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j beede 4th January 2008 10:37 PM

First attempt
 
2 Attachment(s)
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 7th January 2008 04:31 PM

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

Ed

j beede 8th January 2008 02:11 AM

2 Attachment(s)
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 8th January 2008 02:19 AM

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 9th January 2008 08:23 PM

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 10th January 2008 04:56 PM

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 11th January 2008 04:10 AM

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 11th January 2008 10:45 AM

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 12th January 2008 06:13 AM

Quote:

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 22nd December 2008 05:29 PM

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


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