by Bert Whyte
ANYONE who owns a magnetic tape recorder is aware of the basic maintenance procedure of frequent cleaning and demagnetization of the heads, tape guides, and capstan. Great emphasis is given to this procedure in instruction manuals and in almost every book, article, and pamphlet on tape recording. You are given this advice virtually ad nauseam. Some people are very conscientious in carrying out this procedure; many more people pay little more than lip service to the idea.
While the need for cleaning might seem obvious, it is apparent that many people don't seem to realize the importance of this procedure. In a recent conversation with the chief engineer of a well-known tape recorder manufacturer, I learned that quite a few recorders are returned to the factory, with the complaint of poor frequency response, distorted sound, audible wow and flutter. Upon investigation, it was found that in the majority of cases the culprit was oxide build-up on the heads, capstan, and pinch-roller. Obviously, the owners of these machines were either very slip-shod about cleaning or ignored the procedure altogether. My engineer friend said he was amazed at how many people bought expensive tape recorders, and then used cheap "white box" tape which is particularly subject to oxide shedding. However, he also pointed out that most of the people involved were using good quality, standard brand tapes and apparently were under the mistaken impression that this kind of tape obviated the need for cleaning. He said that the degree of shedding varied from brand to brand, but that in all cases oxide build-up was inevitable. There is a positive solution to this which is of course, a thorough application of elbow grease, Q-tips, and cleaning fluid. My professional friends advise me that although there are a number of proprietary head-cleaning fluids on the market, the safest bet is denatured or isopropyl alcohol. Many use Ampex head-cleaner, but warn that this has a xylene base and should not be used on rubber pinch-rollers.
above: This tape recorder requires more than demagnetizing!
Demagnetization is a considerably more complex problem than cleaning. Even those who are very casual about cleaning, are aware that magnetized heads, tape guides, and capstan can add successive increments of noise to the tapes they play. There is also a partial erasure effect and this can cause noticeable attenuation of high frequencies. There is considerable controversy about how often de-magnetization is necessary. Some "experts" say every two weeks, some say at least once a month. Others say it depends on the frequency of use. Many professionals demagnetize every day, figuring that they are "playing it safe." The sad fact is that most of this is guesswork. Which brings me to the point of this brief essay. There is now available an easy, inexpensive, and totally accurate means of determining if your recorder needs demagnetization!
I recently sat in on a technical session devoted to the operation and maintenance of an Ampex MM 1000 16-channel recorder, presided over by genial ex fighter pilot Bill Brock, who is senior instructor for Ampex. Bill was pointing out that noise caused by magnetized parts is particularly reprehensible in the light of low noise tape and the use of the Dolby System. Bill then surprised every engineer in the room by stating that the demagnetization procedures and the degaussing devices they normally used were totally inadequate for the task. Bill went on to say that the familiar degaussing tool, the coil with metal extensions which angle towards each other to form a narrow "gap," is not only inadequate for an 8- or 16-channel recorder, but won't even demagnetize consumer-tape recorders using quarter inch tape! I can tell you that statement shook up the troops! What was the answer to this dilemma? Bill said that some device was needed which would not Only indicate if a part was magnetized, but check on the efficacy of any degaussing procedure. Also needed was an efficient means of totally degaussing the magnetized parts. Then he reached into his jacket pocket and produced a small two-inch diameter meter with a red spot on the outside of the meter case. Bill explained that this was a small but highly sensitive magnetometer which measured magnetic field strength in gauss. This particular unit has a scale which reads 20-0-20. Zero indicates the absence of any magnetism. The scales to the left and right of zero are multiplied by 0.5 to read in gauss.. Deflection of the needle to the right (a plus reading) indicates a North polarity. Deflection to the left of zero is South polarity. In practical use with a tape recorder, polarity is not significant, To use the magnetometer, the red spot is placed against the tape guide, head, or capstan, as the case may be. The slightest deflection of the needle to the left or right of zero indicates the parts are magnetized. The case of the magnetometer is a bit more than a half inch thick. When measuring the heads on most professional recorders, this does not present any problem since the head gates of these units open wide for easy access. For other recorders and particularly consumer machines where many have heads difficult to reach, you must fashion an extension or probe. This can be a small diameter steel rod, or a nail will do. The nail should be bent at an angle for ease in reaching the heads, the sharp tip filed flat and covered with plastic electrician's tape to protect the heads, and finally demagnetized (which you check with the magnetometer). Then of course, one end of the nail is placed against the red spot on the meter case, the other end on the part to be measured. In my experience with this magnetometer thus far, I have found various values of gauss in the guides, heads, and capstan of my 11 assorted tape machines. For what it is worth, the most consistently high values of gauss I found were not in the heads but in the capstan shafts. Needless to say, this magnetometer is invaluable for anyone owning a tape recorder. The unit is known as the Model 20 Pocket Magnetometer Scale 20-0-20. They are available from R. B. Annis Company, 1101 North Delaware St., Indianapolis, Indiana 46202. The price of this boon? A measly $4.45!
Now for the second part of this story. Bill Brock says you can place the common degaussing tool against the magnetized parts all day, and the magnetometer will still indicate magnetism. There simply is too weak a field to totally degauss the parts. The answer obviously is a device with higher field strength. In the case of professional machines, which usually have removable head block assemblies, the entire assembly is placed on a high-output bulk tape eraser, and as Bill puts it, "let it cook for ten minutes." Alternative to this, and a must for consumer recorders with fixed head assemblies, is the use of a portable hand-held bulk tape eraser. These are available at most electronic parts stores for about $9.00. (See page 30 of this issue.) They look something like an old fashioned flatiron, except for an open handle. In use, you run the unit very close to the guides, heads and capstan for several minutes. At the conclusion, check the parts with the magnetometer and if there is any residual magnetism indicated, run the degaussing unit another minute or so, or until you finally obtain a zero reading. As Bill says, measurement is so easy, it's a wise man who checks his recorder with the magnetometer before using it for record or playback. Is it worth the trouble to pay this much attention to demagnetization? Bill states that a reading of a few gauss translates into 3-4 dB of noise. If you play a lot of pre-recorded tapes, and you frequently repeat some favorite works, magnetized parts could be very detrimental.
As you know, for quite a spell there have been no hi-fi shows. Recently I told you about the upcoming IHF shows in Westbury, Long Island; and in Newton, Mass. Well, friends, I've had my fill of shows for some time. I attended the Westbury Show and on Press Day played the Mighty Wurlitzer four channel recording in the Cunningham technique as promised. Everyone was very impressed and most felt as I do, that this is the way to go. Lectured on four-channel sound in a seminar with fellow panelists Len Feldman and John Eargle, chief engineer of Mercury Records. The show was reckoned a great success with over 12,000 enthusiasts jamming (and that's the word) into the small rooms of the Island Inn. This was a very different crowd than is usual at hi-fi shows and is probably a portent of things to come. This was the youth revolution in full bloom. This was an under-thirty group, almost universally accoutered in typical hippie fashions. Man, some of those cats were really far out! One thing was obvious. Hi-fi really turned them on, and many were surprisingly knowledgeable. For the most part they were well-behaved and were content to soak up the sound. Four-channel stereo of the ping-pong variety was their chief enthusiasm. It is said that the young are well supplied with disposable income. That would seem to be the case, as some would casually point to a six-hundred dollar amplifier and say that is what they use at home. As you might have expected, quadraphonic stereo dominated the Show. You could hardly walk into any room without stepping into the middle of an orchestra. Outside of some four channel tape recorders, there wasn't a great deal of really new equipment. Electro-Voice was giving closed-circuit broadcasts of Len Feldman's four channel stereo synthesizer sound. Sansui was demonstrating yet another four channel synthesizer, their QS-1. Bose was showing their new 501 speaker, employing the direct/reflecting principle in a less expensive version. Several firms showed new models of receivers, up in power out-put and in automatic gimmickry. Dolby equipment was a highlight, but difficult to demonstrate except by headphones because of the high noise levels produced by the milling crowds.
Not much time elapsed after the Westbury Show until the Audio Engineering Society Convention was clamoring for attention. Of all places, the Convention was held at the New Yorker Hotel, the scene of fond memories of many Audio Fairs. Oodles of new equipment on display: new mixing consoles, new tape machines from Scully, Ampex, 3M, and Gauss Electrophysics, new Dolby Models 360 and 361, slimline 1 1/2-inch high versions of the Noise Reduction System, Crown's new IC 150 preamp and DC 150 power amp. Steve Temmer's Gotham Audio was showing a new variable time-delay unit which can have considerable application to four-channel stereo, especially of the synthesis variety. Gotham has also become the agent for the remarkable Stellavox recorder I reported on some time ago. Steve had it set up with the ten-and-a half-inch reel adaptor, and the capstan strobe showed the unit right on speed. By design or accident, Electro-Voice and Peter Scheiber were right next to each other, each guiding people through their four-channel maze of matrixes. JVC caused quite a furor with its four-channel discrete stereo disc. I heard it, and it seems to work well, except that the material used for demonstration didn't satisfy my curiosity as to how it would sound with more demanding music. Some eyebrows were raised by the necessity of a 45kHz signal on the disc and the longevity of such a signal under repetitive trackings. In any case this development needs to be closely watched. Highlights of the technical sessions were the demonstration of the fantastic Teldec video disc system, and a symposium on quadraphonic stereo. At the banquet, a much-deserved award went to affable Rudy Bozak for his contributions to audio.
After the AES Convention, I was off to the Newton IHF Show. This was pretty much a repetition of the Westbury Show, except there were more companies exhibiting. With Advent, Harman-Kardon, Fisher and KLH in attendance, Dolbyized sound fared better than at Westbury and there was intense public interest. Four-channel stereo was everywhere, with most exhibitors playing the same Enoch Light music. It is astonishing to me that people who are in the hi-fi business can make such glaring technical boo-boos, but one company (which I shall leave nameless) had set up a four channel demonstration using their new omni-directional speakers in each corner and then proceeded to heavily drape the walls behind the speakers! For the first time in years McIntosh was at a hi-fi show, and it was good to see that diminutive dynamo, Exec. VP. Gordon Gow, who was demonstrating their new MR77 tuner and speaker line. Like many companies these days, McIntosh seems to be striving for an extension of their traditional market, hence the venture into speakers. Astrocom created quite a stir with a four-channel stereo cassette. The four channels are in line on the 150 mil tape, and since no material is available in that format, they "rolled their own" by dubbing from their new four-channel open reel deck. Sony was demonstrating four-channel stereo using their new omni-directional "conga drum" speakers, and one of several new four-channel tape decks.
One thing everyone agreed upon was that the Newton show was unquestionably the best-run show ever. A large part of this was due to the setting, which was a virtually brand-new Marriott Motor Inn, situated on the Charles River. Beautiful decor, and good acoustics in the rooms when you removed one front window drape. In spite of our fears of excessive transmission through the modern thin-walled construction, sound was well isolated.
The service in the Inn verges on the unbelievable in this day and age. They even had mini-skirted girls frequently emptying ashtrays during the show! The crowd in Newton was also predominantly under thirty, but here the hip-types were not so far-out, and for the most part the kids were clean, college types. Better representation in Newton of the traditional "banker, doctor, lawyer" type of hi-fi fan. Had a nice visit from maestro Arthur Fiedler, who, while interested in four-channel stereo, stated that he thought high quality two-channel stereo was hard to beat.
Len Feldman and I lectured once again at the seminar on quadraphonic stereo, and by this time I had almost no voice.
So went the fine Newton Show. Afterwards, most exhibitors returned home, but for myself and a hardy group from TDK, Sansui, Astrocom and several others, it was on to the Canadian Electron Hi-Fi Show at the Royal York Hotel in Toronto, opening just two days after the close of the Newton Show.
The Royal York with 1700 rooms is the largest hotel in the British Commonwealth. It is one of those "grande dame" hotels, once the epitome of luxury (still is, as far as Canadians are concerned)
but to me a bit dowdy now and ragged around the edges. This was a big show with over 75 exhibitors, although not all of them were in the legitimate hi-fi category. All the familiar Japanese and American firms were represented, along with less well-known British manufacturers. At Boston, old friend Woody Herman shared the flight with me, and darned if he wasn't going to the Royal York to open a twelve-day stand with his orchestra. My wife and I attended the opening show and his orchestra is just as wild and woolly a swinging bunch as when I recorded him years ago. At this Canadian Show it was like stepping back in time. Although there were about seven or eight four-channel demonstrations (all except two were rather badly done), things seemed to be as they were in our country about six or seven years ago. The crowd was far older, with "Establishment" types predominating.
They were very serious minded about their hi-fi hobby. Many carried favorite demo records under their arms. Classical music was prominently demonstrated, in contrast to Westbury and Newton, where classical music was almost nonexistent. Probably a good reason for the large turnout of "oldsters" is they are most likely those who can afford the staggering prices of hi-fi equipment in Canada. What with import duty, excise taxes, and federal and provincial sales taxes, equipment is nearly out of sight. Example Crown DC300 amplifier, $1060; Bose speakers, over $750 a pair. Other items similarly priced.
One smart move is company called Radio Speakers, based in Toronto, who build Bozak speakers under license, therefore avoiding all those taxes. I heard these Canadian Bozaks, all the way up to the huge Concert Grand model, and they sound just as fine as their American counterparts. There were several items of interest at the Show. One was a smartly-styled speaker by Bowers and Wilkins of England, with a wide array of electrostatic tweeters on top of what appeared to be a woofer in a fairly large infinite baffle enclosure. A very nice sounding speaker, one of the best of that type.
Another firm had two huge panels about 3 by 4.5 feet, each containing eight electrostatic drivers. It was described as a "full range" system, so I asked to hear a recording with some organ pedal. They seemed to think it performed very well, but as seems to be common with most "full-range" speakers of this type, I didn't hear any real fundamental bass frequencies, and in fact, there seemed to be very little energy below 50 Hertz. I was rather amazed at the seeming indifference many of the exhibitor personnel seemed to display towards good-quality demonstration records. Many of them had perfectly respectable hi-fi equipment, but were using the most miserable sounding records imaginable. Big exception to this rule was Fred Towler's Tannoy exhibit where you could count on hearing top quality classical music at all times. One prominent American tape recorder manufacturer had a four channel stereo demonstration with the channels in the wrong array and hopelessly unbalanced. He had the left front at your right rear, and the right front at your left front! Rather than disappoint the people who would visit his exhibit, I corrected it for him. One final note on the Canadian Show the people who attended were about the most polite, well-behaved, and tolerant I have encountered at these affairs. It was a genuine pleasure to talk to these avid hi-fi buffs.
That is the show roundup for this year, and as expected the main topics of interest were four-channel stereo and Dolby noise reduction. By the time of the Washington, D.C. Show in February '71, we will see considerable progress in these new frontiers of audio.
(Audio magazine, Jan. 1971; Bert Whyte)
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