Toroidal Transformers for ESL Panels

[bentoronto]

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

 

[JonFo]

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.

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.

 

[JonFo]

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.

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.

 

[JonFo]

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?

 

[bentoronto]

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.

 

[JonFo]

^^^ 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.

 

[X83]

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?

 

[bentoronto]

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.

 

[rolls]

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

 

[Tenson]

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

 

[geraldfryjr]

Yes. you can just add whatever value of capacitance in place of your projected panels capacitance.
Just make sure that it has a high enough voltage rating.

I have burned up a few myself !!

Typically all this will do is lower the reflected impedance to the amplifier as the frequency gets higher and won't have much bearing on the THD measurement except for the loading on the amplifier.

I have made many test like these and I would consider for you to build a proper interface for actually measuring from the output of the step-up transformer, if this is what you intend to do.
I explain in full detail of such an interface in the links I posted in post 8 of this thread.

Using the Interface I was able to verify the actual current and voltages flowing through the transformer.
The voltage divider I made is good for up to 10KV peak out put voltage at about 5 watts of dissipation.

You must also use buffer opamp's to insure good linearity as the input impedance of most sound cards do change as the frequency goes up and this changes the loading on the bottom of the Voltage divider with a non linear function and your measurement will not be accurate.
I found this out the hard way!!

I used this jig going directly into my Brand New (at the time) ASROCK 990FX Extreme 4 motherboard and had no issues what so ever except for the errors I was getting due to the crappy drivers of the on board sound system.

I was quite scared at First as you can imagine wondering if I was going to blow up my brand new machine!

Especially when one of the transformers failed!!!

But, It did not hurt my system and I continued on with testing after I repaired the failed transformer and I tested some others that I have as well.

I also used this same Jig with other software such as REW and SimpleS for impedance measurements from the Primary side as well as shown in the plans using just a 1 or 2 ohm series resistor.

Good Luck !!!!

jer

 

[Tenson]

Thanks. I had a look at those posts now but it mainly shows your test jig, not the load you gave the TX?

Simplified equivalent circuits for ESLs in the Borwick book tend to show some inductance and resistance as well as capacitance for the panels. It said this is to emulate the damping on the panel (presumably from stators and dust covers blocking air-flow of the diaphragm). Perhaps this is not important to testing the TXs though.

 

[Bazukaz]

Thanks. I had a look at those posts now but it mainly shows your test jig, not the load you gave the TX?

Simplified equivalent circuits for ESLs in the Borwick book tend to show some inductance and resistance as well as capacitance for the panels. It said this is to emulate the damping on the panel (presumably from stators and dust covers blocking air-flow of the diaphragm). Perhaps this is not important to testing the TXs though.

Hi,

You are correct, the load of the panel is not exactly capacitive in a real world device. The resistive element is composed of : a) Series electrical resistance, and b) Resistance due to energy dissipated mechanically. This includes both damping and sound energy that is radiated away.
Electrical resistance can be significant in case of segmented esl with resistor ladder and/or when filtering resistors are used in high voltage section. This is not difficult to estimate. Now the mechanically radiated part looks not so easy, as it depends on specific construction of ESL. So for some speakers capacitor is an acceptable approximation and others not so much.

There is some interesting about this(although not typically expressed in electrical circuit diagrams) :
http://www.audiocircuit.com/A-PDF/A...-electrostatic-loudspeakers-A-EN1-941-QUA.pdf


Regards,
Lukas.

 

[geraldfryjr]

The load that I used in those test were from only using the Transformer self-capacitance with no added panels capacitances added.

My panels are small and only have 35pf to 50pf of capacitance so it is nill compared to what the transformer has.

I had done some with an added capacitance's but as I said all this does is lower the impedence at 20Khz frequency as a factor of the transformers capacitance plus the added capacitance as per Reactance and ohms law.

After I had burn't that transformer, I had learned what it was that I was trying to find out and I needed to get the thing in an enclosure so I took a break from it.

As well as use some better opamp's that have a lower Vos although the ones I used worked just fine for their purpose.

So I took a break from it until I get everything properly made and then I will continue with describing the testing procedure for all to understand.

Here is a very good presentation of what happens to the impedance when you start adding more capacitance to the HV side,

http://www.diyaudio.com/forums/planars-exotics/225959-toroids-esls-2.html#post3484831

And here is what happened when I basically doubled the transformers capacitance by connecting the two 120v windings (HV) in series.
The impedance dropped by factor of at least Two as expected (in Half).

http://www.diyaudio.com/forums/planars-exotics/233008-esl-hybrid.html#post3439694

This is the main reason why I have found why 4 cores work better then using two and tying the to 120v winding's in Series on each core.
Yes, This doubles the cost, But your amplifier will love you for it!!

I have a few pictures of this same measurement of the left, center, and right, sections blown up so you could see it better somewhere in another thread.
Here,

http://www.diyaudio.com/forums/planars-exotics/161485-step-up-transformer-design-6.html#post3404300

This test is with the two 120v winding's not connected and has the same results as having them connected in parallel.


The Peak in the frequency response at the high end that you see in the charts that I and others have shown is a function of the transformers resonance caused by the Leakage inductance and the total amount of added capacitance plus the transformers self capacitance.

Generally this peak is dampened by introducing some resistance either on the Primary side or the Secondary side.

It is more feasible to add the resistance in to Primary as HV highpower resistors are quite costly and large.
Also it helps by adding more DC resistance to on the primary keep the amplifier DC stable.

The Peak that you see in the Impedance charts shows the function of Inductive Reactance at the low frequency's to the left of the Peak, and, Capacitive Reactance to the right of the peak for the higher frequency's.

It took me awhile to understand that one myself.

jer