Bulk Tape erasing, breathing/pulsing sound?

[Rey1]

Hi everyone,

I just picked up a Geneva PF-215 bulk eraser and it seems to erase type II cassettes great, however I do notice a breathing or pulsing in the resulting blank. Doing a search here, some members say that they get this sound when bulk erasing, some say they never get it and lay the blame on poor technique. I am starting the unit about 1 foot away from the tape, closing in slowly, rotating the unit clockwise around the cassette reel a few times, then backing off slowly, and repeating after flipping the cassette. Am I doing this wrong? Should I move in more slow, not flip the cassette? Or is this the common result?

 

[Sage]

Great question! I have the same problem with my Teac bulk eraser even though I follow the directions for erasing my reel to reel tapes. I can even see the meters and subwoofer cone move to the sound on the supposedly "erased" tape. Anybody know the cause and/or solution?

 

[soviet123]

Same here but it only manifests on CrO2 tapes (haven't tried METAL). It basically destroys the tape as any further recording done on these tapes are practically unlistenable.

 

[Rey1]

My tapes do not appear to be that severe. The VUs do not move and I have to turn up the volume high to hear it, but the sound is there.

 

[Wilhem]

The bulk eraser works by creating a powerful magnetic field at the rate of 60 cycles per second. The idea behind erasure is that bringing the erasure near the tape forces the particles to magnetically align themselves to the signal from the eraser: a strong positive, a strong negative, strong positive, and so forth. Bringing the eraser close to the tape forces all previous recorded patterns to follow the signals from the eraser, erasing the previous patterns. The user very slowly pulls the eraser across the entire reel and then very slowly pulls the eraser away. In an ideal situation, half the particles have a positive alignment, and half have a negative; but they should all be randomized when they all vary in terms of reacting to the slowly retreating magnetic field.

If there is a sound recorded on the tape, it means that a band of particles is left positive and a band is left negative. If those bands are far apart, that can be a very long wavelength between bands, resulting in a recorded tone below 10 cyles per second. That's why you might not be able to hear it, but your speakers are struggling to reproduce it.

The solution is always reversible by trying to erase once again. Move the eraser more slowly, and change the pattern of movement. If you have problems erasing high coercivity tapes such as chrome tapes, you will have even greater problems with higher coercivity tapes such as metal--or video unless you can remove the tape from the housing.

It takes a lot of power to bulk erase tapes. The electro-magnets on tape coaters are enormous, and even studio bulk erasers are large machines with a lot of metal and cooling. Hand-held models can never produce the fields these behemoths can create, but practicing erasing skills can make improvements.

 

[Rey1]

Hey Wilhem,

That did the trick. Following your instructions I have gotten one totally smooth and the other has just a slight rumble. I just need to practice the technique now.

Thanks!

 

[illinoisteve]

This sounds like bulk tape Tai Chi.

I have never had a bulk eraser, but am thinking about getting one finally. I saved this page with Wilhelm's advice as an internet bookmark.

I have just learned, erasing on my RTR, that I get a better erasure at 1 78 ips than at 7 1/2, presumably because the erase head dilly dallies its way along the tape and has more of an effect.

 

[perryinva]

Slow, slow, slow. Really slow, when you move the eraser across the tape. That's why I like tabletop models. It really is a technique.

 

[Wilhem]

The bulk eraser is, in effect, recording a 60 Hz tone on the tape with a tremendous amount of enerygy. Shutting off the eraser in the middle of an erase process will leave a recorded "hum" signal on the tape that may be difficult to erase later because the signal was so strong. The trick is to slowly reduce the amount of energy from the eraser so that a random half of the particles are left in their attempt to record the positive part of the 60 Hz signal and the other random half are left trying to record the negative part. It is the randomness that's important--as long as there is no pattern, the tape does not produce a signal. (Except for hiss, which is a result of friction, amplifier noise, rough tape surfaces, and "mini-patterns" produced by imperfections in the magnetic crystals. Chromium dioxide crystals are the only ones completely free from dendrite flaws; that's why chrome tape has such low hiss levels. Metal particles are very small but very hard to orient properly in a coating, and that's why their noise levels are the highest.)

A good erase head should be able to eliminate most of any residual signal left after an imperfect bulk erasure, but the erase head covers only the tracks on the tape, not the area between the tracks. A low frequency residual signal left in the division between tracks may have some cross-talk effect that can detract from the playback sound quality. It's best to try to do as good a job in bulk erasure as possible to get the tape back to its pristine level as possible. That's why tabletop bulk erasers are very good--they are consistent in their application of the erase signal and its decline.

 

[Wilhem]

The Nakamichi Dragon, like so many other Nakamichi recorders, uses a double-gap erase head for more thorough erasure. It is a very good design.

 

[Wilhem]

If you can't tell the difference, then there is no point in bulk erasing beforehand. Magnetic tape is bulk erased after pigment orientation and before calendering, slitting, and packaging. There is no need to bulk erase packaged tape unless it has been sitting on a powerful magnetic source for a long period of time.

 

[LAB3]

Is it required to to move the tape from a alloy reel to a plastic reel on the Reel to Reel recorder with a hand head eraser??

 

[eddisc]

A look inside a pro table top bulk eraser. There is no name plate on it.

 

[eddisc]

Is it required to to move the tape from a alloy reel to a plastic reel on the Reel to Reel recorder with a hand head eraser??

If you mean hand-held eraser - NO. Even on a table-top one, there's no need to x-fer tape.

 

[LAB3]

If you mean hand-held eraser - NO. Even on a table-top one, there's no need to x-fer tape.

Yes......Thanks :thmbsp:.it's been 25 years and re-learning Pop's Revox

 

[jazzyguy]

Same here but it only manifests on CrO2 tapes (haven't tried METAL). It basically destroys the tape as any further recording done on these tapes are practically unlistenable.

I don't know how you can say that. I have bulk erased many and have recorded successfully .

 

[cgutz]

Do you guys remember the scene from the Big Easy where the police officer was caught on tape committing an offense. The tape is stored in the evidence locker pending trial.

The police officer buys a big old magnet, throws it through a store window at night. The magnet is collected as evidence, and his "buddy" in the evidence room stores it on top of the tape that incriminates the officer.

It goes to trial, the tape is erased, and there is no evidence to convict him.

Too funny!

 

[perryinva]

As Wilhem mentioned, if the bulk eraser "records" a super strong pulsing signal, it can be too much for a weak erase head to randomize. It really is time and technique. SLOWLY bring them together, SLOWLY make sure the tape crosses the actual erase field (why they are never marked I don't understand ) and SLOWLY separate the two. Too weak a bulk eraser only makes a mess of the blank area between sides, so it is worse to use it than none at all. Most (all?) decent erase heads are half track so the space between the L & R channel is covered, but A side vs B may not.

 

[oldvinyldude]

Most (all?) decent erase heads are half track so the space between the L & R channel is covered, but A side vs B may not.

Wow-that does not make sense, so I must be missing something.

My understanding is that all 4 track reel to reel tapes, for example, are recorded such that one direction records on band 1 and 3 (for stereo), and the other direction is band 2 and 4. If an erase head is 1/2 track, wouldn't it erase band 1 and 2? on one pass, then band 3 and 4 on the other?

 

[jlb2]

Anyway any 4-track recorder has a 4-track erase head, so there is no problem actually. It's only if you erase on a 1/2 track machine and then play the tape on a 1/4 machine (or the other way round) that it won't work well, but that's only because the track layouts don't match. A 2-track head will erase only part of channel 2 (track 4 in the other direction) - and a 4-track deck will erase only part of both 2-track channels but that bit is obvious. In both cases parts of the tracks erased on the wrong machine will still have signal that will be read by the playback head.

Or if perryinva meant that his 1/4 track deck does not erase well, then it's just defective and needs an overhaul. Or if he bought a 4-track with a 2-track erase head on the grounds that it erases better, then he quite simply got swindled

 

[perryinva]

LOL, I was talking cassette decks, not RTR! RTRs alternate tracks, cassettes are side by side. Both the OP and Kenwood61's questions were about erasing TypeII cassettes, not RTRs. RTR tape is normally very easy to erase, with no pulsing or after affects, just like standard ferric cassettes, as the majority of it is Type I. The pulsing comes from the higher coercivity (energy required to record) of the chromes and pseudo chromes of TypeII. Metal (TypeIV) and video tapes (which was often metal or Type II) is even harder to erase, and standard RTR bulk erasers do nothing more than dull the sound, and impart noise.

 

[oldvinyldude]

LOL, I was talking cassette decks, not RTR! RTRs alternate tracks, cassettes are side by side.

As usual, I missed that detail :sigh:

Thanks for the clarification. :thmbsp: