From: utzoo!decvax!duke!harpo!eagle!mhtsa!alice!rabbit!wildman Newsgroups: net.audio Title: Re: Pinch rollers and biasing Article-I.D.: rabbit.159 Posted: Wed Jan 5 12:06:07 1983 Received: Thu Jan 6 06:32:14 1983 References: rocheste.364 WE've already been over this once, but here goes again: THE PRIMARY CAUSE OF HEAD MAGNITIZATION IN TAPE RECORDERS IN THE MODERN ERA IS THE TURN ON/TURN OFF TRANSIENTS THAT ARE CIRCULATED THROUGH THE HEAD. THESE CURRENTS ARISE WHILE THE POWER SUPPLY VOLTAGES ARE CHANGING WHEN THE DECK IS IN FLUX BETWEEN ON AND OFF (OR THE OTHER WAY AROUND) The tape itself is a very minor cause of magnitization. If you have played a tape once on a magnitized deck, it doesn't matter any more, regardless of the inccorrect statements that have appeared here regarding coercivity of magnetic recording tapes. For those of you who are knowlegable in circuit theory, the cause of magnitization is the pulse that most head amplifiers send through the head on turn on, and turn off. The second most significant cause is the current leakage through either the coupling capacitors or the input stage of a directly coupled head amp. I repeat: If you have played a tape on a magnitized deck, and then demagnitize the deck, it doesn't matter any more. If you want to know a lot more about this subject that you ever cared to, read the last two years worth of the Journal of the Audiom Engineering Society in your favorite technical library. Use the master index at the end of each year to find the right issues. Please, people, if you don't know what you are talking about, don't talk. If you have to, at least admit that you are speculating. (Some people do that. These people are usually right, which just points out human nature.) I quit! Oh yes, lacquer thinner often has heavier hydrocarbons that will act just like oil when you get done. I wouldn't use it. I use freon for general cleaning and isopropyl when someone has let things get out of hand to the point that I need a firehose.