I had a BAT VK220 for awhile on my CLSIIA's, but it just didn't have enough power and/or control. It did sound very good, but not big enough. I'm sure the VK600SE would be more than ample.
I haven't heard, (on my CLS system), but in others CLS systems, the Pass amps. They are VERY NICE indeed, especially the new series.
After listening to probably a dozen or so different amps in my system, I finally settled on a Sanders Sound Systems ESL amp and couldn't be happier. It's by far the best amp I have heard in my system, on my CLSes. I have actually stopped looking for amps...
Sorry, I might to include this link to the Martin Logan's Users Group. You can read forever here and see that there are a wide variety of amps used. The Pass Labs amps are pretty popular.
I had a VK250Xse with my Aesthetix Janus and it was good, but not amazing. I haven't heard your speakers, so no idea of what it would sound like with your system. A friend did bring over his Pass 250.5 and it was VERY good.
About 5 years ago, starting with the Summit, MartinLogan introduced their first powered hybrid. A hybrid is a combination of both electrostatic panel and cone woofer. A 'powered' hybrid has a built in Class D SS amp just for the woofers.
Previous (unpowered) hybrid models were a problem for those who wanted to get the best sound out of the electrostatic panel, which requires tube amplification. Unfortunately, tube amps aren't so great at controlling the woofers, unless they are really powerful. So you had three basic choices:
1,) Use a SS amp for great bass and put up with bright mids and highs from the panel. And the SS amp will need to be 200W+ per channel in order to deliver enough current to drive the panel at low impedances. You see, a 100 watt SS amps can't deliver much current, which is what stats need. A 100 watt SS amp CAN deliver lots of voltage (good for cone woofers) but electrostats don't need lots of voltage from the amp.
2.) A 100 - 150 watt tube amp. Terrific for the stat part because it provides plenty of current, but guaranteed to provide dissapointing, sluggish bass (no "thwack!") Remember, the original Quad 57 was driven by a 15 Watt Quad tube amp, and later a 40 Watt. It was a pure electrostat, and didn't have much bass, but nobody complained ;-)
3.) You could bi-amp the hybrid using an external stereo crossover and a tube amp for the panel and a SS amp for the woofer(s). If you know what you're doing and have the scratch, this setup can provide spectacular performance. (read my system history.)
Back to the CLS. I've had my CLS-IIz's since 1992, and they aren't going anywhere. In that time I've powered them with the finest amps both tube and SS: ARC M300 Mk2 (8)-6550 power tubes per side (300W ultralinear mode, or 140W triode mode @ 2,4,8 ohms), the incredible Mark Levinson 23.5 SS dual mono (200W @ 8 ohms) and currently, a McIntosh MC275 (95W @ 4, 8, 16 ohms) Due to Mac's proprietary power circuit design, the McIntosh puts out lots of current and predictably sounds better than any amplifier I used so far.
My point is that if you only have to drive the electrostatic panel, there is nothing to gain (and a lot to lose) driving it with a SS amp - even a very expensive and/or high-powered SS amp! This has been shown to be true over and over again. The problem (until recently, when ML finally came to their senses and provided built-in SS woofer amps in their hybrid speakers) was that there were only three full range electostats in the market: the CLS series, the later model Quads, and the SoundLab series. And to be honest, you needed a SS powered subwoofer with the first two. Now ML produces another pure electrostat, the CLX series, which is $25K+ (like SoundLab) and it too can use a subwoofer from all accounts! HOWEVER, it's revealing to note that when ML introduced the CLX at the Munich Audio Show last fall, it was driven by McIntosh 2301 monoblock tube amps!
So: if you want the most out of your CLS, buy it a nice reliable cool-running McIntosh tube amp. BTW, the CLS only goes down to 40Hz on a good day ;-) If you want bass, buy a ML Depth sub to match, and you'll have one of the finest sounding systems any amount of money can buy.
I appreciate all the comments. To Mofimadness: how would you compare the ESL to the Pass Labs on the CLS? To Nsarch: I tried a pair of 200W ARC monoblocks on my CLS and found the bass to be ill-defined. Of course, the amps sounded wonderful in the mid-range and treble. How would you describe the bass on a Mac tube amp compared to a powerful SS amp such as your Mark Levinson 23.5?
I have heard that the BAT amp is very tube like in sound for a SS amp. The Pass Labs seem to be very popular with CLS owners. Of course, it is all about the synergy. I am trying to get a feeling from CLS owners about which amps have a "wow" factor when matched up with the CLS. It is a hassle to audition amps and I want to make a short list. I am the original owner of my CLS and currently power them with a Mark Levinson ML3, which I love. My question is: After 20 years is there a better amp out there for my CLS? Nsgarch, I do like bass. For years I owned a pair of Entecs, but they couldn't handle double duty when I added HT. So, I sold the Entecs and got a pair of Descent i(s). An awesome combination. The bass is POWERFUL and defined. Thanks for the feedback.
Dchazen, "bass" is something a CLS just won't do no matter what amp you use, tube, SS, ML, ARC, Pass, BAT, Mac. Its bass response starts to fall off at around 60 - 70Hz and is down by half at 40Hz and completely gone by 30Hz. So when you say "I tried a pair of 200W ARC monoblocks on my CLS and found the bass to be ill-defined." I'm thinking, "compared to what?" Unless you listen to a lot of solo guitar, small jazz combos, or string quartets, you won't get all the bass that's on the recording. That said, a very small boost starting at 35Hz is all that's necessary to turn it into a full range speaker; and the ML Depth is just the ticket!
The "quality" of the bass the CLS produces is another matter. You can't imagine how well a CLS can do what bass it does do (cleaner, not louder), until you get it up off the floor on stands -- I received a directive from ML regarding just that early on; stands also improve the soundstage by eliminating the 'floor reflection' off the bottom of the panel.
The ML 23.5 is probably, (along with the ML 20.6,) the closest anyone has come to the sound of a thermionic valve using solid state switching; though I must admit, I haven't heard the latest darTZeel or Boulder or Lamm ;-) I used my 23.5 for driving Wilson Puppies as subs in 1992 because they were the only low frequency speakers that had transient response fast enough to match an electrostat (did you read my system page?). I did compare it directly with the MC275 and the tube amp was superior in midrange detail, separation of instruments, air/hall ambience. Doing some tube rolling brought back the high frequency extension of a SS amp but without any glare or harshness.
For bass boost, you only need one Depth (or Descent, although I prefer the Depth for its transient quickness) It should be placed smack between the panels and set to 90 degree phase angle (the phase that exists halfway between the front and back of the panels ;-) and crossed over (rolled off) starting at 35Hz. You won't need a lot of volume - just enough so you notice if you suddenly turn the sub off. Do not low-pass the CLS! Run it full range and just let it naturally run out of gas on the low end ;-)
Thanks Nsgarch. The CLS are up on stands and run at full range. I prefer two subs for stereo. The ARC bass was ill-defined compared to my ML3. Did you trade of some low end definition on your CLS when you switched from the ML 23.5 to the MC275?
Dchazen, the CLS should be able to provide excellent bass down to its design limits as I mentioned - and that's regardless of amp type as long as the amp is a 100W+ toobie (with a damping factor greater than 14) or a 150W+ SS. And it's good that you have the panels off the floor.
Now, there may be other factors compromising their bass performance:
1. If you ARE using a tube amp, you want speaker cables no longer than 2.5 meters (~ 8ft) to get the most out of a tube amp's limited damping. The shorter the better.
2. Make sure you are using a LOW CAPACITANCE speaker cable. This is essential for good stat performance, expecially bass. This means, for instance, NO Cardas speaker cables, which all have capacitance over 400 picofarads per foot. Electrostats require speaker cables with less than 20 picofarads per foot. You can test my advice by going to Home Depot and buying four lengths of 12AWG insulated solid copper wire and hooking your speakers up with it ;-)
3. Another very likely culprit are your TWO subwoofers, which, depending on where they are placed, and their phase, level, and crossover point settings, may actually be cancelling the CLS's output at certain low frequencies. So let me give you my little prepared speech on subwoofers:
a. The human brain cannot locate the source of frequencies below 100 Hz. A true "subwoofer" should be operating below 100Hz, and with CLS's. below 40Hz, so having TWO subs (operating below 100Hz) will NOT contribute to "stereo". And the main speakers, unless they are monitors on stands, should certainly go down to 60Hz or less before thay start rolling off - and that's where your "stereo bass" should be coming from.
b. Subwoofer placement is critical for proper integration with the main speakers; and placing two subs is much, much harder than placing one - so why bother? (unless you're living in a cathedral and need more bass output;-) And if you ARE living in a cathedral, you can put them at the back of the cathedral.
c. And it's damn near impossible to properly locate two subs if your main speakers are panels! This is because, unlike conventional loudspeakers, panels have two out-of-phase radiation patterns. The the sound wave from the front of the panel is 180 degrees OUT OF PHASE with the sound wave coming from the rear (and yes, the front and back waves cancel each other at the edges of the panels.) That is why with panel speakers, the best place for a sub is smack in between (and right even with) the panels, AND set at 90 degree phase angle, which splits the difference and matches the the phase of the two mains at that location. The ML Depth or Descent, with its omnidirectional radiation pattern (due to the three drivers facing in three directions) are ideal for such placement.
This may all sound counter-intuitive to you, but I beg you indulge an old man, who studied acoustics at MIT ;-)
Thanks Nsgarch. However, I have to disagree because I know what I heard from my CLS. The amp does make a difference on the bass. The SS ML3 @ 200W per channel handles the bass nicely. The late model tube ARC 200W mono amps, not as nicely. They are both highly rated amps in their own dominions. Maybe it was the particular ARC amp I used, but I have repeatedly read comments in forums that you generally give up something in bass tightness, definition and impact when a tube amp is used as compared to a SS amp. How did your CLS bass change, if at all, when you used the MC275 as compared to the ML23.5?
I have repeatedly read comments in forums that you generally give up something in bass tightness, definition and impact when a tube amp is used as compared to a SS amp.
Undoubtedly, these people are not doing EVERYTHING ELSE right, or that would not be their experience - trust me! And by the way, are we talking about their experience(s) strictly with CLS's; or with hybrid electrostats?
Tube amps put out a tight accurate bass signal, the same as any SS amp. What tube amps CANNOT do (very well, because of their damping limitations) is they cannot exercise tight control over big, sealed air-suspension cone woofers! However electrostats are quite easy to control, even the bass, even with tube amps, because their diaphragms are very light weight, AND they don't produce a reactive signal like electrodynamic (cone) speakers do.
You seem to be beating around the bush while trying to avoid putting my suggestions to the test -- and did you not own a pair of my favorite speakers, I wouldn't take the time to try and convince you ;-) So before you decide you don't agree with me, why don't you try implementing all the tips I gave you? I think you'll be quite pleasantly surprised:
>Speaker cables (low capacitance and under 8 feet)
>One sub, between the panels. 90 phase angle, 35Hz crossover, lowest possible volume.
>Oh, and make sure whatever preamp you're using has a low enough output impedance to drive a tube amp easily. It should be a tenth (or less) of the (tube) amp's input impedance, or you will get high and low frequency rolloff.