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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 17th Jan 2023, 11:40 am   #1
stevehertz
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Default Bulk erase mini DV tapes?

I recently dug out my dinky little Sony Handycam DCR-PC350E. In case you're unsure which format I mean, the tapes are very small, you can conceal one in the palm of your hand. Anyway, I have a load of tapes that I want to erase now. Putting them into the machine and recording with the lens cap on is out of the question. How can I bulk erase these tapes? Obviously some kind of AC magnetic field, but what to use? I know there are commercial bulk tape erasers but they are quite expensive and I don't expect to get a fortune for the Handycam if/when I sell it.

I realise that the tapes can simply be recorded over etc etc, but as I'm thinking of letting the machine go and including the tapes I don't want my recordings (family gatherings, beach holidays, my collections, guitars etc) to be seen or even used.
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Old 17th Jan 2023, 11:47 am   #2
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Default Re: Bulk erase mini DV tapes?

Why do you want to bulk erase them Steve? Is there something confidential recorded on them? Obviously they'll be erased as part of the recording process the next time they're used.
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Old 17th Jan 2023, 11:51 am   #3
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Default Re: Bulk erase mini DV tapes?

I've edited my post Paul...
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Old 17th Jan 2023, 12:47 pm   #4
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Default Re: Bulk erase mini DV tapes?

Personally I keep hold of all original media of my home movies, whatever the format.

But should you wish to erase, you'll find that the hand held bulk erasers designed for cassette tapes and reels won't work. The magnetic field isn't strong enough for mini DV, nor even VHS and 8mm video tape in most cases. You'll likely need a tabletop eraser designed for data tape, and even then it might not be sufficiently powerful.
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Old 17th Jan 2023, 12:51 pm   #5
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Default Re: Bulk erase mini DV tapes?

Looks like I'm going to spend a few nights erasing tapes in the machine, overnight.
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Old 17th Jan 2023, 1:12 pm   #6
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Default Re: Bulk erase mini DV tapes?

Hi Steve - I have a desk-top type bulk eraser that used to have the task of erasing patients' ambulatory ECG recordings on audio tapes many years ago - (Weircliffe model 26). I'd be happy to loan it to you for this task, or to do a test erase on one of your tapes and return it to prove that it works if that suits you better. I do not have a recorder myself so couldn't check if it erases that type of tape.

Cheers
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Old 17th Jan 2023, 1:20 pm   #7
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Default Re: Bulk erase mini DV tapes?

Mini DV has, I think, a very high flux density (a "metal" tape, or at least a chrome formulation, same as DAT/DDS and more recent computer formulations).

Unless you have a really strong bulk eraser available, you may find it very difficult to bulk them fully.

Manual erase through the recorder may be tedious but may be the best option, unfortunately. I cannot remember if the format has a full width erase head, but it probably does.

Edit: posts crossed, but some models of Weircliffe will probably do it, but older ones probably not.
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Old 17th Jan 2023, 1:46 pm   #8
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Default Re: Bulk erase mini DV tapes?

Mini DV is an obsolete format now. There's a small market for working cameras as people want to access their home movies, but I suspect the market for used tapes for making new recordings is minimal. I've kept all of my DV tapes as backup to the HDD file copies but while the fragile tapes last well unplayed, they can be easily and permanently damaged by playback in a faulty device. Increasingly the problem is finding a fully working DV camera for playback including finding a tech able to service the complex little cameras.

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Old 17th Jan 2023, 4:51 pm   #9
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Default Re: Bulk erase mini DV tapes?

Have you tried a magnet. Permanent magnet. As big as possible?

The AC demagnetisers get hot over time as they're used, so there is a short length of time to do the job, esp if you want to erase a few tapes, doing both sides to make sure, but this does not apply to a perm magnet. Sit tape on a table, put magnet on top, and leave for an hour or so. You don't need a perfect erasure, just enough to destroy the images, as in make unwatchable.

If you've got a suitable magnet, try one and see. When I've erased tapes (cassette and spool) or computer disks with a magnet (just a 1" x 3" bar magnet) I've done both sides, and also moved the magnet around in a circular motion. I've regularly needed to do this with computer disks that are used on different machines as stray data on the edge of a track (from computer A) might not be erased by a recording on computer B so when the disk comes back to A it might read garbage.

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Old 17th Jan 2023, 5:01 pm   #10
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Default Re: Bulk erase mini DV tapes?

A strong permanent magnet or colour TV degausser might corrupt the digital recordings enough to make them unplayable. It's worth a try. To fully bulk erase the MiniDV tapes would require a videotape bulk eraser. These are more powerful than audio tape erasers and certainly did exist. Years ago I used to buy bulk-erased Beta videotapes from a shop in London called Music and Video Exchange. The shop erased the tapes before sale as they may have contained material they weren't allowed to sell. Apparently, before they started erasing tapes, a customer bought a used tape containing a dodgy porn movie and reported it to the police.

If you're selling / giving away the camcorder, your tapes will be of little or no value to anyone else, so you might as well just offer the camcorder on its own or with one over-recorded test tape just to show it working. Most people will be buying a machine to transfer their own tapes. They won't be interested in making new recordings or watching hours and hours of someone else's home videos.

Personally I don't understand the paranoia that some people have. Some years ago I was looking at a DVD/HDD recorder for sale at a radio rally. The seller told me he'd removed and destroyed the hard drive, possibly making the whole thing useless. I asked Why? The response was that there were camcorder recordings of his family on it that he didn't want anyone else to have. But I wondered if any of his family have posted pictures or videos of themselves on Facebook or other social media. People don't think there's anything wrong with that. So why worry about something on a tape or disc that's almost certainly going to be wiped and not watched by a new owner. Each to their own, I suppose.
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Old 17th Jan 2023, 5:15 pm   #11
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Default Re: Bulk erase mini DV tapes?

I wonder if the magnet from a scrap microwave-oven Magnetron might be of use here? They're rather powerful!
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Old 17th Jan 2023, 7:28 pm   #12
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Default Re: Bulk erase mini DV tapes?

Quote:
Originally Posted by GeoffB17 View Post
Have you tried a magnet. Permanent magnet. As big as possible?

The AC demagnetisers get hot over time as they're used, so there is a short length of time to do the job, esp if you want to erase a few tapes, doing both sides to make sure, but this does not apply to a perm magnet. Sit tape on a table, put magnet on top, and leave for an hour or so. You don't need a perfect erasure, just enough to destroy the images, as in make unwatchable.

If you've got a suitable magnet, try one and see. When I've erased tapes (cassette and spool) or computer disks with a magnet (just a 1" x 3" bar magnet) I've done both sides, and also moved the magnet around in a circular motion. I've regularly needed to do this with computer disks that are used on different machines as stray data on the edge of a track (from computer A) might not be erased by a recording on computer B so when the disk comes back to A it might read garbage.

Geoff
Thanks. But how does leaving the magnet in place for an hour so help? I thought that it was a question of magnet strength and maybe frequency etc, but not time? I'm happy to be proved wrong of course!
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Old 17th Jan 2023, 11:11 pm   #13
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Default Re: Bulk erase mini DV tapes?

Huh?

You were the one worrying about leaving something watchable. I suppose that time does have some impact. Remember the warnings about leaving tapes (cassettes) near to your speakers. I've always understood that for the odd minute or two this was no problem, but if sitting there for days, then the recording may not be so good any more.

I admitt, I've not tested this. You might? Try the magnet for a few minutes, check the result. If no good, try 30 mins, then 1 hour, etc. The more powerful the magnet, the less time. Moving the magnet about (circular movement) will prob help a LOT more, but if you've got a pile of tapes to do, this will get to be hard work (on the arm).

Blanking a floppy disk takes a few seconds, but a spool of DV tape is much thicker, more dense, and I would guess will take much longer.

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Old 17th Jan 2023, 11:21 pm   #14
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Default Re: Bulk erase mini DV tapes?

Another thing, as I understand it, the official bulk erasers contain what is basically a transformer. They get hot as the output (electrical) isn't going anywhere. The more expensive ones contain some sort of thermal cut-out, if they get too hot, they stop working, and you need to let them cool down. If you've got something with a big transformer in, try that. Might do the job in a few seconds, each side.

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Old 18th Jan 2023, 12:25 am   #15
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Default Re: Bulk erase mini DV tapes?

So, I looked it up. Google is Great.

Yes, a Tape Bulk Eraser is based on a modified mains transformer. A normal one may well not create enough magnetic field - but it MIGHT do the job?

See this link:

https://www.tapeheads.net/threads/ho...-eraser.20920/

The modified transformer with no load. I assume that if you've got an old transformer, you could use that. I also assume that if you can take it apart to achieve the modification, you can put it back as it was afterwards! The thermal cut-out is not essential, but heed the warnings about it getting hot. I've got a small cheap unit that I used with cassettes. Hand held. When it started to feel hot, stop using it. After you stop using it, it contunies getting hotter for a little while, so stop well BEFORE it gets too hot.

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Old 18th Jan 2023, 12:50 am   #16
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Default Re: Bulk erase mini DV tapes?

I've tried using a standard Weircliffe bulk eraser normally used for audio tapes to erase MiniDV tapes and I can confirm that it doesn't work. Given enough effort, it will increase the error rate so that the picture quality is slightly worse with some sections becoming more blocky but the picture will still be watchable and the people involved recognisable.

I also tried various magnets but they had little or no effect.
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Old 18th Jan 2023, 1:58 am   #17
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Default Re: Bulk erase mini DV tapes?

Hmm?

I wonder why this is?

Firstly, checking details re the miniDV process, I note that the tape is a type of metal tape, I'd assume not THAT different to metal audio cassettes. I'm not sure how different the erase parameters are between normal audio tape, and metal audio tape.

Secondly, the data is recorded as compressed data, somewhat like mp3, so the data on the tape is not the 'actual' data, but needs to be uncompressed anyway. I suppose that there is a lot of ability built into this process to protect the images, so that there could be a lot of scope for getting a viable image even from somewhat corrupted data. I'd guess that even so, there may be a threshold at which point the damage is too much to allow such correction?

Also, there seems to be a lot of digital data for each frame of the video, and this will further increase the robustness of the recording.

The transformer types of erasers might not be practical - to the point of being dangerous, but a strong magnet right on a tape for hours, overnight even, might do something?

Actually, I have a JVC camera that uses miniDV. It doesn't work any more, in that it suffers with the known problem of the image sensor failing so I cannot record, but it plays back fine. The tapes I have have been transferred to PC, but I'm not ready to dispose of the material on the tapes just yet, otherwise I'd try myself. You cannot erase part of a tape using the methods we're discussing here, it's all-or-nothing, and while many of my tapes have some 'rubbish' on, they all have bits that are valuable. I think I have one blank tape, but I cannot record onto it.

Geoff

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Old 18th Jan 2023, 11:55 am   #18
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Default Re: Bulk erase mini DV tapes?

Reasons why demagnetization is quite hard:
1. The tape is high coercivity (hard to magnetize/demagnetize).
2. It's a digital recording. The system doesn't use bias to work in the linear part of the hysteresis curve, it saturates the medium.
3. I'm not completely familiar with the DV format (although i have an ancient semi-pro DV camera), but it probably uses a PRML detection system. Advanced versions of these are capable of retrieving data when the s/n ratio is <1, i.e. more noise than signal.
4. It might also use trellis coding of the symbols sent to tape, such that the error correction is good (comes from modem technology but was adapted for tape in the early 1990s).

Put that lot together and add-in that it's looking for magnetic transitions, rather than absolute magnetic levels, and it's extremely hard to erase.

You might contrive something mechanical involving a powerful permanent magnet, but you'd need to expose the tape to both poles separately and to saturation, and then reduce the field to zero progressively. I don't see that as practical.

And before anyone mentions cooking the tape, the Curie point of those magnetic media is above the melting point of the substrate, so that won't work, either.

My background was in DAT tape for computer purposes (DDS), but there are many similarities and DV format was developed around the same time.
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Old 18th Jan 2023, 12:17 pm   #19
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Default Re: Bulk erase mini DV tapes?

Seems a waste of scarce head hours to machine-erase...
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Old 18th Jan 2023, 1:29 pm   #20
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Default Re: Bulk erase mini DV tapes?

Yes Ted. I think I'll just sell the machine as is, without the prerecorded tapes, but with the unused ones.
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