Solid state amp to drive field coil woofers? Thoughts?

Atmasphere

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I am curious, what are your field coils, and how do you find them compared to other approaches.

Thanks

David
They are made by Classic Audio Loudspeakers. IMO/IME field coils have speed that otherwise you can only get from ESLs and for very similar reasons- both have power supplies to run their motive forces. In a permanent magnet system, when you put current through the voice coil, the magnetic field sags a bit. Alnico sags the least, and is easiest to focus in the voice coil gap, which is why Alnico is the preferred magnet system. Neodynium is the most powerful magnet system, but its harder to focus and sags the most.

Field coil OTOH doesn't sag- so there is less compression, higher speed and lower distortion, and I really don't think its hard to hear that difference. Permanent magnets fall into that same arena of most of the big changes in audio history; they didn't go away because they were inferior, they went away because they are more expensive. This was the same motivator behind tubes to transistors and certainly analog to digital.
 
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dcathro

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They are made by Classic Audio Loudspeakers. IMO/IME field coils have speed that otherwise you can only get from ESLs and for very similar reasons- both have power supplies to run their motive forces. In a permanent magnet system, when you put current through the voice coil, the magnetic field sags a bit. Alnico sags the least, and is easiest to focus in the voice coil gap, which is why Alnico is the preferred magnet system. Neodynium is the most powerful magnet system, but its harder to focus and sags the most.

Field coil OTOH doesn't sag- so there is less compression, higher speed and lower distortion, and I really don't think its hard to hear that difference. Permanent magnets fall into that same arena of most of the big changes in audio history; they didn't go away because they were inferior, they went away because they are more expensive. This was the same motivator behind tubes to transistors and certainly analog to digital.



lovely Ralph, are yours the Hartsfields or the T series?

What are you using to power the motors?

No argument from me on everything you have said!

I always felt that ferrite magnet speakers sounded somewhat grey and dead compared to alnico.

field coils seam to sound even more alive, and I am pretty sure the ultimate quality is dependent on the power supply.

Cheers David
 

Alrainbow

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What’s the imp curve ? Can you post it ? do you have a field coil psu for each driver alone ?
if you can post some pics as asked and if possible vary voltage for drivers. My reason is field coil drivers from what I read and heard do vary greatly per amp used. BI amp is a way to lesson the effect of amp imp interaction. there was a very large horn setup all field coil horns. sadly they used one psu per side for 5 drivers.
 

dcathro

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What’s the imp curve ? Can you post it ? do you have a field coil psu for each driver alone ?
if you can post some pics as asked and if possible vary voltage for drivers. My reason is field coil drivers from what I read and heard do vary greatly per amp used. BI amp is a way to lesson the effect of amp imp interaction. there was a very large horn setup all field coil horns. sadly they used one psu per side for 5 drivers.

Sorry, who are you referring to? The OP?
 

Atmasphere

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lovely Ralph, are yours the Hartsfields or the T series?

What are you using to power the motors?

No argument from me on everything you have said!
I'm using the T-3.3.

I use an adjustable solid state regulated supply that can hold the voltage within 1-2mV. The voltage and current are displayed on the front panel.
 
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dcathro

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I'm using the T-3.3.

I use an adjustable solid state regulated supply that can hold the voltage within 1-2mV. The voltage and current are displayed on the front panel.

Gorgeous speakers!

Your bass drivers are essentially the same as mine, although you have 2 per side and running ported so you have way more efficiency!

I would humbly suggest that you experiment with the power supplies for the drivers. On my bass driver I started with a 20V 5A rated unit (the driver draws less than 1.5A), but found that a much higher rated 10A 30V (HP Agilent) unit made a profound difference. On my mids, I am using low ripple supplies - you can hear any PS noise, but want to try Tungars.

Cheers

David

P.s. love the look of your amps!
 
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Atmasphere

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Thanks!

I built a power supply using Tungars because I'd heard so much about them, but I found them to mostly be a pain in the rear. The big deal is you have to regulate the power supply, since current in the voice coil affects the magnetic field, and that energy comes from somewhere- the more current in the voice coil the more sag in the magnetic field if you don't do something about it. Once there is a regulator in play, its all about the regulator(which is in essence a small power amplifier and so has to be very linear) rather than what rectified the power to it. Any 'quality' the rectifiers have upstream becomes irrelevent in the face of regulation, unless the regulator has a design flaw.

You really don't want the voltage to sag- otherwise it can introduce colorations on two counts- intermodulation and changes in the T-S parameters (including efficiency). While the latter is slight, it is measurable. The former is likely the lion's share of the difference. IME, there is a voltage drop across the wiring between the power supply and the drivers, so I keep the length of it as short as I can and run heavier gauge than it would appear to need.

I'm working on a new regulator using HEXFREDs (mostly for low noise) and a narrower adjustable range. I plan to build in a circuit to turn it on when audio is detected.
 
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dcathro

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Thanks!

I built a power supply using Tungars because I'd heard so much about them, but I found them to mostly be a pain in the rear. The big deal is you have to regulate the power supply, since current in the voice coil affects the magnetic field, and that energy comes from somewhere- the more current in the voice coil the more sag in the magnetic field if you don't do something about it. Once there is a regulator in play, its all about the regulator(which is in essence a small power amplifier and so has to be very linear) rather than what rectified the power to it. Any 'quality' the rectifiers have upstream becomes irrelevent in the face of regulation, unless the regulator has a design flaw.

You really don't want the voltage to sag- otherwise it can introduce colorations on two counts- intermodulation and changes in the T-S parameters (including efficiency). While the latter is slight, it is measurable. The former is likely the lion's share of the difference. IME, there is a voltage drop across the wiring between the power supply and the drivers, so I keep the length of it as short as I can and run heavier gauge than it would appear to need.

I'm working on a new regulator using HEXFREDs (mostly for low noise) and a narrower adjustable range. I plan to build in a circuit to turn it on when audio is detected.

Am I understanding you correctly that the Tungar PS is unregulated, or that once you regulate it, the fact that it is Tungar makes no difference?

Your comments on the cables are interesting. What king of gauge do you think is necessary?

I am interested to know more about your power supply design.
 

Atmasphere

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Am I understanding you correctly that the Tungar PS is unregulated, or that once you regulate it, the fact that it is Tungar makes no difference?

Yes. Well- it'll be a lot bigger if you use Tungars (which was a GE trademark but became generic like Kleenex) and occasionally one will fail :) Honestly I don't see the point unless the glow of tubes is what's important.
Your comments on the cables are interesting. What king of gauge do you think is necessary?

I am interested to know more about your power supply design.

I've been running 10Ga wire. I can't be sure but it seems to make the system slightly faster, although it could be expectation bias.

The supply is pretty simple. I don't have a great degree of current needed since my woofers are Alnico still (I hope to install field coil woofers but I want them to have similar specs to my 1602s). The circuit is a simple pass regulator to filter out the sawtooth; teh resulting DC is applied that to the input side of an LT1083 and a potentiometer to allow me to set the voltage over a small range. I've been thinking about a vintage style meter (probably the same style as we use on our amps) to display the current so I can set that correctly.
 

ack

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I'm working on a new regulator using HEXFREDs (mostly for low noise) and a narrower adjustable range. I plan to build in a circuit to turn it on when audio is detected.

If I may ask, which HEXFREDs are you using? I installed Vishay HEXFRED VS-HFA15TB60-M3 in my DAC, tuner and phono stage, and the results were clearly superior
 
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ack

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Alrainbow

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I'm using the T-3.3.

I use an adjustable solid state regulated supply that can hold the voltage within 1-2mV. The voltage and current are displayed on the front panel.
OMA says the original tube recti used on his field coil drivers of his flagship sounded best but measured bad lol. He is a really nice honest guy I enjoyed my time there. really cool looking Cust audio stuff that sounded As good as it looked.
 

dcathro

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Yes. Well- it'll be a lot bigger if you use Tungars (which was a GE trademark but became generic like Kleenex) and occasionally one will fail :) Honestly I don't see the point unless the glow of tubes is what's important.

LOL, it's surprising to hear a tube guy say that there is no benefit!

I've been running 10Ga wire. I can't be sure but it seems to make the system slightly faster, although it could be expectation bias.

I will definitely try a bigger gauge - I have been running 18awg.

The supply is pretty simple. I don't have a great degree of current needed since my woofers are Alnico still (I hope to install field coil woofers but I want them to have similar specs to my 1602s). The circuit is a simple pass regulator to filter out the sawtooth; teh resulting DC is applied that to the input side of an LT1083 and a potentiometer to allow me to set the voltage over a small range. I've been thinking about a vintage style meter (probably the same style as we use on our amps) to display the current so I can set that correctly.

Sounds good. What voltage range will it have, and how much current?
 

DetroitVinylRob

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Oh, WoW! Very cool kit. The live edge slabs are truly stunning, beautiful.

I too am fascinated with how Radu Tarta is power the voice coils. I’m currently running (18v 5A) SS B & K Precision 1621As on my T3s, but digging around to educate on a valve based solution.

Talk about Tungars “sound” is intriguing aside from the dismal specs.
 
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Atmasphere

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Talk about Tungars “sound” is intriguing aside from the dismal specs.
The reason they have a 'sound' is because its hard to bypass them correctly, and they can have a voltage drop when current is present in the voice coil. In a permanent magnet system this normally would cause the magnetic field to sag. And it does with Tungars as well, because they develop a voltage drop across them. You can fix that by running a higher voltage on the Tungars and then regulating to the voltage you want, but at that point there is no point in the Tungars at all. This is simply one technology that has been surpassed in every way by the succeeding art.
 
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audioquest4life

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@DetroitVinylRob, @Atmasphere ,

Not to derail the subject, but have a quick question regarding the B&K1621 power supplies. I use them for my Classic Audio T 1.5s. My room, lights, audio equipment is so quiet now that I don’t hear any electrical hums or interference from the main audio equipment. I do, however, hear hum from the B&K 1621 power supplies. That is the only noise in my room and I guess I am sensitive to that sound. I tried cheater plugs, moving to different outlets, and adding a Ebtech HumX ground eliminator, to no avail. Tried with lights off too. The only thing that makes noise is the transformer in those field coil power supplies. My brother-in-law in the military was over this weekend and said sounds like poor windings or the transformers are old. He is a electronic maintenance tech and repairs stuff like this. Alternatively, looking at constructing a vented box with sound insulation inside to cover the noise making culprits. Do either of you have hum coming from your B&K Precision 1621 power supplies? Ralph, are you still using the B&K 1621 or another version which has zero ripple current solid state design, I think it is the 1666 model. The 1621 lists that it has low ripple, but yet, the 1665 series has both constant current and constant voltage. The 1621 looks like it only has one or the other, constant voltage or constant current. Any ideas? Thank you.

For the OP, nice setup. Will be interesting to see the outcome of your final selections for amps. I just drive the big field coils with 300 watt Mcintosh tube amps. I am also enjoying my new field coil listening experiences.
 

DetroitVinylRob

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I went to the BK 1621s recently because John Wolfe and I liked the fact that the power supplies appeared more robust than the Mastech HY3006Ds that we had been employing that seemed to not remain stable for me. I had two that after warm up continually fell off in voltage needing constant adjustment. And finding replacements was an issue with many of the various branded clones adding computer style fans in place of heat sinks. The BKs came up for an excellent price, so I grabbed a pair. These units seem to have a slight transformer hum to them but remain very voltage stable. I have put the chassis directly on (sorbothane) buttons, on isolation wood blocks with footers and they are not audible from our listening seats. :) My apologizes to the OP
 
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