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Long reply from J.Carr

192.44.136.113

Posted by Noam on April 11, 2001 at 16:31:55

In Reply to: to demag, or not to demag? posted by clay-boy on April 11, 2001 at 14:35:18:

You might be sorry you asked! I don't think too many people have more knowledge on this subject than Jonathan. I hope he doesn't mind this quote (verbatim from another list) - I kept it for reference and I think he's way too busy to read the forums these days.

Noam

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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
stonking powerful magnetic field.

DC leakage from the phono stage, measuring your cartridge with a
testor, 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.

Stewart wrote:

>The old Sumiko Fluxbuster and the new Aesthetic demagnetizer work on
>the same basic principle where a small AC signal is applied to the
>VC and it effectively demagnetizes the pole piece upon which the
>coils are wound.<

No, the only MC that has coils wound on the polepiece is the
Dynavector. Also, given the need to avoid vaporizing the coils and
the fact that there is no way to remove the primary magnetic field
(unless you remove the stylus assembly from the gap) the
effectiveness of demagnetizing probably isn't very high. That doesn't
mean that the effect isn't audible, however.

>I believe the newer Aesthetic ramps the voltage down at the end of
>the cycle to avoid the spike at turn off which can remagnetize the
>piece.<

I think that every cartridge fluxbuster made to date has had an
amplitude envelope which was gradually ramped down over time. It
wouldn't work right if not. The operating goal is to send an AC
signal with enough wattage through the coils to saturate the existing
local magnetization of the core out of existence, then smoothly
attenuate the signal to zero.

>The Cardas Sweep record applies a similar signal but through the
>record grooves to achieve much the same. The use of the Cardas may
>be the ticket for Clearaudio owners.<

Um, as mentioned above, the Clearaudio probably doesn't even have a
permeable core, so the need for fluxbusting would be far, far less.

George Cardas contends that the "demagnetization" should occur with
the core in the exact configuration that it would be when playing an
LP. Hence his disk. In practice, though, the amount of voltage that
one can derive from an LP and still have cartridges track the grooves
does not come close to that achievable with an electronic circuit.

Still, one can accomplish a very quick and dirty demagnetizing job by
disconnecting the tonearm cable from the preamp, placing a shorting
loop across the ground and hot of each channel, and playing an LP
with the cartridge. In other words, one would drive the raw output
from the cartridge into itself, using the voltage generated by the
coils to fluxbust the core. I don't think that ClearAudio or AJ can
complain too much about this level of fluxbusting.

Paul wrote:

>The effect was a lessening of coarseness and harshness and anytime
>the cartridge started sounding edgy or seeming to be on the verge of
>mistracking, we zapped it.<

In my experience, fluxbusting typically addresses a murkiness or
fogginess in the sound. Transparency and intelligibility usually go
up after fluxbusting. Edginess tends to be a secondary or tertiary
effect.

Jeff wrote:

>I've wondered why some manufacturers still use ferrous/polar cores
>for their coils. (Yeah, it increases output ...)<

The use of iron, permalloy, sendust, amorphous alloys etc will
concentrate a greater percentage of the magnetic flux through the
core. The main point is phono stage compatibility, and how it relates
to cartridge voltage. If only there were more phono stages available
that had super s/n ratios and mind-boggling low-level resolution. If
that ever happened, I'd drop the output voltage, and the permeable
core would be the next thing to go. I'd love to ditch the permeable
core, as I'm not a fan of magnetic materials in general. But
nonetheless, a really good permeable like 5N iron still sounds better
than wrapping lots of wire around a non-permeable core. So unless
there are more phono stages that can deal gracefully with ultra-low
signal levels, I don't think the permeable core will go out of
fashion.

>it also increases mass.<

Not necessarily. For example, while carbon fiber is a low-mass
material, ruby is not. And compared to a permeable core, a
non-permeable core will require a much greater amount of wire wrapped
around it to generate an equivalent output voltage. That means
greater DCR, greater output impedance, greater capacitance, and more
mass. In fact, the original versions of the Denon DL-1000 (before it
got the "A" suffix) used lightweight aluminum wire to counteract that
very same increase in mass. And finally, because of its location, the
mass of the core has the least effect on the high-frequency resonant
point; the mass of the cantilever and stylus have a far greater
effect.

>Does anyone know which cartridges do (not) use such coil cores? Do
>Lyras? Do Transfigurations? Do Koetsus? Etc., etc. ...<

I don't know exactly what Transfiguration uses, but we use the same
stuff as Koetsu - 5N high purity iron.

Brian wrote:

>As far as it helping the sonics of a Sumiko Blue Point by
>de-magnatizing it, nothing short of breaking the cartridge and
>finding another different (non Blue Point) cartridge will help it
>sound smooth on the top end.<

Personally, I think that many cartridges are unjustly maligned
because of weak links in the reproduction chain elsewhere, and the
Blue Point is one of them. It benefits hugely from a good tonearm,
turntable and phono stage, but probably doesn't get them that often,
given its own price point.

For some time, I was running a Blue Point on an Immedia RPM-2,
Wheaton Triplanar tonearm and through a Connoisseur 2.0 phono stage.
I removed the blue metal tab from underneath the magnetic gap, but
otherwise the BP was kept stock. It sounded great! Lively dynamics,
lots of toe-tapping bounce, and none of the high-frequency
aggravation that you normally get with the Blue Point or BPS in most
systems.

Quite enjoyable, in fact.

regards
jcarr

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