Build me a ss direct drive ESL amp, please

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Disco-Pete

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bentoronto said:
Juma, post 5, laid out the liability issues for a person to make a black-box for you that could kill you, your dog, or your kids*, whether or not there are cables across your living room floor and/or whether or not they did it turn-key as a single integrated package with the speakers and/or you signed something that provided the false illusion of a legal release.

B.
*I assume you would turn the amp off once it killed your dog or kids and so no need to say "dogs and/or kids...."** Likewise, I assume your estate would likewise protect your dog after your death.

** I am further assuming your kids are not holding your dog at the time of their joint electrocution nor that the dog was holding your kids; please correct me of those are gratuitous assumptions.
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I take it you read post #8. Excuse me but I'm not the dufus that designed this system that's been around since 1976. You can stick your hand in any amp and kill yourself. Many have died by surprise working on the old tube TVs of the past, far more dangerous. Cite one instance where someone was electrocuted by a DD servo Acoustat OTL? This is false alarm. You have not answered my question to you.
 
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gentlevoice

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@kazap:

I found this in another diyaudio thread:

On the high, well I was hoping an ESL without step-up transformer could do the trick mid and high ( Elektrostaten Project 06 ), unfortunately Peter Scheulderman is passed away and I cannot find anything about his amp. So that basically rules out a one piece ESL for mid/high.
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The link is:

http://www.diyaudio.com/forums/plan...speaker-using-neo-magnets-36.html#post4238499

But maybe contacting esl-club could bring about a schematic?

Cheers,

Jesper
 
Nelson Pass

Nelson Pass

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Broskie's second offering points out the crucial thing - you want to make
SS do audio at these voltages, you must cascode the devices.

Been there, and it's the only way.

There is an alternative approach, which is to take feedback around the transformer
secondary, which is what I did with the 10 KV Dayton Wrights 40 years ago...
 
N

nauta

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Joined 2017
Hi Guys

I believe the ESLs look much like a 1nF cap, which at 20kHz looks like about 8k-ohm. This might be an acceptable approximation for steady-ish signals, but a fast transient would be more like the charging surge for a power supply cap - essentially unlimited current for a brief instant.

I've seen some ESLs that are unipolar and others bipolar, meaning that there is either one driven plane or two (stators), kind of like a giant ESL head-phone. The bipolar drive is lower distortion and allows the drive signals to be half the amplitude which in turn relaxes some of the requirement. As others have requested, the actual drive voltage needed at the stator(s) would be good information. Otherwise, one is designing blind and possibly going to greater extremes than needed.

So, if you were to use those 4500V mosfets in a totem pole and assume that 2kVp is fine, the 8k-ohm approximation suggests a peak current of 250mA. This does not occur at the voltage peak, rather at zero-cross, so the output devices must be burly and have good heat sinking. Fortunately, the power profile of music falls off towards the 20kHz and the extreme loading on the driver is greatly reduced. It is a POWER amplifier despite driving a nearly pure capacitance.

The SE drivers made for ESL head-phones tend to be majorly compromised THD-wise, with the only benefit being a simple circuit where only the output device sees high voltage.Having true push-pull drive for each stator, as Elvee's circuit does, is a better way to achieve distortion from the amp that is lower than the ESL THD.

Much is said about the EQ of the ESL panels. I think the Quad ESL-63 is still the best-sounding of all ESLs offered and its schematic is not simple. The panel is split into sections with the signal delayed into the sections to create a point-source-like output. The intent was for maximum fidelity at the expense of high loudness - so these sound very good at Human Scale listening levels. The usual single-panel hobbyist units and similar offered by current manufacturers have a critically smaller sweet-spot for the listener, which to me a major flaw with ESLs. EQing cannot "correct" this but can improve the listening experience a small way.

This direct-drive amp absolutely must be built into the case of the speaker itself just for safety purposes already detailed by others.
 
MrMagic

MrMagic

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Joined 2017
bentoronto said:
Juma, post 5, laid out the liability issues for a person to make a black-box for you that could kill you, your dog, or your kids*, whether or not there are cables across your living room floor and/or whether or not they did it turn-key as a single integrated package with the speakers and/or you signed something that provided the false illusion of a legal release.

B.
*I assume you would turn the amp off once it killed your dog or kids and so no need to say "dogs and/or kids...."** Likewise, I assume your estate would likewise protect your dog after your death.

** I am further assuming your kids are not holding your dog at the time of their joint electrocution nor that the dog was holding your kids; please correct me of those are gratuitous assumptions.
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Part of the design is and should always be safety measures. All of us are surrounded by dangerous devices -from the microwave oven to a simple floor lamp (that a dog could chew the cable and die instantly), to deadly cars running on the streets (that can also kill a dog or human) and even dangerous helicopters and planes flying on the sky. What keeps as safe is obviously safety measures, and even if we abandon all technology we'll have to face other dangers.

Likewise, you can properly design a DD ESL so that despite the 10KV on the panel, it won't be dangerous at all, to neither kids or dogs.

For maximum safety:
1) Like others have said, completely enclose the amp and cables.
2) Drive the DD panel diferentially so that no DC power supply voltage is applied (the (AC) voltage should only be proportional to the music volume).
3) Put grounded shields on the front and back of the panel, so that (even) touching the shield should be absolutely safe.
4) Put a tough fabric cover (difficult to remove) that will provide an added safe distance from the (shielded) panel.
5) Mount a weight at the base to significantly lower the center of gravity (one or more cheap bodybuilding disks) that along with the extended base design and the addition of soft wheels, will make it impossible to flip over. I personally do that to all my DIY loudspeaker and speaker stands to make them "earthquake-proof".
6) Make the ESL impossible to turn on by anyone else except yourself. There are many easy ways to do that nowadays.

Then you can bet that it will be far more safer and worry-free than your hair dryer.
 
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bentoronto

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Joined 2008
MrMagic said:
Part of the design is and should always be safety measures.
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You seem to require some education in what legal liability entails. And how you protect your back.* Actually, anybody who builds such a device for you needs that education more.

B.
*Forget about it: you can't protect your back apriori. The only place you have wilder wannabee-professional fantasies than law, is DIYaudio with engineering.
 
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