First attempt

j beede

Member
2007-12-24 5:04 am
NorCal
I actually found a couple hours to work on my ES headphone project yesterday. I used my Dremel to rough cut a pair of 2 5/8" stators out of a sheet of scrap perferated steel. I built a little jig that let me grind them round and to size using a disk sander. Plumbing gaskets (a little too thick) and 0.7mil drop cloth completed the BOM. I tensioned the diaphram using celophane tape on a sheet of glass--just tight enough to get the wrinkles out. Radio Shack provided the copper PCB tape for the diaphram contact. I used powdered graphite to produce a very consistent charcoal-colored coating, then cleaned most of it off with Isopropyl. If you can see the photos of my makeshift breadboard, the toroidal transformers are just 30:1, I used one for the 550VDC supply as well. I used two of them to fake a center tap in the secondary. When I powered up the setup I though something was wrong... dead silence. No snapping, no crackling, no crinkling, no hissing, no whirring. I hit "PLAY" and was stunned to hear music coming out of the "panel". I put my ear as close as I dared... Let's just say I am anxious to find time to build the second element and then the frames and headband. Total build time... three hours, not including gathering materials. Fun.
 

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j beede

Member
2007-12-24 5:04 am
NorCal
I have just begun working on the frame and headband. I am using white oak to fashion a round frame similar to the round Stax and Grado RS uses. I am already using two 1:30 toroids for audio step up, I am in the process of doubling that to get 120:1 center-tapped. I don't have a scope so it isn't easy for me to see the stator ac voltage. Maybe I'll try white noise and an ac range on my DMM. My amplifier has ~60V rails. What have you learned about the ratio of DC on the diaphram to the ac on the stators--with respect to increasing SPL?

Here's another photo
...j
 

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j beede

Member
2007-12-24 5:04 am
NorCal
By the way... the panel is 65mm in diameter (sized to fit the gasket I had) which is large for a headphone driver, compared to Grado or Sennheiser dynamic headphones. I suspect it is not large compared to Stax Lambda or Jecklin ES headphones.

I am anxious to try them on. Which brings up another question. An insulating coating is going to be even more important for an ES headphone driver. Maybe I should go binaural, monophonic for safety reasons! I hate to use a fabric/foam insulator. Anyone know how Stax isolates the stator from listener's outer ears?
...j
 

Few

Member
2004-04-14 10:51 pm
Maine, USA
Have you thought about putting a very open (acoustically transparent) and electrically grounded metal screen between the stators and your ears? Finding a gap in the insulation while the stators were strapped on either side of one's brain might make the wearer a contender for one of the Darwin awards. I would think the screen could be very open and still protect the wearer.
 
J Beedee:

Nice work you have done. As I see it, you are using a transformer to step up the voltage 30:1 to feed into your earphone. Please be very careful of that. If there is some leakage in the wire or headphone, you'll be burned.

It is safer to use a small transformer then doublings the voltage to the voltage you want. The current will be very little and you can only get a shock out of it but nothing more serious.

Just my 2 cents.

Wachara C.
 

j beede

Member
2007-12-24 5:04 am
NorCal
chinsettawong said:
J Beedee:

Nice work you have done. As I see it, you are using a transformer to step up the voltage 30:1 to feed into your earphone. Please be very careful of that. If there is some leakage in the wire or headphone, you'll be burned.

It is safer to use a small transformer then doublings the voltage to the voltage you want. The current will be very little and you can only get a shock out of it but nothing more serious.

Just my 2 cents.

Wachara C.


Thanks for looking. I generated the dc bias by applying 8 VAC to the primary side of 1:30 transformer. The ac at the secondary is rectified and doubled then current limited through a series 20M resistor--very small current and little danger there. The ~550 VDC is contained inside the stators in any case. The audio output from the amplifier is stepped up via two 1:30 transformers and applied to the stators. This HV is not current limited and represents dangerous levels near the outer ears. I am working on this.
...j
 

j beede

Member
2007-12-24 5:04 am
NorCal
Time to finish my headphone project... I get about 5 days per year (always around the winter holidays) to work on this project.

I have the frames and earpads almost ready to go. I am still concerned about human exposure to the stators. Martin-Logan has no grounded "safety screen" to prevent a person from simultaneously touching the front and rear stators. Has anyone found a DIY method to reproduce their stator insulation? I dislike the idea of depending on a weak or ohmic ground connection for safety--especially if I use aluminum as the safety shield. I don't have a source for acoustically transparent steel. What sorts of things do you ESL builders use to protect "civilians" from the stators?

...j
 
A search on this site for stator insulation will yield a few approaches, but most folks are also trying to insulate the diaphragm side of the stator and therefore worry about how the insulation is going to affect the operation of the device. If you're just trying to insulate the user side of the stator while leaving the diaphragm side uninsulated, I would think you could get away with quite a variety of coatings. You might consider Calvin's advice in post #19 in this thread.

I know this is comment is likely unnecessary, but be quadruple sure that there's no way your new headphones are going to place the stepped-up amplifier output across your two ears. I once found a break in the sprayed on insulation on my ESLs while they were playing, and I discovered it the hard way. I had to wait for my fingers to recover before I could make good use of a screwdriver. I'd hate to hear somebody had a similar experience using their head. From your earlier posts I sense you're aware of the danger. I just don't want anyone else reading the thread to underestimate the risk.

By the way, the photo looks great! Nice work.

Few
 
You know, I have enjoyed this headphone project and I have acquired and learned to use a few woodworking tools... That said, I am hesitant to move ahead given the risk that ES headphones inherently bring along with them. I often wonder how Koss, Stax, Jeckin, etc. survived their entries into the commercial ES headphone market.

Few, you experienced motor problems after discharging your stators? Scary. I was at Fry's yesterday and experienced a large static discharge when I touched an empty computer case. This was unlike any I have felt before--it felt like someone simultaneously hit both of my elbows with 16 ounce hammers. It took 3-4 minutes before I felt 100% again. I have never felt 2000-3000VAC at any current level, nor do I care to.

Any ES headphone builders out there have any thoughts to add?

Regards, j
 
Hello j,
I don't mean to monopolize the bandwidth, I just want to balance my doom and gloom caveats with a post that's a bit more encouraging. I've long thought about making electrostatic headphones, so maybe it's just selfishness on my part, but I do hope you bring your project to fruition. It looks great so far and I don't think the safety issues are insurmountable. These devices are commercially available, after all.

You may not be too enthused about the idea of a grounded screen between the stators and your ears for fear of corrupting the sound, but it might put your mind at ease as you strap the suckers to your head the first time. I found some very open copper mesh (screen) at the McMaster-Carr site. I think if you had 1/4" holes through the screen, and ~70% open area (which is one of the options I think I remember) you're unlikely to hear much of an effect. If there were a few mm between the stator and the screen I think you could be quite confident you weren't going to reboot your brain when you fire them up. I think the screen cost about $14 for a square foot---a lot for screen, not much for brain safety. You could probably use much cheaper aluminum window screen as well. I just looked into the copper because you could solder a ground wire to it. Just a thought...

Best of luck, and I hope you keep at it! By the way, you can always do your initial listening tests at very low levels so that you can reassure yourself you've not designed a combination earmuff/bugzapper.

I'll now get out of the way so somebody who actually has experience with this sort of project can chime in.

Few
 
Hello J,

I finished my ES headphones last month, and they sound really wonderful. I used PCB as the stators and coated the copper side with paint. The highest voltage I had tried was around 1,200V, and I didn't have any problem putting them around my head. It was quite scary, though.

Your headphones look really nice. Please allow me to copy your idea to make the frames. They look awesome.

By the way, what is the thickness of the spacer you use?

Wachara C.
 

j beede

Member
2007-12-24 5:04 am
NorCal
Hello Wachara,
You used perforated PCB for stators? Copper clad on both sides and you used paint for safety insulation for the "ear" side and for the outside? This means no grounded safety "fake" stators? The PCB I have seen has very small holes, did you drill you own holes?

You are using 1200VDC for diaphram bias? or 1200VAC swing out of your audio transformers?

I have used 3/32" neoprene spacers and will use 1/16" on my next set of drivers. I am using 550VDC diaphram bias through 20 MOhms in series for current limiting.

I don't see much discussion here regarding personal safety and stator danger. Most of the stator coating discussions are focused on diaphram safety. I have owned commercial ESLs since 1975 and have never been shocked. I have never owned or used ES headphones before.
...j
 
Hello J,

I used a one sided PCB and I used my homemade CNC to drill holes on it. I painted only the copper side. Here is a link to my other forum . I'm very sorry that it's all in Thai, but you should get a general idea.

I can't find a better spacer, therefore I stick with the 1 mm PCB spacer. I now bias the stator to around 600V. However, I have made a switch so that I can choose to bias at either 600V or 900V. The voltage is fed into the faked center tap(just like yours) and out to the stators. The diaphragm is series with 20Mohm resister then to ground.

It's a very fun project and it's worth all the time and effort I've put in.

Wachara C.
 

j beede

Member
2007-12-24 5:04 am
NorCal
Hello Wachara C.
The photos on the Thai website were much appreciated. I see that the example there is using larger diaphrams than I am. I am experimenting with different diameters. The spacers there also appear to much wider than mine, I am trying to produce as much radiating surface as I can with the small diameter stators I am using. I am hoping that loose diaphrams and 1.6mm spacers allow me to compensate a bit for my small 51mm driver diameter.
Do you use CNC to cut phenolic spacers?
Regards, j
 

j beede

Member
2007-12-24 5:04 am
NorCal
Few said:
Hello j,

[cut]

You may not be too enthused about the idea of a grounded screen between the stators and your ears for fear of corrupting the sound, but it might put your mind at ease as you strap the suckers to your head the first time. I found some very open copper mesh (screen) at the McMaster-Carr site. I think if you had 1/4" holes through the screen, and ~70% open area (which is one of the options I think I remember) you're unlikely to hear much of an effect. If there were a few mm between the stator and the screen I think you could be quite confident you weren't going to reboot your brain when you fire them up. I think the screen cost about $14 for a square foot---a lot for screen, not much for brain safety. You could probably use much cheaper aluminum window screen as well. I just looked into the copper because you could solder a ground wire to it. Just a thought...

[cut]

Few

Hello Few,
If you look at the photo I posted above you can see the very open aluminum shield (painted black) that I made. Soldering to Aluminum is "iffy" at best, for me. I am ordering perforated steel from small parts to duplicate the shield, but in a material that I can solder to. Obviously I would rather not have to run the extra wire to each panel for the ground path. Since the shield will be isolated from the stator with a 1.6mm diameter silicone o-ring I am thinking that the charge built up on the shield is via ac coupling (per plan) or high resistance leakage path (unplanned). Either would be a potential annoyance, but should not be a hazard. That means grounding the shield should be unnecessary, agree? I will still make the shields out of steel in case I choose to ground them.

FYI--My Stax SR-44 arrived earlier this week and I gave them a listen last night for the first time. Not bad, full range, moderately uncomfortable, not a revelation. I think the hard, flat leather earpads are too thin--locating the diaphragm too close to the ear. The earpads make noise as they move on the outer ear. They are also heavily damped on the outer side making them behave somewhat like a closed design. Lightly covering the outer shield while listening makes almost no audible difference. Doing this with my Grado earphones produces a dramatic effect. If anything I am now more motivated to complete my ES headphones as I think I can do better than the (low end) Stax.

I should mention that I am not a serious headphone user. I have owned full range ESLs for many years and have always wanted to build a set of my own design. The headphone project was meant to be a dry run to start me moving up the learning curve.
...j