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Bulk Erase Tape Reels & Cassettes...?

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Bulk Erase Tape Reels & Cassettes...?

Postby Elephone » Thu Aug 22, 2019 5:01 pm

I hear those bulk erase machines can cost a bit. Came across this method of 'bulk erasing' tape reels on FF>> or <<RW, using a non-electrified strong 'rare earth' magnet:

https://youtu.be/f2egsgHPJ-s?t=146

Any thoughts on whether this is likely to be damaging to tape? Is there anything about polarity than needs to be considered? I presume it won't be necessary to do this on both sides.

Thanks.
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Re: Bulk Erase Tape Reels & Cassettes...?

Postby Elephone » Thu Aug 22, 2019 5:35 pm

hobbyist wrote: As to your rare earth magnet I do not see how it can work. You need an alternating field to DEmagnetize.

Thanks, but this chap manages to erase a tape reel using a DC motor magnet not electrified:

https://youtu.be/d3fQgTrW-aM?t=463

I'm not sure why he doesn't mention or try it on FF>> or <<RW.

There's another video on what a strong non-electrified ('neodymium') magnet did to a tape recording and it did appear to erase parts of it when merely rubbed on the cassette:

https://www.youtube.com/watch?v=xtNgItuSFOE

There is another video for a bulk eraser, electromagnet:

https://youtu.be/jzLAIaJmzJo?t=227

...and this apparently works without even winding the tape through it also.
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Re: Bulk Erase Tape Reels & Cassettes...?

Postby MOF » Thu Aug 22, 2019 6:15 pm

Magnetic fields affect magnetic tape.
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Re: Bulk Erase Tape Reels & Cassettes...?

Postby Folderol » Thu Aug 22, 2019 6:23 pm

Absolutely DON'T do it!
It puts a permanent magnetic 'bias' on the tape, that even the best taperecorders will struggle neutralise when trying to record. It also magnetises anything it comes into contact with (including the precious tape heads).

You'll end up with increased distortion, higher noise level and screwed up frequency response (especially if it uses Dolby).
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Re: Bulk Erase Tape Reels & Cassettes...?

Postby Hugh Robjohns » Thu Aug 22, 2019 6:36 pm

Elephone wrote:Any thoughts on whether this is likely to be damaging to tape?

Well, yes... damaging to the tape and to the machine you later try and record the tape on... :shock:

First, the physical surface of the tape is likely to be damaged by anything it has to scrape over, which is why tape guides are often designed to rotate, and are always highly polished to minimise friction. Edge damage to the tape is also a concern if the tape edges rub against the top or bottom of the guide mounting.

It's true that that basic arrangement -- using a very strong compact magnet moving along the length of the tape -- will probably cause some erasure of any pre-recorded material on the tape... Any strong magnetic field passing through the tape will re-align the magnetic particles in the tape and thus damage the original recording through some degree of erasure.

But how effective that specific technique will be depends on the field strength created by the permanent magnet and the recorded fluxivity on the tape. And it may well take several passes to achieve a satisfactorily complete erasure.

However, the magnetic field left on the tape from the process as described will leave all the magnetic domains facing more or less the same way, and will effectively create a strong DC-bias effect on the tape that will likely cause magnetisation of the tape machine's transport and heads when the tape is re-used. That single-direction field may even overwhelm the machine's head's ability to recording anything new at all... particularly if it's an old recorder working with relatively low recorded field strengths anyway. (Edited: And as Mr G says below, it can also leave clicks on drop-ins and edits!)

Moreover, the idea of willingly placing a strong magnet anywhere near a tape transport in the way illustrated is just wrecklessly stoopid in my view... :o

There's a very good reason that professionals use AC-erasers -- devices with a strong electromagnet running off an AC current -- which is that it leaves the magnetic domains in the tape randomised, not all facing the same way... so there's no risk to magnetising anything!

I've seen plenty of mains-powered bulk-erasers -- like the one in your second link video -- on ebay and various specialist tape machine website before now. If you really feel you need to bulk-erase tapes that's the way I'd do it... and I'd keep the eraser well away from any tape machines (and wind-up watches) too!

With the type show, you place the spindle of the reel on that spigot near one end of the box, and then manually rotate the rape reel a few times so that it is all fully exposed to -- and passes through -- the magnetic field generated by the electro-magnet at the other end of the box. In that way the magnetic domains in the tape see the magnetic field build to a maximum and then decline again. It's normal to turn the tape reel over and repeat the process to ensure full erasure.

But I guess the important question to ask is why do you feel the need to bulk-erase quarter-inch tapes? On most machines the erase head gaps are intentionally wider than the record/play gaps to ensure full erasure anyway. It requires a real-time pass rather than a few passes over the AC-eraser... but it's a lot cheaper and probably better for the tape!

edited -- Folderol got there before me! And he's absolutely right... please don't do the magnet thing!

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Re: Bulk Erase Tape Reels & Cassettes...?

Postby Tim Gillett » Fri Aug 23, 2019 3:03 am

Elephone you haven't said why you need to bulk erase the tapes. Most tape machines will erase the old recording while making the new one over the top.

Adding a story on bulk erasure using a permanent magnet... Years ago when I was tech for some recording studios, a tape operator complained that the tape machine was adding a "click" whenever dropping into record. It turned out all tape machines in all four studios were doing it. The common factor was the newly arrived batch of tapes. It turned out that before being delivered to us, they had been bulk erased with a permanent magnet eraser. As our facility had a large Garner "conveyor belt" type bulk eraser, we ran all of the new tape stock through that and the problem was solved. We also alerted the tape supply company to the problem they had created by using the cheap permanent magnet for bulk erasing.
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Re: Bulk Erase Tape Reels & Cassettes...?

Postby Brian M Rose » Fri Aug 23, 2019 10:57 am

As has been said, proper bulk erasers are both very heavy and expensive. You may be able to address the latter as there are many local Talking Newspapers who have gone over from Cassettes to Digital and therefore have redundant Wiercraft machines. Take a look at the Talking Newspaper Federation's site.
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Re: Bulk Erase Tape Reels & Cassettes...?

Postby Elephone » Fri Aug 23, 2019 3:30 pm

Tim Gillett wrote:Elephone you haven't said why you need to bulk erase the tapes. Most tape machines will erase the old recording while making the new one over the top.

Sorry, I thought people would know. Many times I've recorded onto used tape and there have been slight remainders of previous recordings on the tapes. I don't know if this video explains it:

https://youtu.be/dEO5Lbudj4I?t=315

I understand that "if your machines are good enough to use, they shouldn't..." blah blah, but maybe some aspects of old machines might work better than others and I don't have a lot of spare cash to spend on maintenance, etc.

A lot of what I do is mucking about with substandard/old gear, but it can produce results that are interesting to my ears (rather than 'professional' sounding, resulting from 'proper use' of well-maintained equipment and so on). I can't justify that any more than someone can justify placing metal objects on piano strings, but that's just how it is.

Thanks for the warning! I won't be putting magnets anywhere near my tapes or machines, I just didn't know.
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Re: Bulk Erase Tape Reels & Cassettes...?

Postby Kwackman » Fri Aug 23, 2019 3:55 pm

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Re: Bulk Erase Tape Reels & Cassettes...?

Postby Mike Stranks » Fri Aug 23, 2019 4:12 pm

I used to use one that was about the size of an electric razor... sat nicely in your hand and had a 'push to make' (bell-push) type switch. May still be here somewhere... in a fetching shade of duck-egg blue!

Also handy to use on those screwdrivers you didn't want to be magnetic.

Anyone else remember wrapping your master tapes in kitchen foil before sending them for cassette duplication to be sure they didn't get wiped/semi-wiped on their perilous journey through the postal system?
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Re: Bulk Erase Tape Reels & Cassettes...?

Postby Tim Gillett » Fri Aug 23, 2019 4:38 pm

Elephone wrote:
Tim Gillett wrote:Elephone you haven't said why you need to bulk erase the tapes. Most tape machines will erase the old recording while making the new one over the top.

Sorry, I thought people would know. Many times I've recorded onto used tape and there have been slight remainders of previous recordings on the tapes. I don't know if this video explains it:

https://youtu.be/dEO5Lbudj4I?t=315

I understand that "if your machines are good enough to use, they shouldn't..." blah blah, but maybe some aspects of old machines might work better than others and I don't have a lot of spare cash to spend on maintenance, etc...
. There could be various reasons for not fully erasing the old recording. One is using later type high energy tapes on an older machine never designed for them. Best use tapes the machine was designed for or expect problems like this. Another is a dirty erase head. Not too hard to clean it. Or a misaligned head. The guy in the video seemed to say the erase head doesn't erase a wide enough track. That's not true. The erase head erases wider than the machine's own recorded track to avoid residual recording coming through.
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Re: Bulk Erase Tape Reels & Cassettes...?

Postby James Perrett » Fri Aug 23, 2019 6:20 pm

Elephone wrote:
Sorry, I thought people would know. Many times I've recorded onto used tape and there have been slight remainders of previous recordings on the tapes.

The most common cause of this problem is dirty heads - it doesn't take much crud on the head to stop it erasing properly and sometimes you need something more aggressive than a cotton bud (like a barbecue stick or toothbrush).
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