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Old 18th October 2013, 10:21 AM   #21
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Quote:
Originally Posted by bolserst View Post
I'm guessing the Sanders ESL amp mentioned by JonFo is not a HV direct-drive amp.
Rather it is the current Sanders amplifier designed to drive the difficult load impedance that most ESLs with step-up transformers exhibit.
Sanders Sound Systems ESL Mark II Amplifier
Thanks. Sounds plausible although "Sanders" like "Williamson" ought to be reserved for their special amp contributions, not just to designate a brand.

At the risk of being an unwelcome guest at this party, I can't emphasize enough my belief that a direct-drive high-voltage amp (which of course needs no transformer, toroid or otherwise) is a markedly superior method of driving ESLs.... and really dangerous if you have kids around.

Ben
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Old 19th October 2013, 10:28 AM   #22
JonFo is offline JonFo  United States
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Quote:
Originally Posted by bolserst View Post
I'm guessing the Sanders ESL amp mentioned by JonFo is not a HV direct-drive amp.
Rather it is the current Sanders amplifier designed to drive the difficult load impedance that most ESLs with step-up transformers exhibit.
Sanders Sound Systems ESL Mark II Amplifier
Correct, I'm running one of those for the Monolith panels. I had been running the panels of a Sunfire Signature amp (400w @8 - 800w @4ohms), the Sanders is both measurably and audibly superior with much better control in the midrange to lower end (350hz or so) on my setup.

Quote:
Originally Posted by bentoronto View Post
Thanks. Sounds plausible although "Sanders" like "Williamson" ought to be reserved for their special amp contributions, not just to designate a brand.

At the risk of being an unwelcome guest at this party, I can't emphasize enough my belief that a direct-drive high-voltage amp (which of course needs no transformer, toroid or otherwise) is a markedly superior method of driving ESLs.... and really dangerous if you have kids around.

Ben
Ben, totally agree. I've read all I can about the HV amps, and have some ideas I plan to implement in a few years, but they involve hiring a EE grad student to help with the circuits. No kids, dedicated AV room, so no problem

For now, just looking to address the remaining challenge in obtaining the best ESL sound now that crossovers and amp are taken care of.
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Old 19th October 2013, 10:46 AM   #23
JonFo is offline JonFo  United States
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Quote:
Originally Posted by X83 View Post
I'm currently using an analog active crossover set around 150-180 Hz with the -24db Linkwitz/Riley filter with an Audyssey XT32 calibration system. As you know the ML Monolith-III speakers are rated for 80-250 watts per channel with 500-watts max. Your Sanders ESL amplifier could easily overpower a single 80-watt Piltron ESL transformer so the best option might be to use more than one or find something better with a higher VA or wattage rating. After all the stock ML EI-core ESL transformers are the electrical fulcrum point between your amplifier and the stator panels.
That analog active is surely a lot better than the original passive, man were those bad. Over the past 13 years, I've graduated up to a full Speaker processor (the DBX DriveRack 4800) which along with audyssey pro on my Denon AVP-A1HD preamp results in pretty good in-room sound.

As for crossover points, my tests showed the naked panel could not keep up (or the Sunfires ran out of gas) at 250Hz playing up to my target reference of 105dB SPL at less than 1% distortion. So my crossovers are at 315Hz with 24dB/oct LR.
To do that, I also updated my woofers to models that played cleaner in the mid-bass, see this thread on the MartinLogan Owners board.


Quote:
Originally Posted by X83 View Post
I've been doing a lot of research and found that the grain oriented silicon steel type OA-core toroidal step-up transformers seem to be the best solution. The steel strip construction ensures that the grain boundaries are optimally aligned, improving the transformer's efficiency by reducing the core's reluctance. Since O-Core toroids have no sharp edges, they have a higher kV dielectric rating and require less insulation which can be wound with less fill factor resulting in a lighter & smaller transformer than the conventional box section toroidal cores. The more popular Antek or MultiComp VTX 230/6V 50VA power toroids only have an 84% efficiency rating while the silicon steel OA-Cores with a greater VA rating are capable of 96% to 99% efficiency. My plan is to have some 300VA to 800VA OA-Core toroids custom built with a 1:25 or 1:30 ratio to be used in pairs for each stator section. I may purchase a few of the toroidal OA-cores just wound entirely with a single secondary section and wind the primaries myself. I might be able to wind the primaries using some Litz flat braided wire or flat Laminax which is frequently used for toroidal transformers with higher step up ratios wound concentrically to cover the entire surface of the core just for testing purposes.
Fascinating. Thanks for sharing all that research.

If interested, we might pool resources and get double the number and possibly get a price break.
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Old 19th October 2013, 11:06 AM   #24
JonFo is offline JonFo  United States
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Quote:
Originally Posted by X83 View Post
In my search for a better ESL toroidal with a higher wattage rating, I was able to contact Ir. Menno van der Veen in Netherlands who is the engineer of the Pliitron transformers which are manufactured by company called Amplimo. Ross Whitney from Plitron told me they could custom design an ESL toroidal transformer specifically for this application that would necessitate a non-recurring engineering charge of $1000 US which does not include the price of the transformers themselves. I was also able to get some more information about the existing Amplimo ESL toroidal transformers along with their price list. ...
Very interesting, the cost of a custom design is not outrageous, and if getting two or more of us (one or two more from the MLO forum might hop on this bandwagon), pricing for the units might not be too bad either.

I'll be buying 5 transformers, two for the Monoliths, one for my custom SL3-derived center and two more for the old Sequel IIs I use as rears.

I assume that if designed to handle the Monoliths, that custom model will easily handle the SL3/Sequel class panels. Any thoughts on that?

Is this an option you might consider?
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Old 19th October 2013, 01:08 PM   #25
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Quote:
Originally Posted by JonFo View Post
Ben, totally agree. I've read all I can about the HV amps, and have some ideas I plan to implement in a few years, but they involve hiring a EE grad student to help with the circuits. No kids, dedicated AV room, so no problem

For now, just looking to address the remaining challenge in obtaining the best ESL sound now that crossovers and amp are taken care of.
No intention to hijack (or to start a new thread) but just to note (1) my "Sanders"-like DD amp differed in that it had a large group of power resistors as the load with the ESL panels only an after-thought, loadwise, (2) pretty tricky R&D, and (3) tubes are honky-dory but HV transistors would be nice.
B.
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Old 21st October 2013, 11:07 AM   #26
JonFo is offline JonFo  United States
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^^^ Ben, yes, if doing a DD amp these days, it's all transistors and DSP, at least for me. While there are some HV transistors out there, getting a model that operates cleanly in the audio band will be the trick.
But you are correct, R&D is tricky here.
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Old 22nd October 2013, 04:59 AM   #27
X83 is offline X83  United States
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Since were on the topic of direct-drive high-voltage amplifiers the concept seems very intriguing. I've yet to find anyone other than Innoxx from Germany manufacturing these and it appears most of them have to be custom built to the panels load capacitance . I would presume the amplifier would have to be mounted within close proximity of the panels because running long length high voltage lines seems like a bad idea for many reasons.

http://www.innoxx.com/english/main.html

ESL HV Amp: http://www.audiocircuit.com/DIY/Electrostatic-Speakers/Project:ESL-H.V.-Amp-by-Neil-S.-Mckean

I'd be curious to hear from anyone that has shorted out a Plitron ESL transformer and would be curious to know if they can be disassembled for inspection. From what I've been reading they appear to be using five primary bifilar wound conductors with a single secondary HV winding that's center tapped?
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Old 22nd October 2013, 09:45 AM   #28
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If the amp load is resistive, the capacitance of the ESL might not be important within the audible range. But the capacitance might be important to address in order to keep the amp from of supersonic oscillations.
Not aware of a long-leads problem but I recommend not using varnish insulated wires.
B.
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Old 28th December 2013, 02:53 PM   #29
rolls is offline rolls  Switzerland
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Quote:
Originally Posted by X83 View Post
In my search for a better ESL toroidal with a higher wattage rating, I was able to contact Ir. Menno van der Veen in Netherlands who is the engineer of the Pliitron transformers which are manufactured by company called Amplimo. Ross Whitney from Plitron told me they could custom design an ESL toroidal transformer specifically for this application that would necessitate a non-recurring engineering charge of $1000 US which does not include the price of the transformers themselves. I was also able to get some more information about the existing Amplimo ESL toroidal transformers along with their price list.

ST105PP cost EUR 217.80 (incl.21% VAT)
ST106PP cost EUR 272.25 (incl.21% VAT)
Hello
we are 2 friends owning Monoliths III. Mine has been off service for several years, but now she is back and should play alternatively with my horn system. I have to fix the active crossovers, because one is now humming too loudly, and I have to think about how to fix it, I do not assume that ML has an improved board for it.
We are interested in these Plitron transformers. One thing I did not understand. Why shouldn't we use the stock ones? I you can tell me good reasons, we would be very happy to share the 1000$ bill.
Thank you!

André
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Old 2nd January 2014, 01:08 PM   #30
Tenson is offline Tenson  United Kingdom
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I've got 3 toroids I'd like to test for ESL applications with a distortion sweep in ARTA. I will drive the panels directly (not built yet) so there will be no passive crossover parts.

What is the best way to emulate the load of an ESL panel on the TX? Should I just connect a capacitor, say 200pF across the output of the TXs or do I need some resistance in there too, parallel, series? Please advise
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