ข้อมูลที่น่าสนใจ จาก Mike Lafarve เจ้าของ Magnequest Transformer
::::Amorphous and cobalt core output and parafeed transformers are quite popular among the bottleheads. How do these materials compare technically to the MuMetal cores found typically in line level transformers? What would the suitability of these magnetics be for line level applications?::::
good question... and a full answer would be booklength...
first keep in mind that mu-metal is a particular brand name for a "high" nickel... an alloy which has generally btwn 76 to 80 percent nickel content and then is alloyed with iron and other trace metals.
"low" nickel is a 45 to 50 percent nickel alloy... the balance comprising iron and other trace metals...
the "high" nickels are generally the "kings of perm"... rocket ship high permeabilities... and even at the "incremental" level... their drawback is that they cannot be run very hard at low distortion...
the "low" nickels have the advantage of being able to run double or perhaps triple the flux density of the "high" nickel alloys.... before saturating or becoming limited by distortion...
The senior Mr. Sowter wrote the landmark paper on nickel laminations many decades ago... it's worth a search to find the article (I don't have the url handy) if this topic interests you.
Cobalt (depending on the anneal) will have perm greater than low nickel but not as high as "high" nickel... the advantage of the cobalt is that it's about impossible to saturate.... in theory you can run it up to 18 to 21 kilogauss. I've always run my cobalt at much less flux to keep distortion low...
amoprhous... I don't have ears on experience with amorphous... it is a ceramic glass
material... and in conversations with manufacturer's of the material I've learned that it is highly magnetostrictive.... they advise keeping the ac flux at 2700 gauss or less (as I recall the conversation).... which makes it impractical for power level output devices (
say even an EXO-45)....
for a zero db MOL input tranney or MC step up... it might well be worth investigating... the other disadvantage of the amorphous cores is the very limited range of core sizes that are made... so you lose considerable design flexibility....
traditionally.... the high nickels have been reserved for applications with MOL's of zero db and less. As a rule of thumb the "low" nickels are used in line level apps with MOL's of zero db to say plus 20db.....
again, traditionally, (i.e., if you study archival designs by the greats at companies
WE, Peerless, UTC, Triad, etc)... you would find that these exotic materials were deployed carefully and usually run at only a fraction of the manufacturer's published max flux densities.... this in order to keep distortion down....
all high perm materials are moreso skitzy... compared to say M6 grain oriented steel.... by skitzy I mean several things....
1) the materials are very sensitive to their anneals... and you can have considerable lot to lot variation in perm and distortion... you must be very careful in who you buy your materials from and rely on their expertise and quality control....
2) the exotics are sensitive to mechanical stress and strain... handle them roughly and they will be degraded in performance...
3) they are moreso sensitive to electrical stress and strain... overload them electrically and you can/will alter their magnetic properties...
also... recall that the exotics must generally be run at much lower flux densities.... if you value "clean" performance....
high nickel say a max of 2500 to 3000 gauss (best designs kept the flux to 1,000 gauss and less)
low nickel... rough rule of thumb keep the flux below 10 kilogauss and aim for six to eight kilogauss....
amoprhous.... again... no direct experience... but technical department at manufacturer recommended keeping ac flux to approx 2700 gauss... dc flux can be run quite, quite high accdg to manufacturer (dc flux up to 15kg).
cobalt.... manufacturer's claim this material is good up to 18 to 21 kg. I
to run it at considerably less flux density to preserve magnetic headroom...
Personally... I think some of the best sounding core materials are the "domain refined" silicon steel laminations...
if we look for a good practical balance btwn core losses, permeability, and flux capacity... the newer generations of silicon steel are really quite superb.... and are bargain priced relative to the exotics...
some of these "new" generation steels go by names
M4, M3, M2, MOH, High B and etc...
I just had a conversation yesterday with a laminations engineer at a c-core house re: these "newer" materials...
the aim (goal) of the "newer" gen of steels is to reduce the angularity of the discrete domains (I'm sure I am saying this wrong)... M6 might have a plus or minus seven degree variation in the "orientation"... by special cold processing techniques the "new" gen steels reduce this "randomness" to 1 to 2 percent accdg to the materials engineer.
ironically... the new generation "refined domains" steels... were developed in an economy/performance matrix... wherein many designs are limited in size and weight considerations... and by further refining the domain fiels... studies found that you could run the core at correspondingly higher flux densities while drawing equal or less exciting current than say M6... so you pay more for the material but since you can in theory run it harder you use less material in your design to offset the increased costs....
that is... if your concerned about "costs".... again, when we use these "domain refined" materials I still run them at the same levels I would M6 and take the lower losses and higher perms to the "performance bank"....
don't know if I answered your questions or not... let me know....
Mike
