More about using foil air core, related to a link above about Magnepan's recommendation:
The question should read - MikeCh - Planar Speaker Asylum
The question should read - MikeCh - Planar Speaker Asylum
Very interesting post (thanks, Tom) - I agree with everything he says!
Can I suggest it's a waste of time to just replace the caps, and not the coils as well. IMO, replacing the caps gives you top end beauty ... installing 12g ribbon coils gives you better bass. One without the other will not be satisfying - you'll soon decide to bite the bullet and do the other half!
Now the stock MG-12 is 2nd order on the bass & 1st order on the treble. If you wanted to save 1 component (the 50uF cap in the bass filter), to make the new XO a bit cheaper (so you can afford a good 12g ribbon coil!
), you could use Peter Gunn's (on the Planar Asylum) 6dB series XO - I'm sure he will send you the schematic.Good luck with the mod,
Andy
I'd be interested to know why you think that ... given Magnepan has used all-6dB XOs in their latest models, the 1.7 & 3.7.
Regards,
Andy
Very interesting post (thanks, Tom) - I agree with everything he says!
Can I suggest it's a waste of time to just replace the caps, and not the coils as well. IMO, replacing the caps gives you top end beauty ... installing 12g ribbon coils gives you better bass. One without the other will not be satisfying - you'll soon decide to bite the bullet and do the other half!
Now the stock MG-12 is 2nd order on the bass & 1st order on the treble. If you wanted to save 1 component (the 50uF cap in the bass filter), to make the new XO a bit cheaper (so you can afford a good 12g ribbon coil!
Good luck with the mod,
Andy
Thanks, Andy, but I didn't mean that I would NEVER do the coils. I do plan on replacing them, too. I was actually just expressing my frustration with the three different "out of stock" situations for the steel core coils.
After doing some more reading I think I'll bite the bullet and order some lower-DCR foil air cores. But first I want to measure the actual DCR of the stock MG12 coils, because it looks like I want to make sure to replace them with coils that have a somewhat-lower DCR than the original ones have.
Tom
I finally realized, after looking at the MG12 crossover schematic again, that I could measure the apoproximate DCR (DC Resistance) of the stock inductor/coil without removing it from the circuit, just by disconnecting the speaker from the amplifier and removing the tweeter jumper.
I already had the sock off of one of my MG-12/QR speakers. So I was able to measure the resistance between a) the junction where the coil's wire and the 50 uF electrolytic capacitor's lead are both soldered and b) the junction where the coil's other wire and the black lead from the "negative" speaker input are both soldered.
I did also remember to short the Tektronix DMM916 multimeter's leads together, before and after, and subtract the non-zero displayed value from the resistance displayed during the measurement. And I repeated the measurement several times.
The measured coil resistance was 0.36 Ohms.
Cheers,
Tom
I already had the sock off of one of my MG-12/QR speakers. So I was able to measure the resistance between a) the junction where the coil's wire and the 50 uF electrolytic capacitor's lead are both soldered and b) the junction where the coil's other wire and the black lead from the "negative" speaker input are both soldered.
I did also remember to short the Tektronix DMM916 multimeter's leads together, before and after, and subtract the non-zero displayed value from the resistance displayed during the measurement. And I repeated the measurement several times.
The measured coil resistance was 0.36 Ohms.
Cheers,
Tom
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/MUG/tweaks/xover/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/product_info.php?products_id=41
ERSE FoilQ 2.70 mH, 12ga, air core, 0.365 Ohms DCR, $73.30 https://www.madisound.com/store/product_info.php?products_id=8850
ERSE FoilQ 2.70 mH, 14ga foil, air core, 0.441 Ohms DCR, $42.25 https://www.madisound.com/store/product_info.php?products_id=8907
ERSE FoilQ 2.70 mH, 16ga foil, air core, 0.669 Ohms DCR, $33.50 https://www.madisound.com/store/product_info.php?products_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.
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/MUG/tweaks/xover/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/product_info.php?products_id=41
ERSE FoilQ 2.70 mH, 12ga, air core, 0.365 Ohms DCR, $73.30 https://www.madisound.com/store/product_info.php?products_id=8850
ERSE FoilQ 2.70 mH, 14ga foil, air core, 0.441 Ohms DCR, $42.25 https://www.madisound.com/store/product_info.php?products_id=8907
ERSE FoilQ 2.70 mH, 16ga foil, air core, 0.669 Ohms DCR, $33.50 https://www.madisound.com/store/product_info.php?products_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.
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
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
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.
cPath_9 | Applied Magnets : Magnet Wire & Magnet Wire Spools - discount wholesale prices.
And it's factory-wound spools instead of rewound.
Here is a somewhat-more-general thread that I started, about some possible pitfalls when trying to upgrade crossover components:
http://www.diyaudio.com/forums/multi-way/191087-crossover-component-upgrade-pitfalls.html
http://www.diyaudio.com/forums/multi-way/191087-crossover-component-upgrade-pitfalls.html
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