Different ways of improving your magnetic sound heads

[Osi Osgood]

I personally have not asked this before, but what are ways of improving the sound output of your magnetic sound heads, beyond the obvious cleaning of the heads. For instance, is it possible for the magnetic sound heads to need a de-magnetizing? Any other things to be done?

[Joseph Banfield]

Osi, this was discussed years back on the old forum and this was what was said regarding demagnetizing the heads:


The good news is that, at least with machines with combined REC/PB heads (the vast majority of projectors) it is possible to degauss the heads by simply have the machine run in rec mode with no film and the trick control set to normal recording (with no input signal). This way the AC bias current (a high frequency - usually around 50 kHz at least - signal added to the signal to be recorded) will degauss the head itself.

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Maurizio

[Lee McCaffrey]

Assuming the heads are correctly calibrated, mechanically and electronically, I don't think there is anything else you can really do. If the heads show signs of wear I believe they can be relapped.
Reading up on tape heads recently, I discovered that most read/write heads (ie heads that both playback and record) have a 'compromise' head gap whereas dedicated playback heads have a narrower gap and record heads a wider gap. Whether a dedicated playback head would sound better I don't know, and unless someone out there made one I guess we'll never find out

[Osi Osgood]

Joseph! Thank you for that awesome news! I will try that on my old work-horse of a Eumig 926 stereo. I am assuming that it has the heads you spoke of. Did any of the posts say how long you needed to run it that way?

[Brian Fretwell]

In reel to reel and cassette decks separate record and replay heads meant there was a delay when doing off-tape monitoring (from short to long depending on the design). I would think that on a film projector they would not use this due to the sound, if in sync on the record head, would be slightly out of sync when played back. The replay head would have to be in the correct position for films recorded on other machines.

Weren't a couple of, very cheap machines, playback only but I doubt that they used heads developed for that.

[Ed Gordon]

Here is what was recommended for open reel tape recorders:

Demagnetizing tape heads should be a part of your regular maintenance routine when you own reel-to-reel recorders. Playing tapes causes the heads and guides to become magnetized due since the tape is magnetic. If the heads become over magnetized, your tapes may start to erase themselves, starting with the very high frequency signals. You may not notice this at first, but by the time you realize what is happening, you will probably will have done irreparable damage to the recorded material contained on the tape.

The frequency of demagnetizing will depend on the amount of work your tape recorder receives. When used on a regular basis in a professional recording studio, heads should be “demagged” once a week. The recommended demagnetizer is the “Han-D-Mag” by R.B. Annis Instruments, Inc.

CAUTION: NEVER turn the demagnetizer on or off directly in front of the heads…make sure you are at least 4-5 feet away. The machine should always be powered down during the demagnetizing process.

To properly perform the process, slowly bring the demagnetizer toward the head stack using a circular motion with the instrument coming close, but not necessarily touching and move over each head and guide. Only a few seconds are needed with each area of the tape recorder. Then slowly move the instrument away from the tape machine until you are at least 4 feet away prior to turning off the demagnetizer.

Keep the demagnetizer away from all tapes, credit cards and other items sensitive to magnetic fields.

Link to article here.

Doing nothing or doing it wrong can result in damaging your soundtracks.

[Joseph Banfield]

Osi, no that post did not mention how long you should run it that way. But just guessing I would say a few seconds would be enough to do what he recommended...but running longer sure would not hurt anything either.

[Steve Klare]

Maybe it's not so much a matter of improving the heads as improving the signal that comes out! I have one machine that has less than one lamp's operating time on the head, and that's as good as it gets. It's not noticeably better than the others.

The signal has everything you need: all the voices, all the music, and all the sounds too. Unfortunately it also comes with baggage: power supply hum, ground loop hum, "tape" hiss, wow and gate chatter.

Some of these things actually get worse through an external Amp because they are bassy and the enhanced low frequency abilities of a big speaker just highlight them.

Hiss is helped out by demagnetising the heads.

The low frequency stuff and the hiss can be helped out by the use of a graphic equalizer or some other kind of electronic filtering. You put a notch where there is trouble.

Ground loops are helped by being careful where everything is plugged in: if you have two devices grounded at separate outlets, you may already be headed for trouble. If you've ever been out somewhere and heard a low, buzzy hum in a public address system, this is exactly what you have. There are various schemes of isolating grounds that fix this in cases where you have no choice (-my own setup is a really bad example!).

Chatter is helped out by keeping the rubber on the pinch roller in good shape to help isolate the motion at the gate from the head. It's hard to get it perfect (-actually impossible!). I have one machine where a new set of guides improved this a lot: I think wear on the old guides was impacting the ability of the presser to keep the stripe flat on the heads and it was jumping up and down with every passing frame.

Wow is a tough one: it's basically a function of how well frame rate is maintained, which especially from a standing start can be hard. Even if you could get your own frame rate to exactly a steady 24 FPS, wow can be recorded into sound tracks so years and years later, you are stuck with somebody else's wow! I have at least one print that regardless of which machine I run it on has a disturbing couple of seconds of wow during some great music, where it hurts the most.

I de-mag my heads every time I rotate a machine back into service. This is supposed (among other things) to improve high frequency response. Then of course my next step is to plug in to a system that rolls-off high frequencies because doing this limits hiss and sibilance (that nasty distortion that you hear when someone says an "s"). Then again, de-magnetizing is supposed to help preserve the sound tracks, so why not?

"Clean" is never a bad idea in one of these machines.

[Paul Adsett]

Eumig's produce virtually zero WOW, even from a standing start. Not so Elmo's, which are prone to wow on some prints, and will often take several seconds to settle down after a standing start. And that's even with the mechanism designed in to keep the flywheel rotating while the film is stopped. So, as much as we like Elmo's, they are certainly inferior to Eumigs when it comes to WOW.

[Joseph Banfield]

And so we're back to film chatter yet again in Super 8 sound films. As I've said a dozen times already regarding Eumig machines you must use an earlier model from the 700 series that only has automatic threading through the gate and must be threaded manually through the sound heads to the takeup reel. Simply add a couple of frames after the film gate before threading through the sound head area and there won't be any film chatter in the sound at all, nor will be the sync be noticed on screen. This trick only works on Eumig projectors that do not have fully automatic threading such as the Mark S super 8 and the Mark S 709. Not only that but with their tube amplifiers you also get none of that nasty Eumig 800 series hum and also get accurate screw type focusing that does not drift during the show!