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Old 7th September 2004, 08:59 AM   #1
koldby is offline koldby  Denmark
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Default Class D for electrostatic speakers

Hi all

Anyone considered using a Class D for driving electrostatic speakers directly??javascript:smilie('')
smash

As far as I can see, the concept would be very efficient and the capacity of the speaker elements could be part of the output capacitance..

Of course the high voltages involved could be a problem , but not unsolvable?

Best

Koldby
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Old 7th September 2004, 09:06 AM   #2
Konrad is offline Konrad  Norway
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Do you think tube kaskoding of switching devices as high voltages usually is involved may bee it ?


What a circuit ! ; Tube caskoded digital switched electrostatic driver

There is many sub topics involved here!
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Old 7th September 2004, 09:12 AM   #3
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This would indeed be tempting since the ESL by itself has quite a reasonable efficiency. This has already been proposed by John Watkinson BTW.
It is not easy to build high-voltage class-d amps for several reasons though.

Since many conventional amps are having problems with ESLs anyway, a good start would be to use any of the known class-d amps available and design its output filter accordingly. I think such an ESL specialist amp would sell well (or why not design an amp with an output-filter than can be easily exchanged by the user in order to match the desired load best ?).

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Charles
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Old 7th September 2004, 09:41 AM   #4
JohnW is offline JohnW  Hong Kong
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I can switch a Valve far faster then I can switch a MOSFET, but what about EMC? 3KV - 10nS edges - I know there's CR*P on TV these days but....
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Old 7th September 2004, 10:01 AM   #5
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I was once involved in studies for a switching amp that swings between 0 and 1000 Volts (for a piezoelecric actuator). It is amazing what amounts of power would have been wasted on the snubbers for instance (proportional to V^2 !!!).

But the idea of an amp that is optimised to drive ESLs (on the low-voltage side however) is still tempting.

Regards

Charles
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Old 7th September 2004, 01:47 PM   #6
koldby is offline koldby  Denmark
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JohnW

A couple of PL509 in a faraday cage ? Sounds good to me..3Kv is on the high side...as I remember Quads only needed about 750V. I Know the static charge is far higher, but you cannot get close to that without argching.
BTW isen't it more easy to control EMC when the currents involved is small even though the voltage shift is large??

Konrad

No need for a cascode. Just totempole arrangement as in normal Class D..


Best

Koldby
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Old 16th September 2004, 03:07 PM   #7
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I've the big ESL from Stax and I drive them with a Stax amplifier. Only a few amplifier can drive easely a so difficult load.

I've the project to build an amplifier and connect it directly to the stator. I have thought about a PP 845 but 1250v is not enought.

I've to find tube supporting 3000v or more with 80 - 120W power capability.

brice
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Old 16th September 2004, 03:59 PM   #8
JohnW is offline JohnW  Hong Kong
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The Accustat Servo amps use 6HB5's on about 3Kv rails, circuits are on the web.

Could design a class D 150V OPS and filtering in place of the Accustat transistor driver stage, and then drive the 6HB5's directly, but where to return the FB from the output. Due to the very high impendance of any FB circuit, even very small capacitances will cause signifcant HF rolloff.

John
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Old 16th September 2004, 06:14 PM   #9
JohnW is offline JohnW  Hong Kong
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Here's the orginal Accustat SC-X3 Circuit diagram.

It relatively easy to design a +/- 150V Class D OPS (Digital or Analogue input) to drive the 6HB5's,

Anybody suggest a method to add Feedback from the ESL outputs to the 6HB5?

John
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File Type: pdf accoustat sc-x3 pg1.pdf (68.4 KB, 224 views)
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Old 16th September 2004, 06:15 PM   #10
JohnW is offline JohnW  Hong Kong
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And the second page.
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File Type: pdf accoustat sc-x3 pg2.pdf (52.9 KB, 147 views)
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