Recommended Tube Amp for ML CLS I model

Happy holidays!

I've just acquired a pair of CLS I speakers with recent panel upgrade. I know this speaker is supposed to be tube friendly (higher impedance) and the easiest to drive of the CLS range. I am very familiar with the IIz model, but that has very different characteristics from what I understand.

I'm looking to pair a good tube amp with these speakers, to be driven by a Tact 2.2 Mini digital preamp that will be configured to send lower frequency signal to a REL sub and a time-aligned mid / upper signal to the CLS via a Tube amp. (I used a similar setup with an Accuphase DF-35 Digital dividing network and CLS IIz and REL - the Tact is a cheaper option if you just need to 2-way xover division). The digital discussion can take place in another thread.

For now, I am looking for a good tube amp to drive the CLS I model. Since the digitally split signal will be sans deep bass, low frequency performance is not a high priority. So far, I'm looking at ARC VT130SE and VT150 monos (both nice, but a lot of negative feedback used), Rogue Zeus (triode mode), ARC VT100, ARC VS115, Atma-Sphere OTL (with autoformer?), etc.

Any recommendations from those familiar with the original CLS?

CLS's plus REL are a wonderful combination! I'm on the CLS IIz's, not the original, but my understanding is that the sound is largely the same (when turning off the IIz's high-frequency softening switch as I do).

I went through a number of amps, including the Rogue Zeus, ARCs, VTA, VAC, and Hovland before choosing the Conrad Johnson Premier 12 monoblocks. The Zeus and ARC were way too dry for my taste, the VT slightly too dry. VAC and Hovland were competitive sound-wise. The Hovland was the only solid state piece to make it into final round with me, and I really wanted to avoid the hassle of tubes, but it kept blowing a fuse trying to drive the CLSs.
Hi there, I used to import Martin Logans into NZ many yrs ago along with Conrad Johnson, Quicksilver, Counterpoint etc. They sre actually dificult to drive, although it is very humid here which didn't help. Best sound was with the Quicksilver 8417 monos by far. VTL's couldn't drive them. Big Rowlands are an excellent match either 7's or 5's. We had custom built stands to lift them 12" off the floor and angle slightly forward/down, this really opened them up and improved the bottom end considerably.
Dover - are you referring to the Original CLS, II, IIa, or IIz? I know the IIa was a bear to drive, due to it's very low impedance. The original CLS actually had a very high impedance above 1000 Hz, I believe. This made it ideal for tube amps. The series II versions definitely favored SS amps.
I have the CLS IIA's. I don't think they are any easier or harder to drive than your original CLS's. They both need power and stability. I drive mine with an ARC D250 Mk2 Servo (250W/channel) tube power amp and the sound is magnificent. Originally, I drove them with a Levinson No. 23 power amp. It worked well but not as good as the D250. I also have biamped Kinergetics dual SW800 subwoofers. This is a wonderful combination.

A couple of hints. Do not expect deep bass from the CLS. They just won't do it. Good subs are the answer which will also improve the CLS's dynamic range. Next, the CLS are the most demanding speakers I have ever experienced of the up stream electronics. They are absolutely surgical in their ability to demonstrate flaws in the system. They require first rate preamps, power amps, cables, and everything else. These speakers will not tolerate short cuts. This quality is not a drawback. It's way all speakers should behave but most don't.

For these reasons I do not recommend CLS's as beginner speakers. It takes considerable experience, knowledge and financial commitment to get them to perform to their potential. Sure, you can just hook up your amp and the speakers will speak. But that is just the beginning.

People get drawn into the CLS's because they sound great at a relatively low price. But that is deceiving. To be really successful with them, you will need to buy expensive electronics. If you get it right, they are some of the finest speakers ever made. But you do have to get it right.


I have a tonne of experience with the IIz model and was able to make it sing with everything from Gryphon to Innersound to battery-powered Rowlands.

For CLS I, though, it is clear that modestly powered tube amps should be ideal; unlike the II series.

But, yes, I agree that experience is important with any planar speaker.
12-27-10: Fdriver
Dover - are you referring to the Original CLS, II, IIa, or IIz?
Original CLS, but have also experience with CLS II. My caution would be that some valve amps work, some dont. For example VTL Compact 100's ( 100w ) couldn't drive them, yet a 20w Leak Stereo 20 could. My recommendation would be to audition before you buy if possible. FWIW I preferred the original CLS with upgraded panels ( original single transformer crossover ). The Quicksilvers produced the most transparent and wonderful soundstage despite Mike Sanders rolling his eyes when I told him what we were using with the Q's.
Well, I believe ones results with the CLS speakers will vary upon the type of listening one does. What drives ML's best in general has been beaten to death on previous threads about it. Do a search and you'll get the phone book of opinions.

Having owned the CLSiiz's, on my second pair now, my listening levels aren't demanding. I listen to acoustic jazz, and believe it or not I drove my iiz's to more than adequate levels for my modestly sized room with a 10 watt Class A SET 300B tube amp. The belief is these speakers require high current amps before they'll deliver the goods. That's not been my experience. I've used Plinius and Pass amps of modest power ranges with more than pleasing results.

I agree that it's foolish to expect a planar speaker of the CLS' magnitude to deliver high quality bass. That's not what the speaker was designed to do. Acoustic bass of natural tone and volume is the best one should expect from these speakers. But of course, being the jazz listener that I am that suits me just fine. Earshattering level listener's have far more demanding requirements of the speaker than do I. But I don't believe one has to spend countless or unnecessary thousands on attempting to acquire mega power amplification to gain a reasonable level of satisfying output from CLS's. Having owned a countless number of ML hybrid's the CLS's are the best of the lot as far as my ears are concerned and certainly worth whatever effort necessary to get them dialed in to your liking.

I highly second the poster who suggested tilting the speakers forward at a slight downward angle. I've got mine on a pair of Arcici stands at a slight downward angle which lines up perfectly with my ears at listening chair level. It doesn't get any better than this. Mine are mated to an SVS sub. Enjoy your new purchase!

Was that the walnut pair of CLS's recently observed on ad with brand new panels? Perhaps not, for I could swear those were advertised as CLSiiz's.
HI Dover,
I have an ARC D250 on my CLS IIA's not because I listen at ear shatering levels but because it is a great amp. These speakers need a great amp. Up stream, I have an ARC SP-11 Mk II preamp. I have no idea what the lower power limit of these speakers is and, frankly, low power per se does not interest me. In general I do prefer a lot of power for any speaker as long as it is high quality power. The lowest power I have had on these speakers was the ARC D115 at 100W/chan. It definitely did not sound as good as the D250. Was it the power difference or something else. I think it was both. Besides power, the D250 is just a better amp.

I listen to very broad variety of music, mostly on vinyl. However, I do have a number of carefully chosen CD's that can push the system to amazing levels especially in the bass. This is where the CLS's fail both from a frequency response and dynamic range point of view. Good (underline GOOD) subwoofers take these speakers to world class levels.

The CLS 1 is a very different animal from succeeding CLS models. It is a lot higher impedance and is easily driven by tubes. This is not the case with the later versions.

Our MA-1 is a 'match made in heaven' on the CLS 1 according to our customers. We don't have much experience with our smaller amplifier models on the speaker as it was discontinued early on.

However several of our customers have commented to us that M-L still has all the parts for the speaker, and one of our customers actually bought a set of them and built his own 'CLS 1s'. It seemed that they ran fine with his M-60s, but as that is the only case I know of; I feel like we don't have enough statistics to say more.

It would be my *guess* that the S-30 would need a set of ZEROs to accommodate the high frequencies, but one would have to try it to see.
HI Atmasphere,
I can't believe I spent all my words and you didn't understand that my ARC D250 is a tube amp. I can assure you that my CLS IIA's works great with these tubes.

I would have to check but I don't think the original and succeeding models are all that different impedance wise. I do know they sound different. I didn't like the originals and bought Apogee Calipers instead.

I must admit that my negative impressions might well have been caused by the system it was demoed in. At that time I did not understand the CLS's sensitivity to the system context.

HI Atmasphere,
I checked the Martin Logan Club site where they have a data base with all the ML models and specs listed.

You are right. the CLS is listed at 6 ohms but a minimum value is not listed. The CLS II's are listed at 4 ohms with a minimum of 1 ohm. And you are right that that is brutal load for a tube amp. But my D250 deals with it just fine.

It's the minimum value that is the cause of problems with amps. Four or six ohms is no problem. But the CLS's load is highly reactive with the minimum load showing up at high frequencies.

Appreciate all of the very informative replies. I'll check the db on the ML Club site.

So far, it looks like an A-S MA-1, Rogue Zeus, ARC 130SE or 150 monos would be good candidates for the CLS 1. Others would probably be VTL 450 or Quicksilver's V4.
I used to have two pair of CLS, one the 11a, and the other was the 11z(I've also owned stacked Quad 57, ML Sequel,Quad 63 and Acoustat 3)and neither pair worked well when I tried them with a VTL ST 85.
Bea told me that I neeeded to move up the line and get into the bigger tube units from VTL.
I settled for a pair of Classe DR 8 run as balanced mono blocks and had great results.

Now,an even better match up and the best sound I ever heard from a CLS was with the Audio Aero tube mono blocks.
Not cheap, and too expensive for me, but I never knew how much bass those CLS were capable of until I heard this combination.

The right tube amp is out there,but it may not be one of the usual suspects.