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My DIY electrostatic headphones - Page 35

post #511 of 1465
Thread Starter 

My second pair of Omega clone will be singing very soon.  L3000.gif

 

post #512 of 1465

Warning: reading may cause upset stomach.

   I have not been able to get a CNC yet but wanted to try anyway. 

some of below can be used for "What not to do"

 

Have tried several times but nothing works right yet.

Go ahead and laugh. I am.

 

 Ok here goes: ordered perf metal from Amazon Stainless Steel 304 Perforated Sheet, ASTM-A-176-99, Straight 0.045" Round Perfs, 0.066" Center Spacing, 0.0187" Thick, 12" Width, 24" Length

 

  Machined a 3" PVC coupling to have 93mm opening with shelve on a lathe.

cut metal with snips and sanded with belt sander to size.

 

 Bought Mylar C 2um 20M + Elvamide 60g and made the formula.

 

  Am trying to follow Andrew Radford's guide.....http://gilmore2.chem.northwestern.edu/projects/showfile.php?file=radford1_prj.htm

 

  I do not have a Pro Bias adapter so built one ( with a little help from the Stax Mafia )

It has 610v before the ballast resistor...and is made from a SRD-4 & radio shack parts.

  The radio shack 110v -24v trans shown shorted out on the primary,, so am now using an HVAC 20va trans that I had..

 

  As far as glue, I have tried:

Elmer's rubber cement -  too thick,not enough holding power on mylar.

Gorilla Glue - too thick, foams and make a big mess, thinned down right it does seem to work . does stick to mylar but hard to control application.

 

  Then I read about 3M yellow weatherstrip adhesive #2 thinned down 3 to 1 with MEK,  this seems good,

 

On sweat screens:

  Having read the recent discussion on screens - made the crinkle out of the 2um Mylar..

 

About spacers:

want .5mm

looked for something the right thickness and found two- the plastic For Sale signs - the early glues did not stick- tried pvc glue- that did not stick to Mylar.

plain old file cabinet folder - yep

 

  The problems are:

metal is not flat, may be close enough.

hard to cut film so Bias can not leak to stators,

 

The diaphragm coating does seem to work - unplug and hear the sound go away slowly.

 

How do they sound - BAD BAD BAD max volume is 85DB normal_smile%20.gif

(other than volume- they do work)

 

What do they look like?

 

 

the paint is missing from scraping off old glue..and you can see my homemade Stax connector..

coat hanger wire is the right size and Hot glue with tape around it....

 

At this point you might wonder why this guy doesn't just go earn some money and buy the real Stax...me too biggrin.gif

 

gonna try again today ---this is what labor day weekend is for right?

post #513 of 1465

A few things... As for glue, Elmer's contact cement works well, as dose probably any contact cement. I tried another brand, I forget which and it provided an even stronger bond. That said, I'm done with contact cement and am using double sided VHB 3M tape in my new build which is in progress.

 

As for using paper for holding the film, I don't think that is going to be rigid enough. The tension will most likely be lost in paper deformations. Are the drivers stable? If the film is sticking to one of the stators (a sign of too little tension) it will sound terrible and have lowered volume.

post #514 of 1465
Thread Starter 

o2smile.gifjecklinsmile.gifatsmile.gif

 

Very nice try Congo5!  Reading this reminds me of the beginning of my making of the headphones.  While it's frustrating, it's fun too.  Who wants to spend the money when we can have so much fun doing it ourselves, right?

 

Keep trying, you're getting there.

 

There are a few points I would like to suggest.  The Elvamide coating isn't really good.  It's difficult to make, and it tends to absorb too much moisture.  A lot of the people that have used it don't like it.  I would recommend you to try the antistatic cleaner.  It should be readily available in computer stores.  I have used it for a few years now and I really like it.

 

Using 0.5 mm spacers, while it's good, it's rather difficult to get it right.  You might want to try a little thicker spacer for the start.  In the very beginning, I use 1 mm spacer with a bias voltage of around 900V-1200V and it turns out very well.  This is just to get your feet wet and then you can do further experiment to get everything as you want.  

 

The perforated metal sheet might not be flat enough.  From the picture, I'm guessing that you're using 80 cm diameter active diaphragm, right?  With 0.5 mm spacer, even a small warp on the stators can cause problem.  You can either increase the spacer thickness as I suggested above or you can try inject a small drop of silicone right in the middle of the diaphragm.  This will act like a small spacer in the middle.  The diaphragm will be more stable, but will not make very deep bass. 

 

Please keep us posted of your progress.  Keep trying!

 

Wachara C.

post #515 of 1465
Quote:
Originally Posted by chinsettawong View Post

 

There are a few points I would like to suggest.  The Elvamide coating isn't really good.  It's difficult to make, and it tends to absorb too much moisture.  A lot of the people that have used it don't like it.  I would recommend you to try the antistatic cleaner.  It should be readily available in computer stores.  I have used it for a few years now and I really like it.

 

Where have you read that Elvamide doesn't work well due to moisture? I've been using it for a while and I find it fantastic. It's quite simple to make (I'm not sure why people online seem to say it's really hard, putting pellets into a cup of alcohol and heating it isn't very difficult) and it bonds extremely well to the mylar (another thing people seem to not usually find true... I don't even usually clean the mylar before application, not sure why I'm lucky here)
 

You can also reheat it and use the same mixture several times before it starts to go bad (yet another thing few people online seems to have mastered... reheat, and it's good to go!)

 

 

If anyone hasn't tried it, I would suggest doing so. If you have and had problems, I'd be curious to hear your story about it. As far as I know it is a current industry standard product and is used even in some retail products, so I find it hard to believe moisture is a problem for it. The material datasheet says it can only absorb 3.4% in moisture content, and that is if soaked in liquid water.

post #516 of 1465
Thread Starter 
If it works well for you, I am glad to hear that. At an ESL DIY forum over at diyaudio.com, I haven't heard anybody using it for a while. Many feel that it's a pain to prepare, add too much mass to the diaphragm and too humidity dependent. I guess my information is wrong then.

Wachara C.
post #517 of 1465

thanks Guys for the input..

I am going to try some things today.

there is something I'm missing, or not doing.

 

Last night I looked for movement on diaphragm when applying bias but

could not see any displacement..

 

  These sound exactly like the Stax SR-3N that I got on ebay.

until they were charged several hours. low volume, bad distortion.

 

I have read the arguments on Elvamide, found it slow but easy to cook up.

reheating was obvious to me.

still using the first batch from june.

Have you seen the video of melting it into the Mylar with a heat gun?

Its hard to control the heat- made a few holes- but it can be done.

I also have antistatic spray and use it too.

I like the way Elvamide sticks and coats the surface.

if you spray antistatic on the Elvamide it has an interesting chemical reaction

but I have no way to know what is the result except trial and error.

 

  In Andrew Radford's guide he says:

 

use 115:24 transformer then a 12:115 transformer to get 230V.

well the transformers run hot so gonna try adding a resister in series between them to lower current.

I have some 10ohm 5w or a 25ohm pot...

what do you think?

 

thanks.

post #518 of 1465

If it sounds good for a while, then later sounds bad with no bass and lower volume, that is almost certainly the diaphragm going unstable. I've never had it immediately go unstable, always minutes to hours later. You can often tell if it's stuck to a stator by blowing through each side. If blowing on both sides displaces it a little, then it's still centered. If blowing on it doesn't make it displace, it's probably stuck.

 

As for 110>24 into 12>110, that's not going to work. A resistor won't fix it. That will drive the second transformer way into saturation because you're trying to put 24V onto a 12V winding. The image is not actually suggesting doing so, though. It is showing 230>24 into 24>230, basically an isolation transformer. There is no correct way to get 230V out of a 110V winding, so you'll need a different transformer configuration than what you already have.

post #519 of 1465

Radford's text advice is wrong - likely he never tried it - or used such small transformers the abuse wasn't obvious - physically small xfmr have more surface to volume ratio, high winding resistance/poor regulation - can radiate away the heat from abuse better than larger xmfr

 

dual primary "universal" line transformers can be used if step up from 110/120 AC is needed - a single 1:1 line isolation xmfr can be used, or 2 back-to-back, the smallest VA you can find with matching secondary V

 

the dual primaries may be wired for 110/120 one side, 220/240 the other

 

I would only use "double/reinforced insulation" xmfr here, tested to 4 kV

 

 

 

a Y1 "double/reinforced insulation" safety rated cap based, "capacitively isolated" bias generator would be more compact - may want lower leakage diodes than 1N4007 to keep C values down, diode leakage can be biggest load on ESL membrane bias supply


Edited by jcx - 9/3/12 at 2:45pm
post #520 of 1465

  Thanks JCX

 

I do not understand everything you said --- will google.

 

I do have a triple primary 20va trans for HVAC.

 

Well I did not know the primary's could be used like that,

so one is 208v and one is 240v. now it makes sense.

will check on double/reinforced insulation..

 

thank you


Edited by Congo5 - 9/3/12 at 6:13pm
post #521 of 1465

Re-read this entire thread again making notes until late into the night, and it looks like I may have found a use for these Philips 6326 driver stators ( 80mm too ! ).

 

As you can see here above the green coating is the bonded spacer in this setup.

 But it's only 2mm wide and very shallow not even .3mm i wouldn't think from a rough measurement ( no electronic capliers ) As well due to the poor shot I took there you can't see them, but there are tiny dots of this green stuff between each of the holes on this same side. I assume because it was so close the the electret diaphragm that it hit that thing or had the potential to hit it so this must prevent it from sticking. Sort of see that on the diaphragm there.

 

I'll have to see whether I want to use this face of it and how tall that green spacer ring is. Ideally I am looking for 0.5mm.  If I kept that face towards the diaphragm it has the bonus of all those tiny green dots to prevent sticking just in case, although I plan to avoid that and tension as best as possible, still nice to know some extra insurance in that aspect.

 

 

As the driver these came from is only a single sided one I will need to sacrifice the mint second set of electrets ( yikes ) to get another matching set, but it will be worth it I think considering the possible end result. ( or wait around and pick up a cheapo pair?).

 This way I have factory made  burr-free evenly spaced and perfectly sized stators . Just a matter of getting the rest of the stuff rolling, and time. They are aluminum it seems so I may opt for attaching the leads with the MG Chemicals Electrically Conductive Silver Epoxy. Worked great before on another similarly drivered set i have with absolutley no noticeable difference and the product specifications say the same.

Certainly it had better be good it's not cheap stuff for the miniscule amount you get in the tube.

 

Even have aged Alder wood for the housings.

Whenever I get to these , I can run them from both normal and pro bias stax adapters, so i will be recabling for that. Most likely the Pro. ( SRD-6 and SRD-7Pro boxes.)

 So for now it's a bit before I can start, have to begin collecting the materials.

 

Was going to give the 3.5 or 4.2 micron mylar a shot from that ER Audio site.  Hmm which one to try.

 

Torn between using the Computer anti static application, the stuff rom ER Audio, or simply the old graphite powder rub. With the graphite is it just a general application and how precise to do have to get the resistance on each I assume close. This was the part that was bothering me. The posts i have seen they seem to just do it without regard to precise amounts (?)

 

Has there been any degradation with the antistatic cleaner application? I was wondering how long that will last as obviously it isn't an "apply it once for the lifetime of your computer screen " type of stuff. At least in my mind. I'd rather not rebuild a year down the road.

 

 

Thanks to all in here who have painstakingly narrowed down the materials to find the best solutions for this. Particularly impressive was the set made from shopping bags. Incredible DIY.

And the square drivers are certainly interesting also ( heck everything in here is great! ), for some reason I have always thought that round was the only way to go, but then again the Sony ECR electrets use the offset pentagon shape to minimize resonances caused by the driver shape, and offhand I think there might be one or two orthos like that just can't recall.

 

Just a matter of time now on this end.( so many projects getting burned out )

Have to figure out how to get the pcb spacers ( If I even need spacers due to the already applied green ones ) cut nicely and what to use for the diaphragm ring . Also the spacers for the dust guard on the front. Thinking the green spacers are simply not high enough. Is there a standard width for that also? Have to go back and look again.


Edited by nick n - 9/3/12 at 4:59pm
post #522 of 1465

Whoops. Delete.


Edited by khbaur330162 - 9/4/12 at 12:43am
post #523 of 1465
Thread Starter 

My second pair of Omega Clone is done.  dt880smile.png

 

post #524 of 1465

So... where can I place the order for a set?  tongue.gif  Drill a couple of holes in the sides and the SR-Omega headband should fit perfectly. 

post #525 of 1465
Thread Starter 

Hi Birgir,

 

Thanks for your interest.  As you might have known, I don't sell my headphones.  wink.gif

 

How is your fitting of Stax drivers into Orpheus wooden cup project going?  When you are ready, I would rather let you try the Orpheus clone drivers that I made.  Let me know. o2smile.gif

 

Wachara C.

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