AudioCircle
Audio/Video Gear and Systems => The Vintage Circle => Topic started by: Bumpy on 1 Aug 2017, 12:18 pm
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I am developing an interest in this type of driver, and have some simple questions.
Do field coil drivers have defined impedance (say 4, 8 16 ohms) like permanent magnets?
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Field coil replaces the permanent magnets to create the magnetic gap that the voice coil uses to move. Field coil is not directly related to voice coil. The voice coil (interacting with the magnetic gap) determines the nominal impedance of the driver. The magnetic gap made by field coil is identical to that of permanent magnet other than being variable intensity. They usually sound better with more voltage applied (stronger magnetic gap = better transient response = more detail), but they can over heat if too much DC is applied. Newer permanent magnetic materials like neodymium iron boron have displaced field coils.
I wasn't aware of any current production commercial field coil drivers. Which ones are you looking at?
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The driver impedance depend on the voice coil wire lenght, or layers. The TS parameters change w/the power supply voltage variation.
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I wasn't aware of any current production commercial field coil drivers. Which ones are you looking at?
Just reading around the topic at present. i believe there are models by Supravox, Phy and others
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some current available field coil speakers, Atelier Rullit, Featrex, supervox, fertin, EMS, Cogent, Classic Audio, Voxativ, Line Magnetic and Focal, just a few that came to mind.
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I was hoping you'd show up shooter! I know you know a lot more than I do.
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how does one use a field coil driver? i read it has to be powered by a dc source. not sure what that means.
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how does one use a field coil driver? i read it has to be powered by a dc source. not sure what that means.
Its a power supply usually varying 9 to 16V.
Take alook at EMS/Fertin:
http://www.emspeaker.com/ems_produit.html
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Many field coil drivers run lower volt for safety considerations, mine runs high voltage up to 250v. Many older units the field coil also function as a power supply choke for the tube amp that drives them.
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Ignoring the safety factor are there advantages to the higher voltage drivers.
PS Shooter I love your speakers :)
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Thanks Bumpy!
According to Oleg Rullit high voltage sounds better, I have no experience with direct comparison of the same driver winded for different voltages, it is possible to wind the field coil with taps for series or parallel connections to use different voltages for comparison!
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Another question then :)
Despite having valve amps and sensitive speakers, I sit near field and have a personal aversion to hum through the speakers. The only field coils I ever heard (vintage) suffered enough for me to find it distracting. So my question is:
Is hum an issue with modern drivers and power supplies or are they dead quiet with your ear against the driver?
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does anyone have a photo to how the psu is connected to the driver? i can't seem to find one.
does the driver have a DC input somewhere?
the Atelier Rullit on ebay looks interesting. it has two pairs of binding posts per speaker. I suspect one of them is for the DC but not certain.
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It is nothing more than an electro magnet. But it has more consistent properties than a regular non-powered magnef.
(http://www.tpub.com/neets/book17/0044.GIF)
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does anyone have a photo to how the psu is connected to the driver? i can't seem to find one.
does the driver have a DC input somewhere?
the Atelier Rullit on ebay looks interesting. it has two pairs of binding posts per speaker. I suspect one of them is for the DC but not certain.
The PS connector vary according the manufacaturer.
https://www.google.com.br/search?q=field+coil+drivers&client=firefox-b&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjGqMzehrnVAhVCTCYKHbqGATEQ_AUICigB&biw=981&bih=639&dpr=1.3
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(https://s-media-cache-ak0.pinimg.com/564x/68/3c/ab/683cab8203ab0d7b91db2e1d3aec25ce.jpg)
like this. can i just connect a wallwart (something like a r-core dc psu sold on ebay, splice the cable ends, and connect it to the pair of binding posts that's on the speaker basket?
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I fail to understand it, its a expensive field coil driver?
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can i connect one of these to the back of a field coil driver in order to make it work? if not, what do i need to make one work?
(https://ae01.alicdn.com/kf/HTB1XeB8QFXXXXbKXVXXq6xXFXXXk/180VA-Ultra-low-Noise-LPS-HI-END-Linear-power-supply-DC-12V-10A-19V-8A-Optional.jpg_640x640.jpg)
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You need a PS w/the rated voltage according the driver specs.
If the coil works with voltage above the specified by the manufacturer something will burn, you will smell it, the first sign is the coil hot.
What are the driver supply voltage range?
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All drivers are different.
The quality of the power has an affect on the sound.
Field coil drivers usually cost 10x what a non-field coil costs, sometimes 300x.
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You need a PS w/the rated voltage according the driver specs.
If the coil works with voltage above the specified by the manufacturer something will burn, you will smell it, the first sign is the coil hot.
What are the driver supply voltage range?
those things they can be built to spec but just wanted to make sure it's a matter of getting a wall wart and connecting that to the back of a field coil driver in order to make it work.
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If you do not have the original PS and do not have the specifications to order a suitable one, do nothing, leave the driver stored to avoid disasters.
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oh.. so they do supposedly come with a ps... didn't know that.
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oh.. so they do supposedly come with a ps... didn't know that.
If you buy one as a speaker not just a driver. But as just a driver? Some might come with one, a great many do not.
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If you buy one as a speaker not just a driver. But as just a driver? Some might come with one, a great many do not.
New drivers from the factory without supply?
I think you mean say used drivers at ebay.
I suggest to dont buy used coil drivers without the original PS, unless one have the plans.
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No, I mean new and used.
You have ti understand these are super niche in a super niche market.
To even get the drivers sometimes is complicated because some people making them don't have any normal way to buy anything, maybe not even a website.
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It is common to use battery or lab supply to power low volt field coil drivers, some lab supplies you can select between constant voltage or constant current and they do sound different. Actually field coil supply does not have to be complicated, experience has shown some obsolete rectifiers actually sounds best, if you google informations are out there.
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All good discussion, but I think my question got lost a little way back :(
Another question then :)
Despite having valve amps and sensitive speakers, I sit near field and have a personal aversion to hum through the speakers. The only field coils I ever heard (vintage) suffered enough for me to find it distracting. So my question is:
Is hum an issue with modern drivers and power supplies or are they dead quiet with your ear against the driver?
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No hum in mine or others I have heard, problem could be up stream.
What vintage driver do you have? How do you power it?
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No hum in mine or others I have heard, problem could be up stream.
What vintage driver do you have? How do you power it?
ATM I have Grundig Alnico tweeters, Saba Greencone mids and Altec 416-8A alnico subs. All powered by Welborne DRD 45s. The hum is OK, but I would not want to make it worse.
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You have a nice system, excellent European vintage drivers. I also have a pair of vintage Sachenwerk field coil on open baffle, not bad sounding at all, don't know how they compare to your green cones though.
You have a direct couple DHT amp, it is very difficult to make direct heated triodes absolutely hum free.
My field coils are powered 24/7, they are dead quiet.
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Any voltage ripple in the field coil DC supply will cause the driver cone to move, same as a voltage change in the voice coil, they work against each other. So any hum caused by the field coil is due to voltage ripple in the field coil's DC supply. It needs to be very well regulated to avoid hum. Vintage field coil speakers are from the days before the advent of powerful permanent magnetic materials, so their DC supplies are likely not regulated, using just passive filtering. The old smoothing caps in such a supply will deteriorate over time and loose the smoothing capacity. Modern regulators are incredibly quiet, but a fixed voltage regulator would prevent adjusting the field coil voltage.
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You're right, if you're using power supplies from the 1930's :roll:
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richidoo, The reasoning is sound, experience tells otherwise, regulated supplies are not the best sounding on field coils.
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richidoo, The reasoning is sound, experience tells otherwise, regulated supplies are not the best sounding on field coils.
Technically they won't be the most linear due to the way speakers work (with regulated supplies). The cone driver has limitations in linearity itself. There would be a sweet spot.
I would be interested in the possibility of making a form of feedback for the PSU so that the field coil keeps linearity with the movement of the speaker. A variable PSU that sets strengths based on the speaker movement. This would be independent of the amount of feedback the amplifier you use deploys, so it could suit tastes.
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Technically they won't be the most linear due to the way speakers work. The cone driver has limitations in linearity itself. There would be a sweet spot.
This is a servo control, Velodybe used it in subs in 90 or 80s.This gadget lasts few time.
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I am not talking about the driver, but the field coil "magnet", for its PSU.
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I am not talking about the driver, but the field coil "magnet", for its PSU.
The field coil is a passive element, it just hold on the magnetic field on, who moves in the VC/cone.
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It is not passive. It is by nature an electro magnet. That means it has power.
What I am suggesting is making a correction system for it so instead of regulating the voltage or current to a set amount, I control the exertion of the electro magnet on the voice coil in order to compensate for non-linear behavior. In other words I am suggesting the possibility of widening the sweet spot that is found with certain voltages for a driver, and the music and sound that is appreciated with it.
This control would be compatible with any amp, as it wouldn't change the amp's feedback behavior that is of different personal taste among different people.
Doing this could ads more body and weight to instuments for example, as well as improve tone, dynamics, etc.. well, it could do a lot of stuff any way, depending in the starting point.
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Seems too good, I would like it if these promises are fulfilled since it be controlled by hand, not automatic or pre regulated.
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richidoo, The reasoning is sound, experience tells otherwise, regulated supplies are not the best sounding on field coils.
Regulator quality varies like amplifiers. There are regulators that are fast enough to play music well, like Belleson.
You're right, if you're using power supplies from the 1930's :roll:
That happens to be what I said, vintage PS. Don't be so rude Folsom.
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If you guys think regulated supply is the way to go, go ahead!
Several few field coil speakers manufacturers has discovered otherwise, I have nothing more to contribute.
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Seems too good, I would like it if these promises are fulfilled since it be controlled by hand, not automatic or pre regulated.
It would be auto. It would respond with the music. Think of it as a moving regulation.
As far as I know, no such thing exists.
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If you guys think regulated supply is the way to go, go ahead!
Several few field coil speakers manufacturers has discovered otherwise, I have nothing more to contribute.
Interesting. Do you have any links you can share?
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OK
Here's another question
Has anyone ever encountered a field coil midrange (8") incorporated into a 3 way open baffle using alnico permanent magnet drivers for the highs and lows?
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Bumpy, you can contact me through private message.
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If you guys think regulated supply is the way to go, go ahead!
Several few field coil speakers manufacturers has discovered otherwise, I have nothing more to contribute.
In power tube amps PS regulated are rarely used, they are know to limit the power avaliable.
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OK
Here's another question
Has anyone ever encountered a field coil midrange (8") incorporated into a 3 way open baffle using alnico permanent magnet drivers for the highs and lows?
Lotus Audio Grenada is pretty close, it doesn't need a tweeter though. The main driver is a Feastrex field coil that goes for around $50k/pair... :o
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dear shooter, please tell me what power suplly i must make, or buy to power supravox 215-2000EXC speakers ?
i know what car battery is best option, but constant rechargint is sooo anyoing. linear power supply , lets say 12v capable of 10Amps. for me would be sooo good. please give some links or just more specific info, not just this is good this is not. be more specific, thanks,:)
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dear shooter, please tell me what power suplly i must make, or buy to power supravox 215-2000EXC speakers ?
i know what car battery is best option, but constant rechargint is sooo anyoing. linear power supply , lets say 12v capable of 10Amps. for me would be sooo good. please give some links or just more specific info, not just this is good this is not. be more specific, thanks,:)
According Supravox the supply useful points are 8V to 13V scroll down the page, a tube supply would be great:
https://www.supravox.fr/anglais/haut_parleurs/215_2000_EXC.htm
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i can read:) i know what supravox says.
i asked, what power supply to use ? batery is very anoying with constand charges, and voltage drop during listening session.
i need as i know current regulated power supply,or LCLC type power supply, i just need tested schematics of them :)
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dear shooter, please tell me what power suplly i must make, or buy to power supravox 215-2000EXC speakers ?
i know what car battery is best option, but constant rechargint is sooo anyoing. linear power supply , lets say 12v capable of 10Amps. for me would be sooo good. please give some links or just more specific info, not just this is good this is not. be more specific, thanks,:)
Really 10 amps needed to drive a Supravox field coil 215?
I do want to build my own Supravox field-coil speakers but I cannot get the proper info about the required current at 12V per driver. If anyone can help...
Thanks!
Gianluca
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Really 10 amps needed to drive a Supravox field coil 215?
I do want to build my own Supravox field-coil speakers but I cannot get the proper info about the required current at 12V per driver. If anyone can help...
Thanks!😆 :(
Gianluca
Field coil uses DC supply, so use ohm's law to determine current requirement of power supply by measuring the resistance of the field coil in your driver then:
Current = Voltage / Resistance
What's more important is the wattage rating of the field coil, which you can look up in the published specs of the driver. FC drivers sound better with stronger magnetic field which increases with applied power. But the windings will burn if the power rating is exceeded so figure out what voltage makes max power before you energize as it's easier to monitor voltage than power when energizing coil.
ohms law calculator:
https://www.calculator.net/ohms-law-calculator.html