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In Reply to: RE: Magnepan 12QR crossover question posted by krakus248@gmail.com on August 29, 2014 at 07:10:29
Welcome to the forum, K!
I am still at work but will check later when I get home to see what I can dig out for you this evening. Hopefully, someone with 12's already has this specific stuff and will post it soon anyway.
In the meantime, have you already bought the crossover parts? Do you have a list of specific candidate parts? There are a few of us here who may have various "tweaking ideas".
Follow Ups:
JBen,
Thanks for input - i will wait for your next post...
Here are my new parts for little crossover project :
2x Jantzen wire air coil 2.8mH, 0.443 ohm
2 x Mundorf Mcap EVO Oil kondensator 0,10 uf (shunt for tweeter)
10 x Mundorf Ecap 70 VDC PLAIN 10,00 uF (5x10uF per side electrolyts for bass)
2 x Mundorf Mcap 33,00 uF
2 x Mundorf Mcap 630 0,10 uF (shunt for bass)
Wile choosing above i kept in mind to use original MG 12 crossover space - i want to keep them as close as possible to stock units - so, no external crossover.
I think, that biggest improvement will come from air coil in bass and Mundorf Mcap shunted with Mundorf Evo Oil in tweeter section....
I like Mundorfs for the sound and i hope that this combination will do the job in Maggies.
Because i was not sure about bass caps (if they can influence the sound in such place of crossover) i decided to stay with elcos and upgrade only their quality - so once again good old Mundorfs..
The Ecap electrolytics though much better than older low ESR electrolytics are still not to the level of the other caps you are using. I would suggest you use MKPs instead.
The other Mundorfs I assume are MKP metalized polyprop. They are very good. The oil cap for the tweeter is a very good idea.
Of course MKP's are better than Electrolytics .
But they are much bigger too, so no matter if i use single 50uF, or try to combine 50uF from smaller capacities - there is no way to mount them into MG12 crossover space....
I do not want to have the external one, so this is why i have to stick to electrolytics....
There are lower voltage square stacked film caps that don't occupy as much space, lots of models from Wima for example. Perhaps those would fit.
Later, if you have an extra pair of power amplifier channels, ask us about line-level bi-amp options for Maggies. These can be built active or passive (the latter, rather easily and inexpensively). With these, the issue of the large external xover boxes could be "mostly resolved". More importantly, the true potential of those 12s could be easily tapped.
Have fun! (and pls let us know how it goes)
Super! Neolith made our lives easier with this schematic, which you seem to have understood well.I see that you are all set with new crossover parts. We will have to wait and see how you find them performing after a break in period. IMHO, Neo's mention of a separate crossover box is something that you should consider, along with his other suggestions.
On the question to Neo about polarity inversion, it matters. You should be able to hear it for yourself by testing it with some recordings.
The simple fact is that most Maggies have magnets on only one side of the Mylar. The Mylar moves "out" -- away from the magnets -- with different dynamics than when it moves "in" -- toward the magnets.
This asymmetry will affect the average recording in the same fashion: dynamic impact will be better felt with one polarity vs the other. It actually is more complicated than this but this is the bottom line. The behavior changes, and it is not just about dynamic impact, which is just the most obvious sign.
The other part of your question has to do with the xover parts in one or the other polarity. Some caps do tend to behave differently depending on polarity, though usually in subtle ways. The explanation for this is longish. I'll leave it for others to elaborate. For now, you may want to explore forums where the Mundorf caps are discussed. They may have some hints if polarty should be kept in mind. OTOH, coils, if they are alone, have no such sensitivities, AFAIK.
Finally, "bass caps" as you call them do affect the sound. While I no longer use a regular xover, my [ancient] MMGs had one similar to what your 12 have (newer MMGs are different). Before I biamped them, my initial experiments with a regular xover showed how sensitive the Maggies can be to the wrong shunt cap. Both timbre and "speed" can suffer. You should be fine with the Mundorf, I think. However, if you notice less dynamic impact than before...this is one good place to look. Yet, one needs to wait out the long break-in period first.
Edits: 08/30/14 08/30/14 08/30/14
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