Is tape head degaussing a myth after all?

S

soviet123

New member
Hello all,

New guy here. Recently obtained a WM-D6C, because CDs are not old enough, DAT is digital and vinyl isn't portable. Googling "head demagnetizer", I came upon posts that say it is not needed to periodically degauss tape heads (paths). As I did not make five posts, I cannot post the URLs but they are from this very forum.

1. Operating a tape recorder does not cause anything in the tape path to become magnetized. Not even a tiny bit.
2. All parts including heads have made from materials with a natural neutral magnetic state, to which they tend to return even if deliberately magnetized.
3. The magnetic flux required to affect a recorded tape is much higher than anything anywhere around the tape recorder, except in the erase and record head gaps. The effect of a steady-state magnetic field (a DC field) on recorded tape is first noticed as partial erasure of high frequencies, and that occurred with a field somewhere above 200 Gauss. Tape has very high coercivity by design, meaning you need a high field strength to cross the threshold above which the tape will become magnetized. That's what the bias oscillator does. By being many times hotter than the actual audio signal on the head, the bias forces the signal over the coercivity threshold into the more "linear" range of the tape. But that means it's harder to erase tape than you might think. Typical guide and head residuals were in the zero to 20 gauss range, far below tape coercivity levels.

4. Erase and record heads are self-demagnetized by the bias oscillator, which provides an AC field in the gap that is thousands of times higher than what a de-magnetizer can induce.

5. The field found on recorded tape is incapable of magnetizing anything. It is minuscule, and when the tape moves, it becomes an AC field, which would demagnetize if it had any effect.

6. The effect of a DC field near or in a record head produces two measurable results: First, a significant elevation of even-order harmonic distortion, and second, an elevation in low frequency noise (a sort of gravelly sounding noise). But again, the field has to be fairly high for this to happen. You need a spectrum analyzer to differentiate even harmonics from the normal odd harmonics created in the recording process.

7. If tape machine parts become magnetized, there is a defect in manufacture (the material doesn't have a natural, neutral magnetic state), or a defect in the tape machine, either due to a failure or design flaw. Asymmetrical bias waveforms will present a DC component, any DC on a head due to a circuit defect (bad blocking cap, for example). Demagnetizing may temporarily remove the residual, but if it creeps back, something is "broken", and needs repair or replacement.

8. Lastly, casual use of a demagnetizing device, even if the classic proper techniques are observed (slow removal, switching of when several feet away), sometimes resulted in an increased magnetic state rather than a decrease. There's no way to tell if you are demagnetizing, or magnetizing, without further testing for the effects of magnetism. Once again, these are HF erasure of a recorded tape, or increase in noise and even-order harmonic distortion during record. Yes, you need instrumentation to do this.
Click to expand...

I have no electrical and magnetic understandings (other than don't play with magnets in front of a CRT), so basically is what that person saying true?

Thank you very much.
 
I don't know who wrote that long quote above, but most of it is pretty accurate.
I hardly EVER demag....maybe once a year(?)...and I only do that just for the heck of it, just so's I can say I've done it once in awhile ...just in case. :D

See...I have a Gauss meter, and no matter whenever I'd check my deck with it, the magnetism was absolutely nominal. IOW, I could demag it a thousand times, and the teeny-tiny bit of needle deflection I would see on my Gauss meter would always be there. It's partly just the metal mass of the whole deck and partly the background magnetism of good ol' mother earth.

So...I never give it much thought any more, Once in a blue moon I'll demag, but it's probably not needed.
When I had my first 4-track, I use to demag ALL THE TIME....but not now with my current 16 and 2 track decks.
 
I've had dropouts hiss and clicks in my tape before and demaged the heads and all the issues went away. Not a myth as far as I'm concerned. Tape heads can become magnetized, a demag takes care of that problem.
 
Dropouts/clicks are more from crud/tape shed on your tape path...you probably also cleaned your heads/quides when you demagmetized, and that's what made it go away. ;)

I'm just going by a real Gauss meter. If I don't see any magnetic build up shown by the meter, then there's no point in running a demag...and that's been the case over a long period of tape deck usage. *shrug* :)
 
I just demmaged my Ms16 and can honestly say I dont hear any difference in sound quality or tape hiss. Im going to go with my gut and not demag maybe till next year or so.
 
I've never noticed any difference from demagging and don't worry about it much. I've always just thought that it was something that could happen but usually doesn't. I've definitely read many places where they say to demag every (so and so).
 
I've had a degausser for years and I demagnetize from time to time. I think I've mentioned in a couple of threads here that I haven't got a clue if it does any good or not. Having said that, I had to have the tracks on my 8 track portastudio dealt with a couple of times in the first three years I had it. Since using the degausser (in '95), I've never had a track issue again.
So who can tell ? Not I. But I'm not taking the chance either.
 
It would be really nice if someone with deep electrical understandings chime in on this. Basically everywhere I go says degauss and demag once in a while, some say even per 30 hours.
Thanks for all the replies, guys.
 
2-head decks pretty much never need it, because every time you hit RECORD, the record bias demags the Rec/Rep head for you.
So as long as you do a fair amount of playback AND recording...it takes care of itself. My 16 track is a 2-head deck.
Unless you do rare recording but LOTS of playback of recorded tapes...don't worry about a 2-head deck. Do it once in awhile if you want to feel more comfortable.

With a 3 head deck...the playback head has no recording bias running through it, so may need it from time to time. My 2-track is a 3-head, but it's only used for mixdown purposes, so it can go a long time before demagnetizing is needed.

I think the later/newer decks have better quality metals and heads...so unless up zap them with some large magnetism, like a magnetized screwdriver (or bad use of a demag tool)...they probably don't need it as much some people think. The real old decks had softer metals, so that stuff sucks up magnetism a lot more.

Clean your guides/heads often, before each sessions and sometimes again during longer sessions...that's more important than demagnetizing. :)

Get a finer scale Gauss meter...that way you can actually see how much magnetism is there rather then just guess as to when it's there. ;)
 
fstrat76 said:
The initial quote above came from this thread/post and had some interesting comments recently by jaddie:
https://homerecording.com/bbs/gener...get-tape-head-demagnetizer-16230/#post3560619
Click to expand...

He's certainly right when he says overdoing demagnetizing could potentially cause more problems then skipping it until you really need it, or just doing it very rarely if it makes you feel good. :D

The amount of juice in most decent demagnetizers if pretty strong, and you could easily leave your deck in a greater magnetized state than it was before you demagnetized it.
If you forget to power off the deck...your heads are toast. :(

Also...keep that thing away from VU meters and watches and loads of other metallic/movable parts!!! :eek:
 
Short answer... NO it's not a myth.

Long answer follows:

Yeah, googling key phrases of the OP’s quote only brings us back to homerecording.com to a post by a new member with no other links, references or credentials. All we have is uninformed opinion in the following thread:

https://homerecording.com/bbs/gener...get-tape-head-demagnetizer-16230/#post3560619

Sounds like somebody has Deguassaphobia. LOL It's ok... t’s a common affliction. ;)

But regardless, Demagnetizing /Degaussing is not at all a myth. It is a critical part of regular tape recorder maintenance. As with all maintenance it’s going to depend largely on how many hours over what period of time you use the machine in question that will determine how often you degauss. That may account for differencing experiences, but the need for degaussing is well established and has not changed right up to the latest generation of recorders.

Every calibration tape manufacturer, MRL, STL, BASF, TEAC, etc have always warned to degauss before using a calibration tape. The only one left, MRL still does. The reason being if you don’t, the high frequencies will be reduced in amplitude over time by residual magnetism on the tape path.

Residual tape path magnetism erases the highest frequencies (shortest wavelengths) but does not tend to affect low frequencies. If you don’t degauss you risk dulling the crispness of your recordings a little with each pass. Magnetized heads cause other ills like clicking and popping, especially at splice points. I’ve experienced all these things in the three decades I’ve been recording in audio/video. Degaussing cures a multitude of tape deck ills.

Heres’ some of what Jay McKnight of MRL has to say on the topic:

Magnetic Damage

WARNING: If you are comparing a secondary standard calibration tape to a primary standard, and you have magnetized heads or guides, you will ruin the primary standard tape in the process!

Magnetic damage -- tape erasure -- can come from the tape recorder itself (magnetized heads or guides), or from other fields.

The easiest test for magnetization of heads or guides is this: On a blank tape, record a 16- or 20- kHz signal for about 30 seconds. Note the reproducer level meter reading as you make the recording. Then rewind this recording, reproduce it again, and note the level. Rewind and replay several times (do NOT re-record). If there is magnetization of the transport, the level will drop with each succeeding play. [At the shortest wavelengths (the highest frequencies at the slowest speeds) a small loss (<0.5 dB) is common, and does not necessarily mean that there is any magnetization of the heads or guides.] The effect from multiple replayings is logarithmic: If the level is 0 dB in recording, and drops to -1 dB the first play, it will drop to -2 dB on the 3rd play, -3 dB on the 6th play, etc. If the level of this high-frequency that you just recorded drops with each playing, do not play your primary standard until you have both demagnetized the heads and any magnetic guides, and re-run the magnetization test to prove that there is no more magnetization. See the author's paper ‘Demagnetizing a Tape Recorder’ “


The following or something similar is in every Tascam tape recorder manual up to the last analog products they made:

DEGAUSSING (DEMAGNETIZING)

IMPORTANT:

1. Do not overlook the importance of degaussing. Magnetism in the tape can significantly degrade performance. In extreme cases, the heads may not respond to signals at all.

2. Turn off the deck before degaussing.

3. Do not turn the degausser (E-3) off or on while it is in close proximity to the tape path.

4. Keep all recorded tape a safe distance from the degausser.

A little stray magnetism goes a long way; a long way towards making trouble for your tapes. It only takes a small amount (0.2 gauss) to cause trouble on the record head and playing 10 rolls of tape will put about that much charge on the heads and other ferrous parts of the tape path.

A little more than that (0.7 gauss) will start to erase high frequency signal on previously recorded tapes. Demagnetize the whole tape path, including the tips of the tension arms every six fully played 10-1/2" reels. This is a fair ”rule of thumb" even though it may be a bit hard to keep track of. Fast motion isn't as significant to the heads, so we don't give an hourly reference. It's the record/play time that counts.


The bottom line is that heads and other parts of the tape path contain metals that can become magnetically polarized. It comes down to physics.

There is something what Miroslav says about the erase head degaussing itself because the same alternating process is used to degauss tape. However if the bias on the record head were strong enough to keep it demagnetized it would also be strong enough in relation to the audio signal to erase the tape instead of recording something to it. In that case when you played back any tape all you would hear is hiss and no music. The tape itself leaves stray magnetism on other metal parts of the tape path. ;)
 
I got the impression that there was more science in the stuff that soviet123 quoted rather than in the stuff cited by beck.
 
gecko zzed said:
I got the impression that there was more science in the stuff that soviet123 quoted rather than in the stuff cited by beck.
Click to expand...

After reading Jaddie's post on the topic, I only demag if I notice high frequency loss on playback or uneven tape hiss etc. Basically only demag if something sounds wrong that could be because of magnetized heads. Given that, I haven't demagged in months as I still hear the same great sound out of my decks.

This whole demag thing reminds me a lot of the blown out of proportion (on the internet) 'head wear' subject.
 
I don't feel that degaussing is "myth"...it's just some people seem to obsess over it a bit too much, and the frequency of their degaussing is a little over the top. ;)

My feeling was and is that the best thing to do is *measure* before you degauss. You can get a magnetometer from R.B. Annis (I got mine as a kit with the Hand-D-Mag, along with a clip on probe). If you see sufficient deflection from the meter's "natural" state (whatever magnetism it's already picking up from mother earth)....then by all means DEMAG! :)
But just constantly running a demag can lead to more problems/accidents than you skipping a demag session when it may be needed.

Not sure about 0.2 Gauss mentioned on the MRL websites, as the instructions I have that came with my Hand-D-Mag say that the rule of thumb is any metal tape deck parts with over 1.0 Gauss should be demagnetized.
In ALL the years I've had my 16 track deck (2-head)...no matter how much use it saw between demag sessions, I NEVER got a reading of more than 0.25 Gauss...and ...that same amount was there BEFORE and AFTER I ran the demag!
So...take that for whatever it's worth.

AFA my fairly new 2-track (3-head)...I'm going to check it from time to time to see what if any magnetism buildup is happening. If my magnetometer is not showing anything substantial...why would I want to demag???

I think many people just do it as a habit...needed or not, and some folks think they need to do it almost daily.
I'll demag when I setup/calibrate (which also isn't very often, as I'm not running a commercial studio and all kinds of different tapes)...and if I do a LOT of recordings back-to-back-to-back...so I may demag once after a lot of sessions, just to cover my ass.

Oh...and I've NEVER noticed any real difference after I demag these days...BUT, back in my 4-track days when I used to bounce and bounce tracks and run my tapes for days at a time...I have to say I did notice an slight improvement in upper-end clarity when I did a demag after many sessions.

YMMV.

And as a side comment...the one thing I like about tape is that ROLLS OFF the nasty high-end...so I'm not complaining. :D
 
Beck said:
Yeah, googling key phrases of the OP’s quote only brings us back to homerecording.com to a post by a new member with no other links, references or credentials. All we have is uninformed opinion in the following thread:
Click to expand...

Not sure why or how this comment relates.

It would be interesting if Jaddie could jump in and offer some more of the experience and technical details, measurements, etc.
 
Chilljam said:
This whole demag thing reminds me a lot of the blown out of proportion (on the internet) 'head wear' subject.
Click to expand...
and the " rebias your amp or it'll explode" subject. Things that are good common-sense maintainence procedures take on an air of "do them or you will die" pressure on the 'net.
 
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