Checking magnetism

[cjacek]

Tim [Beck], I'm sure you're going to respond 'cause I recall you mentioning a way to check for tape path magnetism recording high freq tones and replaying them, several times, looking for dips in db.

Can you recommend a specific frequency and level to record on tape, for both a 7 1/2 ips recorder [TASCAM 388] and 7 1/2 - 15 ips recorder [TEAC 3440 and TASCAM 34]?

Also, how long should I record the freq and, most importantly, how many times replay to see if I have a magnetized path?

Lastly, if I may, can you recommend re cassette portas, like the 244 ?

I guess, I'm looking for a procedure, from A to Z.

THANKS!!

[Beck]

I’ve always used the procedure outlined by J McKnight of MRL. See the attached pdf (page 2, lower right).

Since high frequencies are erased first, ideally you want to record 16k or higher. With the portastudios the highs drop off quite a bit before that, so keep in mind the first playback of a 16k tone will be down anyway. Use that first playback as the reference. If you have a magnetized tape path it will continue dropping little by little with each pass. Ten to fifteen passes should be enough. With the 246 you can switch off the dbx, which is recommended. Some models you can't switch off the NR, so you might try a 15k tone in that case.

[cjacek]

Excellent, thanks Tim!

[cjacek]

If I have magnetized heads, will it gradually drop to zero [from the start point] or will even 1 or 2db down be enough? Thanks Tim!

[Beck]

Half a dB after several passes indicates a problem. 1 dB would cinch it... you have a significant problem and need to degauss.

[cjacek]

Ok, thanks again Tim.

[bloomboy]

Whoa... so how often should I be demagging, assuming that I really don't want to lose that high-frequency content? I've been demagnetizing once a week usually, stepped it up to every five days over the last couple of weeks because I've been recording pretty much all day every day. I'm doing some pretty extensive bouncing on 8 tracks, so the tape is seeing a lot of play... probably in the ballpark of 1-200 passes per song when everything is finished.

Is once a week enough? could it hurt to demag at the end of every day? (assuming the power doesn't go out while I'm doing it) I clean the heads and tape path religiously- every break pretty much, which evens out to about every two or three hours of recording time, so I'm not too worried about that side of things.

Also, would plugging the han-d-mag into a UPS maybe be a good idea? Demagnetizing scares the hell out of me

[jjones1700]

Originally Posted by bloomboy

Demagnetizing scares the hell out of me

Me too. I need to do it to my 909 but don't want to screw anything up in the process. Also, the only demag I have access to at the moment is an on RadShack wand type. I think I read somewhere that the wands worked well on cassette, but weren't up to the task of reel to reel. Is that right?

[bloomboy]

I use this:

http://www.usrecordingmedia.com/handmagdebyr.html

I've never used a radio shack demagnetizer but I believe that's correct. And I didn't mean that I was worried about doing something wrong and screwing up the tape deck- just if the power cuts out while the demagnetizer is near the heads then I'm screwed.

[jjones1700]

I haven't used the RadShack one, and I bought it about 15 - 20 years ago.....LOL

[cjacek]

Originally Posted by bloomboy

Demagnetizing scares the hell out of me

Me three.

[Beck]

Once a week is plenty. It takes some time for the tape path to become magnetized.

Degaussing is not that bad. As long as you know what you’re doing the worse thing that can happen is that the power would go out (power usually spikes when it fails, which is bad).

Power has always been stable where I live… almost too stable. There is something fun about losing power and lighting candles, especially in a storm. Speaking of which… don’t degauss during a storm keep pets and kids out of the room and close the door. There are many sources on the web for procedures, most of which we’ve posted in this form at one time or another.

Lately I’ve been plugging into an APC UPS during degaussing just in case. It only takes once to screw things up, so I decided to play it safe. Before that though I did the procedure for 25 years with direct municipal power.

Back in the day, we never checked a tape path with a meter before degaussing. It was just part of the maintenance schedule.

The tests by McKnight are useful to prove the phenomenon, but in a working studio your tape path is going to become magnetized.

Magnetometers and such are for people that are trying everything they possibly can to put off degaussing indefinitely.

[cjacek]

Originally Posted by Beck

Magnetometers and such are for people that are trying everything they possibly can to put off degaussing indefinitely.

True!

[jjones1700]

Forgive my newb question, but what happens if the demag procedure gets cut short (power goes out, etc.)? Can't you simply start over and achieve the correct results?

[cjacek]

Originally Posted by jjones1700

Forgive my newb question, but what happens if the demag procedure gets cut short (power goes out, etc.)? Can't you simply start over and achieve the correct results?

It will leave the tape path permanently magnetized, especially if you use a strong unit, like the HAN-D-MAG. [In that case, a change of heads is neccessary]. If, on the other hand, you use one of those cheap wands and do it incorrectly or the power goes out, you can probably use the Han-D-Mag to get rid of the magnetized parts. That's my understanding so please, people, correct me if I'm wrong.

[Beck]

A degausser is an electromagnet that oscillates between a positive and negative charge very rapidly. The process of degaussing requires that this oscillating electromagnet be applied and removed gradually. Theoretically if the electromagnet cuts out at full power in close proximity to the tape head it will leave a charge with the polarity of whatever point the cycle was in when the power failed.

The act of slowing moving the degausser in and then slowly away has the effect of gradually increasing and then decreasing the power. There are (were) pricy automated degaussers that increase and decrease the power internally without having to physically move anything. There are also cheapy little cassette degaussers that demagnetize the heads only in this way. They look like a cassette tape.

There is a spike in power stronger than the nominal rating of a conventional degausser when it is switched on. There is a similar spike during a power failure. You don’t want the device near the heads when this happens.

As Daniel pointed out it can leave a charge that will take a much stronger degausser to neutralize. A degauuser has to be stronger than the magnetic force present in the object being degaussed.

Well, thank God most people didn’t use the Annis Han-D-Mag, and the people that did were more likely to know what they were doing. So now all one has to do is get one of those and use it correctly.