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Old 9th March 2011, 05:42 PM   #31
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From what I have been reading,manufactures are already using such metals as a standered practice.
It is just hard to pin point which product is using what metal unless you specificly order what you want.
But I can tell you this I have never seen the kind performance I get out of my toriod power transformer for audio.
I have several tube type OPT's laying around and have compared them too.
I have found that the doughnut takes the cake everytime ,ten fold!

As I have stated before where else can you find a transformer cheap that has a flat response well past the audio range,produces perfect square wave at low and high levels , is already made and all you have to do is add a few turns for a new winding.

Give it a thought or try, and let us know what you find and If I get to it before you do I will post my results as well. jer
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Old 9th March 2011, 05:55 PM   #32
jcx is online now jcx  United States
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for tweeter use the mains power cores have way high loss from too thick laminations

better HF "tape wound" core exist - are pricey

for ribbon tweeter use it could use the largest pot core, hi perm ferrite - a consequence of low V, high lf corner frequency

a problem with the required low R is that heavy wire/foil will give bigger loss from skin depth/eddy current in the copper too - the multifilar/bunched winding techniques may help
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Old 9th March 2011, 07:04 PM   #33
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Good point.
However I,m not sure about the validity of your last statement as flat conductors are used in high power rf amplifiers to combat losses due to the skin effect at radio frequencies.
I don't think this is going to be as much of a factor at audio frquencies as having a high leakage inductance will.
And yes, the thinner the laminations the better,but the price factor goes up drasticaly as well. jer
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Old 9th March 2011, 10:14 PM   #34
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Talk to me about that skin depth & eddy current thing with foil??

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Old 9th March 2011, 11:44 PM   #35
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If you google up "skin effect caculator" you will find many articles and discussions on the subject.

Basicaly by using a flat conducter you are increasing the surface area of the wire compared to a round wire of the same cross sectional area thereby reducing the effective resistance at higher frequencies caused by the skin effect.

The skin effect causes the wire to have more resistance at higher frequencies than it would if just a direct current were flowing through the wire.
This is why silver plated copper is used for coils in rf equipment,particularly highpower vhf and uhf amplifiers.

The effect of eddy currents in the windings are nulled by current flowing through it.

Eddy currents in the core are combated by using thin laminations.
The thinner material has a higher electrical resistance thus reducing the eddy currents that get setup in the core material.
Also this is why the laminations must insulated from layer to layer.

I hope this helps you to understand more throughly. jer
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Old 10th March 2011, 01:21 AM   #36
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jcx said that the foil will have greater losses due to skin effect, whereas you seem to say lower losses due to the (skin effect) lower resistance at higher freqs... which is why I said something earlier. Ask first.

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Old 10th March 2011, 01:35 AM   #37
jcx is online now jcx  United States
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I was actually thinking of someting closer to "bus bar" than foil - after all the ribbon load is on the order of few 10's mOhm - say you need ~10x the ribbon length to get there and back and circle the core, if you want 1/10 th the Ribbon's R in the secondary then you need 100x the cross section area (less with Cu vs Al)

Last edited by jcx; 10th March 2011 at 01:38 AM.
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Old 10th March 2011, 02:26 AM   #38
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Yes indeed,you stiil need cross sectional area to handle the current.

The idea with using a foil tape conductor is to try to make sure that all of magnetic lines of force are cutting through the winding by getting 100% coverage of the core.

For an 8 ohm/ .28 ohm (1:26) transformer at 100 watts your talking about 130+ amps so you must have enough combined cross sectional area to handle the current.

I got some 1/4" copper tape from hobby lobby cheap and can be wound around the toriod very easly.
At least that was my intension when a bought It except that I have been working on ESL's instead. jer
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Old 10th March 2011, 05:33 AM   #39
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I had an old H H Scott amp that used square wire on the 2 ohm winding of the OPT. I would go with that. Skin effect doesn't really come into effect till you hit the MHz. But if I was really going to make a ribbon tweeter I'd go with a SS amp!
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Old 11th March 2011, 02:28 AM   #40
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as just mentioned, the problem with thick fat stuff (square or not) is that you don't get enough coverage over the primary windings by the secondary... fine for power transformers, and that's how they used to build monster 5vdc power supplies.

Jer, I suppose that if you made a few windings with that 0.25" copper foil (to cover the toroid surface) and then ran them in parallel, you might have something.

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