Field coil drivers

Bumpy · « **on:** 1 Aug 2017, 12:18 pm »

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?

richidoo · « **Reply #1 on:** 1 Aug 2017, 02:24 pm »

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?

FullRangeMan · « **Reply #2 on:** 1 Aug 2017, 06:35 pm »

The driver impedance depend on the voice coil wire lenght, or layers. The TS parameters change w/the power supply voltage variation.

Bumpy · « **Reply #3 on:** 1 Aug 2017, 07:09 pm »

Quote from: richidoo on 1 Aug 2017, 02:24 pm

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

shooter · « **Reply #4 on:** 1 Aug 2017, 07:45 pm »

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.

Folsom · « **Reply #5 on:** 1 Aug 2017, 08:44 pm »

I was hoping you'd show up shooter! I know you know a lot more than I do.

viggen · « **Reply #6 on:** 1 Aug 2017, 11:31 pm »

how does one use a field coil driver? i read it has to be powered by a dc source. not sure what that means.

FullRangeMan · « **Reply #7 on:** 2 Aug 2017, 12:34 am »

Quote from: viggen on 1 Aug 2017, 11:31 pm

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

shooter · « **Reply #8 on:** 2 Aug 2017, 03:23 am »

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.

Bumpy · « **Reply #9 on:** 2 Aug 2017, 07:11 am »

Ignoring the safety factor are there advantages to the higher voltage drivers.

PS Shooter I love your speakers

shooter · « **Reply #10 on:** 2 Aug 2017, 02:56 pm »

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!

Bumpy · « **Reply #11 on:** 2 Aug 2017, 03:03 pm »

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?

viggen · « **Reply #12 on:** 2 Aug 2017, 03:36 pm »

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.

Folsom · « **Reply #13 on:** 2 Aug 2017, 04:06 pm »

It is nothing more than an electro magnet. But it has more consistent properties than a regular non-powered magnef.

FullRangeMan · « **Reply #14 on:** 2 Aug 2017, 05:18 pm »

Quote from: viggen on 2 Aug 2017, 03:36 pm

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

viggen · « **Reply #15 on:** 2 Aug 2017, 09:18 pm »

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?

FullRangeMan · « **Reply #16 on:** 2 Aug 2017, 09:35 pm »

I fail to understand it, its a expensive field coil driver?

viggen · « **Reply #17 on:** 2 Aug 2017, 09:48 pm »

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?

FullRangeMan · « **Reply #18 on:** 2 Aug 2017, 10:22 pm »

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?

Folsom · « **Reply #19 on:** 2 Aug 2017, 10:45 pm »

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.