MG-1 rebuild and upgrade to 1.7i

I found a pair of somewhat decrepit MG-1s on EBay for $75. I picked them up, brought them home, and got started.

Magnepan has been making MG-1s since the 70s. They got renamed to the MG-1 improved, then MG-1a, MG-1b, MG-1c, 1.4, 1.5/QR, 1.6/QR, 1.7/QR. QR for "Quasi-Ribbon," which means no more wire, aluminum tape instead. The magnet structure never changes. I'll be replacing the diaphragms and using tape instead of wire, so these will be 1.7s when I'm done. I'll also build a new frame - I'm unimpressed with the sheet metal frame. When I do that I'll change the dimensions from the MG-1 standard 60x22 to the 1.7 standard 65x19. The oak trim is gone forever, I have different plans for these guys. I'm going to make them look more or less like factory 1.7s, not exactly the same but close.

I expect this to take a few weeks. I'm not completely ready to do this, I have a couple tools yet to make to facilitate this. I will be documenting it as I go along, with enough information to allow others to follow. If you have a good shop, anyway.

Pictures below:

1. The "new" speakers. Pretty grungy looking. No bases. Holes in grill cloth a mild concern.

2. Remove the Oak trim, which I think looks very 70s. It won't be coming back.

3. Speaker 1. Note the mashed up wires. There's a rip in the diaphragm behind the wires. This one needs a new diaphragm.

4. Speaker 2. Also a very small rip in the diaphragm, hard to spot in a photo.

5. Closeup of the rip in speaker 1.

6. The stereo pair. This is the "front." MG-1s play through the little holes in the metal. I'll be changing that.

7. The stereo pair. This is the "back." After the rebuild it will be the front. Notice that the speakers are mirror images. This lets you play for hours and hours deciding if the tweeters go inside or outside.

The wires are magnet wire. The tweeters are about 7 meters of 32 gauge aluminum. The mid/woofers wire is doubled up, so it's 54 meters of 24 gauge copper.

Tape is better than wire because when you drive the mylar over a larger area the distortion drops noticeably.

The magnets are flexible ferrite, .060" thick, 1/4" wide (mid-woofer) 1/8" wide (tweeter).

I'm not sure what the mylar is because it has a thick coat of 3m-77 and milloxane. I believe the milloxane is to damp diaphragm vibrations. I'll be using .0005" mylar and I expect to have a final coating of 3M 30NF, which is a longer lasting substitute for milloxane. 3m-77 is a poor choice and the cause of delamination in older magnepans; a better choice for wire would be DAP Weldwood contact cement, which actually lasts. But Jim Winey worked for 3M before he started Magnepan, and being from Minnesota he apparently believed anything from 3M was better than anything else. I'm from Green Bay, so I think something very different about Minnesota.
 

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Have you begun working on these? I would say there may be a lot more to it than you think going from the MG-I to MG 1.7.

I'm unimpressed with the sheet metal frame.

The wires are magnet wire. The tweeters are about 7 meters of 32 gauge aluminum. The mid/woofers wire is doubled up, so it's 54 meters of 24 gauge copper.

Tape is better than wire because when you drive the mylar over a larger area the distortion drops noticeably.

The magnets are flexible ferrite, .060" thick, 1/4" wide (mid-woofer) 1/8" wide (tweeter).

The metal/particle board frames are not that bad, may even be better than the baffles of the 1.7 in therms of rigidity.

The wires are probably aluminium even for the bass section, there is a coating (insulation) on them that looks like copper. Very few Magnepan have copper wiring, like the Tympani Bass Speakers.

Tape or foil will reduce the maximium SPL in the bass as there will be less free Mylar that can tension. Tape will also reduce the efficiency by 1.5-2 dB as the tape will not sit where the highest magnetic field strength is.

There are also some tricks when it comes to tensioning the Mylar that may be different between MG-1 and MG 1.7.

I wish you good luck with ypur project.
 
It seems you don't know much about Magnepan speakers. You can't make a set of 1.7i's out of those beat up MG-1's I'm afraid.
Although, as a DIY project, it looks like a lot of fun and work.

However, if you're just interested in listening to 1.7's, I'd look around and just buy a pair. You can find used pairs in good working order for less than $1000.00.

Dave.
 

WrineX

Member
2004-03-25 2:43 pm
Den Haag
I found a pair of somewhat decrepit MG-1s on EBay for $75. I picked them up, brought them home, and got started.

Magnepan has been making MG-1s since the 70s. They got renamed to the MG-1 improved, then MG-1a, MG-1b, MG-1c, 1.4, 1.5/QR, 1.6/QR, 1.7/QR. QR for "Quasi-Ribbon," which means no more wire, aluminum tape instead. The magnet structure never changes. I'll be replacing the diaphragms and using tape instead of wire, so these will be 1.7s when I'm done. I'll also build a new frame - I'm unimpressed with the sheet metal frame. When I do that I'll change the dimensions from the MG-1 standard 60x22 to the 1.7 standard 65x19. The oak trim is gone forever, I have different plans for these guys. I'm going to make them look more or less like factory 1.7s, not exactly the same but close.

I expect this to take a few weeks. I'm not completely ready to do this, I have a couple tools yet to make to facilitate this. I will be documenting it as I go along, with enough information to allow others to follow. If you have a good shop, anyway.

Pictures below:

1. The "new" speakers. Pretty grungy looking. No bases. Holes in grill cloth a mild concern.

2. Remove the Oak trim, which I think looks very 70s. It won't be coming back.

3. Speaker 1. Note the mashed up wires. There's a rip in the diaphragm behind the wires. This one needs a new diaphragm.

4. Speaker 2. Also a very small rip in the diaphragm, hard to spot in a photo.

5. Closeup of the rip in speaker 1.

6. The stereo pair. This is the "front." MG-1s play through the little holes in the metal. I'll be changing that.

7. The stereo pair. This is the "back." After the rebuild it will be the front. Notice that the speakers are mirror images. This lets you play for hours and hours deciding if the tweeters go inside or outside.

The wires are magnet wire. The tweeters are about 7 meters of 32 gauge aluminum. The mid/woofers wire is doubled up, so it's 54 meters of 24 gauge copper.

Tape is better than wire because when you drive the mylar over a larger area the distortion drops noticeably.

The magnets are flexible ferrite, .060" thick, 1/4" wide (mid-woofer) 1/8" wide (tweeter).

I'm not sure what the mylar is because it has a thick coat of 3m-77 and milloxane. I believe the milloxane is to damp diaphragm vibrations. I'll be using .0005" mylar and I expect to have a final coating of 3M 30NF, which is a longer lasting substitute for milloxane. 3m-77 is a poor choice and the cause of delamination in older magnepans; a better choice for wire would be DAP Weldwood contact cement, which actually lasts. But Jim Winey worked for 3M before he started Magnepan, and being from Minnesota he apparently believed anything from 3M was better than anything else. I'm from Green Bay, so I think something very different about Minnesota.

you an use 3m 30 NF only, if you want. no need fo any other glues.

with wired versions i always put the wire in the jig give it a thin coat of 30nf, then coat the the mylar slightly. when dry attach the to, then do a top coat of 30nf to soak in the nooks and crannies of the wires. and ur done :)

when using foil. all bets are off, you can go either way, using thing layer of 77 to tack it down then use 30nf it will hold.
 

Tjk002

Member
2020-11-11 7:53 pm
I found a pair of somewhat decrepit MG-1s on EBay for $75. I picked them up, brought them home, and got started.

Magnepan has been making MG-1s since the 70s. They got renamed to the MG-1 improved, then MG-1a, MG-1b, MG-1c, 1.4, 1.5/QR, 1.6/QR, 1.7/QR. QR for "Quasi-Ribbon," which means no more wire, aluminum tape instead. The magnet structure never changes. I'll be replacing the diaphragms and using tape instead of wire, so these will be 1.7s when I'm done. I'll also build a new frame - I'm unimpressed with the sheet metal frame. When I do that I'll change the dimensions from the MG-1 standard 60x22 to the 1.7 standard 65x19. The oak trim is gone forever, I have different plans for these guys. I'm going to make them look more or less like factory 1.7s, not exactly the same but close.

I expect this to take a few weeks. I'm not completely ready to do this, I have a couple tools yet to make to facilitate this. I will be documenting it as I go along, with enough information to allow others to follow. If you have a good shop, anyway.

Pictures below:

1. The "new" speakers. Pretty grungy looking. No bases. Holes in grill cloth a mild concern.

2. Remove the Oak trim, which I think looks very 70s. It won't be coming back.

3. Speaker 1. Note the mashed up wires. There's a rip in the diaphragm behind the wires. This one needs a new diaphragm.

4. Speaker 2. Also a very small rip in the diaphragm, hard to spot in a photo.

5. Closeup of the rip in speaker 1.

6. The stereo pair. This is the "front." MG-1s play through the little holes in the metal. I'll be changing that.

7. The stereo pair. This is the "back." After the rebuild it will be the front. Notice that the speakers are mirror images. This lets you play for hours and hours deciding if the tweeters go inside or outside.

The wires are magnet wire. The tweeters are about 7 meters of 32 gauge aluminum. The mid/woofers wire is doubled up, so it's 54 meters of 24 gauge copper.

Tape is better than wire because when you drive the mylar over a larger area the distortion drops noticeably.

The magnets are flexible ferrite, .060" thick, 1/4" wide (mid-woofer) 1/8" wide (tweeter).

I'm not sure what the mylar is because it has a thick coat of 3m-77 and milloxane. I believe the milloxane is to damp diaphragm vibrations. I'll be using .0005" mylar and I expect to have a final coating of 3M 30NF, which is a longer lasting substitute for milloxane. 3m-77 is a poor choice and the cause of delamination in older magnepans; a better choice for wire would be DAP Weldwood contact cement, which actually lasts. But Jim Winey worked for 3M before he started Magnepan, and being from Minnesota he apparently believed anything from 3M was better than anything else. I'm from Green Bay, so I think something very different about Minnesota.

Just checking in on your project. How did it go? Any documentation? I'm just about to start a rebuild of MGI improved