The Bottom Line with Demagnetization

[pchorman]

What's the bottom line with tape head demagnetization

Folks:
I believe I searched out and read everything on the forum regarding tape head demagnetization and am left a little puzzled. For one, there seems to be some controversy over whether it's really required for 4-tracks. I'd like to know whether anyone has ever discerned audible degradation or improvement as a result of mag'd or demag'd tape heads.

Also, I just picked up the Tascam (Teac made) demagger today and realized that it comes with no instructions. Is this a packing error? AMS tells me no. If not, it raises an important question: if it's such a critical step in which people have all these taboo rules about turning the instrument on and off from far away, moving in and out slowly and doing things a certain way in order to prevent equipment damage, why the hell wouldn't they bother to pack a precaution with the unit? Where did all these rules & procedures come from if not the manufacturer?

thanks

 

[regebro]

You don't need instructions. You turn it on a way from the equipment, move it close to the stuff and move it slowly away, and then turn it off. Ridicously simple. It's no taboo, its how it works. You demag stuff by subjecting it to a large fluctuating magnetic field, and then slowly making that field weaker. Press "demag" on a computer screen, and you'll understand. If you turn the demagger off near the equipment, you'll make it MORE magnetic.

The bottom line is that most likely you don't need to demagnetize, but figuring out if you need or not is a lot of work, so it's easier to do it.

 

[skippy]

One caveat: do that with the power off on the recorder... The head repro amps will be seeing about +200dBu during the demag cycle! They won't mind (the inputs are diode protected for just this occasion), but if the equipment is on and is in reproduce mode, you'll be sending 60Hz square waves at absolutely full freakin' scale down the chain. Your monitors may not like it.

Had a collaborator do that once- try and demag the record/sync repro head on a Tascam 38 with the thing in sync monitor mode. He said he "wanted to see what it sounded like". He was clipping the repro amps with the demagger still 2 feet away from the deck, and was still laughing like a madman when I threw him out. Sigh...

 

[pchorman]

OK, but this underscores the fact that the procedure should not to be taken lightly and that instructions are rather important. It can either worsen or damage the equipment if not done per recipe. If I didn't research it on the net I would have surely zapped the thing.

By the way, I feel zero attaction between the plastic coated demagger tip and the heads or any other metallic surfaces in the tape path. I've read from some that they can feel the magnetic interaction - not here. Does this merely imply that it's all non-ferrous material in my tape path, or is something suspicious about the demagger? I would expect an AC electro-magnet to attract ferrous objects whether or not they make good permanent magnets. (That's all a demagger is, and AC electro-magnet right?) What do you think?

 

[skippy]

You usually can't feel much more than a light buzzing, in my experience: it doesn't try to wrench itself out of your hand, or anything like that. It also depends on the design of the demagger. The larger ones that are designed for big headstacks will give you more of a senation than the small ones intended for cassette machines and the like. The old Adams demagger I used to have for the big machines put out about 500 gauss: you could use the ass end of that one to bulk-erase reels of tape...

Here's the canonical demag procedure, from MRL (Magnetic Reference Labs), the makers of the alignment tapes that everybody should have for their machines...

http://www.flash.net/~mrltapes/demag.pdf

Ahh. That takes me back.

If that doesn't do it for you, a google search on the phrase "head demagnetization" got me 15 other hits. It really isn't that hard, or that critical, as the MRL paper illustrates...

And yes: you do need to demagnetize, and you do need to do it often. I did it daily on my analog machines. And yes, you can hear the difference. It's a nobrainer, just like Regebro said. Just make it a habit, a procedure that you do every time before you record something you intend to keep.

It takes 15 seconds, and it's like cleaning the heads: the time you decide not to do it will be the time you get the Miracle Take, perfect in every way except for the fact that it ends up sounding like your Strat has 8-year-old strings...

 

[pchorman]

Thanks Skip. I did read that MRL paper. Here's something that I should be embarrased to admit: I just went more than 5 years and hundreds of operating hours on my Yamaha MT50 4-track recorder before cleaning the heads and using a demagger. Here's the kicker: that Q-tip swab (with 91% alcohol) did not show the slightest trace of residue after wiping those heads off - I mean it was as clean as new. Only the rubber roller shows some light coating of tape residue, no build up just some brownish discoloration from the tapes. So what do you make of that? From what I read, you're supposed to pull visible crud out of the tape path. Maybe it's the particular tapes I used? They have consistently been TDK SA90 and Maxell II 90. I feel like it was a waste of my time. Or is the crud not always visible?

 

[skippy]

The crud is seldom visible. If you have visible crud, you have real problems, like a very bad batch of tape. Crud that sticks to the capstan or pinch roller increases your wow and flutter, and crud (even skin oils!) that sticks to the head causes variations in the HF response. Perfect contact between oxide and head is critical for HF response, and doubly critical if you use noise reduction.

I'm certainly glad that you didn't find big junk in the way, and I'm not too surprised that the difference doesn't seem too terribly great right now: you have to listen for it. You'll find the real difference becomes clear when you're 3 bounces away from original, and all the sparkle is gone from your signal. Keeping it clean preserves everything you print to the greatest extent possible, especially if you have to go multiple generations with a 4-track recorder.

Trust me, you didn't waste your time. It's quite possible that doing it as frequently as I did it smacks of religious fervor: but it's my religion, and I'm sticking to it! (;-)

 

[pchorman]

actually, I haven't tried it out yet since the 5-year-overdue cleaning and demagnetizing. I will try it the next time my band rehearses, and will have plenty of takes to compare it too. (It was the fact that nothing seemed to have come off the heads which made me question the effort.)

I hope it's an audible difference after all this time. Ultimately I'm looking for demo worthy recordings. So far out of dozens of taped sessions and experiments in mic placement only one recording was deemed worthy of inclusion. This is what lead me to the tune up.

Thanks again Mr. Skip