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Field Coils for Audio Systems
- Thread starter Audiophile Bill
- Start date
Everywhere I look on Internet audio forums, there is Ralph Karsten imparting knowledge.
I just bought a pair of Supravox 8" field-coil drivers, which will be mounted on JE Labs-style open baffles. I had this setup 15 years ago and I recall it had some magic. I want to see if they can compete with my ten-year standard, rebuilt Quad 63 ESLs (actively crossed to subs at 70 Hz).
Here's my question for you: Are you saying that any lab-grade regulated DC power supply will give optimal performance with these drivers?
Not wanting to put words into Ralph's mouth but, from my experience, no!
There is a massive difference between a lab grade regulated power supply and a high quality CCS power supply such as the Coleman regulators.
I ran my field coils with lab grade supplies for years before upgrading to Constant Current Source supplies earlier this year.
Its tricky.
As the coil heats up less current is able to flow if you have a regulated Voltage power supply. So it will stabilize at a current that tends to run just shy of where it likely should be.
If you have Constant Current, then what happens is to maintain the same current, the current regulated supply will have to increase its Voltage output. As it does so, the coil will heat up more. Seems to me this could produce a thermal runaway condition although there are physical limits that would probably limit this behavior. But it is on the account that I don't want to damage the coils that I've not gone down this route. Since my supplies allow me to set a current limit and a Voltage limit, I've been playing it safe by doing both.
(Anecdotally, one of my power supplies failed recently. It had overheated and two of the final regulator transistors shorted emitter to collector, which is to say the power supply was putting out way more Voltage than it should! When I discovered the condition I shut everything down and prayed the coil wasn't damaged. Turned out the power supply had three pass transistors, one of which had not been soldered in place! So the two transistors had been doing the work of three. I had the transistors sitting on a shelf by luck so was able to make a quick repair and get the supply working the way it was supposed to. Reinstalling it, I found the speaker seemed to work normally as if nothing had happened. So apparently the coils are more robust than I imagined.)
I think that might be why there's a good number of people that prefer the Tungar rectifier power supplies. Tungars change their output as they warm up so they tend to drift to a higher output Voltage over time but can't run away. The problem with them is they can't handle much capacitance at their output so a slight bit of hum is quite possible.
I've had my hands full but I think since the field coil is a bit more sturdy, I might go ahead with a CCS for setting the current and see how that works.
Rod Coleman sells them as kits. If you are handy with a soldering iron and have a little electronics experience you can build them yourself. Otherwise I would find someone local who can build them for you.
The regulator kits are very inexpensive, but you need to provide the mains transformer the PS caps, a case and a few other parts. Rod is good to deal with and will provide some help.
I used bamboo cases bought off Amazon, local supply toroidal transformers and parts from hificollective in the UK. They took about a day to build each one, and cost about $500 (each).
If this sounds too hard there are others who sell CCS supplies like Wolf Von Langa, but these are many multiples in price.
Yeah I can build.
I'm seeing nothing but DHT filament supplies on his website. Google not turning up much else. Have a link?
A pair of lab-type supplies is ~$300 so the cost isn't that bad.
I won't say I'm skeptical of improvements, but - I'd never heard of anyone using power supplies like these on field coils in a lot of years.
Field-coil motors already provide such an improvement IME it's hard to imagine "more." But, maybe.
(My experience: Owned the 8" Supravox FCs, twice. Heard Lowther FCs (against AlNiCo - very obvious improvement) at Jon Ver Halen's (Lowther importer) place. Briefly owned Cogent compression FCs used in conical horns.)
They are the same thing with some slight mods - contact Rod Coleman.
Most of the Field Coil vendors are using this type of supply or Tungars. Audio Note modified their own DHT filament supplies for their field coils. Wolf Von Langa looks to have used a modified Tent labs DHT filament supply.
I have made 4 of these for myself, and 2 for @LanschePlasmaGuy . We both thought the improvement was massive.
It appears Rod Coleman is using the CCS to heat power tubes, rather than simply applying the rated filament Voltage. Do I have that right?
Are we talking about triode amps or field coils?
The field coil supplies have no tubes, just a current regulator.
Right. It appears that the Rad Colemen regulator which you seem to have repurposed for FC use was designed originally for DHT filaments. Is that correct?
David made a pair of supplies for me. The improvement in my very revealing system was absolutely massive. Not small. It was a component upgrade. David makes beautiful pieces and I will be commissioning two more supplies from him for my Wolf Von Langa 20 kg midrange field coil drivers.
I was just using a generic but good quality old school lab supply before these. David had recommended this lab supply being prefereable over many he had tried and much better than the newer style generic supplies.
He put top quality parts in the supplies he made for me and each supply has an around 5 kg purpose wound transformer for the job. David does makes these for fun and not profit so if your in Australia (or further afield) I highly recommend these supplies. The improvement was huge. He is absolutely fanatical about quality and attention to detail.
And yes you could hear the improvement immediately. With running in the units got even better.
If you think field coil supplies don't make a difference to the sound i'm sorry to say you are dreaming. But if you love the idea of a very big upgrade path in performance with your field coils this is it.
LPG
Yes, but Rod provides the kit setup for field coil use. I provided Rod with the voltage/current range and he modified the kit to work with the FC.
I might still. I've been working on a few amplifier projects. But I'd like to do a CCS for my field coils. I don't want it to look like a mancave project though, so I'll have to sort out the parts needed and design a proper chassis for it. I figure adjustable, with a meter.
As mentioned a few times in this thread, Wolf von Langa offers an exceptional quality constant current source supply for those that aren't interested in DIY'ing something together themselves. Happy to help if you get curious.
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