Vintage DD turntables. Are we living dangerously?

The impedance of any ESL is a complex function of many factors, but basically an ESL can be viewed as a giant capacitor. Thus it will tend to have high impedance at low frequencies, and the impedance will tend to fall off at the very highest audio frequencies. More than one ESL measures 2 ohms impedance or less at 20kHz, for example. However, that same panel may well measure 100 ohms at 20 Hz. The step-up ratio of the audio transformer is also a major factor in impedance; many if not most "modern" ESLs present a relatively low impedance load as a deliberate design choice, to make the speaker more friendly to solid state amplification. Martin-Logan speakers are a particular example of this. The impedance seen by the amplifier will vary inversely as the square of the step up ratio of the audio transformer. So choosing a high-ish step-up ratio will tend to result in low impedance even across the mid-band. Crossover networks also tend to reduce impedance around the crossover point. My point is that your Joule amps can certainly drive any ESL that is built or modified to work well with a tube amp, i.e., any ESL with a decent impedance curve (e.g., >8 ohms) at low and mid-frequencies. There is little electrical energy required at 20kHZ, so a very low impedance at such high frequencies is nothing to worry about. For example, my SL speakers measured impedance at ~500Hz in stock form was about 5 ohms or less, not good for an OTL. When I removed all the crossover parts from my SLs and substituted the treble audio transformer with a full-range audio transformer, the impedance now measures 20-25 ohms at mid-frequencies. Needless to say, my Atma amps are in OTL heaven driving my 845PX speakers. And the improvement in sound afforded by getting rid of the crossover brought tears of joy to my eyes.

Try an original Quad 57 or a KLH9. Those great speakers were made to mate with tube amps from the get-go. You will be amazed.

Hello Lewm,

I am well aware of the potential. Acoustat had model X which had the OTL directly driving full range panels.
My "issues" with panels are not how hard they are to drive.
I am well aware of their strengths. My issues is maybe my own personal perception but panels always make me analyze the music instead of listening to it and immersing myself in it. They give me an illusion that the voices come from outer space but the cavity of instruments are missing somehow as if the cavity was blocked or instruments were much flatter than what they really are. To me they sound like they miss the resonances of a stringed instrument but panel guys will say I miss box colorations, which is maybe the case.
Hard to explain why panels sound like that to me, but perhaps it has to do with mid-bass cancelation due to the dipole construction (destructive interference in physics). In addition, I always panels as coherent from the midrange and up but not so from lower mid-range to the deep bass.
I believe that some people are more sensitive to upper frequencies and some are more sensitive to lower frequencies and then you have the horns, which I could never warm up to due to my own preferences in sound reproduction.
In the end, at the highest echelons of audio, when clarity is achieved, our hearing and perception defers and everyone has his own preferences.
Otherwise we were all owning the same exact system, which would have made this hobby pretty boring…:-)

Doron, I misunderstood. Some people like olives and some don't. That's cool. As for me, I have yet to hear any box speaker I could live with, knowing that I could also have what I do have as an alternative. (I don't use the term "panel" speaker, as there are many kinds of panel speakers, e.g., Magnepans, which I do not wish to include in my endorsement. Nor do I feel the same enthusiasm about all ESLs, only certain ones.)

Agree. Not all panels are created equal. I agree with you on the Magnepan.
I heard Martin Logan, King-Sound, Quad ESL and various models of Acoustat including 2+2, 3, 33, 4, 66.
The best of best of the lot was 3 located between two rooms (so it had almost the same distance to the back wall as to the front wall) with very high ceiling in the listening room. Dipole powered sub (two woofers back to back) included.
Driven by push pull tube amps and by OTL's.
Sound stage is huge, clarity is unparalleled, background is pitch black and it's quite dynamic too, unlike Quad ESL 57.
Probably the best implementation of ESL I hand ever heard.
Again, depending on source material, to my ears, mid bass was missing and bass to midrange connection was not to my liking.
Its a very impressive big orchestral pieces material. Just not one that I can personally live with. I am missing the wood:-)
Its interesting that in speaker choices there are camps:
Horn guys can never settle for anything else, ESL ditto (they are very sensitive to "box colorations" and to what they describe as separate drivers rather than one coherent sound wave, at least in the mid to upper frequency) and box speakers guys are also pretty stubborn in their choice.
In the end speaker choices are like "choosing" your wife:
She is not perfect but she is perfect for you, if you know what I mean:-)
I never changed my main "lowly" Sonus Faber Grand Piano Home speakers after hearing countless other speakers, including, comparing them, in the same room to "higher end" Sonus Faber speakers. Just to show there is a reason why I chose them in the first place,
The main thing is to chose a pair of speakers that work in your room (can't over emphasize that because speakers are never one size fits all) and to work with them rather than becoming a "speaker womanizer" who swaps speakers left right and centre to never assume each spraker's potential rather than picking a pair and find out how to make them sing.
Just my opinion based on my experience.

I have noticed that some of the members here had experience witn Lenco and other idler wheels as well and was wondering what was your impression of the results compared to a DD in a heavy plinth.
My experience is limited to a friend's JN Reference with Analogue Instruments, 12" Cocobolo, Uni-pivot tonearm and various cartridges (SAE 1000 LT, Koetsu Black, low output Elac).
On the plus side:This combo had very good flow and sounded very smooth.
On the negative side: noise floor was high, which made dynamic contrasts lacking. Air, 3D and detail were missing.
A while ago, 3 audiophiles from Canada conducted a "Lenco Challenge": building a CNC machined, heavy birch plywood plinth for a donated Lenco drive, greasing the bearing and following The Lenco Heaven instructions.
Results were not super positive when compared to modern tt's like DD Brinkmann Bardo for instance:
http://www.canuckaudiomart.com/forum/viewtopic.php?f=32&t=28246&hilit=lenco+project+brinkmann&start=285

I was wondering what was your experience?