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My DIY electrostatic headphones - Page 60

post #886 of 1588

you don't need enough Gold atoms at the required resistance for the weight to matter - just awesome control in the metalizing process to put down so few, uniformly - not everybody's home diy option

 

organic coatings could be a problem

 

it has been speculated that getting a batch of polymer with the right carbon black loading so the conductivity is a bulk property would be a good option - anyone need a few tons of esl membrane material? - maybe a group buy?

post #887 of 1588

you don't need enough Gold atoms at the required resistance for the weight to matter - just awesome control in the metalizing process to put down so few, uniformly - not everybody's home diy option

 

organic coatings could be a problem if overdone

 

http://www.quadesl.org/Hard_Core/PanelCoatings/OriginalCoating/originalcoating.html

 

 

 

it has been speculated that getting a batch of polymer with the right carbon black loading so the conductivity is a bulk property would be a good option - anyone need a few tons of esl membrane material? - maybe a group buy?

post #888 of 1588

Thought I would just quickly share a little screen shot of the exploded view from CAD of the phones I am currently making (obviously they are the machined blanks and will make some minor alterations like removing the tab from one of the spacers so I can get to the copper on one of them, radiusing, drilling holes for cables and headband). Will be held together with Nylon screws, Outer cup is Cherry wood, spacers are 0.5mm each, main stators just over 1mm thick, 462 x 2mm holes leaving 63% open area but with good stiffness, main active area is about 63x93mm, sheet is 2um thick (will try to get 3um and try that when I can get some) and will use either Anti static spray / gel or Evalamide. Additionally there will be a moisture cover with the 2um mylar on a EPDM spacer and the pads will be custom made leather (on the inside profile from the drivers to get good bass extension) and velvet against the ear......

 

 

 

Quick questions:

- I noticed the preference of etching as much copper away on the stators as possible around the edge, do you guys do this buy sanding them after machinng then colouring it in with a sharpie before putting in the etching solution (Ferric chloride I would imagine)?

- Does this help get rid of the sharp corners on the holes and reduce any arcing?

- Do you bother etching the copper off one of the spacers to make it completely blank board or just turn it around so the copper is facing one of the stators?

 

Thanks,

 

Chaz

post #889 of 1588
Thread Starter 

Hi Chaz,

 

Your design looks really good.  But, if I were you, I would make them bigger.  ;)

 

The reason for etching out the unneeded copper is to reduce the capacitance on the drivers.  The capacitance makes a lot of difference on high frequencies.  When you have high capacitance, it's more difficult for an amp to drive high frequncies.  Nowadays, I always etch out all the copper which is not covering the active diaphragm area.  The way you describe about etching the copper is fine.

 

Etching copper using etching solution can help get rid of sharp corners on the holes, but I think using sand paper does a better and quicker job.

 

I do not bother to etch out the copper off one of the spacers.  I want to make sure that these two spacers are of the exact same thickness.

 

Wachara C.

post #890 of 1588

If I went bigger now where I would I be able to get on the next pair! ;-)

 

Actually I did have a nice thought about being able to maximise the area and keep the same basic shape (which I quite like) and that is to make the elipse slightly square sided, just a bit and should help increase your actual open area in the 10% range with little shape change.

 

Great stuff, good to know I am on the right lines. Did you notice quite a bit of difference when you etched them?

 

I just wondered if you might get some corrosion or capacitance between the two pieces of copper facing each other from the stator and the spacer but if you dont think it will be an issue then will try that.

 

Chaz

post #891 of 1588
Hello all,

Progress is getting there on the phones (had some of the wood cups made but weren't quite perfect so having some more done) and more importantly finally got the Mylar through so plan to do some experiments before I actually make up the films but as always I have some questions for the group please :-)

- I am going to try a few coatings as I have the stuff so might as well. I have some Elvamide but was wondering if I could use isopropanol (rubbing alcohol) as the dissolvant?
- Do you clean the Mylar first and what with?
- What is the resistance band I am aiming for? I was thinking of applying the coating and putting some copper coins 95mm apart and seeing what the read out was....
- With the graphite powder method could I just shave a thick pencil lead for this (as I randomly have quite a few)?
- Right..... Stax plugs! Seen the threads about where to get things similar but only in the US and they want to charge nearly the same in postage as a whole Extension cord!!! Does anyone have the pin dimension and positions so I can make my own please?
- Cabling (seeing as I have access to electronics labs) I have found some nice 3mm 600v cabling, going to be quite chunky but resistance will be super low, anyone see any issues with using thicker cabling?

Will keep you posted as I progress....

Thanks as always forum gurus...

Chaz
post #892 of 1588
Thread Starter 

Hi Chaz,

 

I know the fun of doing experiments.  I've been there and done a lot of those.  Do whatever you feel like doing and come back and tell us your experience.  wink_face.gif

 

If I were to tell you what you should do, would you still want to experiment?  o2smile.gif

 

Wachara C.

post #893 of 1588
Well normal I would be all up for the endless experimentation but having tried the rubbing graphite and anti static with no luck (though not sure if that is due to my cheap multimeter) and an hour and a half trying to get the elvamide to dissolve according to the instructions and not a single change in it might possibly need some help ;-)

Do you still use the mix you specified in the first posts with PVA and graphite or just on the anti static now? Once I have the bits together can try them and mount them in the drivers and see what happens.... What are the obvious issues / what's the best way to tell if the sheets are too conductive / not conductive enough (e.g. Lack of sound, cracking or something)???

Anybody got any info on the cabling and connector please?

Chaz
post #894 of 1588
Thread Starter 

Hi Chaz,

 

The resistance is normally too high for a normal multimeter to be able to measure.  You'll need a high voltage resistance meter to check it.  I normally don't bother to do that.

 

I only use antistatic gel cleanser nowadays for coating.  It's much better and a lot easier to use.  Don't use my PVA glue formula anymore.  About elvamide, no comment.  tongue_smile.gif

 

Thick cable is fine, but it's a waste of resource since the current is so very little.  wink_face.gif  Do a search and you'll find the dimension for the connector.  But if you are just going to make an amp by yourself too, you don't have to use the connector like the one Stax's using.  I like the 5 pin DIN connetors, and I use them on my headphones.

 

Wachara C.

post #895 of 1588

You should find graphite pretty much anywhere. It is used to lubrificate doorknobs and is not expensive at all (~5$). Maybe grinding pencil leads would work, but you should be careful not letting bigger bits go through.

 

Quote:

Originally Posted by Chazman View Post
- Cabling (seeing as I have access to electronics labs) I have found some nice 3mm 600v cabling, going to be quite chunky but resistance will be super low, anyone see any issues with using thicker cabling?

What you have to worry about is not resistance. Most amplifiers have a 5k resistor in serie with the output. What little resistance the cable adds does not really matter after that. But if you choose a bigger cable, you will have to deal with a bigger parallel capacitance and that might be annoying. See stax's website, the cable's capacitance is very close to the headphone's capacitance.

 

Quote:
Originally Posted by Chazman View Post
- Right..... Stax plugs! Seen the threads about where to get things similar but only in the US and they want to charge nearly the same in postage as a whole Extension cord!!! Does anyone have the pin dimension and positions so I can make my own please?

KG posted some informations about the female plug a while back :

"

If you have the right tools you can make your own out of a piece of teflon and some of the yamamoto tube socket pins.

Imagine the socket as a 6 pin with the 6th pin missing, but at position 0,0 (x,y)
The rest of the pins are at
0,.2175
-.2175,0
+.2175,0
-.1087,-.1883
+.1087,-.1883

(in inches)

 "

here is the image used to make the female plug :

(btw the pins themselves are exactly identical to octal pins used in EL34 or 6AS7 for example)

post #896 of 1588

Resistance across my diaphragm (7cm diameter, measuring points 5mm diameter) was about 10 gigaOhm, so you're gonna be smarter than your multimeter to measure it.

Connector dimensions are in mm:

post #897 of 1588
Quote:
Originally Posted by AmarokCZ View Post

Resistance across my diaphragm (7cm diameter, measuring points 5mm diameter) was about 10 gigaOhm, so you're gonna be smarter than your multimeter to measure it.
Connector dimensions are in mm:



Thanks for the diagram very useful :-) That is some serious resistance across the sheet, perhaps this is the issue as mine is only a normal multi meter and goes up to 2000k which is apparently no where near!

Guess I will just have to give them a go and see what works. Again any steers on symptoms of the coating being rubbish?
Quote:
Originally Posted by bidoux View Post

What you have to worry about is not resistance. Most amplifiers have a 5k resistor in serie with the output. What little resistance the cable adds does not really matter after that. But if you choose a bigger cable, you will have to deal with a bigger parallel capacitance and that might be annoying. See stax's website, the cable's capacitance is very close to the headphone's capacitance.

Hmmmm not something I had considered before. Do you have any advice on the best way to match these (e.g. Measure capacitance over the stators then then certain aspects of the cable)?
Quote:
Originally Posted by bidoux View Post

You should find graphite pretty much anywhere. It is used to lubrificate doorknobs and is not expensive at all (~5$). Maybe grinding pencil leads would work, but you should be careful not letting bigger bits go through.

I have read some articles about using graphite with different methods and some suggest just rubbing the powder on then wiping it off (others involving glue), is this right? I did some earlier and none of the graphite seems to stick to the membrane (it's 2um DuPont Mylar) but perhaps there is some there and it's enough...
Quote:
Originally Posted by chinsettawong View Post

I only use antistatic gel cleanser nowadays for coating.  It's much better and a lot easier to use.  Don't use my PVA glue formula anymore.  About elvamide, no comment.

I am getting the impression this Elvamide is a PITA! Going to get some pure Ethanol from work (I am trying to use Surgical spirit which is 90% ethanol, 5% methanol and some other stuff including castor oil which might be the thing causing the issues) and see if that works, might as well as I have the stuff!

Will hunt down the gel stuff! With these if you try them and don't work can you just use Isopropanol or acetone to take it off rather than ungluing the sheet?
Quote:
Originally Posted by chinsettawong View Post

But if you are just going to make an amp by yourself too, you don't have to use the connector like the one Stax's using.  I like the 5 pin DIN connetors, and I use them on my headphones.

Wachara C.

I decided to chicken out for now on finding the bits for the Amp and use a Stax SRD-7 Pro to power them until I can work out how to build (or earn enough money!!) to get a nice tube amp.

Many thanks,

Chaz
post #898 of 1588
Thread Starter 
Quote:
Originally Posted by Chazman View Post

I am getting the impression this Elvamide is a PITA! Going to get some pure Ethanol from work (I am trying to use Surgical spirit which is 90% ethanol, 5% methanol and some other stuff including castor oil which might be the thing causing the issues) and see if that works, might as well as I have the stuff!

 

 

Working with Elvamide isn't easy.  Good luck!

 

You can certainly clean out your coating using alcohol or acetone.  There is no need to redo your diaphragms.

 

Wachara C.

post #899 of 1588
Quote:
Originally Posted by Chazman View Post
Hmmmm not something I had considered before. Do you have any advice on the best way to match these (e.g. Measure capacitance over the stators then then certain aspects of the cable)?

I guess you want a lot of space between the conductors and thinner wires in order to reduce the cable's capacitance. I don't know how stax does it.

Another option is to use a spare cable from koss, they are quite cheap.

 

BTW  you are not supposed to match the capacitance of the cable to the capacitance of the stator (or are you ???). More capacitance for an amp to drive means worse slew-rate so ideally the cable should present no serie resistance (but as I said it is not a real problem) and zero parallel capacitance.

Quote:
Originally Posted by Chazman View Post

I have read some articles about using graphite with different methods and some suggest just rubbing the powder on then wiping it off (others involving glue), is this right? I did some earlier and none of the graphite seems to stick to the membrane (it's 2um DuPont Mylar) but perhaps there is some there and it's enough...


I simply rubbed the graphite onto the mylar using a paper towel, no acetone, glue or alcohol needed. It should take no more than two minutes rubbing it and then the mylar definitely changes color, it looks greyer.

Before doing so you have to stretch the mylar over a piece of glass that you have cleaned as much as possible (I use acetone for this) then you have to expel the air between the mylar and the glass by rubbing it. Once it has attached to the glass it won't scratch (or maybe it will tongue_smile.gif , but it is less likely) so you can put much more pressure on the mylar when you will spread out the graphite.


(at least that is why I understood from Roger R Sander book's. It has worked ok for me)

post #900 of 1588


Here's some of the first bits from the CNC and makings, hopefully will be able to get on it next weekend when I am back from holiday :-)
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