What is the diaphragm rot ?
I wonder if this could be a result of trimming the membrane with a knife rather than a hot wire ?
Like cutting a Nylon rope without cauterizing the ends.
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I feel your pain, I think we have all been there.
I was looking for a photo of a period car and just knew whichever one I posted would strike a chord somewhere on this planet/forum.
If I recall correctly, my 1960 Jaguar Mk!! (and likely earlier versions) had 4 wheel servo-assisted disk brakes, power steering, electric fuel pump.... not to mention overhead camshafts, etc.
The comparison to Quad is really that fact that Jaguars had awful Lucas electrics.
(anyone can find long lists of Lucas-Prince-of-Darkness jokes on the web... my first try at a link didn't work right)
Without pointing a finger at any particular nationality, a company like Quad might do some things very well and somethings the opposite.
B.
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What is the diaphragm rot ? never seen one or i dont know what i am looking for maybe
The diaphragms develop a lot of little slit like cuts and eventually fail. Here's three large pictures of one (kept them large so you can really zoom in)
http://quadesl.com/diyaudio/IMG_3537.jpg
http://quadesl.com/diyaudio/IMG_3538.jpg
http://quadesl.com/diyaudio/IMG_3539.jpg
Sheldon
Interesting pictures.....
If you press a sharp nail against mylar you will see that the Mylar is very strong and not easily punctured.
These cuts on the picture are not from the edge but start somehow in the middle. Could it be that these cuts are caused by Mylar slapping against the stator? Do these perforated sheets have sharp edges?
If you press a sharp nail against mylar you will see that the Mylar is very strong and not easily punctured.
These cuts on the picture are not from the edge but start somehow in the middle. Could it be that these cuts are caused by Mylar slapping against the stator? Do these perforated sheets have sharp edges?
that looks to me like some propper arcing up to the point it fails. also nice to see the very uneven original coating as well as the undercoat (normaly it is rather evenly coat almost looks like non factory coating. or a blue monday thing
). i think that helps being able to spray the damn slippery stuff. although somewhere in the papers it says it soem sort of damping coating.... but it might do both. by the looks of it it is not on the backside.. would be a pain to fabricate to maybe they drive there quads harder now ? also i think the stators are insulated , not the case in the first batch , at least not mine. they might reach higher voltages and when it does arc it might arc considerable. even if there is a protection. seen enough panels with arc holes.
I don't believe the "diaphragm rot" is caused by arcing. When a diaphragm arcs and has a hole burned in it, it doesn't have a tendency to split because the hole is melted into it with smooth edges. This phenomena is caused by something different IMHO. IT's like the mylar was crumpled and then pulled flat again, and those creases from crumpling are a weak spot.
Here's another photo of a diaphragm that has both arcing holes (the round holes with the coating affected around them) and also this splits fro diaphragm rot.
And the stators are smooth, and effectively the same at other panels stators which don't have this problem.
http://quadesl.com/diyaudio/IMG_2887.jpg
Sheldon
quadesl.com
Here's another photo of a diaphragm that has both arcing holes (the round holes with the coating affected around them) and also this splits fro diaphragm rot.
And the stators are smooth, and effectively the same at other panels stators which don't have this problem.
http://quadesl.com/diyaudio/IMG_2887.jpg
Sheldon
quadesl.com
That last pic shows it really well…death from a thousand tiny razor cuts.
Have you per-chance looked at the coating under a microscope to see what the conductive particles look like? It has been a while, but I had seen something similar before and the coating had a high percentage of long, thin, needle-shaped particles. There seemed to be good correlation between panels with problems and the shape of the particles. However, exactly how the particle shape was causing the damage is still not clear to me...it might be unrelated.
How old are those panels?
The slits look a bit like fatigue failure.
If a coating has a polymer component that links with mylar over time there could be a loss of plasticity in the mylar. A hot climate and loud playback would accelerate micro-fatigue failure. In Australia the modern Chinese Quad mylar seems to fail faster in the tropical heat but there is also high humidity there so failure could be unrelated to speculation of fatigue. Some of the tiny slits have a branching pattern reminiscent of early lighting tracks. So maybe the slits are from an intra-membrane high voltage propagation as opposed the the usual through membrane pin holes? Any crystal formation in the coating could serve as a discharge foci.
mylar is knows for not losing plasticizes, thats there whole thing. it should not go brittle thas was even part of the campaign in the 60's
Hmm it reminds me of using to big graphite in a active polymer once. when you upp the voltage bias, it might arc within the panel. so sort of to the next spot on the foil that conducts well. and it burned away the the VHB tape in this case just like wood would do under very high voltage. you might be on to something there !!!
The diaphragm pictured above was about 4 years old. It was one of the bad panels from my 2912's. I've seen that slitting on panels of Chinese origin, but generally not from old English panels.
I have a stereo microscope, that will only get me to about 40X. And I don't have a piece of a split diaphragm like that. Next time I get one, I'll cut out a piece to examine. I have higher magnifications at work in standard microscopes, and we also have a SEM that might be useful. But I try to keep my sideline business out of my main job, so I generally don't use the equipment at work.
I do find it interesting what is happening to those panels. I'd say if Quad could fix whatever that is that is causing these cuts and splits, the panels would be quite reliable with the new stator glue.
Sheldon
I have a stereo microscope, that will only get me to about 40X. And I don't have a piece of a split diaphragm like that. Next time I get one, I'll cut out a piece to examine. I have higher magnifications at work in standard microscopes, and we also have a SEM that might be useful. But I try to keep my sideline business out of my main job, so I generally don't use the equipment at work.
I do find it interesting what is happening to those panels. I'd say if Quad could fix whatever that is that is causing these cuts and splits, the panels would be quite reliable with the new stator glue.
Sheldon
Sheldon I use these cheap USB microscopes that can be attached to your PC / laptop. Maximum enlargement is 1600X.They sell for $ 12,00
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Is this a multi layer coating? I see a white line on the short end that is covered with a black coating that don't match up. Both layers look not very evenly applied. Picture of the left side #3538 looks pretty good, picture #3537 looks terrible. Is this the multi layer coating that Quad is talking about? What is de first white layer? I wonder how thick the coating is if applied in multi layer. Have you measure it? My 2 cents for what happened: the coating isn't flexible enough that causes cracks in the coating that in time tears the Mylar as well.
I believe this is the damping coating mentioned in Post#1094 that is applied to the opposite side of the diaphragm from the conductive coating. Well, at least it was in the in the few panels I have had my hands on. Thickness was variable, but nominally 5µm.
Attachments
If the coating has damping properties why is the cumulative spectral decay of a quad not better than lets say audiostatic? According to measurements done by Stereophile (take a google search) the ES100 does a better job than Quad 2805 regarding the CSD plot. Maybe the CSD plot was much worse if the Quad had not this 'damping' coating, we only can find out when measuring an original panel against a panel with new Mylar without damping......
I also think there are better ways to kill spurious resonances and such thick coatings only degrade high freq. response (quad rolls off at high freq.....)
I also think there are better ways to kill spurious resonances and such thick coatings only degrade high freq. response (quad rolls off at high freq.....)