[analogsurviver]

  Thank you for the useful information. I checked the schematics on the internet and I've only seen some high voltage capacitors, no batteries. I presume these are the 'biasing voltage keepers' those must be kept 'charged' with the audio signal.

It was only Stax that produced SB transformers - even for speakers ( I wouldn't like to see the bill for battery replacement - some 3 thousand button cells per chanell ).
This is if we are talking about true electrostatics, which require polarizing voltage to be supplied by the power supply.
 
If it is electret, which means permanently charged, then you do not need any power supply. Schematics for the two can be completely equal ( if electret is also push-pull design ), the only difference being power supply - or the lack of it.
 
There is no such thing as charging by the audio signal - or at least there should be none. 

 

[davidsh]

 

  Thank you for the useful information. I checked the schematics on the internet and I've only seen some high voltage capacitors, no batteries. I presume these are the 'biasing voltage keepers' those must be kept 'charged' with the audio signal.

It was only Stax that produced SB transformers - even for speakers ( I wouldn't like to see the bill for battery replacement - some 3 thousand button cells per chanell ).
This is if we are talking about true electrostatics, which require polarizing voltage to be supplied by the power supply.
 
If it is electret, which means permanently charged, then you do not need any power supply. Schematics for the two can be completely equal ( if electret is also push-pull design ), the only difference being power supply - or the lack of it.
 
There is no such thing as charging by the audio signal - or at least there should be none. 

But there is 

The Stax srd-6 for example

 

[Nemeske88]

 
 
This is a self-biasing transformer for earspeakers, the SRD6 SB.
I am no tech, but I see only HV ceramic caps, and there are no batteries

 

[analogsurviver]

  But there is 

The Stax srd-6 for example

Nope - please read again.
 
SRD-6 has AC power supply.
 
SRD-6SB has no AC supply - and batteries inside.
 
http://www.stax.co.jp/Pdf/OLD/SRD6SB.pdf
 
It is true that RC constants of ES drivers are long - but not long enough to be capable of somehow bleeding the required polarizing voltage off the audio signal and hope for a full charge after a prolonged "next to silence" in say classical music. It is either electret (permanently polarized) or AC or DC ( Self Biasing in Stax' parlance ) power supply for true electrostatics. 
 
This is the schematics for the SRD-7 - which should differ from SRD-6 in better distortion spec only.
 
SRD-7SB employs instead of mains AC voltage multiplier circuit lots of button cell batteries in series to reach the required voltage.
 

 

[analogsurviver]

 
 
 
This is a self-biasing transformer for earspeakers, the SRD6 SB.
I am no tech, but I see only HV ceramic caps, and there are no batteries

No AC cable on this SRD 6SB ?

 

[n3rdling]

The bias is generated from the audio signal thus no need for ac plug thus self bias thus SB.

 

[analogsurviver]

The bias is generated from the audio signal thus no need for ac plug thus self bias thus SB.

Sorry guys, did not know that.
 
For how long do(es) the SB version(s) hold their charge for the proper operation if there is no audio played for a while ?
 
I've found the schematics for the SRD-6SB : 
 

 

[Nemeske88]

In my opinion, those are that ceramic capacitors those hold that charge until they discharge by leaking or something. 

 

[mtoc]

wow, if there's any progress, please shared with us. friends and I will diy the KG eletrostatic phones!!!

 

[chinsettawong]

wow, if there's any progress, please shared with us. friends and I will diy the KG eletrostatic phones!!!

 
What would you like to learn?

 

[mtoc]

I'll learn silently first

 

[chinsettawong]

  I'll learn silently first

It's better to share what you're doing in public so that we all can learn together. 

 

[Ghost Pack]

Hi
 
I've been lurking in the shadows here for quite a long time and I'm completely amazed by everyone's ability. You guys inspired me to start designing my own headphones, and after a few weeks of designing and ordering parts, I think I'm ready to start construction.
 
I thought I'd share my current design on this thread and was hoping you guys could give me pointers and tell me if I messed anything up too bad.
 
Amplification: Stax SRD-X Normal
-Normal Bias
-Possibility of upgrading to pro w/ external bias?
 
Mylar:
-DuPont 3um
-DuPont 0.5um
-Saran wrap (possibly for dust covers?)
-Anti-Static gel
 
PCB:
-0.060" Copper Clad Laminate Sheet (1.5mm)
-0.031" Copper Clad Laminate Sheet (0.78mm)
 
Vibration Damping:
-1/16" Butyl Rubber Sheet
 
Driver Specs:
-Stator separation is ~0.8mm from stator to diaphragm on each side
-0.5mm stator thickness (on active surface)
-Active area measuring 74mm x 49mm
-4mm difference in radius between the spacers and the stator holes to allow for bass buildup
-37.25% open/closed surface area on stator (excluding supports and bass ring, probably more like 28% with)
 

 

 

 

 

 

 
The stator is slot milled from 1.5mm to 0.5mm before holes are drilled, so as to minimize edge interference while keeping hole diameter to a minimum. The holes in the center are larger to mimic the open section found in the sr-009 driver.
 
I'm not sure what ratio of size to separation to use for my holes, I think with this current design I might not have enough open surface area. I'm a little bit worried about structural integrity. I'm also not sure what thickness of mylar to use. With 0.8mm separation and only 230V bias I might not be able to use thicker mylar or higher tensions.
 
Thanks ahead of time for any advice you guys can give me!

 

[chinsettawong]

Hi,
 
Your design looks good.  But I would use thinner spacers. With the bias voltage of only 230V and 0.8 mm spacers, you will probably have to crank up your volume a lot in order to get enough loudness.  But it will surely work.
 
Please try it and let us know how you like it.  
 
Wachara C.

 

[Ghost Pack]

The thinnest I can get is 4.32mm. Do you think that will be enough? Also, is there a cheap way to measure driver sub-bass responce? I currently have this mic, which does well for simple measurements but is wildly inaccurate past 180 Hz.
 
As a side note, I created a "Version B" stator with a open/closed surface ratio of 43.2% (versus the original ratio of 37.3%). I'll mill both out tomorrow, but without a way to measure sub-bass I'll have to wait until I finish the frame to test the differences.