*Looks to the left*  Yup the silver BHSE is stunning.   

That is easily the nicest photo I've seen of it.

 

Lemme know when and where to send it when the time comes.

 

Send it to me now - John McLean / Australia.

 

pretty

Damn, silver is sexy.

Making me rethink gray.

would it sell better if i called it Mink?

Silver Mink!

 

 

would it sell better if i called it Mink?

Battleship Grey for the shellshocked......

You should buy two.  One in the Mink.  One in brown. 

Edited January 8, 201313 yr by jimmyb233

Sorry, Justin only makes one a year.

Is the bias voltage of the BHSE user changeable?  The reason I ask is that I would like to drive ESP-950's.  My understanding is that the 950's do better at 600 - 620v.  I would also like to drive various other Stax cans which would require lowering bias voltage.  Or do I just not even mess with it because factors other that bias voltage in the BHSE are such that only marginal gains to the 950's come from bias voltage adjustment?

Edited January 16, 201313 yr by jimmyb233

I wouldn't touch the bias.  Very little gains from about 2-3% increase in the electrostatic force. 

Thanks Brigir.  This is now officially an offer I cannot refuse.

I wouldn't touch the bias.  Very little gains from about 2-3% increase in the electrostatic force. 

 

 

That little increase in electrostatic force is an interesting fact.

 

Is there any published graph "bias voltage" (i.e. 0V to 1000V) vs. electrostatic force (with i.e. constant 100V DC at one stator)?

 

Is it possible to simultaneously drive the stators and the diaphragm with audio signal?

 

Well, if it were possible, Stax would have already adopted such scheme from the very beginning...

 

I thought using a third amplifier board, but running the signal at higher voltages than the balanced legs driving the stator.

 

That implies a six pin headphone plug and a balanced + single ended all-in-one amplifier.

 

Besides increasing costs, what are the side effects of such scheme?

There are inverted electrostatic drivers, where the stators are biased and the diaphragm is driven.  I have never seen them implemented for headphones though.  Apparently there are significant benefits in sensitivity.

It's easy enough to calculate the electrostatic force if you know the D/S gap and the bias voltage. Basically it falls with the square of the distance which is why we used 230VDC for a 0.3mm D/S gap and 580VDC for 0.5mm. Go up to 0.7mm and we have at least 1100VDC.

If you were to drive both the stators and diaphragm with signal then you would end up with a bunch of distortion (at least by ESL standards). The best way to get the super low distortion of Stax drivers is to run the diaphragm in constant charge mode. That means high resistance, very high resistance. It is possible to make pretty much anything work though.

For those who don't know this, the seminal article on electrostatic driver design, including why constant charge modes results in low distortion, was written by P. J. Walker of Acoustical Manufacturing (QUAD) fame. It was published in two parts in Wireless World in May and June 1955 under the title "Wide Range Electrostatic Loudspeakers."

 

Several versions of this may be found online; one is:

 

http://www.onethingaudio.net/FOR/QUA/GEN/PDF/9512-QUA-GEN-HIS-WW-PW1-WL.pdf

Thank you cetoole, spritzer and beecee.

I did not know this article.

Now I see the reason for those high ohm resistors in the bias supply ("high resistance, very high resistance").

This led me to my last question. 

Is there a way to supply a low frequency signal (perhaps DC to 400Hz or DC to 200Hz) with a high resistance amplifier leg? So then you would have voltage swings and more and less "constant charge".

Then you would leave the high frequency signal content to the balanced amplifier driving the stators.

Is it possible?

For instance, is it possible to join the same SRM-323 circuit (with a better current source) and a single ended tube amplifier with high resistance (enough to have voltage swing and “constant charge”)?

Edited January 18, 201313 yr by jgazal

I guess it is possible but I just don't get why you'd want that. Varying the bias voltage isn't a good thing in my book especially with the charging issues that come with high resistance.

Now I see the reason for those high ohm resistors in the bias supply ("high resistance, very high resistance").

 

I believe you may have understood how the constant charge concept is realized.

 

It is the diaphragm itself that must be given a uniform, very high resistance coating so that the transducer can operate in constant charge mode.

 

There were also some fine articles in the old Audio Amateur magazine in the 1970's by David Hermeyer and Roger Sanders on DIY electrostatic loudspeakers and direct-drive amplifiers. They included useful tips such as how to create the necessary high resistance diaphragm coating, and the needed for common-mode feedback in the direct-drive amplifier.

 

I don't know how to get the Hermeyer articles except by buying a used copy of the Audio Amateur issue, or by buying the "The Audio Amateur on CD-ROM: 1970-79" CD-ROM.

 

Roger Sanders has made his old articles available here:

 

http://www.sanderssoundsystems.com/audio-related-articles

Thank you again guys. 

 

The more I read, the more I realize how little I know. 

 

I like the graphite-coated diaphragm. Interesting that Sanders admits that "constant charge" is somewhat controversial given that aluminum coated diaphragms also work well... 

 

The idea was to improve voltage swing. So it seems this scheme may introduce more distortion than I thought. So Megatron is the only way to go... 

 

Edited January 18, 201313 yr by jgazal

Wouldn't graphite powder be a poor option for high humidity environments?  What does Stax use for diaphragm coating?

Graphite powder isn't so easy to apply to the Mylar.  To get a nice and even coating is time consuming and can be very difficult.  The problem is that graphite powder just does't stick to Mylar very well.

 

I opened up a pair of Stax SR207 a few weeks ago, and it seemed to me that the coating they used was very similar to what I've been applying to my DIY sets.  I use electrostatic cleaner gel. 

 

Wachara C.

More voltage swing is a good idea generally but there are two things to consider, the sensitivity of the drivers and the absolute max voltage the drivers can handle. Now these get plenty loud with just 100Vrms so the idea of more voltage swing is more about clean power than anything else. The second limit is the absolute max voltage the drivers can take which is roughly 1200Vp-p. This is even lower for the Senn HE's but again, this is very, very loud.

I don't think Stax ever used graphite on the diaphragms. No way it would have lasted 50 years on my SR-1's...