DEMAGNETIZATION

Figure 4: The R.B. Annis Han-D-Mag has a curved tip for hard-to-reach places

The head assembly relies on electrodynamic magnetism to function. Static magnetism—as found in magnetic screw-drivers and loudspeakers—is the devil. Head demagnetization is considered routine maintenance, but only when performed by experienced personnel. Use only the R.B. Annis Han-D-Mag, as shown in Fig. 4. Throw away cheap demagnetizers with an on/off switch as these are extremely dangerous.

Before demagnetization, remove any tape from the machine and turn the power off. Power-up the demagnetizer away from the machine, and do not remove power until the device is at least three feet from the machine. (I am being overly cautious, and I fully understand the inverse-square law). Once powered, slowly move the demagnetizer tip toward the first head—the Han-D-Mag has a protective plastic tip—slowly moving up and down. Continue this motion while gradually pulling away from the heads until each has been demagged. Be sure to demagnetize your tools before playing the test tape. Inexperienced demagnetization is more dangerous than doing nothing, so again, do not attempt this process unless you are confident. An experienced technician will surely show you how to safely use “the force.”

TEST TAPES AND ALIGNMENT BASICS
Playback alignment requires reference tones from either a test tape or the “project” tones that accompany the master tape. A test tape is typically a full-track recording (across the full width of the tape). Unless a test tape claims “compensation for multitrack reproduction,” it cannot be used to set low-frequency playback level. No machine has a low-frequency record adjustment. In nearly every instance, accurate low-frequency playback adjustments are made after first recording a bass sweep, which requires an oscillator capable of the same. On a three-head deck, it is possible to playback while recording. On a two-head deck, the process requires more patience. (Full alignment procedures will be detailed next month in Part Two of this article.)

The most important reference tone is 1 kHz for operating level, specified in nanoWebers per meter (nWb/m). The Equalization (EQ) Curve is specified as either NAB AES (American Standard) or IEC CCIR (European Standard). Make sure the test tape you buy or rent is the correct speed and EQ for your machine. Most narrow-format machines are calibrated as per IEC CCIR with rare exception. The most common error is to attempt narrow-format calibration using an “American” NAB test tape.

Professional machines have a generously wide adjustment range, and many narrow-format machines have extremely limited range. Many Tascam MS-16s do not have enough range in the bias control to accurately find the peak at 10 kHz. Most Fostex machines have a continuously variable bias capacitor. Without a voltmeter or oscilloscope, it is possible to be on the wrong side of the bias peak.

Note: Modern high-output tapes are not a good match for older pro or narrow-format semi-pro machines, which may not have enough current to fully erase previously recorded material. Compared to older generations of tape, modern tapes can be an additional half-mil thicker than the original “1.5 mils,” for which the machines were designed. (One mil is 0.001 inches or 25.4 microns.) Thicker tape is harder to pull and, if tension is not adjusted, can cause more than the usual amount of headwear. Attempting to operate any narrow format machine without its integrated NR is not recommended, nor should the operating level be changed from the manufacturer’s recommendation. While it may be possible to disable NR for selected tracks, there will never be enough headroom to sufficiently lower the noise floor for all tracks.

TRACK WIDTH PHENOMENA
The weaknesses of analog tape are also its strengths, but to compete with digital, the analog envelope has been pushed to new limits. The three high output tape formulations—BASF/EMTEC SM900, Ampex Quantegy 499 and the former 3M product, 996, manufactured by Quantegy as GP9—are not new, but when combined with the “recent” 1-inch, 2-track format, noise is at an all-time low and many of analog’s idiosyncrasies are minimized. I won’t say it’s almost like digital. (Who said that?)

LAST LINKS
At this point, I have enough room to tell you to put up a new reel of tape, route an oscillator set to 1 kHz to all tracks, and press Record. (Noise reduction should be bypassed.) Observe input vs. playback, and note the differences. If input does not agree, you need a voltmeter to confirm that the incoming levels are good. Or route the oscillator to one track at a time to see if there is an improvement (much less fun). Follow the machine’s instruction manual for record level and input calibration. Buy a manual if you don’t have one.

The Web offers numerous useful resources. For more information about MRL and BASF test tapes, visit http://home.flash.net/~mrltapes/and www.emtec-magnetics.com. Quantegy (www.quantegy.com) also offers a really cool interactive site that can show you how to align for elevated levels.

Eddie Ciletti can be reached at www.tangible-technology.com.

Back to Page 2, Page 1; Manufacturer/Company List

Reprinted with permission from Mix Magazine, August, 2000
© 2000, Intertec Publishing, A Primedia Company All Rights Reserved

MDI/Precision MotorWorks
Motor rebuilding, parts, rollers and supplies
241 White Pond Rd.
Hudson, MA 01749
978/562-4420
www.precisionmotorworks.com

Media Tech/Northern Lights Audio
Studer specialists
972 N. Fifth St.
New Hyde Park, NY 11040
516/291-0281
www.northernlightsaudio.com

RTZ Audio
Redesigned Ampex electronics
P.O. Box 872
Alpharetta, GA 30009
770/346-9704
www.rtzaudio.com

Sequoia Electronics
Ampex and Scully parts supply
422 Avenida Abetos
San Jose, CA 95123
408/363-1646

Sprague Magnetics
Heads, repairs and Ampex and general parts
12806 Bradley Ave.
Sylmar, California 91342
818/364-1800
http://sprague-magnetics.com

TSI-Technical Services Inc.
Ampex parts
Vern Sauer
107 S. Prindle
Arlington Heights, IL 60006
847/392-2958