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re: ancient tape squeak
Michael Peters wrote:
>I recently dug up my ancient Revox A77 and I'm planning to salvage a
>number of old tapes (some of them more than 20 years old) and copy them to
>DAT. The tapes carry recordings of my first jam sessions, looping
>experiments, and compositions - musically not of high value but I love
>them anyway of course.
>Unfortunately, some of the tapes (cheaper brands such as Shamrock and
>Sony) have a tendency to rub off their coating very quickly. The effect is
>a very high pitched squeaking noise which begins faintly and gets louder
>and louder. The squeaking can also be heard on the recording - the music
>gets modulated and distorted and is unusable.
>Cleaning the tape heads and tapes helps only for a couple of minutes. The
>squeaking noise comes back. Especially on long pieces (and I did a number
>of very long pieces) this is very annoying.
>If anyone has found a remedy for this problem, please let me know.
This sounds like the irksome and well-known phenomenon called "stiction".
There are several possible causes and a couple of remedies to try.
This problem can occur under certain circumstances even with
well-adjusted machines and high quality tapes. But there is a lot of tape
made in the mid and late 70's that is now shedding like crazy due to
binder formulation problems. That's a widespread problem.
What's happening to cause the problem is that sticky residue coming off
the tape is deposited (not just on the heads but on every bearing and
guiding surface) and interacts with the moving tape in a high-frequency
stick / slip interaction. It's exactly the same method by which the rosin
on a violin bow causes the string to vibrate.
If cleaning (of ALL tape-touching surfaces) doesn't provide a workable
cure, inspect the surfaces to make sure they are truly clean and very
smooth. Maybe in storage, the surfaces acquired a "patina" or even a
slight etching of the metal surfaces. Normal cleaning wouldn't remove
this. You can find out if this has happened by playing the tapes on a
known good machine and see if the problem still occurs.
If the machine isn't contributing to the problem, then it can be entirely
due to tape shedding. There are two possible things to try in this case:
1. Lubricate the tape. Using a silicone-based lubricant, moisten a pad and
use the tape machine in "play" (with the tape bypassing the head assembly)
to move the tape past the lubricant applicator. You can experiment on a
moderate length of tape to see if this will work.
2. Reduce the tape tension. On the A77, this is an internal electrical
adjustment. Also, if the tapes are on 10 1/2" reels, you can reduce tension
by setting to the reel-size switch on the front panel to 7". See if this
makes a difference in the severity of the oxide buildup.
If all else fails, carefully use your finger or a felt pad to gently press
the tape against the play head during playback. It may damp the
vibrations enough to allow a decent one-time transfer.