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Quick-fix: will the IIIa ribbon with fit the 3.7?

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Posted on January 9, 2017 at 12:05:56
Beluga
Audiophile

Posts: 346
Joined: October 8, 2001
 It's been almost three months since I blew one of the (un-fused) tweeters on my 3.7s.

Early November I ordered a repair kit from Magnepan, but it hasn't arrived yet. Now I need to make a temporary fix - even if it means only part of the ribbon works properly. I have made some DIY conductive glue and I plan to make a simple bridge with some IIIa ribbon. Will be testing the glue resistance as soon as it has dried.

Quick (sic!) question - if anyone knows: will the IIIa ribbon fit in the 3.7 cage? Any experience with glueing ribbons, anyone?
---

In Our Ears We Trust!

All is relative ...

 

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RE: Quick-fix: will the IIIa ribbon with fit the 3.7?, posted on January 10, 2017 at 19:21:10
mondial
Audiophile

Posts: 891
Location: S.E. ASIA
Joined: January 14, 2007
 Hi my 3A when it was brought to the factory back in 2008 for rebuilding was fitted w/ 3.6 ribbons .

Mondial

 

RE: Quick-fix: will the IIIa ribbon with fit the 3.7?, posted on January 10, 2017 at 06:30:58
neolith
Audiophile

Posts: 4842
Location: Virginia
Joined: February 21, 2002
Contributor
  Since: December 2, 2004
 The IIIa ribbon is wider than the newer models (everything after the IIIa) and may not fit the cage.
However I think you could easily swap in the IIIa tweeter (cage and ribbon) into the 3.7 since the width of the cages are the same. The IIIa cage is 0.6" shorter than the 3.7 so it will fit in the "groove". The screw holes may not match up but for a temporary fix you could probably forego the screws. Remember the impedance of the IIIa ribbon is only 2.3 ohms so you would need to use the 1 ohm series resistor in the attenuator socket. Omitting it may make your amplifer very unhappy. Also there would be a slight change in the crossover characteristics but again, for a short term fix, it would be acceptable.
Why did your tweeter blow? I don't think the absence of the fuse was an issue (I know Magnepan will disagree). It would be a good idea to trace down the problem so you ribbon replacement does not become a regular feature of your life.



"Our head is round in order to allow our thoughts to change direction." Francis Picabia

 

RE: Quick-fix: will the IIIa ribbon with fit the 3.7?, posted on January 10, 2017 at 09:54:03
Satie
Audiophile

Posts: 5426
Joined: July 6, 2002
 The Adyton amp Beluga uses on the tweeter and mids is not going to have a problem with the low impedance of a 3a tweeter. It might be useful to check how hot it is running, but I doubt it is a problem.

I am going to venture a guess as to the cause of the tweeter failure. I would guess that it is related to the adoption of high rez DSD and 24/96 and 24/192 files. These are commonly mastered with 6db higher levels of deep bass and the transients are recorded more fully so that the average mid content level is going to be 5-10db lower, resulting in the listener raising the volume setting.

This has two results, 1. there is more bass content that can leak into the tweeter despite the 2nd order XO. 2. the transient content becomes far more powerful with a transient crest factor up to 10 db greater than on CD.. This increases the burden on the tweeter. People playing vinyl on idlers and high torque DD turntables already face this issue.

The solution is to watch your listening level with a fast response peak SPL measurement with a hold function. If you are getting peaks on high rez content (drum and rim shots, brass) at 110 db then you should tamp down the volume. The second solution is to raise the crossover HP for the tweeter up to above 4 khz.

The old 2 ohm 3A/ T IV tweeter can be used and it is more resilient - perhaps a better choice for you. It is a 55" tweeter whereas the 3.7 has a 60" tweeter inherited from the 20.x models.
Your HP cap for the tweeter is likely going to need a change in order to retain the same -3db point with the lower impedance tweeter. Measure and fix the cap value accordingly.

 

RE: Quick-fix: will the IIIa ribbon with fit the 3.7?, posted on January 10, 2017 at 11:42:11
Roger Gustavsson
Audiophile

Posts: 2058
Location: Huskvarna
Joined: February 12, 2010
 neolitb wrote:

"The IIIa ribbon is wider than the newer models (everything after the IIIa) and may not fit the cage.
However I think you could easily swap in the IIIa tweeter (cage and ribbon) into the 3.7 since the width of the cages are the same. The IIIa cage is 0.6" shorter than the 3.7 so it will fit in the "groove"."

The cages that I have, have the same measurements, not sure about the screw holes. Mine are Tympani IVa and 3.6. Both cages are 60 inches long, 1524 mm. Width are also the same.

 

RE: Quick-fix: will the IIIa ribbon with fit the 3.7?, posted on January 10, 2017 at 17:54:07
neolith
Audiophile

Posts: 4842
Location: Virginia
Joined: February 21, 2002
Contributor
  Since: December 2, 2004
 The 60" v 60.6" length info came from Magnepan and I did have to rout out the tweeter channel so the 3.7 ribbon would fit in my IIIa's.



"Our head is round in order to allow our thoughts to change direction." Francis Picabia

 

RE: Quick-fix: will the IIIa ribbon with fit the 3.7?, posted on January 11, 2017 at 18:51:02
Satie
Audiophile

Posts: 5426
Joined: July 6, 2002
 The manuals up to the 3.6 indicate a 55" ribbon, I don't know at which point in the course of the 3.6 model's life they started using the 60" ribbons. It has been quite a while that when they get both speakers of a 3A or 3.3 and 3.5 for restoration they swap the origina short tweeters for the long one, at least if asked to.

How about we all measure the length of our ribbons and note the model?

 

RE: Quick-fix: will the IIIa ribbon with fit the 3.7?, posted on January 11, 2017 at 22:35:44
Roger Gustavsson
Audiophile

Posts: 2058
Location: Huskvarna
Joined: February 12, 2010
 55" is what Magnepan say in the manual of the Tympani IVa, that is for the length of the ribbon - not the cage which is 60". My T-IVa are from 1986 and my 3.6 from 2003. Both have 60" cages!

Cross sectional view:

 

RE: Quick-fix: will the IIIa ribbon with fit the 3.7?, posted on January 9, 2017 at 16:48:54
riley804
 " Early November I ordered a repair kit from Magnepan, but it hasn't arrived yet."

before you do anything crazy, have you tried to contact them and see where your oder is at ?

 

RE: Quick-fix: will the IIIa ribbon with fit the 3.7?, posted on January 9, 2017 at 23:53:30
Beluga
Audiophile

Posts: 346
Joined: October 8, 2001
 Hi! Yes, I emailed them several times. They finally answered me with a short email saying they had been without a service manager and that a new service manager, Pat, starts Monday (that is yesterday).

Seems like they are thinly manned. For years I have had contact with Sheila Reynolds (during my IIIa period), but I guess she is away. Last fall Mick Bucher and Kari Hoffman received and answered my order, but after that silence - until now. No signature on the "new service manager" mail, though.
---

In Our Ears We Trust!

All is relative ...

 

RE: Quick-fix: will the IIIa ribbon with fit the 3.7?, posted on January 11, 2017 at 15:21:57
josh358
Industry Professional

Posts: 12332
Joined: February 9, 2010
 Sheila left and her replacement became seriously ill. The other employees tried to fill in while they were finding a replacement, but inevitably fell behind. Unfortunately, they aren't a large company so when a key employee with specialized knowledge leaves or is indisposed there isn't always someone who can cover for them.

 

Buluga....email sent...., posted on January 10, 2017 at 13:57:28
riley804
 ....

" Perhaps Magnepan was acquired by a company in China? "

No....

 

RE: Quick-fix: will the IIIa ribbon with fit the 3.7?, posted on January 10, 2017 at 13:30:32
Norman M
 I called the service department about 2 weeks prior to Thanksgiving. I got a recorded message saying that I should send an email to servive@magnepan (?) and I did twice since I received no reply, then about three days ago, when I received an email saying I should call them.

Perhaps Magnepan was acquired by a company in China?

(It's understood that sometimes an individual has to be away from for a number of valid personal reasons, however responsibility dictates that someone takes over for them until they return. In the worse case scenario an individual can't return. Should matters of this type come to a grinding halt. I have to wonder if the person who upgrades 3.7s to 3.7is, similarly indisposed.

 

RE: Quick-fix: will the IIIa ribbon with fit the 3.7?, posted on January 10, 2017 at 02:37:21
Roger Gustavsson
Audiophile

Posts: 2058
Location: Huskvarna
Joined: February 12, 2010
 As far as I know, the ribbon cages are identical. I have both types! The difference is the size of the magnets and the width of the ribbon.

 

RE: Quick-fix: will the IIIa ribbon with fit the 3.7?, posted on January 18, 2017 at 10:25:18
Beluga
Audiophile

Posts: 346
Joined: October 8, 2001
 Hi guys - thanks for the follow-up!

I still haven't received the repair kit nor further response from Magnepan service dept.

I seriously consider doing a "IIIa"-fix just to get some sound from "the rest of it". Probably just a connection bridge in some way.

Hope Magnepan catches up soon - of course understandable when illness happens but they could at least set up an automatic mail response explaining the delay. But maybe they didn't have time to upgrade from WordPerfect yet ... :o

Sorry ...
---

In Our Ears We Trust!

All is relative ...

 

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