System that sounds so real it is easy to mistaken it is not live

Mijo, You wrote, with reference to our SL speakers: "I went back to Sowter and they will make custom transformers. I drove the Acoustats with 100:1 transformers from 125 Hz up and it worked well. Right now I am crossing out of the stats at 100 Hz. I also am thinking about getting RAAL ribbon tweeters too cover 12 kHz up. I wonder if the bass transformer would handle that range or should I have 100 or 150:1 transformers made. The Plitron is too small."

My questions are with reference to your last two sentences.  What range are you talking about that you wonder whether the bass transformer could handle it?  If you are thinking about, say, 100Hz to 12kHz, I would say no.  One reason for my opinion is that when I measured the OEM bass transformer, it rolls itself off at or around 2kHz, probably due to self-inductance.  Another reason is that you need to keep in mind the effect of the ESL step-up on impedance seen by the amplifier is the converse of using a SUT with a phono cartridge.  The impedance seen by the driving amplifier is the intrinsic Z of the screen with no transformer divided by the square of the turns ratio.  So as you go up in frequency, a 1:250 turns ratio is going to result in a very low impedance for the amplifier, except as the self-inductance of the transformer seemed to dominate when I measured Z with the bass transformer alone driving the speaker.  Anyway, I would not be hopeful that this is a good idea.

And what makes you say the Plitron audio transformer is too "small"?  Have you ever seen the audio step-up transformers used by Martin-Logan and some other companies?  They ARE tiny, but SL use substantial transformers, and the Plitron 1:75 full range step up appears to be about the size, at least, of the OEM SL toroidal transformer they use for treble. Or is it the turns ratio (1:75) that you think is too small? To that I would only say that 1:90 of my Australian sourced transformer is excellent.  1:75 in terms of voltage is not that different, and because of the effect of the turns ratio on impedance (see above), Z at higher frequencies will be a bit higher than what I observe with a 1:90 ratio.  So it might be a trade-off with no untoward effects on perceived efficiency.  Anyone, like Intact Audio, who actually knows transformers is welcome to correct me on these generalizations.

@rauliruegas , at $85K a pair I would hope so,  but from a cost/performance ratio I will take the JC1+ any day. Is Meitner any better than John Curl? I do not know the answer to that question. At this point due to the reputation of the Atma-Sphere MA 2s driving my speakers. I am spending 1/2 that amount on them. We shall see how that works out. The JC 1s will be shifted to subwoofer duty. 

@lewm , The Plitrons will not handle the power I plan on dishing out. I can have a pair of 100:1 Sowters made that will and I should think would do a dandy job of driving the SLs from 100 Hz to 12 kHz.

What do you mean by "power"?  I get that you want to play at high SPLs, but if you are going to use bass and high treble supplementation and probably roll off the response of the SL speakers with very steep slopes, given your penchant for digital crossovers, then why do you anticipate needing the transformer to take lots of power?  Have you evaluated the specifications of the Plitron toroid, so as to form a basis for your belief they cannot be driven hard, or what?  Anyway, I have no compulsion to dissuade you from your aim to use Sowter transformers. (1:100 would be technically more correct than 100:1, BTW.)  Sowter certainly is well regarded, although I did not associate them with making audio step-up transformers to drive ESLs.  Sure, go for it.  My recommendation of Plitron was solely based on the idea of your driving the speaker with two transformers (one for bass and the other full range) and dumping the RC network in the process. However since you are venturing into the unknown, you might want to find a way to experiment with using a single 1:100 step-up before investing in a custom build of two of them.  (Acoustats are not identical to SLs in terms of stator to diaphragm spacing and bias voltage, although using separate bass and treble transformers was originally the idea of Acoustat, borrowed by SL in the late 90s or so.)

@lewm  Plitron is no more. It was bought out by Noratel Canada. They do have a custom transformer department and will design transformers for audio use in larger lots. I doubt they would just build two, but who knows. If I remember correctly the 1:75 Plitron was good for 100 watts. I have much more power than that. Remember, I have already burned up a brilliance control. My old Sowters were good for 300 watts. If I do this the plan will be to use one transformer, straight up to power the SLs from 100 Hz to 12 kHz. This would get rid of the RC networks. Correct, all the crossovers will be digital handled by the soon the be released DEQX Pre8 which has the capability to do four 2 way crossovers. I will use a small class A amp to drive the tweeters which I will hang at  ear level on the medial sides of the SLs. ESLs do not do the highest octave well, the diaphragm falls away from pistonic motion and starts vibrating haphazardly. Ribbons are perfect for this but again because of their very low impedance a transformer is required. The Magneplanar 20.7 tweeter would be perfect but they will not sell a pair separately. I would have to have the serial number of a pair to order replacements. 

If memory serves me, you felt in the end that you had burned up your brilliance control because your equalizer was boosting the signal by 10 or 12 db at a frequency that was traveling through the brilliance control. So that was in medical parlance iatrogenic. A problem you can easily get around by ceasing to cause it. anyway, I am sorry to learn of the demise of Plitron. They made good stuff. Sowter is also a very good company, and I am sure they can do a good job as well. To my knowledge they make only EI type transformers. Is that still correct? My other point was that you are taking a shot in the dark as to whether a single transformer with a 1 to 100 step up ratio can adequately drive the panel at frequencies as low as 100 Hz with vigor to satisfying levels. I wonder about this because Although I did not measure the frequencies involved, my memory tells me that when I tried to drive the panel full range with my 1 to 90 transformer the response was unsatisfying at frequencies that went well above 100 Hz, at least up to 200 or 300 Hz or so However, one could argue that because you are taking the onus of driving very low frequencies away from the ESL transformer, perhaps it will perform better at the higher frequencies (above 100Hz)  that will be required. Anyway, you will find out if you do this experiment. I personally would not add a tweeter to Soundlab ESL or any othe high quality ESL, but that’s just me.