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Old 18th January 2010, 11:13 PM   #281
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i just spent over an hour on a reply only to find out it did not go through for some reason.i hate to type let alone retype every thing! so here it goes : on my first prototype i made a double sided coating,by disconecting the bias on one side at a very very low level i could hear a .5 to 1db drop in level(maybe more) not scientificaly measured but noticeable.at a higher level it was not as noticeable but was still there.I concluded it was not worth the extra licron(as it is not cheap per can) or mass it add to the diagphram.I had talked to roger sanders about this (and a whole bunch other) he suggested too coat both sides and stated either way it would work and it did.then we discussed different types of coatings and he explained that using graphite renders a smoother surface with no sharp peaks that could disipate the charge and cause arcing thus burning a hole.i did expreince this but i solved that with better stator insulation and the arcing went away.so therefor i did not have any issue after that.now,i have not tried the pva glue trick yet. maybe a higher dilution with more ink or graphite could work.but the wetting of the film becomes an issue here,the same for licron also,it can be done with one coat but difficult so i use two.isn't that what r&d is about (i love to r&d)!anyway,i use a micrometer to measure the thicknes of the mylar&coating on .25 mil i get .5 to .65mil and .8 or more using .5mil mylar.I have even got good results using monokote before i discovered that the adhiesve backing could be washed off with acetone.which is a .5mil "p.e.t. film" as they call it.the question is can you hear the difference?i can if i know what it is i'm looking for.the average person cannot nor do they care espeicialy when they just paid $400 to $800 per box and they get p.o.ed when you tell em it only cost $200 to build 2 or 3 pair(he,he,he)!just some food for thoght.anyway, i cherished the conversation i had with guru of esl's. so feel free to pick my brain at anytime as i will learn from all of you aswell. jer p.s. working on d.d. amp also if good quality can be acheived at any level it is more than worth the weight(wait) of a transformer at todays prices! by the way "can't" is not in my vocabulary.

Last edited by geraldfryjr; 18th January 2010 at 11:27 PM.
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Old 19th January 2010, 08:51 AM   #282
Calvin is online now Calvin  Germany
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Hi,

regarding the glue-formula.
The water-based glue consists mostly of water, which evaporates while drying. The amount of solids in the glue is of low percentage. So You could as well speak of contaminated water with a certain sticky feature
This solution is thinned further by lots of more water.
If You add now a tiny amount of black ink, typical writing ink for pens, which is a low-percentage-of-solids-water-based solution too, the added mass is in the ĩg-range. For 100mL of coating I add 2 small drops of Ink, that I pull with a toothpick. The coating looks slightly greyish then.
The wet thickness of a sprayed-on water-based coating is between 25ĩm-50ĩm when the wet surface is perfectly smooth and You can expect that only around 1% of that is left after drying. So You can expect the dried coating to be in the sub micron thickness range.
It seems that either the PVA or maybe the ink reduces the surface tension of the water. If the coating builds up droplets You may add a small amount of surfactant.
Alternatively You can wipe the diaphragm with a lint free cloth.
Wiping produces an even thinner coating. So thin that You only can see -watching against a light source- glares like gasoline on water.
Resistance may be too high with this way of applicating, but You may simply overcoat a second or third time.
Using alcohol based glue makes only a difference in drying time and visibility. The alcohol evaporates within a few seconds and might generate white streaks and it might be dry before You finished the coating procedure. Water based coating dries within a couple of minutes which leaves enough time to dispense the coating evenly and uniform.

jauu
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Old 19th January 2010, 11:34 AM   #283
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Default Scrath proof?

Calvin,


I find this coating not very scratch proof, but maybe it's something that I shouldn't worry about?

I do not in any way suggest that scratching is a good way to determine if the coating is long lived!
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Old 19th January 2010, 11:58 PM   #284
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i agree.i had only stated that because it had happened and at the time i too questioned duriablity and adhesion to the mylar in my own designs. sorry im not trying to answer for anyone else. jer
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Old 20th January 2010, 10:15 AM   #285
Calvin is online now Calvin  Germany
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Hi,

I didnīt test scractch resistance, but havenīt experienced efficiency losses over several years and quite stressing circumstances either and I havenīt heard of others suffering from SPL loss so far.
To my experience the glue formula is in the group of the few reliable and stable coatings.
One remark. I usually mix a second solution with increased conductivity which I use to īspillī over the metal connection strip. It is often the joint between high conducting metal and low conducting coating that fails overtime. Someone else mentioned he used a small strip of coating-sucked paper between metal and coating.
The problem of the joint failure seems to increase with incresing voltages, which is besides safety another reason for low voltages/low stepup figures.

jauu
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Old 20th January 2010, 11:04 AM   #286
bentl is offline bentl  Norway
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Elvamide dissolves fine in denaturated alcohol or technical spirit. It takes about an hour of stirring (I used a milk "frother" /blender thing) and kept the temperature at about 65degC.

I will coat diaphragms and assemble my stats this weekend and will post some photos possibly also microscope photos of the diaphragm.

Regards

Bent
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Old 21st January 2010, 08:06 PM   #287
bentl is offline bentl  Norway
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Hi,

my first attempt of coating with Elvamide was done tonigth.

I used the "standard" Elvamide solution as described on AudioCircuit. Elvamide dissolved in alcohol. I also added 2 drops of black india ink.

This produced a black solution that I rolled on the mylar diaphragm that was taped to a tamporary frame.

I leared two things:

The elvamide solution does not wet the mylar perfectly; I will try to wash the diaphragm with alcohol before next coating.(old photo film developing trick to avoid marks and bubles on film when developing)


After coating the diaphragm the diaphragm was slightly grey and cloudy.

As others have described, the Elvamide did easily rub off after drying for 20 minutes.

Then I fired up the hot air gun and heatet the mylar to it shrinked and tensioned on the frame. The clouding dissapeared, and the Elvamide solution fused to the mylar perfectly.

I did burn a hole in the diaphragm as I wantet to test how much heath I could apply, but it is not a problem to heath-shrink mylar as long as one keep the hot air gun at a few inches distance, and keep it moving constantly.

I would have discarded the diaphragm anyhow because of the poor wetting.

I was planning on building a advanced diaphragm stretcher, but found that the mylar stics perfectly to a table. I just flattend it out at stretced out all wrinkles, and placed my temporary frame on top. Then I wrapped the mylar around the frame and stretched and taped it thoroughly.

I will take some photos on my next try.

Regards

Bent
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Old 22nd January 2010, 03:11 AM   #288
Clarkcr is offline Clarkcr  United States
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I don't understand the Elvamide "rubbing off" bit. I would have thought that it would bond to the mylar. Please explain.
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Old 22nd January 2010, 06:30 AM   #289
bentl is offline bentl  Norway
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Well, the elvamide solution becomes a layer on top of the mylar. When it has dried, it becomes "flake" that rubs off if you scrats on it with a finger.

But, after heathing with the hot air gun it "fuses" or glues to the mylar perfectly and becomes perfectly clear. I believe that was the point of the youtube video referred to earlier in this thread.

Anyways, I will take som photos during my next attempt.

Regards
Bent
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Old 22nd January 2010, 07:01 AM   #290
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With Elvamide, you probably don't need the two drops of black Indian ink.

Wachara C.
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