switches and mechanical components. Later model duplicators use electronic logic circuits to control the operation of the mechanisms.
Demagnetisers (also called "Degaussers")
[Note 9: Degauss is an older term and was derived from "Gauss", which is an old unit of magnetism named after an early physicist of that name.]
Two types of demagnetiser are generally used in the duplicating of cassettes. The first is a generally larger unit used to demagnetise the copy cassettes before use. It is sometimes called a "Bulk Demagnetiser" or "bulk eraser". Not all duplicators are provided with erase heads, and in the case of a duplicator without erase heads, it is necessary to have some means of ensuring all cassettes have been erased before they are used to make copies - even nominally "blank" cassettes may have something accidentally recorded on them, and there are often cassettes which have been wholly or partially recorded, that can be reused after demagnetising. Even where the duplicator is provided with erase heads it is good practice to bulk erase cassettes before copying onto them.
[Note 10: The Erase head may only erase a "track" with a width approximately equal to the "track" which the record head will record. It is possible this will leave some of the previous signal still on the tape, and if the tape is played on a machine, which has a slightly different head width, or location to that used by the duplicator, some of the unwanted signal may be reproduced as well as the wanted signal.]
The second type of demagnetiser is a "Head Demagnetiser". This is a smaller handheld unit, which has a pole piece long enough to reach the faces of the heads. The end of the pole piece should have a plastic covering so that it can touch the face of the head without scratching it. In use, it is switched on; the end of the extension is rubbed over the face of the head, and then, whilst still switched on, slowly withdrawn well away from the head. It must not be switched off until it is well away from the head. (See first paragraph of "Magnetic Principles" above.) It should also be used in a similar manner to demagnetise other metal objects near to the tape path.
It should not be necessary to demagnetise erase heads, as normally the erase signal does this, but it is a good practice to do so and give confidence that the head is demagnetised.
IMPORTANT: When demagnetising a duplicator, or any tape machine, the electrical power to the machine MUST BE TURNED OFF and if possible unplugged.
[Note 12: The strong magnetic field of the eraser generates high voltages in the head, which could possibly damage the electronics which are connected to the head. Also, if the duplicator remains connected to the mains, an earth leakage path could exist which could result in damage.]
If you are wearing a spring driven watch it is also wise to take it off and put it somewhere away from the items being demagnetised to avoid any possibility of damage to it.
Low grade cassettes which may operate satisfactorily at normal speeds may not withstand these higher tape speeds. In recent years examples have been found of quite good tape which was let down by being loaded into poor quality shells.
[Note 13: The following problems are typical of inferior cassettes:
Before large quantities of tapes are purchased it is recommended that a few be obtained for examination, testing and assessment of the recording quality. If necessary the tapes may be sent to the GRN Technical Team or nominee for assessment.
Using the Duplicator
Because of the differences between the various duplicators used in GRN, it is not possible to give a detailed method of operation which will suit all cases. It is highly desirable that each Facility where duplicators are used has a copy of the Operational Manual provided by the manufacturer for the make and type of machine they use. If there is no manual provided for your machine please contact the Technical Team, giving the make and model number of your duplicator, and every effort will be made to provide a copy of the manual.
Duplicators need to be cleaned and demagnetised on a regular basis. Care must be taken when cleaning heads to make sure the face of the head is not scratched in any way. Cleaning should be done with a cotton bud and alcohol. Where it can be obtained, pure ethyl or propyl alcohol is the best, but methylated spirits can be used. Do not use "rubbing spirits" or "rubbing alcohol" as these often include oily components.
Tape guides and the capstan shaft also can be cleaned with alcohol, but the pinch roller should be cleaned using rubber cleaning fluid made to the following formula:
|2ml||Washing - up detergent|
|50 ml||Methylated Spirits|
|Remainder||Water to make up to 500ml|
[Note 14: This is the formula to make 500 ml of cleaner. The actual quantities are not important, what matters is the proportions. To make up some other quantity, use: 1 part by volume of washing up detergent, 25 parts by volume of methylated spirits or other suitable alcohol, and enough water to make up to a total of 250 parts by volume.]
Duplicators should be cleaned VERY FREQUENTLY during a duplicating session. We recommend after every five (5) to ten (10) copies. If you have good copy tapes you may only need to clean the heads after copying twenty (20) tapes.
It is VERY IMPORTANT to clean the duplicator after finishing a duplicating session. This will protect and increase the life of the heads. If the duplicator is well covered to protect it from dust, after cleaning it should be ready for the next duplicating session. However, check again before commencing to make sure that it is completely clean.
Duplicators, which are in more or less daily use, need to have the heads demagnetised at least once a week. When the duplicator has not been used for over a week, the heads must be demagnetised before the first use.
IMPORTANT: When demagnetising a duplicator, or any tape machine, the electrical power to the machine MUST BE TURNED OFF.
Checking and Storing Cassettes
Copied Cassettes should be checked for satisfactory quality. Not only does this provide a check that the duplicator is functioning satisfactorily, it also provides a quality control check on our main product! The duplicating process should be tested on a good quality player and speakers to compare the difference between the Copy Master and Duplicates. This is a quality control check, and any significant drop in quality is a sign of problems with the duplicator, copy cassettes, or even the Copy Master. Both sides of each Duplicate should be spot-checked after high-speed copying.
Unless being played/recorded, all cassettes should be kept in their boxes to protect them from dust or other damage. They must be stored in a cool, dry environment away from any magnetic fields.
Sample cassettes of a new program should also be checked in a portable playback machine similar to that which the customer will use. Preferably this should be done by the person who produced the program. This is the check that the program came out the way he or she had intended.
Care of the Duplicator
When not in use, the duplicator should be kept covered with a dust-proof cover.
Any visible wear on the faces of the heads, or on tape guides, or noticeable decrease in sound quality that cannot be corrected by cleaning, demagnetising or using better cassettes, is an indication that maintenance by a competent technician is required.
We recognise the great importance and the difficulty of servicing and maintaining cassette copiers. However under no circumstances should equipment be sent to a local repair shop for repair, nor given to just anyone who claims to be a technician or an electronic engineer. There are very, very few technicians with the skill to service this kind of professional and expensive equipment, and many cassette duplicators have been ruined by unreliable technicians. All repair or equipment needs should be referred to the GRN Technical Team. We will attempt to meet this servicing need with our own technicians visiting the various GRN Facilities where technical help is needed.