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Tape recorder maintenance - Overview

Analogue tape recorders need special care and attention in order to get maximum sound quality


Wolfgang Bleier, Austria
July 2008



Professional analog tape recorders are quite complex audio equipment known for their warm and most lifelike sound reproduction. Their sound quality is influenced by a number of factors and - whether to the better or to the worse - depends on how much attention we pay to allignement and calibration. Above that, analogue tape recorders more or less degrade the recording signals by adding distortion, hiss, frequency response alterations, speed variations (wow and flutter), print-through effects, and drop-outs. But still, even a good semi-professional tape recorder is a match for the finest audio equipment available today, provided that it is properly calibrated and maintained. It is an effort to make them sound good, but once aligned and calibrated they sound really good… incredibly good.

Maintenance of an analogue recorder and a digital recorder is quite different. First of all you do a lot of basic maintenance on an analogue recorder. On the contrary you can't do much more than run a cleaning tape on a digital recorder. Secondly, you have to do maintenance and regular cleaning of an analogue tape recorder, otherwise its performance may considerably suffer.

Alignment and Calibration

Alignment and calibration has two functions: one is to get the best out of the machine in combination with the audio tape of your choice; the other is to make sure that a tape recorded on one recorder will play properly also on other recorders. The following parameters are aligned to specified or optimum values:
  • Azimuth - the heads need to be absolutely vertical with respect to the tape otherwise there will be cancellation at HF. The other important adjustments are the head-zenith, wrap and height.
  • Bias level - optimises distortion, maximum output level and noise
  • Playback level
  • High frequency playback EQ
  • Record level
  • HF record EQ
  • LF playback EQ
In the past the calibration procedure used to be part of the engineer's day-to-day routine, but nowadays it is mostly a job for specialists. For correct calibration and alignment of a tape recorder you need first of all experience, the right equipment, a service manual of your recorder and of course calibration tapes. An elementary guide, which calibration tape to buy, is provided in a paper published by Jay McKnight of Magnetic Reference Laboratory, Inc.On their website you may find a lot more information about different calibration tapes and gain in-depth knowledge about analog tape recorder adjustment techniques.


Cleaning

Tape heads and other metallic parts that get in contact with the tape must be cleaned gently with a cotton bud and isopropyl alcohol. Isopropyl alcohol has good cleaning properties and is absolutely safe and recommendable.
The pinch roller of a tape recorder is made of rubber or a rubbery plastic. Actually it shouldn't be cleaned with isopropyl alcohol, but it often is. You can also buy special rubber cleaner, or you can use also water and a mild abrasive household liquid cleaner. Pinch rollers are made from different materials, and in worse case may react on various cleaning agents.
I clean the tape heads and other metallic parts always after a couple of tapes have passed the tape path, so in average I clean once a week. Do not soak the cotton bud or make the head dripping wet, it should be rather damp. Do not just distribute the contamination, but rub firmly in only one direction until the cotton no longer shows contamination being removed.
The pinch rollers I clean frequently using only a wet cloth, from time to time I use a special rubber cleaner. To me nothing is worse than good but filthy audio gear. That means regular cleaning outside and once in a while also inside of the recorder.

Demagnetizing heads and tape path

Over the time, the magnetically charged audio tapes leave residual magnetism in the metallic parts of the tape path that impairs the ability of subsequent tapes to record or playback accurately. A special demagnetizer, for example a Han-D-Mag made in the United States by R.B. Annis Co. which can be purchased (also for European 230V voltage rating) at Audio Village, Palm Springs CA (contact: audiovlg@gte.net), is used to remove residual magnetism in metallic parts of the tape path.
Correct use of a demagnetizer requires some exercise and experience, otherwise the condition of the tape heads can be made even worse. How frequent the tape path must be demagnetized depends on several factors, including the tape speed, recording levels, the type of tape, the composition of the tape head, and whether a recorder is used rather for recording or for playback. I demagnetize after approximately ten tapes have passed the heads or after approximately 15 to 20 operating hours. In any case I demagnetize the tape path before a recording session, unless I have done it recently. Here is in detail what I think I know about Demagnetizing a Tape Recorder.

Without doubt, if you want your tape recorder to hit the highs of musical excellence and produce that natural, lifelike sound, professional maintenance and care is required. If you are looking for professional alignment and calibration service for your tape recorder in Austria, Germany or Switzerland, you may find it here:

  Revox in Perfektion..., Michael Müller, the successor of Mr DiBenedetto, Switzerland
  Austrian Analog Audio... Anton Straka, Austria (abandoned website)



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