how to design a power amplifier for electrostatic speaker

[snowcatmaiden]

hello

i have no idea about electrostatic loudspeaker ESL
and just searched and knowing it could be a capacitive load which require different design compare to conventional amplifier. but cannot find how to.

question is,

what is the problem when conventional amp uses with ESL?
impedance or phase or any reasons?

and what is the different of amplifier for ESL?
can i convert a conventional amp to ESL amp, or probably can drive both without sound degrading?

Thank you very much.

 

[AlexQS]

You might find this discussion interesting: http://www.diyaudio.com/forums/chip-amps/285145-lm3876-powered-li-ion.html#post4582469

It's a little over my head, but I think they're talking about Thiele Networks, which I believe may be at least part of the answer to your question.

 

[jan.didden]

hello

i have no idea about electrostatic loudspeaker ESL
and just searched and knowing it could be a capacitive load which require different design compare to conventional amplifier. but cannot find how to.

question is,

what is the problem when conventional amp uses with ESL?
impedance or phase or any reasons?

and what is the different of amplifier for ESL?
can i convert a conventional amp to ESL amp, or probably can drive both without sound degrading?

Thank you very much.

ESLs are normally driven through step-up (often 1:100 or more) xformers. I'm surprised you can't find anything - there's tons about it here and through Google.

Your amp must be stable for capacitive and/or low impedance loads, but other than that there's no special need.

Jan

 

[hahfran]

a very old design is quite interesting : direct coupling of the electrostatic speaker to a high voltage tube push pull. All you need is these high voltage tubes and a power supply 5,000 Volts at 50 mA . I tried that once with a Quad Esl and FM transmitter triodes made in Russia. Was absolutely excellent sonic quality until the triodes begun to glow bluish... that was it.

 

[hahfran]

nothing beats class a push pull triodes but these could be replaced by hi voltage SiC MosFets

 

[Ketje]

Long time ago Elektor has published an amp for high voltage output.
Perhaps you can find the description and prints still there.
Mona

 

[snowcatmaiden]

ESLs are normally driven through step-up (often 1:100 or more) xformers. I'm surprised you can't find anything - there's tons about it here and through Google.

Your amp must be stable for capacitive and/or low impedance loads, but other than that there's no special need.

Jan

Thank you for reply.

as i did some research, ESL requires voltage rather than current.
So it may not good to design for both conventional speaker and ESL.
they seems require different design.

 

[hahfran]

The membrane moves between the two electrodes which have the signal , since capacity is reversely proportional distance between membrane and electrode, the capacity changes with the signal amplitude , as capacity is Asec/Volt , current is required for charging and decharging. The force that drives the motion is in first approximation a Coulomb force which is proportional to charge. If charge were constant then the membrane could not perform sinusoidal motion.
If the speaker electrodes are directly coupled to a push pull amp, then this is basically a voltage amplifier.

 

[clog]

I use the PA03 chipamp on my Quad 2805 esl's with excellent results. No sweat at all. See also http://www.diyaudio.com/forums/chip-amps/280949-newbee-build-pa03-amp-lm4780-7.html#post4540606

 

[jan.didden]

Thank you for reply.

as i did some research, ESL requires voltage rather than current.
So it may not good to design for both conventional speaker and ESL.
they seems require different design.

They are quite different designs, but that doesn't mean they cannot be driven from the same amp - with the step-up xformer. ESLs require high voltage across a cap, so they STILL need current - to charge the cap.

In fact, the tend to draw more current from your amp than a 'normal' driver; the cap is transformed back to the amp output as a quite large cap that requires quite large currents. How would a 1nF cap at a secondary of a 1:100 look at the primary??

Jan

 

[danny_66]

Here's a new design with a tube amplifier and the output transformer directly connected to the panels.

 

[hahfran]

no output transformer required. You need just one choke for each tube with a high enough
imaginary resistance at low frequency to feed the plate current. Mechanically skilled can easily make an ESL . Just precision.

 

[hahfran]

They are quite different designs, but that doesn't mean they cannot be driven from the same amp - with the step-up xformer. ESLs require high voltage across a cap, so they STILL need current - to charge the cap.

In fact, the tend to draw more current from your amp than a 'normal' driver; the cap is transformed back to the amp output as a quite large cap that requires quite large currents. How would a 1nF cap at a secondary of a 1:100 look at the primary??

Jan

Electrostatic and electrodynamic speakers behave differently the latter becomes inductive at frequencies above resonant, the first capacitive. That is the reason that ESL perform poorly in bass range which must be compensated by large membrane area. But once they have some 2 m² they will have a bass performance which is the best of all way outperforming speakers that rely on resonance effects such as vented box.