DIY Magnepan SMGa repair - diyAudio
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Old 31st July 2008, 10:57 PM   #1
diyAudio Member
 
Join Date: Dec 2004
Location: Mountain View, California
Cool DIY Magnepan SMGa repair

Hi folks,

Here is a brief progress report on rebuilding my SMGa speakers. As mentioned elsewhere, I tried localised re-gluing of the original wires. This lasted for a while, but eventually they started to detach and rattle against the diaphragm.

The problem was not being able to remove the old, soft adhesive sufficiently to get good clean surfaces for the glue to do it's job. In my opinion the only way to tackle this problem is to strip the panel and replace the wiring (salvage of the original is not really an option). To help with this I purchased the repair kits available from Magnepan, one for Bass and one for treble wiring. This seems to be the only (easy) way to get hold of insulated aluminium "magnet" wire. I spent nearly a day on the 'net seeking alternatives....

Progress:

Yesterday the left speaker was dismantled and a careful note of the "voice coil" wire patterns made, along with photographs to complete the record. These have proven essential to get the details correct during reassembly.

The old wires were removed by softening the adhesive with acetone. The remaining residue was cleaned up with more acetone. Luckily I have a covered outdoor workspace, as quite a lot of solvent is required and breathing the vapur is not recommended.

Today I set things out for rewiring. At first I planned to build a jig so that I could string the wires, then offer them up to the panel (pre coated in contact adhesive) in one go. Thinking about this further, I decided instead to run the wires by hand. The diaphragm was sprayed with 3M super 77 contact adhesive - as recommended by Magnepan's instructions.

It was possible to place each 4' run of wire, shape it around a suitably sized dowel, tack down the "loop" then run back to the bottom of the panel. In this way the pattern for the bass wires was completed in about 10 minutes. Care is needed to ensure the loop ends do not lift (I weighted them down as recommended elsewhere).

After this the wires receive 2 coats of a water based adhesive to complete the bond to the panel. There is some risk of this upsetting the tack layer of "Super 77" but I had little problem in this regard. (I did some experiments with a length of old wire and a grocery bag to gauge handling & drying times)

The bond between wires and panel appears to be very secure.

The treble wires were set in a similar manner, though being of finer gauge, this was easier to apply. There is also a much smaller, simpler pattern, so it was very easy in comparison to the Bass section.

Next I need to solder the wires to the terminals at the panel edge (aluminium compatible solder included in the repair kit) and test the speaker.

If that works out, I'll pull the other speaker apart and repeat the experience.

Cheers,

Ed

References:

http://www.opus45.com/magnepan/

http://www.integracoustics.com/MUG/M...nn/repair.html


http://www.integracoustics.com/MUG/MUG/
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Old 1st August 2008, 03:39 AM   #2
ktuuri is offline ktuuri  Canada
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Join Date: Nov 2007
Looking forward to the finished project. Are you taking any pics, care to share some. May be good to document the process, could be helpful to others.
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Old 4th August 2008, 12:31 AM   #3
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Join Date: Dec 2004
Location: Mountain View, California
Good Idea. I'll upload some pictures when I have a chance. Certainly it might be useful to others if there's a record of the wire pattern. The bass section is a mixture of single and double passes between the magnet rows, and the layout needs careful attention to detail.

No chance to hook up the panel to an amp yet, but it did get a signal form the radio in the work area. Both sections played music, so we're well on the way.

Ed
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Old 6th August 2008, 04:50 PM   #4
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Join Date: Dec 2004
Location: Mountain View, California
This is rear of the left speaker (in my setup) before repairs were started. The tweeter panel is normally on the extreme left, when one is in the "listening position" in front of the speakers. Here it is just visible on the right of the panel, comprising the fine red wire.

The bass section makes one full circuit, beginning on the left and completing 12 upward and 12 downward runs between the magnet poles. The wire then runs along the base of the diaphragm to begin another partial run, with 4 upward and downward passes on the extreme left side. The centre is bypassed, then a further 3 passes are made on the right. The wire is then returned to the terminals.

The ends of the first and second passes are offset by 3/8", and I used the end of a 5/16" drill to form the end of each loop.
Attached Images
File Type: jpg panel bottom resized.jpg (48.2 KB, 1198 views)
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Old 6th August 2008, 04:52 PM   #5
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A better shot of the bottom of the panel
Attached Images
File Type: jpg panel bottom resized 3.jpg (95.2 KB, 1136 views)
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Old 6th August 2008, 04:54 PM   #6
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And here is the detail of the layout at the top of the panel.
Attached Images
File Type: jpg panel top resized 2.jpg (87.1 KB, 1103 views)
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Old 6th August 2008, 04:58 PM   #7
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The tweeter circuit simply makes one simple pattern of 3 upward and 3 downward passes between the narrower magnets. It is easy to set by hand, Though some care is necessary in handling the fine wire.

Cheers,

Ed
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Old 6th August 2008, 11:31 PM   #8
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Join Date: Dec 2004
Location: Mountain View, California
Second panel is underway. Though I hadn't noticed whilst listening, the bass wires were in a poorer condition than the first speaker. Many were loose and overall, very poorly stuck at this stage. Production notes on a label inside the speaker indicate that this pair was made in 1987. If I get this repair right, I can hope for another 20 years!

New bass wires are in place, with their first application of overcoating adhesive applied.

Ed
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Old 7th August 2008, 10:17 AM   #9
ktuuri is offline ktuuri  Canada
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Thanks for the pics, looking forward to pics of the finished project.
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Old 7th August 2008, 01:56 PM   #10
wboyd is offline wboyd  United States
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Join Date: Aug 2004
Location: Louisville, KY
WOW...Great thread! I was actually getting ready to start repairing my SMGa's this weekend.

I was not sure if I was going to try just regluing...or complete wire replacement. Ed, what would you say is the level of difficulty on this project? I am fairly new to the Magneplanar speaker line (owned mine for about 4-5 months so far)....so I don't wanna destroy them...just make them sound the way that they should.

So any advice from you, Ed, or any other Magneplanar guru's would be much appreciated.

Thanks,

Wayne Boyd
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"I am always doing that which I cannot do, in order that I may learn how to do it"
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