My DIY electrostatic headphones - Page 2

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Amazing

Quote:

Originally Posted by chinsettawong 

Hi guys,

 

I like to build another set of headphones, and if possible I would like to have some inputs from you what to do in order to improve my previous design.  Since there are so many Stax users here, I would appreciate if some of you who have ever taken dimension measurements of the spacer and stator of Stax headphone can share with me the info.  The dimensions will be used as the reference for my future build.  I would really appreciate it.

 

Wachara C.

 

Stax used to post this info in their instruction manuals but the older normal bias system runs on a 200-230V bias (150V for the very first SR-1 units made in 1960) and it has a 0.3mm diaphragm-stator gap.  The Pro bias system has a 580V bias voltage and a 0.5mm D-S gap.  They did experiment with 1100V bias (0.7mm D-S gap) but never made a production model. 

The thinnest mylar they've ever used was 1um but they stopped using is as it was quite frankly too thin.  Went back to 1.5um and then settled on 1.35um for the current range. 

Some of the Stax drivers are just works of art:

That's the super rare SR-Omega driver, 90mm across. 

As for the 6S4A, it's one of the best tubes you can find for driving electrostatic headphones.  It's a single triode that can handle just enough power for our needs (sits easily at 4W) and can withstand plenty of voltage too.  Cheap as well since nobody has any use for it besides us... 

If you want to step up the amp game, I'd recommend building the Stax SRX design which you can find easily by googling it.  It's the same basic design used in the Single Power ES-1 which you can find a link to in my sig and it sounds very nice with some ECC83's and 6S4A's as output tubes.  Even better with EL34's. 

Quote:

Originally Posted by chinsettawong 

I'll look for 6S4A ...

 

I had to go and have a look, these are also the tubes used in the hybrid design by Runeight , you will have the hybrid board from the group buy so it seems a logical choice..dB

WOW.

Quote:

Originally Posted by chinsettawong 

Hi Spritzer,

 

Thank you so much for sharing with me the information.  90mm sounds like a nice number to try.  For the SR-Omega driver, I guess that its spacer is around 0.9 - 1 mm in thickness, and the bias voltage is probably around 600V.  Are the 2 circles in the background the stators?  I'll make a new design and post to show you later.

 

I'll look for 6S4A and try as you suggested.

 

Thanks again.

 

Wachara C.

 

I haven't measured them in a while but the metal rings were roughly 1mm brass and the stators are recessed to make up for the difference down to 0.5mm.  That's how Stax usually does it, the Lambda driver has metal plates for stators which is held in place by a plastic piece while the diaphragm is mounted to large brass rings.  The bias voltage the Omega drivers is 580V. 

Those circles in the background are the stators, gold plated copper mesh secured to a resin frame.  Very ambitious driver design but fragile and the chassis isn't robust enough to deal with the mechanical output at high volume.  Stax fixed that with the Omega 2 but also changed to PCB based stators. 
 

Just want to say great job! I've been wanting to make a pair of electrostats but haven't had the money or know how to do it yet. What you have done is amazing and I can't wait to get started making a pair.  

On a side note, I remember seeing you on the diy loudspeaker forum. I am very impressed with what you've done and I can't wait to make a pair.

Subscribed.

Quote:

Originally Posted by chinsettawong 

Hi Spritzer,

 

That's what I think when I see the picture.  The stators made up of such fine wires are probably too soft.  They will require a lot of support, and will probably ring with high bass or high volume level.

 

The spacer sitting on top of the recessed stator of 90 mm in diameter would probably have more than 0.5 mm gap to the diaphragm.  If that is so, the tension on the diaphragm would have to be very high in order to prevent the diaphragm collapses to one side, and the bass might suffer.  Plus if the stator to diaphragm space is indeed only 0.5 mm, then I think that the bias voltage of 580V is a little on the high side.  

 

Anyway, thanks very much for your information.  I'll try to design something and come back to show you soon.

 

Wachara C.

The diaphragm is tight as a drum, it has to be so that it will last 50+ years or when ever the SR-1's will give up the ghost.  Mine are in perfect working order so probably a while until that happens...

580V for 0.5mm is actually quite conservative.  The air around us has an average insulation resistance of 3000V/mm and given the Stax sets should never see more then 1200V P-P on the stators this gap is way more then enough.  Add to this the fact that the electrostatic force decreases with the square of the distance and there is no chance in hell of arcing a Pro bias driver.