Zen And The Art Of Cassette Deck Maintenance

Tips & Techniques

Published in SOS July 1994
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Technique : DIY

 

Love it or loathe it, the analogue cassette looks set to be the primary medium for the distribution of recorded music for the foreseeable future, and we have to make the best of it. PAUL WHITE shows you how...

 

The compact cassette format is now over two decades old, and though there have been improvements in hardware design, noise reduction technology, and tape formulations, the cassette is still considered by many to be the carbuncle on the backside of modern-day audio. A significant number of SOS readers' telephone enquiries or Crosstalk letters relate to difficulties in either producing a cassette recording of acceptable quality, or the age-old problem of a recording sounding OK on the machine on which it's made, but quite different when played back on someone else's machine. Perhaps we're expecting a lot of the humble cassette in an era when we take CD and DAT for granted. Nevertheless, when on top form, analogue cassettes can sound very good indeed. There are several factors that can cause a cassette machine to perform below par, most of which, fortunately, we can do something about.

CLEAN MACHINE

At the risk of sounding like someone's mother-in-law, I'll start off on the subject of cleaning the cassette deck, because, even though most of you get around to doing it, some ways of cleaning are more effective than others. Furthermore, there's still a hard core of reactionaries out there who refuse to clean anything at all!

My advice is to forget all about head-cleaning tapes, and use the traditional cotton buds and alcohol method. For this, you'll need a pack of ordinary cotton buds (the things that people poke -- wrongly -- into babies' ears), and either an exorbitantly expensive bottle of head-cleaning fluid (which is really isopropyl alcohol with a small amount of dye added) or a bottle of isopropyl alcohol from the chemists. A litre of the latter will cost you about the same as a tiny bottle of the former, and though you may have to wait a day or two while the pharmacist orders it for you, a litre will last for years. Cotton buds with wooden stalks are recommended, but the plastic type seem to work fine too.

If your cassette deck has a removable door, this will provide better access for cleaning purposes, but even without one, you should be able to reach the tape heads, capstan shaft and tape guides. It is generally known that dislodged particles of tape oxide build up on the heads, causing a loss of top end or even dropouts. However, a lesser-known problem is that of oxide adhering to the tape guides, which can interfere with the smooth passage of the tape, resulting in wow, flutter, and a phasey kind of sound as the tape snakes across the heads in an uneven way. Using a cotton bud soaked in the alcohol, clean the record head, the playback head, the capstan and all the guides, then repeat using a new cotton bud. When no more brown oxide comes off, wipe away any excess alcohol with a dry cotton bud, and wait a couple of minutes for any remaining alcohol to evaporate before putting a tape into the machine. Figure 1 shows a typical cassette deck head and tape guide layout.

So far, I haven't mentioned the rubber pinch roller, also shown in Figure 1. This also picks up oxide from the tape, and eventually the surface loses its traction, resulting in tape slip and speed instability. Alcohol isn't really suitable for cleaning these rubber parts, as excessive application can cause the surface of the rubber to perish. Proprietary rubber cleaning fluids are available, but most of these are simply detergent in a weak aqueous solution. In other words, a drop of washing-up liquid in a cup of tepid water works just as well, and is infinitely cheaper. The cleaning process is the same as for the heads, the aim being to end up in a position where no more brown oxide is coming off on the cotton bud. Clean the machine thoroughly before every important recording project, and, in any event, at least once a week.

ALIGNMENT

Like open-reel machines, cassette decks have to be aligned, a job which is done at the factory, and, in most cases, never gets done again, unless the machine goes in for a head change. Because most cassette decks use the same head both to play and record, they'll play back their own tapes pretty well, even if the head is quite severely out of alignment. However, play that same tape on another, properly-aligned cassette deck, and the result will be a noticeable lack of brightness and clarity. For this reason, it pays to have your studio cassette deck alignment checked and adjusted if necessary, a task that any reputable hi-fi service department will be able to carry out. Of course, this still doesn't guarantee that you won't have any incompatibility problems -- that would require everyone else on the planet to get their machines aligned too -- but at least it won't be your fault!

Before leaving the subject of alignment, it also pays to get the speed of your cassette deck checked too, as manufacturers seem very lax on this matter. Again, this won't affect tapes recorded and played back on the same machine, but as soon as you put the tape in another machine, the tempo and pitch will be different.

Noise reduction systems are also a source of incompatibility, not only because of the different types available, but also because they too are subject to misalignment, this time electrical rather than mechanical. Dolby B is still the standard for mass-duplicated tapes, but as many car cassette machines aren't equipped with Dolby, my preference is to record cassettes without noise reduction at all. Providing the brand and type of cassette is good, and providing you record at as high a signal level as possible, noise is unlikely to be unduly obtrusive, unless you're doing classical music with a wide dynamic range. In any event, a little hiss is less of a problem than a totally wrong tonal balance.

THE TAPE

Most machines are delivered having already been set up for a certain type and brand of tape. The reason for this is that all tapes have different magnetic characteristics, so the bias, record, and playback circuits of the cassette deck have to be set up to give a flat frequency response with a specific type of tape. Having said that, many tapes have similar enough characteristics to be interchangeable, and it's not at all uncommon to find a machine performing better with a brand other than the recommended one. For example, my long-suffering Sony cassette deck, which was introduced to studio life in the early '80s, still gives excellent results when used with Thats EMX tape, a metal particle tape designed for use in machines with a Chrome or Type II tape switch position. As is the way of things, Thats no longer make this particular tape, so when my dwindling stocks run out, I'll have to check out its replacement to see if it works as well.

I recommend always using Type II tapes rather than Ferric, and even though TDK's SA is still the most popular Type II cassette on the market, try out a selection of equivalents from other top manufacturers, to see if one or more of them performs better in your machine. To do this, record a selection of pieces of music from DAT or CD, then listen carefully for overall tonal balance. Quite often the bass end will sound wrong if the cassette type is unsuitable -- you might notice too much or too little bass, or even a bass sound that seems loose and unfocussed where the original was tight and controlled. At the top end, listen for overbrightness, dullness, or sibilant distortion on bright sounds such as hi-hats. Finally, listen to the overall sound and try to judge whether it sounds as clear as the original, or whether it sounds in any way muddled or cloudy. If you find a brand that passes all the tests aside from sounding a touch too bright, you might find this more acceptable than one that sounds a little dull.

Once you find a brand and type that works, stick with it and run a few more tests to see how much level you can put on it before it distorts. Most cassette deck meters are rather inaccurate, so use your ears rather than your eyes, and make a note of what the meters are reading when audible distortion becomes evident. If you record so that the peak levels register a dB or two below this figure, you should get the best of both worlds, in that your level will be well above the noise, but not high enough to distort. Finally, avoid unbranded or low-cost tapes like the plague, as many of these shed oxide at an alarming rate, and invariably sound dire.

TAPE CARE

Cassettes should ideally be wound to the start or end after each recording session so as to persuade the tape to pack evenly, and always store cassettes in their library cases to protect them from dust. The ideal storage environment is in a room-temperature cupboard where the temperature stays reasonably even and where there's no excessive dampness in the air. The shelf at the top of your wardrobe will do as well as anywhere. Avoid leaving valuable tapes in the car, and under no circumstances leave tapes in direct sunlight, as the heat causes irreparable damage.

If you want to make multiple copies from a master cassette, don't use the original, as repeated playing will cause it to deteriorate; make the best quality copy you can and then copy from that. If you can copy your cassettes from DAT, you're likely to end up with a better-sounding result than if you copy from one cassette to another.

That's it; sermon over. Compact cassettes are a compromise, and maybe they are an anachronism in the modern age of digital audio, but we're stuck with them. If you take just a little care over the kind you use, and how you maintain your recorder, you might find that the cassette isn't as black as some paint it after all.

 

DEMAGNETISATION

Though a conventional tape demagnetiser (like those used on open-reel tape recorders) may be used on a cassette deck, the battery-powered automatic types that come built into dummy cassette shells are both easier and safer to use. If you don't already own a demagnetiser, then I'd recommend you buy one of the cassette types, which are available from any decent hi-fi shop.

The reason a tape deck needs demagnetising is that a magnetic charge gradually accumulates on the heads and guides as the machine is used. If this is allowed to build up to excessive levels, not only will new recordings be noisier and duller than they should be, you could also damage your existing recordings, as the stored magnetic charge erases some of the high frequency information from the tape. Because there's no easy way to measure the magnetic charge build-up, routine demagnetising is the only practical measure you can take. Running a demagnetising cassette every month or two should be adequate, but if you use a hand-held demagnetiser, be sure to follow the instructions carefully, or you could end up adding more magnetism to the heads than you remove. It is particularly important not to switch a hand-held demagnetiser on or off when it is closer than a couple of feet from the cassette machine, and, equally importantly, make sure the machine is turned off while you work on it, otherwise you could damage the machine, your monitors and your ears all in one go!

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