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Old 18th April 2003, 06:15 PM   #1
Milo is offline Milo  Italy
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Default ESL amp: tubes vs solid state: where is the winner?

Hi all,

this message is dedicated to those who built an ESLoudspeaker and wanted to couple it to a suitable amp. Many pages has been written about this argument.
Some prefer tubes because you can couple the plate to the ESL without the step-up transformer. Transformers are not so cheap, if you want to buy the best on the market. Solid state amp has to be able to sustain a capacitive load with an impedance reaching even 1 Ohm. This means a lot of final transistors able to split the large amount of current.
On the other side, working with 4,000 0r 5,000 VDC is not so easy. Nobody wants to gamble. And tubes are not so cheap and could be microphonic.
This intro to the final question. I have to build an amplifier for an ESL. I want to build one, and this has to sound very well, has to be rugged, strong and reliable. I don't want to experiment hundreds, just one. Do you have some suggestions about this project?
Remember: I don't prefer transistors vs tubes or viceversa, I am only looking something very good for my ears.

Thanks all able to help me

Milo
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Old 18th April 2003, 07:01 PM   #2
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wouldn´t it be possible to build a solid state amp for direct drive ESL with high voltage Mosfets or some output devices in series?
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Old 18th April 2003, 08:29 PM   #3
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There was an ESL version of the John Linsey Hood amp (transistors); if it's any good as the original you'll love it!
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Old 18th April 2003, 08:38 PM   #4
qwad is offline qwad  Australia
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HI MILO, have a look at the classic JLH SE TRANSISTOR AMP AT
http://www.gmweb.btinternet.co.uk/index.htm#index there is a version featured in the index to mate with the quad esl, if it works with that it should be ok cheers, TJB
IT IS SIMPLE TO BUILD AND VERY VALVE LIKE SOUNDING sorry for shouting read through all the articles AND I AM SURE YOU WILL BE INTRIGUED, it may be an oldie but from the correspondence here on this forum and elsewhere it is a goodie do a search here on this forum under JLH SE and i am sure you will be surprised at the number of people who have built one who are highly satisfied
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Old 19th April 2003, 03:46 AM   #5
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this is just what I am looking for to.

With tubes you end up with powerfull HV types which must dissipate a lot of heat, since the biasing
of the output-stage defines the available current to the load.
And you need current to charge and discharge the capactive load formed by stator and foil, and this
at the speed of the signal.
A good bias value would be 50mA, with an anode voltage of 2500V you end up with 125W of heatdissipation
per tube, not including heaters. To drive symmetric you need 2 output stages per ESL.
So you end up with big, heat dissipating amps. The sound will excel, if designed correctly.

With solid state you need the same voltage and current, but must stack the ouput devices as
I don't know devices which can stand more then 1200V. This devides the dissipation per device, which
makes cooling easier. The total amp can be build smaller and heat will be less.
I have once heard such a unit and it sounded good, the owner wouldn't give the schematics.

So to make things easier and cheaper I will go for the last option.
Maybe there is someone with such a schematic as I also don't want to build lots of amps

Dick
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Old 19th April 2003, 05:46 AM   #6
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Hey guys....why does it need the full bias on the stators?
Run tubes at like, 1kV, and bias the ESL at -1kV (or 3k).

Tim
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Old 19th April 2003, 01:05 PM   #7
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Exactly. You're looking for 1kV RMS of audio between the stators, and 5kV of DC bias on the diaphragm. Whichever way you do it, direct drive is expensive. Mind you, my Stax in-ear electrostatics have a direct-drive amplifier running off a pair of AA batteries in a box the size of a cigarette packet. Amazing.
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Old 19th April 2003, 08:48 PM   #8
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sorry you guyz, but 1kV rms is not enough.
certainly for those large full range panels.

Even on my panels, which are mid & high, 1kVrms out of the step-up transformer is not loud.

Thats why you need a 5kV supply for the amp. Maybe the bias-current can drop to 20mA, but it depends on the capacity to be driven.

Dick.
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Old 19th April 2003, 09:59 PM   #9
Milo is offline Milo  Italy
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Default Re ESL amp

Thanks all for your suggestions. They are helpful.

Reply for Till. I have heard ST Microelectronics produces some HV MosFets. I don't know their specs, but, even if they reach more than 1 kV VDS, how about their fT? Are they so fast to reproduce perfectly transients in audio range?

Reply for Lisandro. Thanks for your info. I have a subscription to Electronics World (former Wireless World) and I didn't have a look at this project. Is it the same as showed in Class-A website? If yes, I am a little bit confused. Some people (expert) says you must have, for driving an ESL, an amplifier with at least 100 W RMS and more, since, as you know, ESL are not so efficient, normally 86 dB. This amp, at first lok, seems not to be so powerful. Where is the truth?

Reply for Qwad. Thanks for your info. This site is precious! By the way, could you bring my best greetings to Adrian an Leon Saturno, owners of Victoria Hotel, Norwood, Adelaide? They are very good friends of mine. I was in Adelaide 3 times. It is a beautiful city.

Reply for Djmiddelkoop. I realized you are looking for the same project as I am. Let's be in touch. If I find something very interesting, I want share it with you. The same you could do with me, if you want.

Milo
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Old 20th April 2003, 12:14 AM   #10
qwad is offline qwad  Australia
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MILO, you should go back to the class A site and read everything again, as the quad esl 57 is quite inefficient and also a very complex load to drive, the mods that were made to the circuit if adjusted to the description on it; is capable of delivering 20w without breathing hard so if it can drive the quads I don't know what the problem is unless you want head banging levels out of the ESL which quite frankly they are incapable of delivering regardless wether you are driving them with 20w or 200, what they will do then is self destruct right in front of your very eyes as a dodo cheers, and best regards TJB
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