I wouldn't suggest demagging a MI or MM cartridge without first removing the stylus assembly!
And despite the controversy (eg. AJ van den Hul) surrounding their use, cartridge demags do work. This was written by Jonathan Carr on the subject many years ago on Audioasylum:
Some comments on fluxbusting.
First, fluxbusting was "invented" by Luxman, and they released a
battery-powered unit in Japan which was copied in short order by
Namiki (the cantilever and sometimes cartridge maker). The Sumiko
unit was a rebadged Namiki.
When you fluxbust, you are trying to get rid of a rather local and
small-scale form of residual or remnant magnetism of the coil former
- perhaps you could refer to it as "stray magnetism." You cannot
really affect the large-scale magnetic polarization of the coil
former, as this is defined by the fact that it is suspended in a
strong powerful magnetic field.
DC leakage from the phono stage, measuring your cartridge with a
tester, DC level shifts caused when you cue a cartridge, and to a
certain extent, even the act of playing an assymetrical waveform (as
can be found on most LPs) will cause corresponding current to flow in
the coils, and this can impart a certain amount of residual magnetism
in the coil former around which the coils are wound. Now, you don't
really want the former to be a magnet in its own right (although you
do want the magnetic field in the gap (H) to induce magnetism (B) in
the core), because if it were, it would interact with the primary
magnet field gap and move erratically (especially if the magnetic
field in the gap is not entirely uniform or symmetrical, which is a
pretty common problem with traditional-style magnetic circuits.)
Also note that remnant magnetization can shift the coil-former's
magnetic bias away from the most linear point in the B-to-H
magnetization response curve, although this is normally accounted for
(we hope).
Are the leakage currents flowing in coils enough to cause local
magnetization of the coil former? As indicated above, in any case,
the degree would be rather small. But again, the details in an LP
groove are pretty small, too. Judging from the sonic before-and-after
effects, something along the lines of the above is likely going on.
I think that ClearAudio winds their coils directly on the cantilever
(fore and aft of the suspension pivot point), so as far as I know,
there is no permeable core to warrant fluxbusting. In other words,
not much return for the risk.
Also, ClearAudio does use thin wire and lots of it, so perhaps you
can burn out their coils if you pump too much power through them.
Remember that when the wire diameter is halved, you have less than
1/4 the conducting area (because the insulation thickness cannot be
reduced beyond a certain point, unless you want insulation pinholes
and broken coils). "Coil rattling" is likely an excessively
picturesque phrase to describe what could happen, but if importer
tells you DON'T, and you want to keep your warranty, I see no reason
to ignore Joe's warnings.
I don't have that much repair data on other manufacturer's products,
but I dare say that most coils are broken due to assembly issues
(lack of stress relief), chemical reaction through insulation
pinholes, physical handling (poking in the wrong place is an obvious
no-no, but if you drop a cartridge or hit it with a sharp, intense
blast of air, you can crack a coil, even if the cantilever appears
intact).
I believe that Van den Hul has stated that degaussing reduces the
number of magnetic complexes in the permeable core. While I am not
going to dismiss this issue out-of-hand, it should be noted that it
will be material-dependent. I don't know what AJ uses, but it is true
that permalloys (especially the 78 - 80% stuff) are pretty sensitive
to this sort of thing. Other materials are not, including the
chemically purified 5N iron used by ourselves and Koetsu, I believe.
Certain magnets are prone to easy demagnetization - namely Alnico. If
you wish to play it safe, you may want to avoid fluxbusting these
designs (which include the Denon 103 family). Samarium cobalt,
neodymium, presidymium and other rare-earth magnets are probably safe
enough. A special case is the platinum magnet currently used in the
top-line Koetsus. It behaves (and sounds) like a super Alnico, but it
isn't nearly as prone to demagnetization. We used it for years on the
first-generation Parnassus, and it didn't seem to mind fluxbusting in
the least.
I suggest though, always contacting the manufacturer before using. Periodic use will add many hours of use to a cartridge.
Now I don't normally demag my LPs and I'll be damned if I can give you a good reason why it should work. I have in the past used on and off a Furutech destat. Was it a huge difference? Not really. I also tried another product from the late Brian Kyle that used tourmaline crystals in a converted hair dryer. Now that made a difference! And not a subtle one at that. There was no question that the record was MUCH quieter. On the other hand, the dynamics also seemed to have decreased. Nor could I seem to get around the downside by reducing or increasing slightly the exposure time. So I gave up.
