[eightbitpotion]

I've decided to see how well I can make a pair of electrostatic phones....currently, I'm looking for a great type of stator....I'm thinking about one of two things- first one is using a pretty good conductive material that's non-oxidizing....OR I'm thinking about using a non-conductive stator and using gold leafing to make a conductive face towards the mylar.

Does this seem dumb? Gold leafing that is? I was going to go to a home improvement store and buy some copper screen filters...but once these oxidize and tarnish...it may not seem like the best choice after that. Gold however seems to be the best without tarnishing and losing conductivity...

What are your thoughts? Has anyone in here built a pair of ES earspeakers before?

 

[heatmizer]

Take a read on this:
http://www.hifihacks.com/?page_id=17

 

[eightbitpotion]

Quote:

Originally Posted by heatmizer /img/forum/go_quote.gif Take a read on this: http://www.hifihacks.com/?page_id=17

Neat! But is SS really the best material for some stators? I mean...I know I may be talking about small beans....but I don't know if I am or not. Since I'm still not comfortable with my electrical abilities... I'll ask: If it's less conductive of a material...would this sacrifice sound quality or does it just mean I'll need more power?

 

[eightbitpotion]

That's a pretty cool article...the graphite trick is wonderful.... Is there a "big" difference in electrostatic amps compared to everyday amps? I know a headphone amp probably wont run them, but would say a stereo amp if I plugged them up through the speaker ports? Or would that be bad joojoo?

 

[ericj]

Don't forget these articles:

http://headwize.com/projects/showfil...dford1_prj.htm

http://headwize.com/projects/showfil...=cmoy3_prj.htm

And, yes, there is a big difference between speaker amps and electrostatic amps.

Speaker amps swing double-digits of volts, at the most. Electrostatic amps output almost no current at all, but swing hundreds of volts. They are also necessarily differential-drive ('balanced') where not all speaker amps are differential-drive.

And then there's the question of bias voltage. You have to supply the headphones with a few microamps of anywhere between 200v and 1kv depending on the design.

More often than dedicated amps, 'stats are driven by box that contains the bias supply and a pair of step-up transformers for speaker-level audio. They need a speaker amp capable of driving between 6 and 10 watts at a bare minimum (T-Amp *MAY work) but obviously the quality of the speaker amp and 'synergy' come into play in a big way.

fwiw, yes, graphite works, and possibly a little too well. There are anecdotal reports that it is far too conductive, and that an accident can result in the frying of a Stax amp.

 

[eightbitpotion]

Quote:

Originally Posted by ericj /img/forum/go_quote.gif fwiw, yes, graphite works, and possibly a little too well. There are anecdotal reports that it is far too conductive, and that an accident can result in the frying of a Stax amp.

Thanks for the links! I'm aware of the super conductivity of graphite....I'll playing with many different thickness of mylar...it's available in the oddest places, so it's a free experiment. It would seem that these diaphragms are much more "touchy" with the power source....as in it would seem that too much power would be much more devastating than with a cone driver... don't tell me if I'm wrong or not...maybe it'll just make me be overly cautious .

Based on what you said about the amp.... is there any alternative amps that I can buy and use until I build one? If I build the phones first...I won't know what the sound like without an amp, and if I build the amp first...I won't know what it sounds like without the phones....which neither one will really hurt, but if I mess up on one or the other it'd be excessive trouble shooting.

 

[ericj]

The cheapest route would be to find one of the less-sought-after stax transformer boxes and plug it into whatever speaker amp you have handy. SRD-5 or -6 for example. Some of these are available in a "self-bias" configuration where they derive the bias power from the audio signal, but self-bias is generally inferior to a dedicated bias supply.

Don't get the SRD-4 unless you want to build your own bias supply and modify or replace the socket. It's an electret transformer box and has no bias supply, but the SRD-7 schematic is available and it would be fairly simple to convert a -4 to roughly a -6 (the SRD-7 has better transformers than earlier transformer boxes, thus the increased value vs. an srd-6).

Basically, the bias supply in an SRD-7 is just a voltage doubler hooked up directly to mains AC, plus rectification and small capacitors.

 

[eightbitpotion]

So these stax units are nothing more than transformers? Transformer + Amp = what I need if that's the case, and will be looking for these units that you just recommended. Thanks! You've saved me a bundle of cash.

 

[eightbitpotion]

While looking for the SRDs...I ran across a picture of the Omega IIs....and I've seen them many times before, but this time I noticed the stators....they holes are freakin huge.... I may try a few different materials with different sizes to see how it impacts the sound.

Any thoughts on if I should go for a smaller diameter or something similar to this or does it really even matter?

 

[ericj]

Yeah, the SRD-5 -6 and -7 are a couple step-up transformers and a bias supply, nothing else. You hook them up to a speaker amp.

 

[ericj]

Quote:

Originally Posted by eightbitpotion /img/forum/go_quote.gif While looking for the SRDs...I ran across a picture of the Omega IIs....and I've seen them many times before, but this time I noticed the stators....they holes are freakin huge.... I may try a few different materials with different sizes to see how it impacts the sound. Any thoughts on if I should go for a smaller diameter or something similar to this or does it really even matter?

You know I'm not sure if that's the stator. I guess it probably is.

You have to keep stator resonances to a minimum. To that end i believe the O2 has some exotic materials in that position. It shouldn't matter tremendously what you use, as long as it is at least 20% open and reasonably stiff.

DIY projects occasionally come up for discussion in the headphone forum, "The Stax thread", which should generally be somewhere in the first few pages. It's a monster thread with plenty of good reading on electrostatic theory.

As for diameter, real bass is easier to accomplish in planar headphones when the driver is bigger than your ear.

 

[Thermionic]

Hi gentlemen,

The large holes in the Omega picture are I think just holes in the capsule / transducer casing for the sound to pass through, and are not the actual stators.

While I don’t own a pair of these headphones, the Omega does remind me of the layout of their older phones such as my SR5s. These have a pair of thin gold-plated stators with fine chemically-milled hexagonal holes. The transparent diaphragm is stretched over a flat circular metal ring, and this is held in a pair of clear plastic rings (Perspex?) which hold the stators at the correct distance from the diaphragm. A further pair of plastic rings (and screw fixings) clamp the whole transducer together. Connections are made by soldered joints directly on the stators and by a spring-loaded ‘point’ pressing on the diaphragm ring.. The circular transducer sits in a moulded recess in the headphone bowl.

No doubt the Omega is a highly refined machine compared to my Jurassic SR5’s, but the view looks fairly similar through ‘the sound holes’.

Hope you don’t mind me butting in.

 

[eightbitpotion]

Useful stuff Thermionic....

I think I may get some speaker grid cover (like on boomboxes)... and maybe gold leaf that, and pull out my multi-meter. I don't know anything about gold leaf...but from my understanding it's just a sheet of gold that can be applied to any surface. I'll go to the home improvement store tomorrow...I'm just not sure if a non-conductive stator with a gold plate on one side would be better than a...say aluminum or ss stator. I guess it'll be trial and error. Has anyone ever listened to these DIY SE headphones before? Am I looking at a novelty or can these things really sound good? :-\

Sorry for the babbling...it's 5am and another hour before the home improvement store opens -_-. Just getting fidgety.

 

[spritzer]

The plate you see in used to hold the earpad in place so it's not the stators. The stators are prefabricated PCB boards and it is pretty good as a stator but has it's own issues. Perforated metal is a good point to start with or even wire wound as a simple alternative. All metal should be insulated to prevent arcing. If you are going to use some conductive paint or something similar on a non conductive stator use it on the side facing away from the diaphragm to avoid contact burns.

Using graphite is a very bad idea and the phones won't last long with it. It's much better to design your own semi-conductive coating or buy something pre made. There are quite a few places that sell materials for DIY electrostats or to repair old ones.

I have been experimenting with a few designs and have quite few working prototypes (there will be no pictures or other information on those because they will reveal to much of how I build them and I want it to stay private). In the end it's pretty hard to diy a good set of cans that can stand up to the retail stuff but if you are careful and have a good design they will work fine. A small difference somewhere will be magnified in SPL levels so driver matching isn't easy. The stretching techniques have to pretty good to get consistent results but you can also use a larger sheet and take both diaphragms form the same spot so thy will be as close as possible. You can also heatshrink them but it's hard to control the exact heat amount to use on any given spot so use it only as a last ditch effort.

The problem is to source a diaphragm that is thin enough for headphone use. A 3.5um is too thick for much HF output unless you stretch it a lot but then you kill the bass. You can find a good middle ground but it's would be much better to use a 2um film or thinner. Don't use anything except Mylar-C film as it is the only film strong enough and with the right properties for ESL use.

The tension of the diaphragm matters a lot and a tight diaphragm will give you more HF but less bass and a loose one will be the opposite.

The glue is very important and so is the way you use it. Epoxy should be avoided like the plague so use a slow curing glue that is strong even when spread extremely thin (0.05um or thinner). Let it cure for a few days as if the stators shift just a bit you'll be in trouble.

I recommend you read a book on ESL design because there a few rules about stator design, spacer thickness, coating materials, diaphragm dimensions, supports, bias voltage, the configuration of the bias supplies and etc. that can't be broken or you'll end up with a distortion riddled panel or a nice fireworks show. The Sanders book is ok but his obsession with dynamics bass drivers is tiring.

 

[Thermionic]

Sounds like you’ve got it bad…

Some fairly random thoughts (made before spritzer‘s more meaningful contribution):

I’m no electrostatic headphone designer but I have admired (and enjoyed) various electrostatic transducers over many more years than I would like to admit. My Quad ELS57s were made in 1970 and I still use them almost daily and that goes for some Lambda Sig Pros and the SR5s. The SR5s have though recently been displaced by some Senn 650’s but I still have them near to hand. I suppose what I am trying to say is that while no expert, because most of my stuff is so old I have over the years had most of it apart to clean, fix or ‘improve’ it.

Now it seems to me (IMHO etc) that the electrostatic transducer as a concept is seemingly very simple and can be stunningly good at making music. The big but is that there looks (to me at least) to be a fair amount of magic needed in making a successful one. For what it is worth my own assumptions in making a pair of electrostatic headphones are that:

The stators need to be quite rigid, only slightly conductive and have lots of holes in them. (Certainly the SR5’s I have had apart have very nice gold-plated perforated discs). But there again I am looking at a pair of AE Eggo satellites on my desk that have perforated metal grills that look ideal stator material. Its not that the stators are conducting current, it’s just that they are holding an electrostatic charge that varies with the audio signal. Stainless steel is probably perfectly good. Solid silver might be nice from a psychological point of view but in reality it would be no better than SS and would tarnish. Some people have used what we call matrix/Vero board - drilled pcb material with lots of parallel copper strips ) They are after all just capacitive plates, not conductors. I am not sure about the gold leaf option, as real gold leaf requires quite some skill to apply properly, and anyway I doubt that you can buy it from a DIY store. It comes in small ‘books’ about 6-Inches square and is very difficult to use without destroying it. I am not sure how much it costs but it is real beaten (very thin) gold. Drilling an un-etched copper clad PCB board might be a better way to go. Drill (say 3-500 .5mm holes in a 10Cm) disk of glass fibre PCB material and then de-burr, polish and lacquer the surface. If you paint on both sides your ‘copper screen filters’, that might work if they are nice and rigid. Martin Logan uses painted perforated (steel?) stators for their loudspeakers. You will need to keep them dust protected as I understand ML owners eventually find out…

You need to be able to reliably hold the stators away from the diaphragm by around 1mm or less, and the spacer needs to be a very good insulator. Again un-clad PCB material might be an option.

The diaphragm is a whole mystery in itself… It has to be light (slightly) conductive and flexible, though I believe that the tension across it is critical for frequency response and output level (to lose - arcing, to tight - no bass). So it probably needs to be in some sort of frame or ring. Mind you my Koss ESP6s have quite floppy diaphragms that look like they have been painted with conductive silver paint. Their bass is a bit down so old age might be creeping in here. Making a conductive diaphragm is (as you know) an art in itself, some people just ‘polish’ the surface with a graphite pencil. Have you seen Sheldon Stokes web site on electrostatic speakers? If you go the graphite way you might consider using a high value resistor in series (say 1-10meg Ohms) to keep the conductivity down.

You have to keep the transducer dust tight and the stators away from your ears or the loud notes may be shocking in more ways than one! I think that the dust covers could be made with something like (what we call) ‘clingfilm’ food wrap. But there again the stuff Stax uses is very much thinner and more flexible.

As far as I know, with the exception of the tube energisers, most driver boxes use step-up transformers to drive the stators (at 250 to 500ish Volts) with the audio signal and a ladder (forget the name - diodes and caps) network to provide somewhat more DC bias volts to the diaphragm. There again the bias voltage will effect the dynamic qualities of the headphone. But you can probably get an old Stax box quite cheaply.

Of course you could also restore an old set of Stax phones with a lot less trouble than making your own. My own 20+ year old phones started making odd noises, so before dumping them I had them apart and noticed that the diaphragms were a bit cloudy (like dirty window panes). So with nothing to lose I just got a clean, soft, slightly damp cloth and gently wiped away the fog. Result perfect working headphones again. With some home made silver wires to the energiser they sound only slightly less good than the Lambdas. Old Stax electrostatics are not expensive…

I think that’s enough waffle for now, hope it’s further food for thought and my respect to ericj and spritzer.