Biasless ESL?

[Ridin '24'z]

I'm not sure if this has been discussed before but I couldn't find anything on it. Tiawan electric seem to have come up with an ESL that doesn't require a bias supply. This video from CES2010 shows:

YouTube - Taiwan Electric's Electrostatic Speakers Require No Bias Pow

Anyone seen or heard this stuff? Looks like a very promising prospect for ESL headphones.

[beun]

Nothing new, its an electret, there used to be electret headphones from I think AKG back in the 80's.

[kavermei]

Another possibility which works with normal non-electrec films too is to 'steal' power from the music signal.

[Ridin '24'z]

I was having a read of that electret stuff, seems to be kinda low-fi technology.

kavermei, you say "steal" power from the music signal, how does that work exactly? I was trying to design portable ESL Headphones a while ago and I can't seem to get all the circuitry small enough to fit into the headphones themselves.

Would be amazing to have a passive headphone with full blown ESL quality.

This is a project that has been pushed to the side since researching in ESLs, I have however somehow managed to design full size ESLs discussed in another thread you may recognise :P. I may pull the ESL headphone project out again and see if I can take it anywhere in my free time ^_^.

[kavermei]

Originally Posted by Ridin '24'z

kavermei, you say "steal" power from the music signal, how does that work exactly? I was trying to design portable ESL Headphones a while ago and I can't seem to get all the circuitry small enough to fit into the headphones themselves.

Yea I vaguely remember some commercial units did it (can't remember names, sorry). Might be worthwhile to see if schematics can be found on the web. Anyways I made a quicky schematic to illustrate the basic idea, which is to rectify the music signal from the stators and use it to keep a capacitor charged. The resistors R1 and R2 are there to reduce the effect/load of the circuit on the amp&transformer.

This arrangement works because the required current for the bias supply is so very low. The drawback is that the speakers need to charge up if they have not been active for some time. The values of the resistors and capacitor must be chosen so that the HV bias can be maintained (depending on how much HV leakage your build has) but all the while not excessively loading the audio circuit.

Disclaimer: I never built such a HV supply myself, and this schematic is only to illustrate the basic idea!

If you ever build a similar HV arrangement, let me know if it works out!

[kavermei]

By the way it might be wise to incorporate a voltage multiplier into that circuit, rather than a simple rectifier.

[bolserst]

Originally Posted by Ridin '24'z

I "steal" power from the music signal, how does that work exactly? I was trying to design portable ESL Headphones a while ago and I can't seem to get all the circuitry small enough to fit into the headphones themselves.

JonasKarud described his signal driven bias supply here:
My speakers

Also, Calvin had referenced two different patents that include circuit details.
ESL Power supply fed from audio signal?

[Ridin '24'z]

Looks promising! I'm giving it a go in LTSpice now :P what kind of transformer would be needed? Something standard for ESLs?

[oublie]

stax did this with their srd7 pro sb mkII headphone energizer.

they took the voltage supply from the amp min 13w @ 8ohm from what i can recall and fed off, multiplied rectified and limited the max voltage (580v) using zeners from what i recall.

essentially it was a low voltage (amp voltage) step up transformer this ran side by side with a a pair of step up transformers.

[Ridin '24'z]

I've been trying to design something more portable that can run off a standard MP3/mobile phone level output. I've got a working direct drive amp designed (4 op amps and two high voltage transistors configured as class A). The thing eats like 4 Watts though, Li-po powered would be the way to go and the required charge controller would have to cram in somewhere. If it's possible to put together a transformer in the self supplying configuration and small enough to fit in the headphone casing, it'd be a perfect solution.

Would I be correct in looking for an iron core to get a good frequency response? I have some 44AWG wire that would make a very compact set of secondary windings =]. My knowledge on transformer design is still full of equations I don't really know how to use but somehow memorised for uni exams :S