Philipwu and Olympicman: please both forgive me for this slow reply. I haven't been checking in with Agon lately.
Let me say some general things about powering electrostatic speakers, and MartinLogan speakers specifically. Especially because many of you younger audiophiles who are smart enough to consider older model speakers (like the CLS's ;~) may benefit from a little history. First, it is important to remember that of ALL the models MartinLogan EVER produced, only two of them, the various CLS's, and the CLX, have truly "full range" electrostatic panels! All other models are hybrids. That is, they include a woofer(s) to provide low frequency response. Either self-powered (by an internal amp) or powered by an external amp (supplied by the user.)
The electrostatic panels in all the 'hybrid' models have limited low frequency response; they cut off anywhere between ~ 200 Hz and 500 Hz depending on the model. The CLS and CLX go all the way down to 40 Hz and 55 Hz respectively (although not with a lot of oomph -- and they certainly don't cover that critical last octave or octave-and-a-half ;~) But for certain kinds of music, they are absolutely perfect; and give all the bass response needed for those kinds of voices and instruments.** The only other "full range" electrostatic (STILL!) which produces full frequency response down to 20 Hz is of course the largest models of the SoundLab, but that's a whole other discussion.
Both solid-state amps and tube amps require certain electrical "considerations" when used with stats; however, once those considerations have been addressed, it is ABSOLUTELY NOT POSSIBLE to say one type of amp is clearly better than the other, for driving electrostatic panels. There will be some "musical" differences however; and while subtle, these musical differences should be considered when choosing tube vs. solid state amps. However (and I want to be real clear about this) these "musical" differences have to do ONLY with the way solid state circuits versus tube circuits handle music signals. Power output, impedance matching, and all those other electrical considerations that people are always raising as being important issues?: they can all be "handled"! What can't be changed is the way valves and transistors, each in their own way, amplify music signals! And so there will be some trade-offs.
Electrostatic panels are the most accurate audio transducers so far devised (for large scale use.) Meaning, they can change (transduce) an electrical signal into a sound wave more faithfully than any other device commonly available. So why not drive them with the most accurate amplifier? OK . . . . and what would that be? Do you want every last morsel of musical information to make it into your speaker?; or do you want the information that DOES make it into your speaker to be utterly free from distortion, of ANY kind? You can't have both! If you want EVERYTHING in the music signal to be delivered to your speakers, then you will need to use tubes. If you want to know that the signal going into your speakers is free of any kind of electrical (ie non-musical) adulteration, then a solid state circuit can provide it. And PLEASE UNDERSTAND, I'm talking about apples-to-apples comparisons, meaning high-quality, time-tested, and yes, kind of expensive examples of audio components here -- regardless whether they're tube or transistor!
So, what do you get with tubes? You get the ultimate in signal PRESERVATION. All of the (OK, as much as possible ;~) of the micro detail, vocal sibilants, and supersonic overtones that are contained in real, live music. (Almost) nothing missing. What do you get with transistors? You get QUIET; especially when there is supposed to be nothing to hear. And when there is something to hear, get a music signal that is (in the best cases) free of any electronic "artifacts" that either join with the signal, or worse, modify it! As long as you understand that some of the "small stuff" isn't going to make it through a solid state amplification circuit . . . . . Oh sure, you can argue that these descriptions/distinctions don't apply to say Boulder or DarTzeel solid state amps, or to any number of five/six-figure tube amplifiers, but let's not go there right now, OK?
So what is it (if it's not the other silly, but correctable stuff) that produces these two different audio outcomes. The answer is speed; maybe "agility" would be a better word. Tubes turn on and off slowly, like light bulbs; transistors respond (almost) at the speed of light. When a pair of tubes (in a typical push-pull amplifier circuit) hand the signal back and forth to each other, there is some "lag", like a relay runner who doesn't fully let go of the baton until the other runner has a good grip on it -- no chance of the baton getting dropped! However, with a pair of transistors in the same application, unless they are PAINSTAKINGLY (and expensively) matched, a "crack" will open up in the "on-off" cycle, and unfortunately, some of the tiniest signal components will fall through those cracks . . . . . The upside is that transistors don't need ancillary power (like filament current) to make them work. Basically (and I'm over-simplifying here) transistors run on signal alone -- and so as long as they are operated withing their design limits, they won't mess with your music signal -- however, their circuits might lose some of it ;~)
Another time, I will try and add to this post regarding what to consider when combining tube amps or solid state amps with electrostatic panels; and the somewhat different considerations when talking about a full range versus hybrid electrostat. Thanks.
** So if one only listened to string quartets, light jazz vocals (without heavy drums or upright bass), solo guitar, Gregorian chant, etc -- a pair of CLS's or CLX would be fine and you wouldn't miss any bass.
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