Air core inductors

40+ years in audio and I've never seen an inductor like that. Do you mind telling me what they do in the amp?

Jason
Wondered how the CLCLC PSU worked out? As I am considering a choke regulated supply with my Aleph X.
Not sure from your picture where the connections for the inductor are.
Any chance of more pictures of your PSU?
Did you try the cap across the transformer secondaries as per thread http://www.diyaudio.com/forums/showthread.php?s=&threadid=26223&perpage=15&pagenumber=2 ?

thanks Simon

The coil calculator website doesn't seem to work...

Hi Jason,

I came across that website last night while trying to design some inductors myself, but I could never get it to work. I enter the desired inductance and it alsways comes back with a server error.

Have you used it lately?

Here's one that is just as good, although you have to supple the coil diameter and width (called "length").

Coil Calculator

Jason, Can you post a close up picture?

Of that coil inductor. I'm thinking of winding my own and was wondering just how perfectly commercial coils are wound.

Thanks

I've been reading up on coil making(long)...

the last few nights because I want to upgrade the x-over's in my speakers. I have Hammer Dynamics Super-12 high efficiency single-drivers.

They feature a 12" driver which handles 45-10kHz with a super tweeter crossed in above that. John Wyckoff, the designer, wanted the crossover point well beyond the range of critical hearing where normal crossovers work ~ 2k-4kHz. The tweeter is mounted directly infront of the main driver to maintain time-coherence much like a coaxial (see picture below).

The tough thing for me is that I have two coils in series on the main driver(0.65 mH & 0.24mH) that have to handle a very wide range of frequencies well.

Common belief is that heavier gauge wires handle low frequencies far better than thinner gauges at the expense of high frequency performance and vice versa.

I don't have a lot of money to experiment with different coils, so I thought that I would go with a known winner for my speakers - Solen Hepta-Litz multi-stranded since the maker of my speakers said that they were the single most impressive upgrade they've ever heard.

I talked to a Solen technician who actually suggested that I use their $5 16 gauge Litz coils for my 12" and their standard (and cheap) $1.75 20 gauge coils for my tweeter. Now, that is a value buy!!!

But, having said all that, I'm still intriqued by Northcreek coils which are reputed to be some of the best made for deep, detailed, bass. Northcreek swears by the belief that the larger the gauge the better. In fact, their top coil is a whopping 8 gauge!!! They even use 10 gauge coils on the tweeters in their top of the line speakers.

This kind of flies in the face of all that talk about "skin effect" and poor high frequency response in heavy gauge wires.

Of course, Northcreek coils, especially their heavy gauge ones, are way out of my price range. There's no way I can afford to spend $200 on coils as an experiment.

**BTW, the Solen technician told me that their 10/12/14/16 ga. standard single wire coils exhibit "non-linearities" above 5kHz. The 18 & 20 ga. extend to 26kHz before problems.

More surprising was that their Hepta-Litz has problems at:

10 ga. >300Hz
12 ga. >500-1kHz
14 ga. >8kHz
16 ga. >25kHz yet extends up 100kHz

I can't afford to risk big money(for me) on the unknown like heavy gauge coils like Northcreek, but I still want to try them out. I have heard really great things about their big coils.

So, that's what got me thinking about making my own. It's no where near as complex as transformers. Although, one supposed problem with winding large gauge coils is that the high tension necessary to bend the wire while winding causes micro-fissures and irregularities in the crystalline structure of the copper(I said supposedly). Northcreek claims to use a "low-tension" method of winding which avoids this.

I was thinking about how many "low-tension" ways there are to bend wire and the only thing that I can come up with is to heat it. Most large magnet wire is rated to 200C (391 F), so it can handle pretty high tempetures. Why not slowly heat the spool of wire in a pot of boiling water to get it up to 100C(212 F) so that it is plyable enough to unroll and roll easily without too much tension or stress.

Northcreek also talks about a DIY method of "goop-wound" winding which is done by adding an adhesive like hot-melt glue while the coil is wound.

Goop-winding is the process of winding an inductor inside a bobbin or former, while a bonding agent (usually hot melt adhesive) is applied directly to all of the windings throughout the entire process. Goop-winding makes a very unattractive inductor, but they sound remarkably good. This is the only method recommended for those that wish to "wind their own".

So, all you need to do is spread hot-melt glue to each layer and around the outside when it's done. Allow the coil to slow cool and your done.

The way to make sure that you get the exact value needed is to use a multimeter with one of the wire penetrating points and test at different lengths of the last layer until it reads the proper value., then cut.

An 0.65 mH 9 AWG coil like I need would have:
4.0" inner diameter
1.5"x1.5" winding
76 ft of wire
81 turns
6.18 layers
13.11 windings per layer
3.01 lbs weight

And a DCR of 0.05 ohms. just a little over Northcreeks 0.03 ohms rating. Of course, in the real world it probably won't rate that low, but who cares in that region.

Now, I don't expect it to be anywhere as easy as I've discribed it, but I can get 350 ft. of 9 AWG copper magnet wire for $25 from a local surplus store. That's enough to do all 6 coils I need. And it won't hurt to give up if I find out it's too much hassle.

What do you think?

Re: I've been reading up on coil making(long)...

darkmoebius said:

.

So, that's what got me thinking about making my own. It's no where near as complex as transformers. Although, one supposed problem with winding large gauge coils is that the high tension necessary to bend the wire while winding causes micro-fissures and irregularities in the crystalline structure of the copper(I said supposedly). Northcreek claims to use a "low-tension" method of winding which avoids this.

I was thinking about how many "low-tension" ways there are to bend wire and the only thing that I can come up with is to heat it. Most large magnet wire is rated to 200C (391 F), so it can handle pretty high tempetures. Why not slowly heat the spool of wire in a pot of boiling water to get it up to 100C(212 F) so that it is plyable enough to unroll and roll easily without too much tension or stress.

Click to expand...

This statement is 100% BS, You can mistreat copper to insane levels and still have the same electrical properties. If this wouldnt be BS, all the wind turbines around the world would be in deep...I wouldnt expect that they had not found out by now if that was the case.

You can rest assured that your inductors will be fine if wound on a former of reasonable size. The only crac ks youd ever see during winding would be cracks in the insulation.

Instead of using hot melt glue, use slow epoxy and bake the inductor afer winding. This gives a stronger and beautiful result. Thats the way they do when made for industrial purposes, though they use heat hardening epoxy.

Magura🙂

P.S. The shavano inductor calculator is a little off, but not much.

Heating up the wire to those temps will create a problem with heat expansion and contraction when it cools. The layers might crush as it cools.

markp said:

Heating up the wire to those temps will create a problem with heat expansion and contraction when it cools. The layers might crush as it cools.

Click to expand...

No, the thermal expansion of copper os low, you cant possibly wind an inductor tight enough to get such a problem when wound without PRO equipment, and even if wound real tight, I still doubt it.

Again, there is no need to heat the wire in the first place. Reasonable quality magnet wire is soft annealed allready.

Magura🙂

Thanks for the advice Magura....

The stuff about micro-fissures isn't my idea, it was from the Northcreek website. That's why I included the "supposed" in brackets.

Anyway, I was laying in bed last night obsessing about this stuff and came to the realization that when the original wire manufacturer initially winds the spools of copper wire, it is probably done at room tempeture. And once again when it is coated with enamel. And probalby a few more times as it is wound onto smaller and smaller spools.

I'm interested in seeing how soft the 9 gauge actually is and how hard it will be to get it to form to a fairly tight coil.

As for varnishing, the problem would be getting varnish to the center layers of the coil. Simple dipping may do, or may not. A vacume approach sounds good, but I don't want to deal with that on a first try. I also don't want to have to buy any type of oven to bake them in 'cause it ain't happening in the kitchen!!!

It sould be nice to find a not-melt glue that becomes fairly liquid like, not the thick goop I'm used to seeing. Perhaps, that's why the commercial houses varnish.

As for a winding mechanism, I was thinking of something like they have at Home Depot(but on smaller scale) for measuring bulk wire. Just a hand crank and a counter. Although, the center spool of their winding contraption is slatted to allow easy tying of the bundles. This would help to keep the coil shape.

Anyway, I'd love to get some more advice if you have any, Magura.

BTW, how far off is the inductor calculator?

I ran the specs for the coils I have on my desk and it was dead on. But, when I entered the specs for 9 awg 0.65mh coil it came back with a 0.66mH value.

Jason,

I think you may be right about the differing DCR ratings of coils that are the same mH value. I spoke to an Aplha Core technician about their foil inductors and he made a point that it might be necessary to fine tune the values of the other components in the x-over after switching from different types of coils.

The DCR of a 12 AWG .30mH inductor is:

0.17 ohms Northcreek single conductor
0.129 ohms Alpha Core copper foil
0.16 Solen single conductor
0.24 ohms Solen Hepta-Litz

This may not be much in real world, but I do have two coils(0.24mH also) in series in my main driver circuit, so the resistence would be nearly double that and twice the others.

You can also just use simple 24hour araldit. Thin it with alcohol to make it almost like water, coat each layer as you wind with a brush. This would take a while to harden, but will work just as well.

9 gauge (2.91mm) is no problem to form. Its so soft that you can easily control it by hand. I use 2mm wire frequently, its like butter.

The original manufacturer actually only wind it up on the spool you get it on. If you wind it several times it hardens up.

If you need a specific value I would wind a few extra rounds, and then cut off as you measure till it fits the bill. You cant count 100% on the math cause you also influence by the way you wind, your level of skill and how tight.

If you have to make more than one, make a form by finding a plastic pipe (plumbers have a wide selection) cut a piece as long as the inductor should be wide. Cut two round sheets of plywood and drill a hole in the center. wax the plywood on one side (to be the inside in order to make it possible to get it to let go of the epoxy after it have hardened) and put the whole thing together with a bolt through the center, fix it with 2 nuts in order to make sure it dosnt come loose accidentally during winding.

Then you have the end of the bolt to mount in whatever you are planning to wind it in. After youve wound the inductor and the epoxy is hardened, you take out the bolt and take the plywood sides off. now you can heat the plastic pipe with a hairdryer or a heatgun ( i usually bake the inductor) , the plastic pipe will become soft and can be removed....viola..you got a pro looking inductor.

Magura🙂

Right On, Magura!!!!

Man, have you saved me a lot of unecessary effort, I was seriously overcomplicating things. I love your idea for a winding wheel - it's simple and cheap.

I've never heard of Araldite, but it looks to be the same as what we call Epoxy which I've used quite a bit. My only concern is whether Epoxy will dissolve the enamel coating on the wire. It seems that there are specific forms of Araldite designed specifically not to do so.

If you are really hard core and you care about the crystalline structure of the copper, you could anneal it after you wind it. Stick it in a kiln until it reaches 1000°F and let it air-cool (or even better, cool it in a nitrogen atmosphere).

This might be a problem if the enamel melts below 1000°F.

Araldite is just the brand that everybody uses in europe, any epoxy will do. Just make sure you thin it enough to float in between the wires.

The enamel coating of the brands ive been working with is amlost indestructable, epoxy sure wont harm anything.

Magura🙂