Hello everybody, I've been on the site often and picked up a lot of useful info but now I've got a question of my own to ask. I recently bought a revox b77 mk2 which worked fine but after I cleaned and demagnitized the heads it now records very badly. The newly recorded sound is very dull and weak with very little movement on the V.U.s. When I tried recording after the clean up I had my monitors too close to the mike and got a big feedback loop going and I wonder if it could have damaged the recording amp. Playback works fine. Could I have demagnitized it badly? So many questions, any answers? I'll say thanks in advance and looking forward to your suggestions
recording problem on revox b77
- Thread starter anxios
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Hi Jay, thanks for the reply. Yes, it happens on both channels and when I record through the mike and the line inputs. I've cleaned the heads as well as I can, but no differance. It was going fine until I demagnitized it. " Better can be the enemy of good", as they say down here in France.
steerpike2
Super Member
Was it powered up when you demagnetised it?
goldear
Certifiable Audio Junkie
Yes, was it powered-on during the process? Also, could you please describe the procedure which you used to demagetize it? The improper use of a demagnetizer can actually magnetize the heads, so please describe how you went about this, so that we can rule-out this possibility.
jayk
Super Member
FYI.
"Degaussing
"As the magnetised tape travels through the tape path the magnetic flux on the tape progressively is transferred to the metal parts such as the tape guides and heads. This build-up if left unattended will induce magnetism onto these parts and they will progressively erase the high frequencies on the tape as it passes. Therefore regular degaussing of these parts is a necessary maintenance procedure. A degaussing tool is required for this operation.
It is common practice to wrap a layer of insulation tape around the head of the degausser so that the metal doesn't damage your heads if you accidentally touch them.
((The technique here is to first turn off the tape recorder. If you don't you'll blow out all your circuits!))!
Then switch on the degausser with the head 1m(3ft) away from the recorder. Slowly bring the degausser head up to the play head and move the degausser slowly down and back up the head then slowly draw it away around a foot, then do the same to the next head and the next if there is one. Then using the same technique do the tape guides, rollers etc. Finally draw the degausser away from the machine around 1m(1ft) and switch the degausser off. Your machine is now degaussed."
"Degaussing
"As the magnetised tape travels through the tape path the magnetic flux on the tape progressively is transferred to the metal parts such as the tape guides and heads. This build-up if left unattended will induce magnetism onto these parts and they will progressively erase the high frequencies on the tape as it passes. Therefore regular degaussing of these parts is a necessary maintenance procedure. A degaussing tool is required for this operation.
It is common practice to wrap a layer of insulation tape around the head of the degausser so that the metal doesn't damage your heads if you accidentally touch them.
((The technique here is to first turn off the tape recorder. If you don't you'll blow out all your circuits!))!
Then switch on the degausser with the head 1m(3ft) away from the recorder. Slowly bring the degausser head up to the play head and move the degausser slowly down and back up the head then slowly draw it away around a foot, then do the same to the next head and the next if there is one. Then using the same technique do the tape guides, rollers etc. Finally draw the degausser away from the machine around 1m(1ft) and switch the degausser off. Your machine is now degaussed."
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Hi, yes the machine was unplugged and I followed all the right ways to do it. Machine off, demagnitizer on at about 3 metres away and slowwly in to the heads. Small circular movements about 1mm from the heads but not touching them, one head after the other with no jerky movements and finally back off verry slowwly to about 3 metres away before switching the demagnitizer off. I used a cigar shaped demag. which I've since seen as not advised as it is not powerful enough to do the job, would it be powerful enough to damage it? Thanks for your help, I'm so sad because it was fine before and I should have left it alone. If it ain't broke....... It's never too late to learn
SaSi
Seriously Illogical
I'm guessing here but an underpowered demagnetizer could (in my mind) cause the heads to get magnetized. Try the demag once more. Cover the tip of the demag with a piece of thin rubber (like a piece of a baloon) to avoid the tip scratching the heads. Try to bring the tip as close to the heads as possible and swipe it left-right a few times, then retract it.
I tried demaging a cassette deck while powered on and it didn't fry anything. It could fry the speakers if the deck was connected to the amp and selected - I just monitored what was happening using a pair of crap headphones. I don't advise demaging with the deck on, can only cause problems, but I wouldn't consider the amps destroyed by that. If they were fried, it would either not record or not play back. What you describe sounds like magnetized heads.
You might need to get a proper demagnetizer though - prefferably AC mains powered. Can you post a picture of the one you have?
I tried demaging a cassette deck while powered on and it didn't fry anything. It could fry the speakers if the deck was connected to the amp and selected - I just monitored what was happening using a pair of crap headphones. I don't advise demaging with the deck on, can only cause problems, but I wouldn't consider the amps destroyed by that. If they were fried, it would either not record or not play back. What you describe sounds like magnetized heads.
You might need to get a proper demagnetizer though - prefferably AC mains powered. Can you post a picture of the one you have?
Thanks Sasi, the demagnitizer I've got is one of these cuban cigar shaped objects. I've since seen it singled out as "not to be used for reel to reel heads" on another site. I bought it at one of the revox repair centres here in France and, really, it was after using it that the trouble started. I've sent a photo of it and a couple of the heads, which look pretty good to me, the heads, not the photos. I've sent out smoke signals to all my friends in music and recording down here to see if someone has something better. I've been thinking along your lines too, that if a weak demagnitizer can magnitize then perhaps a strong demagnitizer can bring the world to rights. Fingers crossed. As far as the recording amp is concerned, I was worried that the blast of feedback it got might have fried a few composants, it's old and I know how it feels! Thanks again
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audiofred
Active Member
Your demag looks good from the pix. A demagnitizer is a demagnitizer. If you plug it in and it will pick up a ferrous object, like a nail , then it will demganitize your tape heads.
Something ripped from the Internet
Efective demagnetizing applies the strongest possible magnetic field to all metal tape path parts. This requires
that the demagnetizer’s tip makes close contact with the parts, because a magnetic field’s strength lowers with
the square of the distance. So, choose a demagnetizer that creates a strong magnetic field, the stronger the better.
Avoid cheap demagnetizers because they are barely strong enough to demagnetize a cassette machine head, and
will not demagnetize a capstan or a metal tape guide. The Han-D-Mag, made by R. B. Annis Co., is the strongest
unit made. Contact: R. B. Annis Company, Inc.; 1101 N. Delaware Street, Indianapolis, IN 46202. Or contact
them by telephone at (317)-637-9282.
When you buy your new demagnetizer, cover its tip with heat shrink tubing or plastic electrical tape so it will not
scratch the delicate tape heads.
1.) Turn the power off on the tape recorder or duplicator. Demagnetizing with the power on can damage the
recorder’s circuitry.
2.) Turn the demagnetizer on 3-feet (one meter) or farther from tape or tape machines.
3.) Move the demagnetizer in, very slowly, so its tip touches the head(s), guides, and the capstan.
4.) Move across the surface of each part, and from one part to the next, very slowly and smoothly. If you
accidentally move quickly, go back over that part.
5.) After you have gone over the surface of every metal part in the tape path, very slowly and smoothly
move the demagnetizer away from the recorder until you are at least 3-feet (one meter) away.
6.) Turn off the demagnetizer.
You do not need to hold the demagnetizer in position for a long time; a second or two is sufficient. The only way
you can cause damage while demagnetizing would be to leave the recorder’s power turned on, or to shut off the
demagnetizer while it is close to the recorder or to tapes, or to move the demagnetizer quickly or jerkily. Some
technicians are concerned that the flux from the demagnetizer may damage transistors by strong currents induced
by the play head, even with the power off. This has never happened to my knowledge, but this emphasizes the
need to move the demagnetizer toward and away from the recorder slowly.
Fred
Something ripped from the Internet
Efective demagnetizing applies the strongest possible magnetic field to all metal tape path parts. This requires
that the demagnetizer’s tip makes close contact with the parts, because a magnetic field’s strength lowers with
the square of the distance. So, choose a demagnetizer that creates a strong magnetic field, the stronger the better.
Avoid cheap demagnetizers because they are barely strong enough to demagnetize a cassette machine head, and
will not demagnetize a capstan or a metal tape guide. The Han-D-Mag, made by R. B. Annis Co., is the strongest
unit made. Contact: R. B. Annis Company, Inc.; 1101 N. Delaware Street, Indianapolis, IN 46202. Or contact
them by telephone at (317)-637-9282.
When you buy your new demagnetizer, cover its tip with heat shrink tubing or plastic electrical tape so it will not
scratch the delicate tape heads.
1.) Turn the power off on the tape recorder or duplicator. Demagnetizing with the power on can damage the
recorder’s circuitry.
2.) Turn the demagnetizer on 3-feet (one meter) or farther from tape or tape machines.
3.) Move the demagnetizer in, very slowly, so its tip touches the head(s), guides, and the capstan.
4.) Move across the surface of each part, and from one part to the next, very slowly and smoothly. If you
accidentally move quickly, go back over that part.
5.) After you have gone over the surface of every metal part in the tape path, very slowly and smoothly
move the demagnetizer away from the recorder until you are at least 3-feet (one meter) away.
6.) Turn off the demagnetizer.
You do not need to hold the demagnetizer in position for a long time; a second or two is sufficient. The only way
you can cause damage while demagnetizing would be to leave the recorder’s power turned on, or to shut off the
demagnetizer while it is close to the recorder or to tapes, or to move the demagnetizer quickly or jerkily. Some
technicians are concerned that the flux from the demagnetizer may damage transistors by strong currents induced
by the play head, even with the power off. This has never happened to my knowledge, but this emphasizes the
need to move the demagnetizer toward and away from the recorder slowly.
Fred
Hi Fred, don't worry, I won't get angry. I already did it myself the first day I got the machine. I've had another go at demagnitizing the head and it works a bit better, should I keep doing it? The han- d - mag is the bee's knees but it's three times what I payed for the revox and its americain voltage.I've spotted an Akai model on ebay in europe so I'll have a go at that. I tried picking up a nail with my demag. I started with a 2 1/2" nail and it didn't budge, finally it just picked up the end of a wee skinny 1 1/2" one. Mabye I should try with two of them, get a bunch of pals round for a demag. soirée. Thanks for your help
steerpike2
Super Member
The demag, shouldn't "pick up" things like a permanent magnet - the magnetic field is constantly peaking and falling to zero.
It should make close proximity metallic (iron, nickel) objects buzz and vibrate severely.
When you bring it close to the tape path, you should feel it vibrating as it attracts itself to the metal parts 100 times a second.
It should make close proximity metallic (iron, nickel) objects buzz and vibrate severely.
When you bring it close to the tape path, you should feel it vibrating as it attracts itself to the metal parts 100 times a second.
audiofred
Active Member
ANXIOS
Give it a few more tries to de-mag the heads. You may have accidently magnitized them and it will take a couple of operations to get it reduced.
I remember the color TV days and moving a color TV from one wall to an opposite wall. It could take several times to demag and possibly readjust the "purity magnets" on the CRT. That's another forum.
Fred
Give it a few more tries to de-mag the heads. You may have accidently magnitized them and it will take a couple of operations to get it reduced.
I remember the color TV days and moving a color TV from one wall to an opposite wall. It could take several times to demag and possibly readjust the "purity magnets" on the CRT. That's another forum.
Fred
jan_stevns
Super Member
steerpike2
Super Member
funny current you're using down there
Well, the original poster is in France, so 50Hz AC.
The tape path is just 'soft' ferrous metal; it's not a permanent magnet with north & south poles, so there will be magnetic attraction on both the positive AND negative peaks of the AC wave-form. 2x50 = 100 attractive pulses per second.
(The same principle applies to AC relay coils - the relay doesn't chatter because you only get an attractive force around the magnetic path, not repulsion as well)
jan_stevns
Super Member
nevertheless AC 50 Hertz means the voltage changes polarity 50 times each second, thus 25 positive, and 25 negative highs