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Old 8th July 2012, 07:27 AM   #1
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Default quick question about inductor

I'm building an Extreme Slop Crossover for the Klipschorns. the inductors are very big (~2-3-4 mH) so I decided to test my skill in winding them myself. the result is far better than I expected. all wires are twisted in order and side by side BUT I used an aluminum core as bobbin, I know aluminum is a metal of no magnetic properties, but wanted to check if it would cause a problem in sound any help appreciated

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Old 8th July 2012, 10:33 AM   #2
PLB is offline PLB  United Kingdom
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Hi ARIYAHOOR,

I have to say that your inductor looks great and you were wise to raise the question about the aluminum core. Unfortunately, having an aluminum core will significantly affect it. The problem is that the core acts as a shorted turn and affects the main winding via transformer action.

Regards

Peter
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Old 8th July 2012, 10:36 AM   #3
tvrgeek is offline tvrgeek  United States
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Not inductive, but you could set up eddy currents in it.

You have quite a piece of art there that took a lot to build. I try and make my air core coils purely air core. I wind them on a wood rod with wax paper protecting the spool sides. Then dip in varnish. When dry, slip it off and a nice neat coil. Will it effect the sound of a K-Horn? I doubt it.
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Old 8th July 2012, 10:44 AM   #4
ODougbo is offline ODougbo  United States
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What's your day job?...Nice work!

Alum...I don't know, I would have used wood.

What is the value? It doesn't look much bigger than a 1mh.

I'm surprised more speaker companies don't install/show XO's on top, back, etc. They are nice to look at and would make it easier to work on them.

btw, how did you cut the slots?
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Old 8th July 2012, 10:57 AM   #5
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Quote:
Originally Posted by PLB View Post
Hi ARIYAHOOR,

I have to say that your inductor looks great and you were wise to raise the question about the aluminum core. Unfortunately, having an aluminum core will significantly affect it. The problem is that the core acts as a shorted turn and affects the main winding via transformer action.

Regards

Peter
Uh thanks Peter
so aluminum is not good as a bobbin I have to use wood ... what about Plexiglas?

Quote:
Originally Posted by tvrgeek View Post
Not inductive, but you could set up eddy currents in it.

You have quite a piece of art there that took a lot to build. I try and make my air core coils purely air core. I wind them on a wood rod with wax paper protecting the spool sides. Then dip in varnish. When dry, slip it off and a nice neat coil. Will it effect the sound of a K-Horn? I doubt it.
thanks. yeah they look great to me. I didn't expect this look . actually I didn't use varnish. the sides are made of Plexiglas cut using Laser CNC. there are 8 chambers so I could easily tie them using plastic wire tie to steady the wires in place so tricky and it worked

so what to do now? I can't wind them without any core. the bobbin won't come out after winding. it's tightly stuck and berried under a ton of wires
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Old 8th July 2012, 11:06 AM   #6
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Quote:
Originally Posted by ODougbo View Post
What's your day job?...Nice work!

Alum...I don't know, I would have used wood.

What is the value? It doesn't look much bigger than a 1mh.

I'm surprised more speaker companies don't install/show XO's on top, back, etc. They are nice to look at and would make it easier to work on them.

btw, how did you cut the slots?
Uh thanks
actually my job has nothing to do with any kinda hi-fi activity
and yes. I think a well-designed and good-looking XO is worth to be at sight . they are piece of art work, just like tube gears so why hid them inside?
BTW, slots are cut using laser CNC as I said.
look at these extreme XOs:
Click the image to open in full size.
Click the image to open in full size.
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Old 8th July 2012, 11:32 AM   #7
PChi is offline PChi  United Kingdom
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My crossovers looked good until I used a Cartridge of Silicone Rubber to glue all the components down to the PCB to prevent any buzzes or rattles.
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Old 8th July 2012, 11:42 AM   #8
tvrgeek is offline tvrgeek  United States
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Hmmm. Might take a look at those resistors. Are they non-inductive wound?

I use the wax paper to keep the varnish from sticking to the spool. I wrap enough on the bobbin that I can get it to slide off with a piece of tubing pushing the bobbin side.
What is killing me around here is a spool of wire to wind my own costs more than buying coils from PE. It is hard to believe 500' of wire from the factory costs more than manufactured parts, but that seems to be the situation.

How to get your spool out? I think I would try to press it out with a wood or plastic plug of the same size. The plug becomes the new spool. Looks like a job for a hammer!
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Old 8th July 2012, 06:09 PM   #9
system7 is offline system7  United Kingdom
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To get an idea how bad the effect of aluminium on a coil is, you can look at Troels Gravesen's experiments. A sheet of aluminium near a coil reduced measured inductance form 3.3mH to 2.832mH, never mind resistive changes. Yours is worse, I'd reckon:

Placement of coils in crossover networks

Shame that such a nice piece of work is messed up. I made a similar error "tidily" fitting a capacitor inside a coil, which AllenB put me right about. You can just see it inside the red coil here.

Click the image to open in full size.
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Old 8th July 2012, 06:56 PM   #10
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To get an idea how bad the effect of aluminium on a coil is, you can look at Troels Gravesen's experiments. A sheet of aluminium near a coil reduced measured inductance form 3.3mH to 2.832mH, never mind resistive changes. Yours is worse, I'd reckon:

Placement of coils in crossover networks

Shame that such a nice piece of work is messed up. I made a similar error "tidily" fitting a capacitor inside a coil, which AllenB put me right about. You can just see it inside the red coil here.

Click the image to open in full size.
Uh you're hundred percent right. it was my first experience of winding inductors and I think I did it fine as everybody who saw this inductor kept telling me "it's wonderful ... a piece of art ... etc..) I think my only mistake was about aluminum but it's ok. you're right about the affect of aluminum on magnetic field. I used 18# wire at 195 turns and diameter was 1.58inches and length of coil is 0.68" ... on the paper it would show 2.4 mH but it turned out to be 1.8 mH!!! but it'd ok. it was just a prototype. I'll use non-metal bobbins in next ones I hope Plexiglas is just ok
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