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Old 15th February 2008, 12:14 PM   #1
MMeche is offline MMeche  United States
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Join Date: Jan 2008
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Default Inductor advice

I have asked a portion of this question in another string but want to expand the discussion a bit. I have read a great deal of discussion on just how important it is to have good sounding caps in your signal path and fortunately I have had no problem sourcing quality caps.

I have seen little discusssion on the matter of inductors. My first project was a North Creek kit so I thankfully had very few decisions to make. For my second project, I am building one of Tony Gee's designs and before I start improvising, I intend to build it precisely as designed. The XO specs out two inductors wound from 2.0mm wire. I have no problem finding inductors that have the appropriate inductance value but since most of the products I run across are wound from AWG wire, the DCR is off depending on the particular gage. So here is the barrage of questions that come to mind.

Tony's spec calls for 2% tolerance, this suggests to me a fair degree of precisions, is it likewise reasonable to assume that the resistance specification is important to the performance of the systems?

If my set of choices gives me the appropriate inductance, should I select for the lower or higher DCR? (I'm guessing lower here)

I have found a precise match in the Geortz foil inductors at Madisound. Is this an appropriate substitution?

I did find one supply house that has the precise specification but for some reason, they only use 1 or 2 day international delivery which makes the shipping costs insane; If I have to, I will spend the extra money to do this but I want to make sure I am spending where it counts.

Is there some place else I look to find one of these?

I am very much a newbie but eager to learn. When I get a chance, I plan to model Tony's XO and see what happens when I change the specs a tiny bit. I also plan to keep the XO external to the box initially and actually listen to some alternatives but I do want to start with a precise design for reference purposes.

Next question, should I drive myself as crazy on resistor choice?
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Old 15th February 2008, 07:25 PM   #2
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Join Date: Feb 2002
Location: Western Sydney
5% is OK,
Correct, lower,
buy a cheaper one locally and spend the money you save on beer,
a resistor is a resistor is a resistor (just make sure it's non-inductive)
Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 15th February 2008, 08:28 PM   #3
MMeche is offline MMeche  United States
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I went ahead and order the foil type inductor, what do you think about those?
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Old 15th February 2008, 09:10 PM   #4
palmas is offline palmas  Portugal
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Originally posted by MMeche
I went ahead and order the foil type inductor, what do you think about those?
Probably the best inductors for speaker filters!
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Old 15th February 2008, 09:19 PM   #5
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Location: Santa Cruz, California
The series resistance of the inductors IS important. If you upgrade to a better inductor with lower ESR this will change the crossover. Depending on the circuit position a 5% error in ESR could be inaudible or it could make a big difference. Try and match both inductance and resistance to duplicate the original design.
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Old 15th February 2008, 09:47 PM   #6
MMeche is offline MMeche  United States
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Thanks to all. I assumed that changes to the DCR would change the circuit, I just have insufficient experience to judge whether or not I would be able to hear it.

In the end, I ordered the foil inductors from Madisound, they provided a very close specification match and compared to the imports are a reasonable price.

Based on the collective comments, I have confidence the XO will perform according to the designer's intention and I will have a little money left over for beer. Actually, I am more of a music and wine kind of guy. I save the beer for ball games and such.
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