DIY 802 field coil drivers may be a reality!!

[LowOhms]

@ BillWojo yes i've seen his work, the reason i subscribe to his thread because few months ago i visited a diyer guy who's doing customized / personalized tube amplifier and i get surprise that his using a fieldcoil 6.5 inch fostex driver for his demo tube amp. It sounds so good and seems like love at first sight/hearing the first time i audition the said speaker. From that day i start drooling around and searching for information about the field coil.

6.5 inch fostex fullrange speaker converted to fieldcoil with tube rectified power supply.




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Were you able to determine, from this good sound, what was attributable to the field coil conversion, and what was attributable to the amplification, if this guy is an amp builder. ??


I personally have been designing and building DHT amps since 1982.

One part in an amp, can ruin or " make " the musical experience, about five times more-so than a difference between any alnico and a field coil driver I have owned or heard.

So what I am trying to point out to everyone is, in this, a strange system, ass/u/me ing it was the field coil that was making for great sound, may be your honest / novice error !!


Low Ohms......Jeff Medwin

[GM]

For me, there's only two audible advantages to field coils and that's until the advent of Neo mag drivers there's been none as strong as a field coil can be made for lowest practical effective motor strength [Qts] and its ability to be quickly adjusted to vary it over a wide [Qt] without having to insert any parasitic device[s] in the signal chain and all the sound quality [SQ] potential this implies.

GM

[Elitopus1]

For me, there's only two audible advantages to field coils and that's until the advent of Neo mag drivers there's been none as strong as a field coil can be made for lowest practical effective motor strength [Qts] and its ability to be quickly adjusted to vary it over a wide [Qt] without having to insert any parasitic device[s] in the signal chain and all the sound quality [SQ] potential this implies.

GM

So your magnet of choice would be neodymium? I think I have heard you mention this before.

How about ranking them by strength? From strongest to weakest

Neodymium
Field coil
Ferrite
AlNiCo

Is that correct? I would think that ferrite and AlNiCo would be close.

Also where does cobalt fall in this list?

[GM]

Yes, correct; pound for pound, that's my understanding as borne out doing R&D of SOTA slot car motors, but shouldn't be compared on strength alone since each requires its own optimization and the main reason AFAIK why some of the 1st gen ferrites generally don't perform as well as their AlNiCo counterparts.

Neodymium
Field coil
Samarium-Cobalt
Cobalt
Ferrite
AlNiCo

Again, based on doing R&D of SOTA slot car motors between 1965 [AlNiCo SOTA]-2002 [Samarium-Cobalt SOTA]. Ferrite was/is strictly for toys, entry level racing. Like in most racing, weight was a major factor, so with each material change, weight came down significantly for a given motor strength and since armature, brush technology set the upper RPM limit, the S-C magnet was little more than a small sliver of the AlNiCo. Haven't kept up, but assume they're using Neodymium only a fraction of the S-C.

The Cobalts gave no real improvement overall until we decided to grind some up and tested various powder densities in epoxy molded magnets, which netted a big improvement in weight reduction while maintaining field strength.

AlNiCo and S-C really came alive after being broken, so while we sold them intact, those few of us 'in the know' experimented with various configurations of machine damage with nicked corners working for AlNiCo and slicing the S-C into numerous bars spaced slightly apart; a major pain to assemble, but worth it to a true competitor.

Fun times, really miss them!

GM