Field coil drivers

viggen · « **Reply #20 on:** 2 Aug 2017, 10:59 pm »

Quote from: FullRangeMan 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?

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.

FullRangeMan · « **Reply #21 on:** 2 Aug 2017, 11:06 pm »

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.

viggen · « **Reply #22 on:** 2 Aug 2017, 11:13 pm »

oh.. so they do supposedly come with a ps... didn't know that.

Folsom · « **Reply #23 on:** 2 Aug 2017, 11:38 pm »

Quote from: viggen on 2 Aug 2017, 11:13 pm

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.

FullRangeMan · « **Reply #24 on:** 2 Aug 2017, 11:51 pm »

Quote from: Folsom on 2 Aug 2017, 11:38 pm

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.

Folsom · « **Reply #25 on:** 3 Aug 2017, 12:47 am »

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.

shooter · « **Reply #26 on:** 3 Aug 2017, 01:41 am »

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.

Bumpy · « **Reply #27 on:** 3 Aug 2017, 07:13 am »

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?

shooter · « **Reply #28 on:** 3 Aug 2017, 01:25 pm »

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?

Bumpy · « **Reply #29 on:** 3 Aug 2017, 04:28 pm »

Quote from: shooter on 3 Aug 2017, 01:25 pm

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.

shooter · « **Reply #30 on:** 3 Aug 2017, 07:23 pm »

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.

richidoo · « **Reply #31 on:** 3 Aug 2017, 09:41 pm »

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.

Folsom · « **Reply #32 on:** 3 Aug 2017, 09:59 pm »

You're right, if you're using power supplies from the 1930's

shooter · « **Reply #33 on:** 3 Aug 2017, 10:29 pm »

richidoo, The reasoning is sound, experience tells otherwise, regulated supplies are not the best sounding on field coils.

Folsom · « **Reply #34 on:** 4 Aug 2017, 12:05 am »

Quote from: shooter on 3 Aug 2017, 10:29 pm

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.

FullRangeMan · « **Reply #35 on:** 4 Aug 2017, 12:54 am »

Quote from: Folsom on 4 Aug 2017, 12:05 am

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.

Folsom · « **Reply #36 on:** 4 Aug 2017, 01:44 am »

I am not talking about the driver, but the field coil "magnet", for its PSU.

FullRangeMan · « **Reply #37 on:** 4 Aug 2017, 01:54 am »

Quote from: Folsom on 4 Aug 2017, 01:44 am

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.

Folsom · « **Reply #38 on:** 4 Aug 2017, 02:26 am »

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.

FullRangeMan · « **Reply #39 on:** 4 Aug 2017, 03:29 am »

Seems too good, I would like it if these promises are fulfilled since it be controlled by hand, not automatic or pre regulated.