Magnapan SMGa no tweet

Rev. Hayes

I picked these up just this afternoon only to find that the tweeter end of the ribbon is not working on either speaker. Pulled the fuses and cleaned the contacts... nope. It was at this point I noticed that there were 3amp fuses in place of the correct 1-1 1/2. Hmmmm.


So I pulled the sock off one. I found one very small point of white corrosion in the wire of the "voice coil" but no breaks or delamination.


If the speakers were pushed too hard with the wrong fuse how would it effect this style of speaker? (I have no experience with the ribbon thing)

What should I look for next?

Did I skip a step in the trouble shooting?

Rev. Hayes

By putting the leads of my multimeter on the contact points of the fuse holder I have verified that I have no breaks in the tweeter coil. Is there some failed crossover component that could cause a lack of high frequencies?

AudioGenics

you could connect a known working tweeter to the crossover in question
at the same termination point that would have gone to the ribbons-high.

also see http://www.opus45.com/magnepan/
except from there:
if you look closely you can see the little white zits on the wires. These are pockets of corrosion that eventually disintegrate the wire, and cause an open circuit.

and check continuity across each component in the crossover.

I had a pair of Magnepan but they were MG1 and it was just a coil and capacitor for the Xover. You can use an external Xover for them .

geoff727

I believe the SMGa has a series (not a parallel) crossover, does it not?

Rev. Hayes wrote: »

By putting the leads of my multimeter on the contact points of the fuse holder I have verified that I have no breaks in the tweeter coil. Is there some failed crossover component that could cause a lack of high frequencies?

If I read you right, it sounds like you just verified continuity across the fuse/fuse holder.

AudioGenics wrote: »

and check continuity across each component in the crossover.

Actually, there won't be continuity across capacitor leads (or at least there shouldn't be!)

Rev. Hayes, have you tried looking up Magnepan Users Group? The tweaks and info section probably will have a schematic of the crossover buried somewhere. At least that would give a starting point in making sure things are wired up right.

Good luck with these.

G~

AudioGenics

how about a picture of the Xover.

Mine had a electrolytic Cap.
electrolytic will look like a short when it has no power stored in it.

I agree that it is best to test out of circuit and
may charge from the meter and then resistance would rise until it appears "open circuit".

nooshinjohn

Contacting Magnepan is not a bad bet either. Though it has been a LOOONG time since I have dealt with them, I hear they have great customer service and still support their older equipment. You can also get NEW MMG's from them direct for about 600 bucks!

http://www.magnepan.com/model_MMG

Rev. Hayes

geoff727 wrote: »

I believe the SMGa has a series (not a parallel) crossover, does it not?


Rev. Hayes, have you tried looking up Magnepan Users Group? The tweaks and info section probably will have a schematic of the crossover buried somewhere. At least that would give a starting point in making sure things are wired up right.

G~

The series crossover is what messed me up in my initial continuity check (which I did without the fuse installed by the way ). Dim lights and no schematic lead to an erroneous diagnosis. Fact is that both tweeter voice coils had a VERY small break in them. Burned out by pushing with the wrong fuses installed I suspect.

I've stripped and replaced the wire in the left speaker so far.

This was actually one of the more entertaining things I've done in this hobby thus far. The whole Magnepan concept is very cool and when you tear one down and replace the wire it really brings you to a state of understanding that a simple crossover rebuild doesn't quite reach. IMO

Oh, and if anyone wants more info on this stuff then MUG is the place to go.

geoff727

Cool.