Friday February 7, 2003
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There is a difference between the maintenance of an analog recorder and a digital recorder. Firstly you can do a lot of first-line maintenance on an analog machine. You can't do more than run a cleaning tape on a digital recorder. The second is that you have to do the maintenance, otherwise performance will suffer. These are the elements of maintenance:
- Cleaning: the heads and all metallic parts that the tape contacts are cleaned gently with a cotton bud dipped in isopropyl alcohol. Isopropyl alcohol is only one of a number of alcohol variants, and it has good cleaning properties. It is not the same as drinking alcohol, so don't be tempted. Also, drinking alcohol - ethanol - attracts additional taxes in some countries, therefore it would not be cost-effective to use it
- The pinch wheel is made of a rubbery plastic. In theory it shouldn't be cleaned with isopropyl alcohol, but it often is. You can buy special rubber cleaner from pro audio dealers but in fact you can use a mild abrasive household liquid cleaner. Just one tiny drop is enough
- Demagnetizing the heads: After a while, the metal parts will collect a residual magnetism that will partially erase any tape that is played on the machine. A special demagnetizer is used for which proper training is necessary, otherwise the condition can be made even worse
- Line-up: Line up, or alignment, has two functions - one is to get the best out of the machine and the tape; the other is to make sure that a tape played on one recorder will play properly on any other recorder. The following parameters are aligned to specified or optimum values:
- Azimuth - the heads need to be absolutely vertical with respect to the tape otherwise the will be cancellation at HF. The other adjustments of the head - zenith, wrap and height are not so critical and therefore do not need to be checked so often
- Bias level - optimizes distortion, maximum output level and noise
- Playback level - the 1 kHz tone on a special calibration tape is played and the output aligned to the studio's electrical standard level
- High frequency playback EQ - the 10 kHz tone on the calibration tape is played and the HF EQ adjusted
- Record level - a 1 kHz tone at the studio's standard electrical level is recorded onto a blank tape and the record level adjusted for unity gain
- HF record EQ - record a 10 kHz tone at a low level and adjust for flat HF response
- LF playback EQ - record a 100 Hz (or as recommended by the manual) tone and adjust for flat LF response.
The line-up procedure used to be considered part of the engineer's day-to-day routing, but is now often left to a specialist technician.