Magnepan MG2.6/R possible blown crossover need info/help - diyAudio
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Old 28th August 2007, 07:07 AM   #1
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Default Magnepan MG2.6/R possible blown crossover need info/help

Hey everyone,
After a nightmarish month or so thinking I had blown out my Hafler Xl280 amp, I find I may have done something much more nightmarish.
I am the original owner of a pair of 1990 Magnepan MG2.6/R speakers. These things are six-foot ribbonated monsters that sound as soft as a down pillow. Problem is, I was listening to them at a fairly high sound level recently and one side seemed to kind of 'fizzle'. That is the best way I can describe it. I was sitting there and I heard some distortion and lowered output before I jumped up and switched everything off.

So I let the system cool, and thinking it was the amp, started doing left/right A/B testing to figure out what went wrong. It turned out to be one of the Maggies.

The problem all along since the fizzle has been reduced/slightly fuzzy bass output, especially the very bottom around 40/50Hz seems to be missing. The tweet seems fine, and the bass panel reproduces fairly low bass and midrange without any buzzing or flapping like a loose or broken voice coil wire on the panel.

BTW, I measured the resistance across both speakers, they both measure right at 4.75 Ohms - I think that's what they should be.

Everything tells me it seems like a cap in the crossover.
I would be confident disassembling/testing a crossover, but how do you get at it?
It looks like you :
1 Lay the speaker face down, 2 remove its legs, 3 remove screw caps from screws on back panel, 4 remove screws and screws/trimplate from terminal/fuse area. 5 remove back grill.

Is this right? I certainly do not want to hurt this thing any more than it is, so I want to know what to expect and how to do it before getting into this project.

So lets hear it forum, I need to know:
1. How to get at the crossover of a Magnepan MG2.6/R.
2. How to get a MG2.6/R crossover schematic, if necessary.
3. How to check/test the big inductors if it's not a cap.
4. If possible, how to know if it is the bass panel or the crossover.

I know you guys wanna help with these speakers, they are what 'audiophile' is all about for me. I have never heard a more three-dimensional soundstage from any speaker.

Thanks in advance
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Old 28th August 2007, 08:23 PM   #2
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Default Maggie Users Group

Sorry about my previous post, I apparently had not searched enough through this forum and I know that is a faux pas. I searched on 'Magnepan' in titles only and found the 'Maggie Users Group' along with the schematic for my 2.6/R crossover.

I was still hoping to hear from anyone with experience with one of these speakers.

On the schematic, there is 75uF cap on the bass side, how many think that this is my quarry?
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Old 28th August 2007, 08:46 PM   #3
mlloyd1 is offline mlloyd1  United States
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hello again
:-)

I saw this schematic:
http://www.integracoustics.com/MUG/M...s/mg2.6xo2.gif
is this yours?

i'd think if a parallel cap goes out, your low frequency driver will try to make more noise (attempting to reproduce frequencies it shouldn't) instead of less.

maybe a series inductor opened or suddenly increased resistance thereby reducing the bass level.

mlloyd1
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Old 28th August 2007, 09:34 PM   #4
mlloyd1 is offline mlloyd1  United States
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also, are you able to physically inspect the woofer to make sure there is no obvious damage (like torn surrounds, which would not affect the dc resistance measurement, but definitely would impact the sound).

sorry i didn't suggest this earlier. as i get older, i find i tend to take the obvious things for granted ...

mlloyd1
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Old 29th August 2007, 04:50 AM   #5
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Default Hope it's not an inductor

Hey mlloyd1!

Awesome, it's nice to know that someone is taking an interest in my predicament.

Yes, that schematic and the original are posted at that location. The original looks like this:
http://www.integracoustics.com/MUG/M...ks/mg2.6xo.gif

An alternate version that has been changed to allow for currently available inductors is here: (This is the link you have mlloyd1)
http://www.integracoustics.com/MUG/M...s/mg2.6xo2.gif

I was REALLY hoping it's not an inductor seeing as the original parts appear to be quite exotic. I was afraid of that. I may try contacting Magnepan when I determine what I need.

SO, this leads me to many new questions like,
'The original inductors on the bass side are 2.17mH and .70mH, the alternate schematic changes these to .39mH and .15mH respectively, won't this drastically alter the cutoffs or slopes? Won't my sound balance be different? I absolutely do not want to touch the working speakers crossover, so it has to match.'

'The alternate schematic also adds a 35uF cap and reduces the tweeters inductor from .75mH to .56mH - does anyone out there know if this makes any sense?'

So you say to reduce bass from the crossover side, it is probably an inductor and not a cap - great. Is there even such a thing as a cheap inductance tester? Should I send this xover to Magnepan?

BTW mlloyd1:
I have not actually removed the rear grille so I have not physically inspected the woofer panel (remember these speaks are planar, no surround or inductive voice coil). The thing is, the woofer panel IS working, and the sound is clean, just no deep bass. I have to assume that the panel wire and connections are Ok, that is why I think it is in the crossover. If you are careful, you can gently press on the rear grille until you feel the driver panel, and it is definitely vibrating and making sound, just no deep bass. Weird, eh? Maybe I should go back to testing the amp!
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Old 31st August 2007, 07:21 PM   #6
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Default Crossover Info

Hey everybody,
Judging by that ominous silence I suspect some of my posts have been a little on the ignorant side, but I did want to post some great info I found on passive crossovers.

I recently retested and reconfirmed that my reduced bass problem is, for sure this time, the speaker. Because the woofer panel functions with reduced lower bass output, I have assumed that my problem is in the crossover (probably an inductor).

At first, I was quite worried that this would prove difficult or expensive to repair, but I do have some hope after reading how easy it is to construct custom inductors. If I had to, I suppose there is a wealth of info out there that could even help me create 'better than stock' crossovers - but that isn't really what I'm going for, I just want to fix my Maggie.

Here is a great article on making a 'good' passive crossover:
http://sound.westhost.com/lr-passive.htm#s4.3


The next step in this project is to disassemble the speaker to a point that I can get at the crossover, I have not done that yet, but I assume hands-on measurements will point the way to go next...
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Old 24th September 2007, 04:05 AM   #7
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Have you tried posting your question over at the Planar Speaker Asylum of the Audio Asylum site. There is a WEALTH of info on Maggies there. Whatever your problem is, it's a good bet that someone else has had the same problem, and found a fix already. There is also a very large DIY contingent on the site as well. It seems as though each Magnepan model has it's own following.

Have you had a chance to lift the sock to get a look at things yet? Have you considered that your problem may just stem from a loose solder joint somewhere?
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Old 26th September 2007, 06:07 AM   #8
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Default Dazed and confused

Greetings,
Thanks for the suggestion, but after all of my efforts to diagnose my missing bass problem, I have returned to my precious (but apparently broken) amp.

Good thing too.
I laid my speaker down and removed the terminal trim plate to peek underneath the grille. Crossover looked fine along with DC resistance. I also removed the ribbon tweeter. What I found was lots and lots of staples. Quite simply, removing the rear fabric was more 'change' than I was willing to accept with these speakers.
I put everything back together and physically switched the left/right speakers. Oh yeah, even one of these beauties sounds amazing when it's running right.
At this point, I am so sure that it is the amp, I am willing to do a lot of late night disassembly / solder / clean / test / matching / investigating / ordering / learning / sleuthing / ebaying / shall I go on?

We all know the drill.

I will prevail - and the music will be sweet!!
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Old 1st October 2007, 02:00 AM   #9
kh6idf is offline kh6idf  United States
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When you swap the speakers does the problem stay on the same side or move with the speaker? From what you are saying about being certain it's the amp I assume the problem stays on the same side when the speakers are switched.
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Old 1st October 2007, 06:05 AM   #10
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Yes, after many tests and another set of speakers that actually helped confuse the issue, the problem always eminates from the same side of the amp.

I haven't had much of a chance to work on things lately, but I am staying positive due to the fact that most signs do not point to bad output MOSFETs which are very carefully matched in this amp and thus, unobtainable.

Hopefully when it is all soldered back together I can at least take it to a shop for diagnosis (if it still doesn't sound right).

I MISS my Maggies!
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