Almost everyone who has owned even the simplest analogue tape recorder knows how to undertake the simple cleaning and maintenance required to keep it up to scratch. When an analogue tape machine gets dirty, you simply scrub the heads and guides clean with an alcohol-soaked cotton bud, and if its alignment starts to drift, a deteriorating top-end response gives you plenty of warning. The situation isn't so simple with the digital tape machines which increasingly form part of studios at all levels. Just what can the typical user do towards maintaining a digital tape machine? According to Joe Fialho, chief service manager for leading studio equipment manufacturer Tascam, if you're working with a machine such as Tascam's own DA88 digital 8-track, good working practice starts with the choice of tape.
"Most reputable DAT tapes will work OK in a DAT machine, but with the DA88, which uses 8mm tapes, there's a wide variation in performance, so there are only certain tapes we recommend. When the DA88 was launched, tapes were available from both Sony and 3M, but neither of them had been conceived specifically for digital audio use and I don't think many people realise the demands made of tape in a digital recording environment. Now there are two tapes designed to meet our needs, which we specifically recommend; the Maxell HMBQ metal-particle tape, and a new tape from Sony. The original Sony tape we recommended was an HMEX formulation, but although it works perfectly, it is a metal-evaporated tape. Metal-evaporated tapes give you a higher signal back off the tape, but the coating is incredibly thin (around a quarter of a micron) and therefore more prone to wear and damage than the metal particle types. In situations when there's a lot of shuttling and scrubbing, there could be problems. A metal-particle tape should be good for at least 1000 passes, whereas metal-evaporated tape is only good for around 300 passes. The Maxell tape has proven to be very reliable.
"The differences in the composition of metal-evaporated tape and metal-particle tape also influence the head life of a machine. Metal-particle tapes are generally more abrasive than their evaporated counterparts -- typically by around 20%. This element has been designed into the tape formulation to reduce the likely effect of head clogging, so as to maintain consistent recording fidelity and performance. To balance this, they are usually cheaper than metal-evaporated tapes. Sony now have a new DARS dual-layer tape, which is a metal-particle tape with a special surface coating. It's claimed that this combines the mechanical benefits of metal-particle and metal-evaporated tapes. Fuji are also now making a dual-layer tape.
"Once you've bought the right tapes to use, you have to look after them. Because DAT and DA88 tapes are small, they tend not to get treated with the respect they deserve -- I've seen tapes just lying around in studios. They really need to be put into their storage boxes when not in use, otherwise dust will get in. With an analogue cassette, a dusty tape will usually still play, but in digital systems, the dust can get between the tape and the head, which causes increased wear and dropouts. The DA88 has mechanical tape and head cleaners built in, but that doesn't mean you can neglect your tapes. These cleaners were not fitted to early machines but we fit them whenever a machine comes in for service or for a software upgrade.
"It's also important to wind the tape to the start and remove the tape from the machine at the end of a session -- if you leave it threaded in the machine, once again dust can get in. Another recommendation is to wind a new tape through to the end and back again before use, because this can help to loosen it up and it also cleans the tape to some extent. With the DA88, you also have to ensure the tape is wound right back to the start before you format it, otherwise you can end up with a short piece of unformatted tape at the start, which the machine won't recognise.
"Only stick labels where they are intended to be fixed. If you put them somewhere else, you could foul the opening tape flap, or a label could curl up, allowing some of the adhesive to get onto a moving part. The cassette tolerances are also very tight, so a label in the wrong place could make the cassette too thick to fit in the mechanism.
"In the longer term, metal-particle tape holds the recorded signal better than metal-evaporated tape, so for long-term use, we'd recommend you use a metal-particle tape or a dual-layer tape. It's also wise to clone important recordings, even if you don't envisage any problems, because faults can occasionally occur in both tape cassettes and machines; the last thing you want is for your only copy of a DAT or multitrack master to get chewed up. Digital tape should be treated in the same way as you treat floppy disks -- the data isn't completely safe until you have a backup."
There are quite a lot of moving parts in a rotary-head, digital tape machine. Is it possible for the user to lubricate these parts?
"It is essential that the user does not attempt to lubricate any part of the machine, because of the danger of oil getting onto the tape path and being carried by the tape to the heads. There's a special molybdenum lubricant used for the cam gears, and specialist greases for the various pivots and slides. We recommend a 500-hour service on all digital machines and we'd lubricate the machine at that point. We've seen a few horrors where people have tried to oil the machines themselves, and oil has got straight onto the tape."
Which parts of a digital machine can go out of alignment?
"The tape guides, in the main, because the rotating head is fixed, as is the capstan guide, which is set from manufacture. The pinch roller may need changing periodically, though. While almost anyone can line up an analogue machine using only a test tape, setting up a digital machine requires quite a lot of specialist equipment, including a very good oscilloscope and an error rate counter, as well as factory test tapes. You also need a current probe to verify the head current, which must be set up very accurately.
"Even the apparently simple mechanical servicing tasks, such as changing a pinch roller, are not as simple as on analogue machines, because the parts are so small and quite easy to bend. With the machine I'm working on now, the pinch roller has been changed, and the arm holding it has been bent slightly because it wasn't supported properly while the job was being done. This causes the tape to wander over the heads, and the error rate has increased because of that. We've had worse cases, where people have bent something without knowing it, then they've gone around and adjusted all the other guides to try to put things right. One was a nightmare to fix -- we had to start right from scratch! Rotating-head digital machines are definitely not serviceable by your average studio engineer, even though he may be perfectly competent at fixing analogue machines."
Having explained what we shouldn't do, could you tell us about the preventative maintenance tasks that can be carried out, with a little care?
"Cleaning can be carried out relatively easily and will go a long way towards maintaining performance. Dry cleaning tapes are only partially successful and are abrasive, so you don't want to use them very often. The most important task is cleaning the head drum. Once you've taken the top off a DAT machine or a DA88, it should be fairly accessible, and with the DA88, you can improve the access further by removing the loading cage from above the transport; this is fixed by only four screws and all the wiring is on connectors.
"We have a special cleaning cloth which is lint-free, and we can supply it to end-users if necessary -- this is an alternative to the chamois leather pads sometimes used to clean video machines. This cloth is a fine material, almost like silk, which cleans and polishes at the same time. It should be used with a good quality head cleaning fluid: although you can use isopropyl alcohol, we have found a better commercial alternative made by EMMARC, which is far more effective, and we can supply this as well. Never, ever use cotton buds, as the fibres can clog up the gaps around the head. Don't even use them to clean the guides, as the tape can carry the fibres back onto the head." (See 'Cleaning the DA88' box for a full explanation of the correct cleaning procedure.)
Is there anything users can do about the environment in which their machine is used, which may prevent trouble?
"Nicotine and tar from cigarettes poses a great danger to digital tape machines, because it coats the head drum and then abrasive particles of oxide and dust stick to it. In a professional broadcast environment, smoking near a tape machine would be a sackable offence, yet we still have users who are indignant when we tell them they shouldn't allow smoking in their control room. Atmospheric dust is also an important factor, because you can't have a hermetically-sealed tape machine -- there has to be a door for the tape to get in and out, and there are slots for ventilation. If dust does settle on the machine, particularly near the tape door, it should be removed using an anti-static brush, preferably in conjunction with a portable vacuum cleaner. Don't use a brush on the transport, though, as bristle fibres can get onto the head and guides.
"Obviously, the room should be kept as clean as possible, but it would help to cover the machines with a clean cloth when not in use. In recent months, we've devised a thin plastic shield which fits over the DA88's transport to help keep the dust off -- but that doesn't mean you can work in dirty conditions."
I would imagine that taking a DA88 on the road is more likely to cause problems than using one in a fixed studio location.
"The main problem in a live situation is people taking a cold machine out of a vehicle and then using it in a warm room before the machine has had a chance to warm up properly. Under these conditions, condensation can form on the metal parts in the tape path, which is obviously undesirable. It's important that both the machine and the tapes be allowed to attain a stable room temperature before the tape is put into the machine.
"Physical vibration during transit can cause the mechanical alignment of the machine to drift, so proper packaging is important. A conventional flightcase transmits all the shock to its contents: the type we've found best is the type where an inner rack is mounted in solid foam rubber inside an outer case."
Because of the error correction systems used in digital tape machines, there's usually very little warning that something is wrong, so preventative maintenance is essential. Manual wet cleaning can be carried out every 50 hours or so, while dry cleaning tapes should be used no more frequently than every couple of hundred hours or so, because of their abrasive nature.
After 500 hours, the machine should be returned to an authorised service centre, where it can be professionally cleaned, lined up, and any worn parts (such as pinch rollers) replaced. Tascam offer a particularly fast turnaround (between 24 and 48 hours), with labour charges of £35 per hour for servicing. Heads should last around 1000 hours, for both DA88s and DAT machines. This figure is comparable to the life of analogue tape heads, and on a multitrack digital machine, they're cheaper to replace than analogue heads. Again, a full line-up is needed whenever a head is changed so it's not a job the studio technician can do without specialised equipment and training. Cleaning the machine on a regular basis, which is something you can do for yourself, will make it more reliable, as well as reducing the rate of head wear.
When a digital tape machine is aligned, a test tape is used to check the high-frequency carrier signal, and the tape guides are then adjusted to produce a maximum output level. The level of the data bursts from the heads must also be reasonably even in amplitude, especially at the leading edge where the sync and ABS data is recorded. An error meter is connected at all times and the error count checked at every stage of the adjustment.
Once the tape path has been mechanically optimised, the playback EQ circuits are adjusted. These circuits are not concerned with the audio EQ, but determine the shape of the waveforms being replayed. In the case of the DA88, separate adjustments are used for metal particle and metal evaporated tape types, and the machine automatically switches to the right one when a cassette is inserted. While the EQ is being adjusted, the waveform pattern of individual cycles is closely monitored on an oscilloscope, and the error counter is checked. When properly set up, the error rate on both playback heads should be virtually zero, and certainly within single figures.
The third main setup check is the head current, which involves the use of a calibrated current probe. This current must be set to an accuracy of around 5%, so a very good oscilloscope is required. An experienced engineer should be able to complete these adjustments in less than an hour, and Tascam routinely check all these parameters whenever a DA88 is returned for service.
Joe Fialho demonstrated the correct DA88 head-cleaning procedure for the benefit of SOS readers.
HEADS: Joe first wrapped a piece of the special cleaning cloth recommended by Tascam around his finger and dampened it with the cleaning fluid. The cloth-wrapped finger was then held lightly against each head in turn (the heads are identifiable as tiny dark windows about midway between the top and bottom of the drum), while the other hand was used to rock the drum gently back and forth by touching it on the upper edge, not on the face. About a dozen rocking motions per head is enough, finished off by a gentle wipe around the whole drum surface, and the whole procedure only takes a couple of minutes. Note that though the DA88 has four heads on the drum, DAT machines usually have only two.
GUIDES: To clean the guides, Joe recommends cutting a thin strip (around 10mm wide) of the cleaning cloth mentioned earlier, moistening it with cleaning fluid, then passing it around the guide and gently rocking the cloth back and forth. The cleaner used by Tascam is also safe on rubber parts, whereas isopropyl alcohol will cause deterioration of rubber rollers in the long term.
BRUSH SYSTEM: The third area that needs cleaning is the sliding brush system which transfers the signal to and from the rotating head. Joe: "There is a system of slip rings above the head, and fine, sprung-wire contacts touch these to carry the current. Over a period of time, they tend to accumulate a thin layer of oxide, and it's quite easy to remove the whole mechanism (which is held in by just four screws) for cleaning, if you wish. While you can dismantle the brush assembly to gain access to the slip rings, it may be safer (the brushes are easily bent), just to hold a moistened piece of cleaning cloth against the slip ring on the side opposite the brushes, and rotate the head by hand to clean it. Obviously, the machine should be disconnected from the mains before any cleaning or disassembly is attempted."