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-   -   Fuses and Ribbons in the 20.7 (https://www.audioaficionado.org/showthread.php?t=36096)

nicoff 06-15-2016 05:45 PM

Fuses and Ribbons in the 20.7
 
If I understand it correctly, fuses are supposed to protect the ribbon by breaking/burning before the ribbon does. That has NOT been my experience with the 20.7s.
In my case, more often than not, the ribbons break and the fuses remain intact. In about two years of ownership, I have broken more ribbons in the 20.7 than I did in over a decade of ownership with 20.1 and 3.6 prior to that. Is anybody else experiencing something similar with ribbons breaking before the fuses?

ehoove 06-15-2016 06:09 PM

Only had that happen once in my modified MGIIIa's, blew the fuse twice though. That time was my stupidity, The ribbon let go during an audio get together at my house only to notice the next day. :^(
Regards,
Jim

audio bill 06-15-2016 06:41 PM

I don't own the 20.7, but I run the 3.7i speakers and haven't had any trouble with blown fuses or ribbons. I play them reasonably loud at times, but never push them too hard. Typically fuses can only protect drivers by limiting the current flow and resultant power delivery, whereas if you push your amp too hard distortion can cause the driver to blow without blowing the fuse. When you have blown the ribbons are you playing them very loudly and possibly pushing your amp into clipping distortion? The amp driving Magnepans needs to have sufficient current capability into their four ohm impedance, and higher power amps tend to be best suited to driving them effortlessly in my experience without damage.

nicoff 06-15-2016 09:36 PM

Quote:

Originally Posted by audio bill (Post 785881)
I don't own the 20.7, but I run the 3.7i speakers and haven't had any trouble with blown fuses or ribbons. I play them reasonably loud at times, but never push them too hard. Typically fuses can only protect drivers by limiting the current flow and resultant power delivery, whereas if you push your amp too hard distortion can cause the driver to blow without blowing the fuse. When you have blown the ribbons are you playing them very loudly and possibly pushing your amp into clipping distortion? The amp driving Magnepans needs to have sufficient current capability into their four ohm impedance, and higher power amps tend to be best suited to driving them effortlessly in my experience without damage.

Thanks! I never had repeated ribbon failures with the 3.6 as I have experienced with the 20.7s. I use a very powerful amp (Classe M600), so I don't think that the amp is the culprit. I do admit to playing music loud on certain occasions, but my point is that the fuses should burn first not the ribbons.
I just had two blown tweeters and the filament in the fuses did not even curl. In the past, if I was playing the 3.6s very loud, I would check the fuses afterwards and if the filaments looked a little bit 'crooked' I would replace them. This time, with two ribbons gone, the fuses look like nothing happened. It is very odd.

cma29 06-15-2016 11:05 PM

Sorry to hear about your ribbons failing. Frustrating.

I've had my 20.7s for over three years and they are working flawlessly. I even changed the tweeter fuse for one with a slight higher current rating than the original(3.0 amps instead of 2.5 amps) and I have not had any failures yet.

You might have a flawed crossover that sends too much current to the ribbons. :scratch2:

Poisonm 06-16-2016 02:55 AM

Quote:

Originally Posted by nicoff (Post 785874)
If I understand it correctly, fuses are supposed to protect the ribbon by breaking/burning before the ribbon does. That has NOT been my experience with the 20.7s.
In my case, more often than not, the ribbons break and the fuses remain intact. In about two years of ownership, I have broken more ribbons in the 20.7 than I did in over a decade of ownership with 20.1 and 3.6 prior to that. Is anybody else experiencing something similar with ribbons breaking before the fuses?

One of the reasons I quit the 20.7. Started a thread at the Asylum about it perhaps about 2 years ago. There was a user in HK that also experienced same problem. Never had an issues with 3.7 or the 1.7.

Robert_Anderson 06-16-2016 03:47 AM

I have had no trouble with my 20.1's, but I had a ribbon just die in my old 3.6R's. It was never explained.

AudioGremlin 06-16-2016 06:35 AM

Seems odd that the fuse doesn't protect. Sorry if its an obvious question but is the fuse the correct rating and type i.e.delay or instantaneous. You could try a slightly lesser value of fuse if you still get a persistent problem. I also wouldn't think the Classe is to blame.

Poisonm 06-16-2016 10:57 AM

In my case as well as the other few users, the fuses are stock standard fuses and have never been swapped out.

jimsofranik 06-24-2016 03:32 PM

blown ribbons
 
I too have had multiple ribbons go..in both channels, not due to amps..bryston 28sst2's..spoke with bryston and magnepan ..wendell informed me to make sure to notify him directly of blown ribbons in 20.7's.
Hope it was just a bad batch of ribbons..so far so good..6+months with no problems...in the first 2 years I think i went thru about 4 tweeters....lol


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