Winding ferrite corred inductors

[pjpoes]

I need some inductors in the higher range (over 4mh) with as low dcr as possible. While there are plenty of options available, they are all too expensive. I've been thinking about making my own by winding onto a ferrite core, at least for initial testing purposes. I can buy toroid cores and wind those, they actually seem like one of the easier options, and may offer the lowest dcr and best packaging. I'm not sure what core size or even how many winds, as there aren't many sites indicating that, but I can measure, so I may just need to experiment. Other options are to buy ferrite rods or even ferrite inductor cores and wind onto those. I understand that epoxy coating or insulating the core can be important, is this true? To keep from a possible short? Any feedback on this idea is appreciated.

I didn't end up getting the winder to make my own aircores, cheap enough to buy them I guess, but at 10-20 dollars for larger ferrite cores, it seems to make more sense to wind them myself maybe.

Oh what about steel laminate, is that literally just a series of sheets of thin steel placed together, with the wire wrapped around it? Is there an advantage tot he steel laminate design over ferrite core? I mean, in that case I could buy a thing piece of steel, cut it with some sheers to size, laminate them together (should I use an adhesive for this?), and wrap away.

Before you all try to talk me out of this, one reason I want to make my own, besides saving money, is that I'm still debating the woofer configuration, which will change the impedance, and thus change the values needed. The difference in cost between a 9 or 10mh inductor and a 4 or 5 mh inductor is pretty substantial, I don't want to buy both, and I'd rather not buy the larger one and unwind it either. Also, the woofers can handle well over 600 watts total, and while I probably won't feed them that much, the inexpensive steel laminate inductors with 18 gauge wire are only rated for 200-250 watts. The next size up gets me into 30-50 dollar inductors, which I really want to avoid.

[infinia]

Originally posted by pjpoes

Oh what about steel laminate, is that literally just a series of sheets of thin steel placed together, with the wire wrapped around it? Is there an advantage tot he steel laminate design over ferrite core? I mean, in that case I could buy a thing piece of steel, cut it with some sheers to size, laminate them together (should I use an adhesive for this?), and wrap away.

In regards to LF distortion i.e hysteresis ranked by least first
1) Air coil
2) Steel Laminate
3) Powdered Iron

Steel laminate is special steel designed for power Xfmrs.
Suppose you could locate sources by either distributors or OEM Xfmr houses. Thinner lams are used for higher frequencies.

edit>Tips
Lower impedance drivers help.
Yet another reason for active Xovers.

[pjpoes]

I'm not going to get into arguments over active crossovers vs passive, that's been talked about a lot on these forums, and my stance is very clear. I would need 8 amplifier channels just for the front speakers in order to use fully active for my design, not a lot of crossovers can handle that, nor do I have enough amplifier channels, so its not going to happen. Are we really going to get into a cost comparison there?

This is to test some ideas out, so I really just need to be able to obtain the parts cheaply enough, with some flexibility in values. I might even be considering unwinding and rewinding some steel laminate core inductors I have to obtain the values I need.

I've read that the distortion of the toroidal core inductors from Jantzen is the lowest of their offerings, and I'm wondering if there is any truth to this. Unlike some other companies, they don't show distortion graphs, but I could always measure to see for myself.

The problem with air core is DCR. I would need to wind coils with 10 gauge wire to equal the dcr of a cored inductor, and even 12 gauge gets into an unmanageably large and expensive part. Since higher distortion in these devices is generally more in the higher frequencies, and distortion is less audible in the lower frequencies, I have two factors going against worrying about inductor distortion vs dcr losses and power handling.

[infinia]

Sounds like you painted yourself into a corner.
http://www.national.com/mpf/LM/LM4780.html
It's what Linkwitz would do.

[Eva]

This link is switching mode power supply related, but you may find some info on getting cores and calculating inductors on it:

http://www.diyaudio.com/forums/showt...03#post1393703

Don't forget saturation current when calculating cored inductors. It's a very important parameter because the inductor becomes a plain piece of wire as soon as instantaneous current exceeds that value.

Consider doing the lower crossover in active, the upper ones are not so troublesome. If you don't feel confident on active crossovers, read about Siegfried Linkwitz, his speakers and his methods.

Otherwise, consider bringing bass impedance down to 2 ohms or so by paralleling low impedance drivers, this really has an impact on inductor requirements.

[pjpoes]

I'm confident with active, thats not the issue. I'm testing ways of dealing with three bass drivers, wiring the three in a series/parallel configuration vs a sort of 3.5 way, hence the need for different values. It's a sort of proof of concept, so again, I need the inductor, active won't cut it give what I'm trying to test. Plus I can more easily make this work passively. None the less, if you read my posts, you will see I have extensive enough experience with active and could make that work just fine, I'm just not a fan of the digital crossovers out there.

I have a calculator I found for various types of inductors that tells me how many turns and the saturation points based on the material used and core size. The inductor core I want to use is large enough that saturation is way outside range I will be using them in, and the frequency issues are into the 30-50mhz range, again, way outside what I need. Sounds so far like my basic understanding is good enough from my reading, but thanks none the less.

One problem with 3 bass drivers is that no matter how I wire them, I get a load I don't want, too high or too low, unless I mix the series parallel, I think.

[Moondog55]

Query are the three drivers all 8R??
I have tried all sorts of confirurations and one that worked for me needed 4 or more woofers, what I did was to wire the top in parallel, twist all the negative wires together, put a largish inductor in series and then wire that load to the next woofers in line.
I have tried something similar using 2 8R woofers in parallel with an old style 4R car sub last in line, wired series to give nominal 8R load