DIY 802 field coil drivers may be a reality!!

[BillWojo]

I don't understand this "bucking" either. Jeff, can you give us a detailed explanation of what your referring to?
As I understand it, a FC motor uses a strong electromagnet fed with a robust, filtered and regulated DC voltage. There is no ripple or any disturbance in the field coil gap either from the DC power supply or induced by the voice coil. As long as the DC power supply is working properly, there is never any change in the magnetic flux in the gap surrounding the voice coil. It remains the same from day one to the date that the system is retired.
That is very unlike alnico magnets that are always loosing there magnetic field strength due to aging, a well documented problem. Not to mention that over powering an alnico driver will also substantially damage the magnetic fields strength. Also well documented. And that may be the weakness in alnico or any permanent magnet structure. If playing a strong signal through a voice coil can damage the alnico magnet, what is a weaker signal doing to the magnetic field in the gap? It may be causing distortion of the signal being reproduced.
Think about it.

BillWojo

On Edit: Steve, I want to thank you for your explanation, it gives one enough to calculate the coil specs.

[LowOhms]

I don't understand this "bucking" either. Jeff, can you give us a detailed explanation of what your referring to?
As I understand it, a FC motor uses a strong electromagnet fed with a robust, filtered and regulated DC voltage. There is no ripple or any disturbance in the field coil gap either from the DC power supply or induced by the voice coil. As long as the DC power supply is working properly, there is never any change in the magnetic flux in the gap surrounding the voice coil. It remains the same from day one to the date that the system is retired.
That is very unlike alnico magnets that are always loosing there magnetic field strength due to aging, a well documented problem. Not to mention that over powering an alnico driver will also substantially damage the magnetic fields strength. Also well documented. And that may be the weakness in alnico or any permanent magnet structure. If playing a strong signal through a voice coil can damage the alnico magnet, what is a weaker signal doing to the magnetic field in the gap? It may be causing distortion of the signal being reproduced.
Think about it.

BillWojo

On Edit: Steve, I want to thank you for your explanation, it gives one enough to calculate the coil specs.

Hi Bill,

Decent question, nicely put, thank you Bill..

I will not be able to help you, the way you would like. Mine were listening observations, between myself, and a close friend who spent his lifetime in the movie theater service and ownership business. The listening covers literally hundreds of movie-quality field coil speakers between us, mostly Western Electric, RCA, and some modern ones. He is far far more experienced than me. I only "audiophile" owned 13 of the RCA Mi-1428B or 1443 field coil drivers.

One can ascribe "reasons" for one technology being better than another, as you do, and you nicely discuss, in this exchange between us. It is called theorizing. Nothing wrong with that. I did the same thing 25 years or so ago, when I was using field coils. The main thing in audio to me is " how does it sound??"" It seems, if I read Elitopus correct, he tried a 802 field coil recently and reported his " first listening impression was - it was not High Fidelity, but OK for Musical Instrument or Guitar reproduction. " if I were " hot to trot " on 802 field coils as you are, I would be questioning him further, as he seems to have direct 802 experience.

As for me, and what I hear in 2017, I still feel (a) amplifier implementations, (b) system wiring, and (c) capacitor choices, make far greater performance differences, and offer room for real improvement, than any of these speaker ( alnico / ceramic / or field coil ) topics one may discuss. The better ALTEC drivers, are NOT the weak link, but I find from my own building and experimenting, and LISTENING, (a ) though (c) certainly are.

Have fun, enjoy the hobby, I do ! Lately, I have been trying to mentor others, privately. Its a good thing to do, some lovely people did so for me, when I was younger. We had a Type 46 Direct Coupled two stage DHT amp " born " this afternoon, ( first fire-up) and the DIY builder seems very pleased. That is exciting, it was my own, from-scratch design.

Low Ohms ..... Jeff Medwin

[mah]

mah,

I am plenty credible. And I offered sound and credible advice. Who are you, who probably has zero field coil listening experience, to contend that my comments are ill advised?? Me, and my closest of audio friends have direct experience with hundreds of such field coil drivers, over many years and many venues.

I was very clear in what I stated, that the coils buck each other. Everyone hears it, but not everyone recognizes what they are hearing.

This is just my opinion. I am free to state it up here.

No rigid theoretical proof, ( which may or may not be correct ), is needed. The proof of the pudding ......is in the eating.

You, and others, are welcome to have a different opinion, but it would be much more credible to me and others, if you had field coil experience..

This of little consequence to me. I am happily using an 802D, remagnetized by GPA in 2015, as the top-end on A7-800s. My system's wiring, and amplification, is at a level that very much pleases me.

This is an open Forum where we can share our listening experiences, hopefully for the betterment of all. Each individual reader has the mental capability to discern who or what ideas they prefer to follow in any audio discussion, ....it is a right we all have.

Now, for a fifth time, lets get back to the idea that "we two" do not post after each other in the same thread. Its a waste of bandwidth. Anyone can see that is needed. Are you willing to address that ??

Jeff Medwin.....Low Ohms.

LowOhms,

You make an appeal based on a call for openness and then expect me to forgo that openness because you don't like some of my comments. Huh?

Just take responsibility for what you say in public( i.e. the internet) and let this thread(and Forum) return to its original purpose.

Don't try to self-interestedly censor me again!!


Be very careful and relative, legally, with what you say in any reply.

[mah]

Bill, Because I can't get PM to you, I'll put this up on the forum.

Rusty voice-coil gap on compression drivers, if not too far gone, may respond to Ultrasonic Cleaning. If you have a metal cleaning specialist in your vicinity it could be worth a chat. Mention that the concentric phase plug is an aluminium alloy.

[gvasale]

Evaporust may be a little more effective than ultrasonic. You would have to try samples of both to find which is better. No special equipment needed for Evaporust.

[BillWojo]

Surface rust is not a real problem except that indicates that the protective coating (zinc or cadmium plating) is used up. The problem is when the rust is deeper and changes the physical dimensions of the gap. I don't have the math handy to prove it but I highly suspect that even a small change in the gap width will have a much larger change in the gap magnetic field strength.
Thanks guys.

BillWojo

[mah]

Bill, look what this project could lead to:

Western Electric 13A Horn


Western Electric 16A Horn

[BillWojo]

Marshall, thanks for the links. What I find very interesting is a bit of information in the first link.
Seems the Western Electric 13A horn was actually manufactured by the Victor Talking Machine Company. Look at the brass plate in the last picture.
I live less than 15 miles from the old plant. That's really cool that these were built locally. Now if I could only find a set. LOL

BillWojo

[GM]

The problem is when the rust is deeper and changes the physical dimensions of the gap. I don't have the math handy to prove it but I highly suspect that even a small change in the gap width will have a much larger change in the gap magnetic field strength.

I don't remember there being a simple ratio, but making the gap irregular causes non-linear distortion, though in a compression driver I doubt it's a mechanical issue, just increased VC heating. If the gap is narrower, then it can shift the frequency response lower with increased VC heating and vice versa, so tis better overall to increase the gap a tiny bit with proper tooling to make it uniform, clean, cooler running.

GM

[mah]

Inside shots: Field Coil conversion for JBL, Altec, and Western - diyAudio