First attempt

[j beede]

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.

[Ed Holland]

Nice! Keep us posted with your progress - this is interesting.

Ed

[j beede]

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

[j beede]

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

[ak_47_boy]

A coat of two of enamel paint on the ear side of the stator will more than likely be sufficient. I think you can actually get paint that is specifically made for insulating things.

[Few]

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 beede]

Yes, I have a set of aluminum stators that could serve for this purpose. The difficulty in making an electrical connection to aluminum is the main reason that I used steel for the stators. I wonder how Stax and Jecklin have avoided lawsuits over the years.
...j

[chinsettawong]

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]

Originally posted by chinsettawong
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]

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