Hi there.
I can confirm the copper foil theory, at least from listening perspective.
I am using a copper foil air coil. The sound definately improved, compared to the earlier air coil made out of wire, which had been regarded as a real good coil by many listeners.
Low level details clearly improved.
Another aspect, I learned, with coils are vibrations. Tests have been shown that wire based coils are much more sensitive to vibrations than foil coils. They measured differences of 20db!
Foil coils can provide you lower resistance and capacity, if done right.
I am running the foil coil with a T-AMP at a 2-4W power level. It seems that I don't have an issue with strayfields, distortions etc.. Of course I tried to shield the coils as much as possible.
I am wondering why you folks don't discuss air coils here!?
I think it has been discussed a lot of times that the air coil sounds superior to other coils, at least on the different T-Amps.
I can confirm the copper foil theory, at least from listening perspective.
I am using a copper foil air coil. The sound definately improved, compared to the earlier air coil made out of wire, which had been regarded as a real good coil by many listeners.
Low level details clearly improved.
Another aspect, I learned, with coils are vibrations. Tests have been shown that wire based coils are much more sensitive to vibrations than foil coils. They measured differences of 20db!
Foil coils can provide you lower resistance and capacity, if done right.
I am running the foil coil with a T-AMP at a 2-4W power level. It seems that I don't have an issue with strayfields, distortions etc.. Of course I tried to shield the coils as much as possible.
I am wondering why you folks don't discuss air coils here!?
I think it has been discussed a lot of times that the air coil sounds superior to other coils, at least on the different T-Amps.
I think one of the reasons air core and foils are not discussed is EMI and cost. If someone can get normal wired coils to work very good, there's more technology and experience involved, cheaper, and less EMI as well.
Remember in another thread that someone mentioned the "bert" coils for Tripath amps? Well it seems that Thomas came out with a coil with only 13 turns versus the 29 turns (as I recall) that the 41Hz kit had, and it seemed the improvement was very significant. This means the wire length is reduced to less than half of what it originally was (proabably only 60cm of wire now maybe?). So if the core does not saturate, the foil type may not perform much better, but nobody had tried it yet. I think a few people were going to try it, but never hear back from them.
Remember in another thread that someone mentioned the "bert" coils for Tripath amps? Well it seems that Thomas came out with a coil with only 13 turns versus the 29 turns (as I recall) that the 41Hz kit had, and it seemed the improvement was very significant. This means the wire length is reduced to less than half of what it originally was (proabably only 60cm of wire now maybe?). So if the core does not saturate, the foil type may not perform much better, but nobody had tried it yet. I think a few people were going to try it, but never hear back from them.
Foil Coils are really not that expensive, compared to wire coils. In perspective of the whole amplifier module, the price difference is very small. So it's not a matter of price, rather a matter of establishing whether they are actually better or not.
Best regards
Lars Clausen
Best regards
Lars Clausen
Lars Clausen said:
I wish it were that way with inductors. Right now they are at least twice the price for foils.🙁 I wish they were a lot cheaper. For long runs of wire like applications in speakrs, they are much better. I'm not so sure with short runs as in cored output inductors though. I'm more familiar using them in speakers with audible and measurable differences.
Come on folks ! Lets not talk about money here.
I paid 8€ for each of them - customized at Mundorf.com.
To repeat what you're saying: EMI/RFI are the killer criteria for air coils.
Doesn't that also depend very much on the output-power!
If you run at a very low ouput power on a high sensivity system, radiation shouldn't be much of an issue. If you shield the coils it would even be less of an issue!
BTW - I even shielded my T-AMP chip as good as the coils.
I paid 8€ for each of them - customized at Mundorf.com.
To repeat what you're saying: EMI/RFI are the killer criteria for air coils.
Doesn't that also depend very much on the output-power!
If you run at a very low ouput power on a high sensivity system, radiation shouldn't be much of an issue. If you shield the coils it would even be less of an issue!
BTW - I even shielded my T-AMP chip as good as the coils.
One way of reducing EMI is to use two coils elecrically in series but mechanically parallel- so that the fields cancel to some degree.
8 Euros is indeed not that much money. A good ferrite core with coil former and all the other accessories costs at least half of that and you would still have to work to get it together.
OTOH shielding measures needed for air cores can definitely be a killer criterium for a commercial design (cost and size !!!).
Regards
Charles
8 Euros is indeed not that much money. A good ferrite core with coil former and all the other accessories costs at least half of that and you would still have to work to get it together.
OTOH shielding measures needed for air cores can definitely be a killer criterium for a commercial design (cost and size !!!).
Regards
Charles
phase_accurate said:
Good that we are all or at least most of us are DIYer at DIY-Audio and do not have to care about commercial implications such as cost and size. That gives us a little more flexibility in tweaking
commercial designs! 😉
Klaus
phase_accurate said:
Hi,
that's interesting. Can you please make a practical example for a non-technician like me?
Thomas
If you have mutual coupling between two coils so that the fields partially cancel out to reduce the stray flux, you will also have a reduction in inductance. You can't get something for nothing here!
soundcheck said:
I think it's interesting to explore both because there might be a point where the difference isn't much.
phase_accurate said:
Normally we don't do it like that because you are relying on the proper magnetic field generated to maintain the inductor performance. This is one reason why two inductors are placed such that the magnetic fields are perpendicular to each other in speaker XO design. The same applies in output inductors.
With the RM core or Toroidal design, you are not canceling the magnetic field but sort of containing it.
I think you are comparing apples to oranges here ! In an x-over you definitely don't want the tweeter highpass to interfere with the woofer's lowpass but I don't see a problem where a single inductor split into two halves interferes with itself.
And yes, inductance could be lower in some cases than using a single coil but that depends on construction (hint: two coils of half the length) but it would still be higher than the inductance of an air-cored toroid of approximately the same dimensions.
Regards
Charles
phase_accurate said:
Just for an experiment, I took two 2mH inductors and put them on top of each other such that the widings were in different directions and connected in series. Resulting inductance is 2.6mH. I do not believe that this will actually behave like a 2.6mH inductor because if the magnetic fields are not balanced, the resulting signal will be distorted.
Has anyone actually tried this in practice?
The additional wiring to create the same inductance would be increased such that the resulting inductor would not be a good inductor.
You would have to place them beneath each other and wired such that the inductance increases. Then a large part of the field lines will go through both coils like in an R-core transformer. It does definitely not cancel the stray-field but it reduces it.
Regards
Charles
Regards
Charles
phase_accurate said:
If the inductors are connected such that the inductance increases, now the inductance will be 5mH, and the coils actually run with the windings running the same direction, thus the EMI problem would be worse.
I doubt there is any actual application using two coils, it just contradicts basic physics.
Edit:
R-core is a different animal. I have one sitting there waiting for an amp.
Oh, side by side.🙂
This does contain the magnetic field, but I wouldn't call than cancel. But I do wonder what it would do to signal passing though it.😕 These have to be matched very well to avoid distortion. Same in R-core transformers. But transformers are operating at a fixed frequency, this kind of arrangment with the way flux changes with frequency, I would think there would be quite some distortion.
This does contain the magnetic field, but I wouldn't call than cancel. But I do wonder what it would do to signal passing though it.😕 These have to be matched very well to avoid distortion. Same in R-core transformers. But transformers are operating at a fixed frequency, this kind of arrangment with the way flux changes with frequency, I would think there would be quite some distortion.
I nevcer said that they really cancel but the stray field will be reduced in the mid- to far- field and that could make a difference in some applications.
And I don't think that the topology alone will lead to nonlinear distortion if used with air coils
Regards
Charles
And I don't think that the topology alone will lead to nonlinear distortion if used with air coils
Regards
Charles
Indeed: no combination of linear coils, balanced or otherwise, can produce non-linearities; there is no "magic" in magnetic fields: they simply add and substract vectorially.phase_accurate said:
LV
As a comment for the ongoing discussion about foil coils, here is a comparation for post #52, it is the saturation curve for a 30uH foil coil, on RM10.
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