Field coil driver for OB design advice sought!

Well... why do you think I replaced the original coil of 1470 ohms with a 15.1 ohms? The field coil need 10-30 watts of power (source: Hentai user who made a few of these from scratch, see ProjectRyu thread).. .after you make the calculations you realize you need 1-2 amps at 12 volts... that's battery territory. The magnetic strenght is currents x turns in the coil... so making a coil with less turns with thicker wire means you can get same amgnet strenght with higher amps but also you need a lower voltage at the power source.
Hentai did not use any humbucking coils.

That sounds good except for a couple of things.

First, vintage Field Coil Speakers operate at a higher voltage because they were serving as the choke of its tube amp, with high DC voltage directly from the tube amp. That’s how they did it. Does that sound about right? Not pretending to be an expert here. So anything vintage or a vintage design will be like this.

Secondly, some people deep in the field feel that the higher voltage gives a better sound. I would love to go with the 12 V power supply battery because I use a batcap for 12V gear, which is like a very high performance battery meant for competition audio, that discharges as fast as a capacitor, but in this case fast discharge doesn’t matter so much since it is only to keep the field coil field constant.

Again, I’m no expert on this. Does that sound about right? Or am I off a bit here?

So if you want to go 12 V you can get Voxativ (?) Field Coil Speakers for tens of thousands of dollars. There are less expensive FC 12V speakers, probably only $3000-$5000 a pair.

Or you can roll your own and go that way. Whatever works I guess. But I think we are talking about getting a good high voltage supply for more vintage designs. But you are absolutely right, there are 12 V designs also.

Oh yeah, there are the Musical Affairs loudspeakers that require 12 V DC, but Hans the owner and brains And designer died and the company fell apart and they are scarce to find. Again, tens of thousands of dollars for a pair of loudspeakers.
 
Personally I was not aiming for very high quality sound reprodution... just sniffing arround at the field coil thing.
This table shows AFT model 7 - a maximum of 28.5 volts... much closer to the 12 volts I was talking about than 100+. I also suspect the value of the Qts is not taken into account here (for perceived sound quality) the minimum value in the table was 0.56 ? and maximum of 1.75... but when people buy speakers they search for Qts of 0.15 to 0.7... something is not right here. Are these units meant to be heard at higher Qts? Is that what people are hearing? (and for higher qts you need lower value of magnetic strength).
 
So if you want to go 12 V you can get Voxativ (?) Field Coil Speakers for tens of thousands of dollars. There are less expensive FC 12V speakers, probably only $3000-$5000 a pair.

Or you can roll your own and go that way. Whatever works I guess. But I think we are talking about getting a good high voltage supply for more vintage designs. But you are absolutely right, there are 12 V designs also.

Oh yeah, there are the Musical Affairs loudspeakers that require 12 V DC, but Hans the owner and brains And designer died and the company fell apart and they are scarce to find. Again, tens of thousands of dollars for a pair of loudspeakers.


Hi Gary,


Hans from Musical Affairs has, before he took the big black ship, used EMS drivers from France. Easy to find and less than several thousand dollars, SOLEN imports them to the American continent.
The SUPRAVOX drivers are as well not exactly cheap, but are attainable, if one really wants a FC.
All are nominally 12 V.


For my Fertinacoustics FC drivers, I tried several PSUs (I drive them at 12,5 V), but after some time I´m always back on Li-Ion batteries. I would be interested in current-regulated FC PSU, but not being an electronics guy, all searches for infos, plans or even readymade modules weren´t successful.
So, batteries for me.


All the best


Mattes
 
Hi Gary,


Hans from Musical Affairs has, before he took the big black ship, used EMS drivers from France. Easy to find and less than several thousand dollars, SOLEN imports them to the American continent.
The SUPRAVOX drivers are as well not exactly cheap, but are attainable, if one really wants a FC.
All are nominally 12 V.


For my Fertinacoustics FC drivers, I tried several PSUs (I drive them at 12,5 V), but after some time I´m always back on Li-Ion batteries. I would be interested in current-regulated FC PSU, but not being an electronics guy, all searches for infos, plans or even readymade modules weren´t successful.
So, batteries for me.


All the best


Mattes

Hans did use those drivers, but they also did a special thing for just him. They shipped him the drivers partially assembled, so that Hans could put leather surrounds and spiders on and do other special things. That is what attracted me to Oleg’s Field Coil drivers - he uses leather surrounds. To be fair I have not heard Musical Affairs speakers, but it seems like Hans was a real innovative guy when it came to such things. In a year or two I could’ve been ready to buy some of his speakers but alas, the big black ship.

Like I said, I am using Oleg’s lab8 Field Coil drivers (Still a long ways from being fully broken in), powered by three 36 V DC power adapters in series, and I like what I am hearing a lot. And I have a feeling the DC voltage is very clean.

You might look into a BatCap 3000, I’m told equivalent to a 3000 farad capacitor, and much like a car battery. I have used them for years with great results for a Audio things that take 12 V DC. Be aware that such batteries also make their own chemical noise, so I use an iFi Audio DC purifier and that helped. If you do use their purifier, just make sure that you don’t draw too much current through it.
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HelmutHolz

Member
Paid Member
2009-03-16 7:53 am
Germany
Nice discussion.
I started with Fertin field coil in year 2003, actually I use a pair of Sonidos SWR 222(8"), also 12 V (about), the speakers are available with constant current PSU, different currents (4 positions are given) for adjusting the QTS of the Speaker: open baffle, closed, vented, horn. So there are Speakers out there with adapted constant current PSU and they cost less than 700€ incl. the shipping in Europe. And the Sound is quite good, comparable to the Fertins Mk3 I used to have (the field coil fried the voice coil).
 
... So he used also phenolic spiders an leather surround. And this drivers sound much better than original EMS
How do you know they sound better? Presumption? Someone's testimony? Personal experiente? I have noticed people saying about Oleg Rullit's modified drivers that they are "artwork" and that sort of comments... so I must presume some are inclined to say "they" sound better because of the way they are "dressed"... and yes I am aware of this video: YouTube but I consider that in the rumor category, from personal experience I can tell you that leather absorbs some of the highs so it may only work on large speakers where the highs never (or in diminished quantity) reach the surround. Notice that for the 10 cm unit (YouTube) they eliminated the surround - zero leather here - and voila! the highs now go higher.
 
How do you know they sound better? Presumption? Someone's testimony? Personal experiente? I have noticed people saying about Oleg Rullit's modified drivers that they are "artwork" and that sort of comments... so I must presume some are inclined to say "they" sound better because of the way they are "dressed"... and yes I am aware of this video: YouTube but I consider that in the rumor category, from personal experience I can tell you that leather absorbs some of the highs so it may only work on large speakers where the highs never (or in diminished quantity) reach the surround. Notice that for the 10 cm unit (YouTube) they eliminated the surround - zero leather here - and voila! the highs now go higher.

Unless you want to buy both kinds of speakers and figure out the best power supplies each and do your own subjective measurements, like I said before, I am going by the word of those who probably would know. But you should always do your homework, and in this case it means investing in both types of speakers, an excellent high-voltage power supply, and then just do listening tests. Up to you what you want to do.

Either way you go, I bet if you invest a lot of money in 12 V full range Field Coil Speakers you will have excellent results also.

So many possibilities… :)
 
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paulfk

Member
2008-10-15 3:00 pm
Unless you want to buy both kinds of speakers and figure out the best power supplies each and do your own subjective measurements, like I said before, I am going by the word of those who probably would know. But you should always do your homework, and in this case it means investing in both types of speakers, an excellent high-voltage power supply, and then just do listening tests. Up to you what you want to do.

Either way you go, I bet if you invest a lot of money in 12 V full range Field Coil Speakers you will have excellent results also.

So many possibilities… :)
I listened to voxativ field coils in ampeggio due in a dedicated listening room with Yamamoto 45 and I remember at the time it was on par with my DIY front horns. Thinking where I am today I would say they were both very ordinary, that also means that most of what I've heard sounded broken. I have been preparing Oleg Rullit's open backed speaker boxes with biscuit joints and will be making the driver holes before glueing them up. Then it's on to the power supply. When I collected the silver lab 8 drivers I was surprised how light they are but then they don't have huge permanent magnets.
 

thisisvv

Member
2012-04-19 3:03 am
I am starting to read and learn about Field Coil. Rather spending $$$ i was hoping i could make my own using japense washi paper. I am preety sure there are other things as well. Anyone made /recommend any place i can buy these field coil or suggest. I plan to have Open baffle Field coil with some ribbon tweeter or Bass unit
 
I am starting to read and learn about Field Coil. Rather spending $$$ i was hoping i could make my own using japense washi paper. I am preety sure there are other things as well. Anyone made /recommend any place i can buy these field coil or suggest. I plan to have Open baffle Field coil with some ribbon tweeter or Bass unit

I have a coil winder that I’ve never used, but my plan was to wind my own Field Coils. Why not? It won’t cost that much, and my Field Coil Speakers are full range. While the lab8 speakers from rullit won’t hit the lows of the subwoofer, I am amazed at how low they go. I play the violin and have played in orchestras for over 50 years, and can tell you that artificial low subwoofer bass is nowhere to be found in real music. Now if you are talking about amplified music like electric guitars, etc. that could be different. But if you go to a rock concert the only thing you hear is speakers, not actual instruments.
 

paulfk

Member
2008-10-15 3:00 pm
I am starting to read and learn about Field Coil. Rather spending $$$ i was hoping i could make my own using japense washi paper. I am preety sure there are other things as well. Anyone made /recommend any place i can buy these field coil or suggest. I plan to have Open baffle Field coil with some ribbon tweeter or Bass unit
You could buy old telefunken, Siemens or klangfilm field coil drivers on eBay and replace the cones if needed or that's what you want to do.