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Magnepan MG-12 Crossover upgrade
Magnepan MG-12 Crossover upgrade
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Old 6th June 2011, 12:14 AM   #31
gootee is offline gootee  United States
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So NOW I have to try to decide what to do.

Is it worth switching to a foil air core coil for the crossover's bass circuit, even if its DCR is HIGHER than that of the stock coil?

A lower DCR is said to make the bass better or louder and have better bass slam. So why did this guy at the link below report the bass going lower and having more slam when using a foil air core coil that has a DCR spec of 0.669 Ohms versus the 0.36 Ohms of the metal core stock coil that he replaced?

Does using a better 50 uF bass cap perhaps have a lot more effect than people might think? Or is there some other benefit that the foil air core provides that could account for it? Or is it something else that he did?

Here is the link: magnapan3

Here is the schematic of the the stock MG12 crossover: http://www.integracoustics.com/MUG/M...ver/mg12xo.jpg

Here are the current stock coil and most of the foil air core coil choices that I could find:

Stock 2.8 mH (nominal), not foil, not air core, 0.36 Ohms (meas) DCR

Alpha Core Goertz 2.7 mH, 14ga foil, air core, 0.370 Ohms DCR, $49.75
https://www.madisound.com/store/prod...products_id=41

ERSE FoilQ 2.70 mH, 12ga, air core, 0.365 Ohms DCR, $73.30 https://www.madisound.com/store/prod...oducts_id=8850

ERSE FoilQ 2.70 mH, 14ga foil, air core, 0.441 Ohms DCR, $42.25 https://www.madisound.com/store/prod...oducts_id=8907

ERSE FoilQ 2.70 mH, 16ga foil, air core, 0.669 Ohms DCR, $33.50 https://www.madisound.com/store/prod...oducts_id=8759

Alpha Core Goertz 2.7 mH, 16ga foil, air core, 0.583 Ohms DCR, $36.25

Those all seem to have a DCR that is higher than the stock crossover coil.

BUT, from the following link, Alpha-Core Goertz Inductors , it is clear that if Goertz would offer a 12ga foil coil value of 2.7 or 2.8 mH, then it would have to have between 0.202 and 0.304 Ohms DCR, and would probably be closer to the 0.202 than the 0.304, since those are the values for their 12ga 2.0 mH and their 3.9 mH coils. The Goertz website seems to be acting strangely, right now. But maybe they would custom wind some coils.
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Old 6th June 2011, 02:16 AM   #32
gootee is offline gootee  United States
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Since this is for a bass coil, maybe it's time to look at a large-gauge wire-wound air core coil.

Has anyone tried winding their own?

I wonder if using laquered copper tubing might work better than solid wire.

It looks like it's time for some coil inductance and DCR calculations.
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Old 10th June 2011, 03:58 AM   #33
gootee is offline gootee  United States
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Wow, copper magnet wire is expensive:

Magnet Wire - $7.34

But it looks like a little less than 5 lbs (250 feet or about 76 meters) of 12 AWG wire would make two 2.8 mH air core coils, each with a DCR of 0.18 Ohms, for a wire cost of about $50 each, plus shipping.

The length needed and thus the DCR will vary depending on the coil's dimensions. I used the calculator at Pronine Electronics Design - Multilayer Air Core Inductor Calculator to play around with the dimensions. Note that you need to adjust the coil "length" parameter so that you get a whole number of turns per layer (i.e. with no fractional part). And, if you bought a 250-foot roll of 12 AWG wire (5 lbs), you would need each coil to be made with less than 125 feet of the wire.

Using 8 turns per layer of 12 AWG (0.66133 inch width) would make a narrow, tall 2.8 mH coil. It looks like 6 to 8 turns per layer uses less wire than fewer or more turns per layer, at least with the small inner diameters that I tried.

If the inside diameter was 0.5 inch, then the 8-turn-per-layer coil would have 188 turns (23.5 layers) and a 4.47-inch outside diameter, with 115.76 feet of wire and a DC resistance of 0.18 Ohm.

If the inside diameter was 1.0 inch, then the 8-turn-per-layer coil would have 172 turns (21.5 layers) and a 4.64-inch outside diameter, with 120.98 feet of wire and a DC resistance of 0.19 Ohm.

I tried calculating a Brooks Coil configuration for it, too, but for 2.8 mH with 12 AWG wire it turned out to be 13 turns per layer for 13 layers (170 turns) with a width of 1.075 inches and an inner diameter of 2.15 inches and outer diameter of 4.47 inches, giving a wire length of 139.43 feet and a DCR of 0.22 Ohms. So that wouldn't be as good, in terms of DCR and wire length, and two of them couldn't be made from a 250-foot roll of 12 AWG wire. (Interestingly, maybe, the outer diameter is the same as for the first 8-turn-per-layer example, above.)

Or maybe I was doing something incorrectly. And even if I wasn't, there may be other configurations that are better.

Cheers,

Tom
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Old 14th June 2011, 04:30 AM   #34
gootee is offline gootee  United States
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Here's some MUCH CHEAPER magnet wire:

cPath_9 | Applied Magnets : Magnet Wire & Magnet Wire Spools - discount wholesale prices.

And it's factory-wound spools instead of rewound.
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Old 22nd June 2011, 03:04 AM   #35
gootee is offline gootee  United States
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Here is a somewhat-more-general thread that I started, about some possible pitfalls when trying to upgrade crossover components:

Crossover Component Upgrade Pitfalls?
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Old 14th July 2017, 09:36 PM   #36
udailey is offline udailey  United States
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Magnepan MG-12 Crossover upgrade
Hey Tom
I'm working on the same project for my 3.6R. Did you find closure and what were your conclusions about DCR effecting SQ? I'll try active afterwards but I want both passive and active to be as good as possible.
Thanks
Uriah
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purchase LDRs anytime Also try my Resistor Replacers or LDR based Input Selector Email me. diyldr@gmail.com
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Old 24th July 2017, 12:11 AM   #37
DeltaStar is offline DeltaStar  Canada
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I have MG2b's and just did the xo's, 2-12ga alphacore 2mh, and 4 Obligatto gold supreme caps 630v, cost $300.00 cdn, paid 200 for 2b's, first thing I noticed was far more transparent, cleaner sound, very worth while investment. I got rid of the fuse as well, no need for it.
Al
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Old 24th July 2017, 12:44 AM   #38
Davey is online now Davey  United States
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Al,

I would have left the fuse in for your initial evaluation. (Just for a baseline subjective evaluation.) I suspect the fuse and/or related connections were a not insignificant problem.

Dave.
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Old 24th July 2017, 02:09 AM   #39
DeltaStar is offline DeltaStar  Canada
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Dave, They blew fuses like popcorn even went to 5 amp, been driving them real hard with no problems without fuses.
Al
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Old 24th July 2017, 02:16 AM   #40
tyu is offline tyu  United States
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Right about the fuse.....hehe....30 year old wire.....Magnepan dose not have or sale the tweeter wire any more....good luck with that
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