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Old 28th October 2012, 10:58 PM   #11
bdjohns is offline bdjohns  United States
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Thank you, Jer!
I actually have some Rust-oleum clear gloss, so I think I'll put a few coats of that on. Now that I've got about 10 mils on each side, do you think it's necessary to any further build up the non-diaphragm side of the stators?

I read in one thread how you were contemplating building a powder coat oven. Have you considered a barbeque grill? My stators will fit in my Weber, so I may try it for curing spray paint - as my wife hates the stink when I've put them in the kitchen oven .

Last edited by bdjohns; 28th October 2012 at 11:13 PM. Reason: grammar
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Old 29th October 2012, 01:23 AM   #12
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Usually about 10 mils is good.
You can set them up in a mock configuration without the diaphragms with the bias supply and transformers and run a signal into them to make sure that they don't arc.
I have seen many skip this test only to have to tear them apart again and add more coating to the stators.

I did finally get some powder coating material to try out,But I haven't had the time to mess with it yet.
I need to make me a fluidizing bed to coat the screens with next.

My next panels I will be using the paint method on some TIG wire stators.

I also just made a quick sample of some screen sprayed with polyurethane as well.
This came out good as it was just a test and the coating is not thick enough yet to be used as a ESL but I will use this method possibly to finish my ES headphones.

jer
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Old 11th December 2012, 02:46 AM   #13
bdjohns is offline bdjohns  United States
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Default Pneumatic Stretcher

I am really trying to get these panels up and running by Christmas. I have the power supplies and transformers put together, thanks to Jazzman's plans. I am now working on the pneumatic stretcher. The perimeter of my rectangular board is about 76", which calculates to a 24" tube. Should I go with a 20"? What should the approximate width and depth of the trough be that the tube lays in? Also has anyone used Gorilla Glue polyurethane adhesive to attach the mylar to the frame? I would use the recommended 3M Scotch Grip, but I'm not too comfortable with an instant bond. Thanks! Bruce.
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Old 11th December 2012, 04:04 AM   #14
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Gorilla glue won't work with mylar and it foam's up and this would cause an irregular surface and might cause wrinkles.
Plus it needs to be exposed to the air in order to cure.

I use epoxy to bond the mylar to its frames.

Use a slow setting type as this will allow you to get it on your frames all you need is a very very thin coat.

I have never had any bonding issues yet with epoxy, although you can peel it off with a razor blade should you need to replace the Diaphragm and/or start over.

You can also scuff the frames up a bit with some fine 220 to 320 grit sandpaper if you like as this helps too.
It holds well enough that I have snapped a frame from over tensioning the diaphragm with a heat gun while it was unmounted, once, as a test.

After I lay the frame down on to the mylar I sandwich it with a piece of glass and weight it down.
It is best to just drop it in place so be accurate as if you try to move the frame you will risk wrinkling the mylar and make a mess of the epoxy causing you to have to start over with a fresh piece.

Keep a sample of the epoxy you had used and as it starts to harden this is the time to carefully take the top piece of glass off.
This is because some of the epoxy will ooze out and can get stuck to the glass.

One time I wait too long and nearly lost the frame but I got it unstuck by carefully using a long craving knife and a razor blade to pry it off of the glass.

Of all of the times I have done this I think I only screwed one up and had to start over because I smeard the epoxy all over the diaphragm.
This was because I was mounting two within the 12.5" width and missed my spot laying it down and one other one that had moved causing a wrinkle.

The wrinkled one was still worked and functioned fine but it irritated me so I replaced it anyhow.

Once you lay it down and if you feel that there is to much epoxy oozing out on the inside of the frame you can carefully scoop it up around the perimeter with a toothpick and wipe the excess off on a paper towel.

Thus one of the main reasons to use a slow setting type.
I used a 1 or 2 hour type at first and once I got it down I started using a 30 minute type.

Then weight it down.
Weighting it down is basically optional but it will assure you a super flat piece in the end as this is something that you will have perfect for your method of construction.

Even if you use the DSTape method the process is basically the same.
You just drop it on to the mylar and push it down so that it sticks all of the way around the perimeter.
Sorry I don't have any pictures of this process but I will in a few days from my newest build that is almost complete here,

A Segmented Stator Desktop ESL

The trough for the tube need only be deep enough to keep the tube from slipping out or shifting and if a 20" will stretch that far it might work but then again that is stretching it a bit (he,he,he).
You might be better off getting a 24" tube.

Cheers !!

jer
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Old 11th December 2012, 12:12 PM   #15
Bazukaz is offline Bazukaz  Lithuania
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Quote:
Originally Posted by bdjohns View Post
I am really trying to get these panels up and running by Christmas. I have the power supplies and transformers put together, thanks to Jazzman's plans. I am now working on the pneumatic stretcher. The perimeter of my rectangular board is about 76", which calculates to a 24" tube. Should I go with a 20"? What should the approximate width and depth of the trough be that the tube lays in? Also has anyone used Gorilla Glue polyurethane adhesive to attach the mylar to the frame? I would use the recommended 3M Scotch Grip, but I'm not too comfortable with an instant bond. Thanks! Bruce.
You can also use various contact glues. Its easier to work with. Some will work when applied to one side ; others need to be applied on both.
The key to success is to use a very thin layer of glue and wait until the surface is dry. Then the film must be pressed hard into the spacer by using fingers. Some experimentation is needed. Many polyurethane based contact adhesives can be diluted with Acetone to a ratio ~3:1(acetone:glue) or so depending on initial viscosity, then applied with a brush to one or both sides.

Regards,
Lukas.

Last edited by Bazukaz; 11th December 2012 at 12:16 PM.
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Old 12th December 2012, 01:52 AM   #16
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Quote:
Originally Posted by bdjohns View Post
... I am now working on the pneumatic stretcher. The perimeter of my rectangular board is about 76", which calculates to a 24" tube. Should I go with a 20"? What should the approximate width and depth of the trough be that the tube lays in?
Hi Bruce,

I suspect either size tube should work-- the larger tube would be fine if it fits tight enough to not hang loosely, and the smaller tube would certainly stretch to fit. The stretcher jig should have rounded corners/edges which are sanded smooth, and the height of the jig sides needs to be greater than the width of the tube. Rubbing some baby powder over the top edges of the jig will allow the film to slide easy without snagging and tearing-- but if you use baby powder be sure to clean any powder residue off the diaphragm with an alcohol wipe before applying the conductive coating. The jig doesn't need a trough for the tube unless you just want one-- the tube just sits on the side edges of the jig. You want all air sucked out of the tube initially so that it lays flat and you want the tube positioned near the top edge of the jig so it pulls the film over the jig edge at a shallow (not sharp) angle.

BTW, were you able to find the toroidal transformers? The last time I checked, the Antek AN506's were sold out.

Good luck with your project!
Charlie (jazzman)
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Old 16th December 2012, 03:58 AM   #17
bdjohns is offline bdjohns  United States
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Thanks for the advice guys. I'm going to go with the epoxy on both the polycarbonate spacers and the mylar. Got 9 oz, 30 minute stuff at Hobby Lobby for $11. I've done some tests on the 1/16" Lexan and epoxy. It doesn't hold real great but should do the job. At least I'll be able to get them apart if needed.

Charlie, I got my Antek transformers around a year ago. Glad I got them - if those units were not available and work as good as it sounds they will, the higher dollar transformers may have dissuaded from me not to even starting the project!

Almost have the stretcher completed. I understand the recommended stretch on 6 um film is 1.5% ?
Thanks,
Bruce
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Old 16th December 2012, 07:24 AM   #18
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You can add a custom primary to any toroid power transformer.
That is how I run mine, added a 10 turn winding to give me 1:67 per core.

I explain how in this thread,

Step-up transformer design


Step-up transformer design

Good deal that you already have them!!

Yes. the epoxy will peel off easily but it is strong enough to hold mylar to the frame with much lateral tension.

Have you tested the integrity of the stator coating yet?
Now that you have the bias supply and the transformers ready?
Sorry I can't stress this enough I have seen nearly every new build fail on the first fire up and have to be torn apart just to make it thicker and destroy a perfectly good piece of mylar!!

My 1st ELS build - first question!

Great job on your interface units!!!
Except I would keep the input Primay wires very much away from the secondary side and bias supply!!!
That barrier strip is not enough to keep 5kv to 10 kv and more isolated enough from jumping over and possibly damaging your amplifier.
Even if your bias supply is only 2kv to 3kv the peaks coming out of the transformers will be much much higher especially if your amp can produce a large voltage swing !!!

Cheers !!

jer

Last edited by geraldfryjr; 16th December 2012 at 07:47 AM.
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Old 16th December 2012, 03:31 PM   #19
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I had added to the previous post, But, I had went over the 30 minute time limit for editing.

I do get about 1:134 transformation using one core with a ten turn primary, But I use 4 cores right now for the following reasons.

#1 I'm using smaller panels so I need to double my transformation ratio in order to match the efficiency of the woofer that I am using.

#2Using multiple cores also lowers my lowest frequency point of core saturation.

#3 The two 120v windings are bifillar wound and this greatly increases the transformers self capacitance not to mention all of the extra winding's that I have yet to remove.

Even though my cores do measure better than the Antek's as posted by Bolserst, I do have issues with my cheapy amp with even just two of them.
This is mainly due to the very high 1:268 (1:256 as measured) transformation ratio that it takes to achieve my goal of good low frequency response while maintaining a high level of efficiency.

This keeps the impedance range and saturation limits well within the capability's of my Aiwa CX-NA707 without it shutting down.
My bigger amps are monsters and don't have such issues and thus the cause of my last panels burning up !!! He,he,he,he

I like to at least get down to about 240hz to 300hz at full power without any saturation of the cores.

I just wanted to clarify my statement of 1:67 ratio per core.

I am currently finishing up my new panel and then I will be working on a transformer recipe that DIYers can use and build for much cheaper than what is currently available and still achieve a higher level of performance than using the current methods.

I believe this is very possible and I have done quite a few preliminary calculations as I have been through the very same struggle as every one else has.
In fact it was the main reason it took me from 2004 to 2010 to actually get back into it......The Transformer Issue.

More on that later and keep up the great work!!

jer

Last edited by geraldfryjr; 16th December 2012 at 03:36 PM.
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Old 16th December 2012, 04:28 PM   #20
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Quote:
Originally Posted by bdjohns View Post
Almost have the stretcher completed. I understand the recommended stretch on 6 um film is 1.5% ?
Thanks,
Bruce
Opinions differ on how much tension is best. I can tell you that I stretched my 6um diaphragms to 1.5% elongation and it works well for me. I would not go with less than 1% or much above 1.5%.


Nice work on that interface!
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