Portable direct drive amplifier for ESL headphones

[shyfx]

Hi, this may sound crazy, but I am wondering if anyone knows of portable direct drive ESL headphone amplifiers? I figure that you want high voltage and not large currents so power supply shouldn't be a problem.
http://www.emcohighvoltage.com/Qseries.PDF
There are ultra miniture DC converters to use for the bias. They use ****** all power too. Just need really a whole amplifier section which can swing high voltages, rely on a portable power supply and remain a portable size (perhaps the size of a pack of a cigarettes would be good)

Can anyone suggest if this is even possible and if so, perhaps know of any projects?
This would be the best, to have awesome quality music on the road!

Mikey

[fr0st]

I was considering maybe a TI digital amplifier and a high voltage output stage for a ESL amp.
The problem is finding a driver that can do 3Kv. Putting the Fets in series would create the voltage handling capability.

Also, this might help your cause
http://headwize2.powerpill.org/proje...=cmoy3_prj.htm

-Matt

[unitgain]

Originally posted by fr0st
The problem is finding a driver that can do 3Kv. Putting the Fets in series would create the voltage handling capability.

Kilovolt FETs in full-bridge configuration?

[shyfx]

Originally posted by fr0st
I was considering maybe a TI digital amplifier and a high voltage output stage for a ESL amp.
The problem is finding a driver that can do 3Kv. Putting the Fets in series would create the voltage handling capability.

Also, this might help your cause
http://headwize2.powerpill.org/proje...=cmoy3_prj.htm

-Matt

By digital do you mean class D or do you actually mean an amplifier which works directly from a digital source? If it is the latter, it'd be a little hard to find a portable device which can output raw digital signal unless someone knows of any?

Also how much voltage would you actually need for a headphone amplifier? 3kv sounds pretty high.

[shyfx]

Hi, I am back to dig up an old topic!

Regarding voltage supplies... do you need to swing such high voltages? Isn't the bias supply on the diaphragm the voltage that's extremely high and the voltage across the stators, although still higher than normal, significantly lower than the bias?

I understand the higher the voltage, the higher the electrostatic force between the diaphragm and the stators, but you can compensate up to a point with the bias voltage if your signal voltage is too low.
That is right yeah?

So how many volts would you need for bias on headphones and how much voltage would you need to swing to get decent volume? If my physics is right, the diaphragm will have a uniform electrostatic field which will be attracted to the negatively charged stator plate. The force of this attraction is related to the voltages, so you can probably write up an equation so that you can get the input voltage needed by inputting the bias voltage which maintains the ideal force between the stator and diaphragm.

If that's right you should be able to find a reasonable voltage at which you can find solid state devices for and perhaps build an amplifier?

I also understand there must be some reasons why you cant have the voltage too high... I am not too sure on many... I think arcing is one because the potential difference is so high and the distance isn't great enough that there is a break down in the insulator (the air) and currents flows nuetreulising the field and usually burning your diapgrahm. Any other reasons?

[jcx]

check out Stax for some electrostatic headphone numbers in amongst the product descripitions and data sheets

http://www.yamasinc.com/SR-001MK2.htm

also search for Kevin Gilmore's posts on HeadWize

http://gilmore.chem.northwestern.edu/

[martin clark]

Find yourself a Stax SRM-212. It's the energiser used by the current Stax ' Basic' package - though it ain't basic, it sounds great!

This provide the ESL amp and bias, and is powered by a 12V offboard supply. The whole SRM-212 module is...*leans over and checks*... exactly the same size as 3 CD jewel cases stacked, draws 300mA at 12V, so it and a small Yuasa 12v Lead-acid battery and you're sorted. The amplifier circuit is *exactly* the same in the bigger Stax amps - solid-state ones, anyway - but includes onboard DC/DC converter to provide +/- 200v amp rails and the bias supply.

It's easy to mod, or add a full-blown offboard supply to, as well ;-)

M.