Field Coils for Audio Systems
- Thread starter Audiophile Bill
- Start date
Many thanks for sharing your experience. My findings with the Classic Audio tungar supplies are similar to yours. The first thing I noticed was how plucked bass seemed to have more of the "elastic" feel. I think this is due to hearing more of the resonance of the string after it has been plucked, which was missing before. The three dimensionality of voice and string instruments also stood out with a more life-like illusion. Overall, I am very happy with the decision to take the plunge, given the expense and the space requirement.
Congratulations on starting to get real settled. Very nice to see you and the pup getting the room situated. A dedicated space for audio is such a wonderful advantage, a true luxury really. I’m sure your sound is truly quite amazing. Nice job.
These Classic Audio speakers really bring a whole nother dimension to a life like reproduction of a performance. I love Mine.
I just might have to give the Tungars a chance. Glad they have made a substantial contribution for you.
Are you going to make it to Capital AUDIO Fest? It starts today, 10 November through Sunday 12 November. I am heading there in a short while. Classic Audio Loudspeakers will have a great demonstration.
Flying into Detroit today. Unfortunately can’t make CAF this year. Just too much going on. We’ll have to catch up another time. Enjoy
Spent a good part of the day at the show. The T1.5s with the Tungar power supplies sounded absolutely superb. Going back tomorrow to discuss business.
We should connect sometime this year.
Do you guys know how many volt amps the Classis Audio tungar supplies are rated at. If possible would you be able to ask tomorrow, good luck with them… think they look fantastic and much thanks in advance.
I will check. This is good information that any Tungar owner should know. I am sure that I was told but forgot. I am out of state for work so can’t look on my own Tungar power supplies.
Here is what I got from John when I asked this question a few months ago
“Standard is 28VDC+/- 2Amps+/- for Woofer side.
20VDC+/-1.75 Amps+/- High side
This can be somewhat modified if you require something else.
We also make a Giant 6Bulb unit for larger applications.
Let me know your specific requirements
John”
JOHN WOLFF
CLASSIC AUDIO LOUDSPEAKERS
5115 RED FOX DR.
BRIGHTON, MI. 48114
810 229-5191
Many thanks Glide3,
I’m hoping to find out the maximum total volt amps that the supplies are rated at to see if 2 x tungar units are in the ballpark for powering field coil woofers that I’m considering using for an OB project.
This looks like 91 volt amps is the range required for the Classic Audio speakers but will check if that’s also the maximum one supply can deliver.
I’ll wait to see what Audioquest4life found out and look to discuss it more with John if it looks at all possible… this is just an initial inquiry as I’m just in the early stage looking at options for something that I’ve been thinking about for a while and things are just still forming up including how many field coil drivers I may plan to go for.
I’m hoping to find out the maximum total volt amps that the supplies are rated at to see if 2 x tungar units are in the ballpark for powering field coil woofers that I’m considering using for an OB project.
This looks like 91 volt amps is the range required for the Classic Audio speakers but will check if that’s also the maximum one supply can deliver.
I’ll wait to see what Audioquest4life found out and look to discuss it more with John if it looks at all possible… this is just an initial inquiry as I’m just in the early stage looking at options for something that I’ve been thinking about for a while and things are just still forming up including how many field coil drivers I may plan to go for.
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Good day. I spoke with John about the Tungar power supplies current draw. While he does not recall the exact current draw from the wall for the entire unit, he did state that the woofer side of the Tungar power power supply has roughly a 4 amp draw on the woofer section and 2 amps on the mid/tweeter side.
Looking at the back of the Tungar power supply, the fuse holder has the amp rating so that can be used as the potential overall amperage draw. Unfortunately, I did not take a close up of that section so can’t tell from the pics. When I return from a business trip next week, I will look at the fuse rating and the internal power supply rating and post the information. Additionally, I will plug in my voltage/amp meter to see what the actual current draw is from the wall. I will do this test sequentially, first with the woofer power switch on and then the midrange power switch. Also, John mentioned the current draw is higher for the woofers because it is powering 2 field coil woofer Magnets. For the T 1.5 reference, this means a 18“ woofer and a 15” woofer are each being supplied by the woofer (4 amp) section of the Tungar power supply. So, roughly 2 amp draw for each woofer, probably the 18” slightly more and the 15” slightly less. To be accurate, this would entail additional measurements and opening the back panel.
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Thank you for all of this. I had been thinking John might just have had this info off the top of his head but also didn’t want to bother him while he was caught up in doing the show.
That is genuinely very kind of you to follow through but if it becomes at all involved please there is no immediate hurry for me so while it would be great if you do get an idea of what the draw is when you are home that’s awesome but honestly I can wait till John is back from the audio show. I’ll send a message to John to ask a bit more about this and also about the other larger 6 bulb tungar supply unit that Glide mentioned. I think I saw pics of one of these as well somewhere online when I was searching about John’s tungsten supplies.
So thanks again. Great gear you have and it’s much very much appreciated that you checked in with John on my behalf. Look forwards to reading more about your system and your classic audio speakers. Very cool gear.
Apparently John’s Tungars are driving the field-coils today much higher VDC then what he recommended for my T3.4 and (x4) BK Precision SS to drive at (The Mid Driver will draw approx.. 1.25 Amps at 15 VDC. The 2 Woofers will Draw approx.. 2.75- 3 Amps at 18 VDC). This was his thinking back on 6/20/23 yet the amperage is not that far off. (and as we have spoke about earlier in this thread, current may be the important component here). Also perhaps there is a diff 15” to 18” woofer thing too.
It is interesting how the Tungar VDC vs amps is so different then the solid state supply numbers.
I also realize this is an evolutionary process.
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i have a 4 way custom horn system with john's active drivers that is north of 300K Just incredible sound. so fast. and the detail and tonality made me very happy
BUT .....I saw what John had been working on for a better power supply, and because he has done incredible work with sound, and because of his great integrity, I bought a pair of his PS, and wow! Everything improved. It was apparent immediately, even to my wife who blames John for my audio poverty. The detail and resolution got even better. Way better, and i thot i was at the end of the road. but the purity and tonality was so stunning and surprising. very happy and for a modest amount of dollars. You think it can't get better?
BUT .....I saw what John had been working on for a better power supply, and because he has done incredible work with sound, and because of his great integrity, I bought a pair of his PS, and wow! Everything improved. It was apparent immediately, even to my wife who blames John for my audio poverty. The detail and resolution got even better. Way better, and i thot i was at the end of the road. but the purity and tonality was so stunning and surprising. very happy and for a modest amount of dollars. You think it can't get better?
I thought that field coil speaker magnets being powered by external power supplies do not change the fact that the speaker is typically a passive crossover. An active crossover will mean that separate power amplification can be used for the tweeter, mids and bass. That’s my simplified statement. More technical is that an active crossover is a device that modifies an audio signal before the amplifier. It works on line-level or preamp signals only. Active crossovers combine op-amps, resistors and capacitors to alter different frequency ranges of the signal. Unlike passive networks, active crossovers can be designed to increase the level of the signal, but only in the case of powered filters. Active networks often include other functions, such as remote level controls and bass, mid, and high frequency boost circuits.
I am assuming in your custom speaker system build that you adopted John’s drivers and made them active. Can you explain your process? Sounds very interesting. John did mention that someone had bought his drivers for a custom build system during the Capital Audio Fest. Perhaps this was you that he was talking about.
Interesting thread.
My first exposure to field coil drivers was with RCA 1428B drivers on RCA multi-cell horns around 2000. Even in a mismatched system kludged together the RCA drivers produced the most effortless and natural midrange I had ever heard. This was at the home of the late Steve Steve Schell who was an encyclopedia of audio history and became the instigating force behind the limited production Cogent field coil drivers. During the '00s and teens I worked with Cogent to produce a few systems.
But still so many people are stuck with typical 15" midbass–usually ported–and a compression midrange and some tweeter. While there will be significant gains over permanent magnet drivers such systems still have many longstanding limitations built into the designs.
Where Cogent went one better was the design of their DS-1448 midbass drivers. With compression midbass giving high output down into the 70-80Hz range the transparency and transient response dramatically improves. Distortion is greatly reduced and the presentation becomes even more life-like.
And not content with just that in my own installation I built in bass horns. Originally 30Hz flares that put out ~106db w/m, when I reconfigured my space for the Cogent arrays I added so eq for a solid 20hz.
The main arrays are Cogent DS 1448 and 1428 field coils and Fostex T-925a tweeters driven with Western Electric 300B amps tweaked for me by Cy Brenneman. The bass horns are driven with VTL MB-125 mono amps. So it's all horn loaded and yet when listening there is no sensation of the mass of equipment producing the sound.
I got pretty lucky with the implementation. Oh, and I cannot overstate the impact of effective room treatment on the system: a good room can make mediocre equipment sound far better while a poorly treated room can make the best equipment unlistenable.
eso
My first exposure to field coil drivers was with RCA 1428B drivers on RCA multi-cell horns around 2000. Even in a mismatched system kludged together the RCA drivers produced the most effortless and natural midrange I had ever heard. This was at the home of the late Steve Steve Schell who was an encyclopedia of audio history and became the instigating force behind the limited production Cogent field coil drivers. During the '00s and teens I worked with Cogent to produce a few systems.
But still so many people are stuck with typical 15" midbass–usually ported–and a compression midrange and some tweeter. While there will be significant gains over permanent magnet drivers such systems still have many longstanding limitations built into the designs.
Where Cogent went one better was the design of their DS-1448 midbass drivers. With compression midbass giving high output down into the 70-80Hz range the transparency and transient response dramatically improves. Distortion is greatly reduced and the presentation becomes even more life-like.
And not content with just that in my own installation I built in bass horns. Originally 30Hz flares that put out ~106db w/m, when I reconfigured my space for the Cogent arrays I added so eq for a solid 20hz.
The main arrays are Cogent DS 1448 and 1428 field coils and Fostex T-925a tweeters driven with Western Electric 300B amps tweaked for me by Cy Brenneman. The bass horns are driven with VTL MB-125 mono amps. So it's all horn loaded and yet when listening there is no sensation of the mass of equipment producing the sound.
I got pretty lucky with the implementation. Oh, and I cannot overstate the impact of effective room treatment on the system: a good room can make mediocre equipment sound far better while a poorly treated room can make the best equipment unlistenable.
eso
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This is very interesting and a beautiful build, @ArtisanalAudio, congratulations!
Are those Bill Woods Conical horns?
I would love to see more photos of the speakers, especially the frame and how the drivers are attached to it.
Looks like you are using an active crossover?
Can I ask how you have implemented the 1448 and 1428 drivers? What are the differences?
“My first exposure to field coil drivers was with RCA 1428B drivers on RCA multi-cell horns around 2000. Even in a mismatched system kludged together the RCA drivers produced the most effortless and natural midrange I had ever heard.”
I am biased, but I agree that the RCA1428/1443 on a conical horn has unmatched midrange tone and realism. I auditioned the Wilson Chronosonic XVX (with the intent to purchase for a second system) and they did not achieve the same level of realism in the midrange.
(It’s surprising and embarrassing how few very high end speaker manufacturers use field coils…but that’s a different topic.)
I got quite lucky with my setup, using the Fostex T500aMkII and Supravox FC woofers in the upper bass, and a transmission line active sub, I have flat (+/-5db) response in my room from 20Hz to 20K. Not that frequency response defines a world-class system, but it’s a good foundation.
The Duelund CAST crossover has made a big difference, in addition to room treatment and vibration control and AC and ground filtering for the FC field coil power supply. The PSU itself also makes a tremendous difference - the magnetic field is in the signal path, after all.
Are those Bill Woods Conical horns?
I would love to see more photos of the speakers, especially the frame and how the drivers are attached to it.
Looks like you are using an active crossover?
Can I ask how you have implemented the 1448 and 1428 drivers? What are the differences?
“My first exposure to field coil drivers was with RCA 1428B drivers on RCA multi-cell horns around 2000. Even in a mismatched system kludged together the RCA drivers produced the most effortless and natural midrange I had ever heard.”
I am biased, but I agree that the RCA1428/1443 on a conical horn has unmatched midrange tone and realism. I auditioned the Wilson Chronosonic XVX (with the intent to purchase for a second system) and they did not achieve the same level of realism in the midrange.
(It’s surprising and embarrassing how few very high end speaker manufacturers use field coils…but that’s a different topic.)
I got quite lucky with my setup, using the Fostex T500aMkII and Supravox FC woofers in the upper bass, and a transmission line active sub, I have flat (+/-5db) response in my room from 20Hz to 20K. Not that frequency response defines a world-class system, but it’s a good foundation.
The Duelund CAST crossover has made a big difference, in addition to room treatment and vibration control and AC and ground filtering for the FC field coil power supply. The PSU itself also makes a tremendous difference - the magnetic field is in the signal path, after all.
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The base design is from Bill Woods. Bill provided the basic design used by both Cogent on the West Coast and ΩMA on the East Coast.
Cogent principal Rich Drysdale and I devised what we felt was a cleaner connection between the drivers and horns that eliminated Bill's throat castings. Those castings limit the thickness of the wood sides and I wanted thicker material for a better visual balance. After experimenting with the basic design of Bill's I shortened the mid horns a couple inches while maintaining the mouth diameter. This increased the internal angle of the horns and makes a better match with the internal phase plug geometry.
The 1448 are on the truncated midbass as designed by Bill Woods. The networks use a 1st low pass at ~350Hz if I recall. The Mids are a simple 1st order high pass as are the tweeters. In my system the networks use charge-coupled capacitors and the inductor for the low pass is a custom wound 10Ga coil with negligible insertion losses due to the large gauge wire.
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