Using tube amp with electrostatic speakers.

Moons ago I started similar discussions and thought I had been given enough good advice not to approach the subject again. Here goes anyway. I've used Martin Logan electrostats for well over 30 years with quite a few different amps but have recently switched to a tube amp and dynamic speakers with which I am very satisfied.  It consists of the Cary Rocket 88R amp and Serie Reference 3 speakers. 

My brother was visiting last week and was so impressed with the sound that he decided that he might want to try a tube amp also (probably the same one as mine).  However, he is using a pair of SL3's that I gave him years ago and I'm concerned primarily about the current requirements of the Martin Logans as well as other concerns that I'm not thinking of.  I don't want him spending money on something that may not bring him improved sound so would appreciate more advice to pass on to him.  He currently uses a Rogue Audio SS amp with his SL3 speakers and, to me, it sounds very good. 

 I had a pair of ML SL3s for years driven with an Audio Research V70 and then a Ref 110. Ideally you would want at least 100 wpc to drive the SL3s properly. I don't think the Cary Rocket 88R  would be powerful enough. The SL3s will tend to sound closed in without enough power. 

 I had a pair of Cary SLAM monos in my system for a while. They drove the SL3s without a problem. But I will be honest, my V70 was a much better sounding amp. 

If you plan to use Martin Logans with a tube amplifier, you will want to investigate getting a set of ZEROs (

These will help that tube amp play the speakers without high end rolloff.
It’s not like the end of the world will happen if you go with tube gear, and different tube gear will yield different results.

If you randomly picked out a half dozen beefy solid state amps and equal number of beefy tube amps though, you might find 1 tube amp really does justice to the midrange and treble they are capable of, while almost all the solid state amps would.

However, if you are up for the challenge, you may very well find something you really like. :)

Personally, I would try to make my life easier with a nice CJ pre and a very solid SS amp, like a Sanders ESL for instance. That's just me, and my lack of desire to look very hard though. :)


Tube amps or tube/FET hybrids, work best with electrostatics IMO.

I have never heard the Sanders.

Why do you keep pushing ZERO?


Most all tube amps use output transformers with impedance taps that work just fine into 4  or 6 or even 16 ohms!

The Zero is of NO VALUE to most tube amps!
Primaluna Dialogue HP integrated or separates.
Upscale Audio  should be able to answer your questions. They carry both the ML and the PL.

BTW: I have no affiliation with Upscale Audio
Most all tube amps use output transformers with impedance taps that work just fine into 4 or 6 or even 16 ohms!

The Zero is of NO VALUE to most tube amps!
Don, the impedance of many electrostatic speakers, including most Martin-Logan models, decreases to very low values at high frequencies. The SL3 model the OP referred to, while having a nominal impedance of 4 ohms, is spec’d at 1.5 ohms at 20 kHz. Some other M-L models have impedances at 20 kHz in the vicinity of 0.7 ohms.

Most tube amps have effective output impedances on their 4 ohm taps that are comparable to or even greater than 1.5 ohms. The interaction of that kind of output impedance with that kind of load impedance variation will result in a greatly under-emphasized upper treble region relative to the response that would occur with a solid state amp. A Zero would either eliminate or considerably reduce that problem (note Ralph’s reference to avoiding high end rolloff), and I suspect it would also reduce amplifier-generated distortion.

-- Al

P.S. to my previous post: The Audio Research V70 that was referred to in the post by Lostbears had a MUCH lower effective output impedance than most tube amps, due in part to very liberal use of negative feedback. Specifically, according to it was spec’d as utilizing 20 db of overall feedback, resulting in a damping factor of 30 (the highest damping factor I can recall ever seeing for a tube amp), which theoretically corresponds to an effective output impedance on the 4 ohm tap of 4/30 = 0.13 ohms, essentially in solid state territory.

Generally speaking, Audio Research and also McIntosh tube amps tend to have lower effective output impedances/higher damping factors than most other high quality tube amps.

-- Al
Yes, I also agree with atmasphere as I once had some Wilson Sophia speakers, 4 ohms nominal impedance, and a pair of Fourier Panthere OTL amps whose output impedance was around an ohm or so.  Adding a pair of autoformers made a huge difference in sound, particularly dynamics, bass depth and tightness, soundstaging, detail, just as you would expect with the amp being able to more fully control the speaker drivers.  Once I did this I loved what tubes can do for panel speakers.
Ralph was too modest to claim it, but he is a high level expert on tube electronics and electrostatic speakers. I would trust him implicitly.

Furthermore, I have run a pair of his 'circlotron' tube amplifiers, Atma-Sphere M60's, into the ESL panels of ML speakers. They sounded very good indeed.
jimbreit - I have some experience with your question . I also posed the same question a few years ago . Only a few people responded with less than great advice . Most stated a couple hundred Audio Research watts would be needed with my stats (King Sound). I pretty much was convinced i would never have a pair of tube monoblocks in my system due to the economics involved and focused on ss . 
Fast forward to last year . I picked up a Primaluna Dialogue 2 integrated rated at 35 wattts . At the time i had 6 pairs of boxed speakers that the plan was to use the primaluna with . One day i decided to put it in the main system with my King Sound stats and was pretty impressed with what i was hearing. Zero distortion as the volume increased to very high db's . I was able to play the primaluna just as loud as the solid state .
I have never purchased a amplifier unheard but plan on getting a Primaluna Dialogue premium hp some day . I can only imagine having the extra 35 watts over the dialogue2 will sound like .
My main point would be don't get hung up on the watts of a tube amplifier and research the current it can provide . 
Without the ZERO’s Ralph’s amps sound poor with 80% of the speakers out in the world!

How many people use Zero’s anyway?

And those that do not, do just fine IMO!

There are lots of tube amps that will sound fine on ML speakers without Zero’s.
Most speakers have "roller coaster" impedance curves, and do just fine with most all tube and SS amps.

Do not buy into this "theoretical nit picking" impedance BS.

That does not matter much in the "real world" listening experience!
After hearing and owning a few different tube amps. I suggest having a listen to Linear Tube Audio transformerless amps. I have the ZOTL 40 driving my Janszen zA2.1 hybrid electrostat speakers and it's the best sound I've ever heard. I believe Upscale has them as well as Urban Hi Fi.

A real nice tube amp for ESL’s is the Music Reference RM-200 Mk.2, designed and built by Roger Modjeski, an amp maker who is also an ESL speaker expert. Roger currently makes his own ESL’s, and was involved in the design of the legendary Beveridge ESL’s of the 1980’s.

The RM-200 Mk.2 uses only two KT-88 (or similar) output tubes per channel for 100 watts each, and does so without running the tubes hot or hard. One of the bargains in hi-fi, $4200 new. It imo resides in that perfect price vs, performance sweet spot. Currently in Stereophile’s Class A Tube category.

Don_c55 10-12-2016
Do not buy into this "theoretical nit picking" impedance BS.
The impedance interactions I referred to can easily make a difference of several db or more in the uppermost octave, with electrostatic speakers such as the M-Ls.  That is certainly not nit-picking or BS. Although within the range of possible interactions preferences may of course vary widely depending on the particular listener, system, and room. And yes, many people use M-L speakers with tube amps, without using Zeros, with results that are satisfactory even if not theoretically optimal. But Ralph’s suggestion was legitimate and well worth considering, IMO, and did not warrant the cynical response it received.

-- Al


Most all tube amps use output transformers with impedance taps that work just fine into 4 or 6 or even 16 ohms!

The Zero is of NO VALUE to most tube amps!
No- I have no financial relationship with Paul Speltz or his company. He just makes a good product that I believe in.

The latter statement is false when the loudspeaker has lower impedances nor is it limited to tube amplifiers (see below). It turns out that on almost any tube amplifier employing an output transformer that when using the 4 ohm tap, bandwidth (particularly in the bass) is reduced and distortion is increased, while total output power goes down slightly. It will be found that the transformer runs warmer too (this is where the loss in output power goes- it is used to heat the output transformer). This is because nearly all output transformers are less efficient into their lowest impedance tap. This is not only measurable but is also audible and that's as real as it gets.

How many people use Zero’s anyway?

And those that do not, do just fine IMO!

There are lots of tube amps that will sound fine on ML speakers without Zero’s.
Turns out that the ZEROs are used in many installations that don't involve OTLs. Some of the Martin Logans have impedances at 20KHz of only 0.5 ohms. That's a problem for most tube amplifiers even though there isn't much energy up there its likely you will hear a rolloff or power will be limited or both. The ZEROs solve the problem easily.

Paul Speltz has a letter from Steve McCormick which states that while Steve's amplifiers can double power form 8 ohms to 4 ohms quite easily, they actually sound better driving 4 ohms through a set of ZEROs. Although power is cut in half (8 ohm power), its a simple fact that all amplifiers including solid state amplifiers like those of Steve McCormick *sound better* into higher impedances because they make less distortion.

Martin Logan has always made ESLs, and ESLs traditionally have their best combination when used with tube amplifiers. This has been the case since ESLs were developed in the 1950s. However what ML recognized was that the transistor amplifier market is much larger than the tube market, so to make their speakers work with solid state better (greateer sales), they set up their matching transformers (similar to an output transformer in a tube amp- all ESLs have them) so that the speaker presents a 4 ohm load or less to the amplifier. This makes them an often very difficult load for a tube amplifier even if it has a 4 ohm tap, since with any ESL the impedance curve varies by about a 10:1 value from 20Hz to 20Khz. So a four ohm ESL will have about a 0.4 to 0.5 ohm impedance at 20KHz (Sound Labs, which have a maximum of about 30 ohms in the bass, tend to be about 3 ohms at 20Kz but can be as low at 1.5 ohms depending on the setting of the Brilliance control).

The thing is, impedances like this are not really all that great for solid state either, especially with less expensive solid state amps that might lack for heatsink area. So a set of ZEROs can put them in much more comfortable (read: cooler running) territory! Plus they will have audibly and measurably less distortion. Now ESLs tend to be very fast and detailed loudspeakers, so if you can reduce distortion the speaker will reveal that very quickly by sounding smoother and more detailed. This is because the human ear/brain system converts distortion into tonality, and the distortion we are reducing by using the ZEROs is going to be the higher ordered harmonics which audiophiles call 'bright' and 'harsh' because of how the ear/brain system reacts to them.

Now I mentioned that ML wanted to make their speakers more drivable with solid state by keeping their impedance low. To give you an idea of what is meant, look at a Quad ESL 57 or 63, or a set of Sound Labs. These ESLs have much higher impedances in the bass region- anywhere from 30 ohms (Sound Lab) to as much as 95 ohms (ESL 57). Solid state amps have troubles making power into those impedances and this is in the bass region where most of the power demands exist. So ML's solution was to reduce the impedance.

To further illustrate, in the case of a Sound Lab, if using solid state usually people use amps that make 400-600 watts into 8 ohms. In the case of 600 watts, what will happen is that into 30 ohms of the Sound Lab ESL in the bass region the amp is going to make slightly more than 150 watts at full power. what this means is a tube amp of only 150 watts can keep up with a 600 watt solid state amp on a set of Sound Labs. Do you see the problem? That is why ML went for much lower impedances and that is why the ZERO is such a handy problem solver when working with them.

Have the Nobel Committee (Patience Prize) been in touch yet, Ralph?

@don_c55 Well, yes, but how low and how high is what matters really. Getting significantly below 4 Ohms for instance.

The theory is solid, and if you see Stereophile's FR plots they do one into a simulated speaker load that's pretty good at showing the difference between tube and SS amps.

However! None of this really helps you determine what you may like. Listening is key.

Having said that, I've heard several electrostatic speakers, and when I had a chance to compare, tubes generally lost. I walked into one store with fairly young salespeople. They had a pair of ML's that had been sitting unsold for a while.  All tubes. I suggested they would sound better with SS. They changed it and the pair sold in a week.

@almarg That makes sense. High feedback --> Low output impedance, especially when that feedback is taken from the transformer outputs. :) Not sure what that amp is doing. Would be worth checking out.

Again, I'm not suggesting anyone get religious about it. Sound quality wise though, I would be perfectly happy with tube pre and SS amp. I would not chase a tube amp just for chasing a tube amp.


One last thing, most ESL's are really not very neutral. Almost all can benefit significantly from digital EQ from the midrange on up.

Unlike dynamic speakers which can often be measurably neutral fairly inexpensively.

Again, don't get religious. I'm just saying, you are trading.


One last thing, most ESL's are really not very neutral. Almost all can benefit significantly from digital EQ from the midrange on up.

I find that ESLs can be quite neutral! You are correct though that if there is a problem on the amplifier side, it will be from the midrange on up that it most likely manifests.
Ralph, Erik, thank you for the detailed explanation of how electrostatic speakers work with different types of amps.  A nice education.
Hi @atmasphere

To your own ears be true. :)



Ralph, I think that there must be some other reason that ML designs their panels with such a low impedance at 20khz. It’s such a radical design that there must be a sound quality reason for it, don’t you think?  I don't think anyone would think, I'm not going to buy those speakers, they're not hard enough to drive.

How do you feel about McIntosh gear with their amp-specific autoformers?

I'm going to assume the original Quad ESL is not amongst those considered "really not very neutral". That would be quite silly.
Post removed 
Tomcy6, what Ralph is saying that relates to your first question is that the very low impedance at 20 kHz is a byproduct of M-L’s decision to avoid extremely high impedances at low frequencies. The maximum power capability of nearly all solid state amplifiers decreases dramatically as the load impedance increases to high values, and therefore what M-L was trying to avoid was forcing the customer to use much more powerful solid state amplifiers than their designs require. Especially given that most music contains most of its energy in the lower part of the spectrum.

In contrast, depending on the specific design a tube amp will often be able to supply more power into high impedances than into 8 ohms, up to a point, and in any event whatever falloff may occur in its maximum power capability into impedances that are above a certain level (but still within reasonable limits) will almost always be much less than in the case of a solid state amp.

So M-L’s choice of impedance characteristics works in the direction of making their speakers more practical choices for users of solid state amps, since less powerful amps can be used than would otherwise be the case, while making them less friendly to tube amps than would otherwise be the case. While also, to some degree, adversely affecting amplifier sonics in both cases, as Ralph indicated.

-- Al


I think your skepticism, in general, is well placed. I've seen speakers who have crossovers DELIBERATELY designed to be hard to drive.  That's not the case with electrostatics however.

Plug: Has anyone seen my LM-1 monitor kits? Easy to drive, completely neutral, and free designs. :)

There's just no way to avoid the impedance dropping at the top when you are making an ESL. The entire panel is basically a capacitor, as opposed to a dynamic speaker which is an inductor + resistor. That's one of the main reasons Roger Sanders got into offering amps specifically designed to be excellent with ESL speakers.

I have however read about some radical designs where ESL's are driven from tube amps WITHOUT a transformer. Those who hear them say they are breathtaking. The amps are carefully designed around the ESL's though.

Not all panel speakers are the same though. The old Apogee's did have a ridiculously low impedance but it was relatively flat.


^^ to further build on that, many transistor amps can't continue to increase power into low impedance loads like 0.5 ohms. Further, the speaker cable itself becomes a significant factor when dealing with impedances like this!!

This works in ML's favor to help tame high frequencies, because the impedance curve of any ESL is not also an efficiency curve. What I mean by this is that if you put a watt into the speaker at its four ohm impedance level for a given output you should not be seeing 8 watts into the 0.5 ohm impedance level to get that same output level.

It is this 10:1 impedance ratio which is why tube amps are usually favored on ESLs as they tend to be less bright and there is a better ability to play bass. The brightness in this case is a simple frequency response error caused by a solid state amplifier's tendency to act like a voltage source (which is another way of saying that it tries to put out the same voltage regardless of what the load impedance is). By setting the impedance as low as they have, ML has limited the ability of most amps to be too bright, but I suspect various users will find that a lot depends on the amp and the speaker cables.

Erik, Roger Modjeski is indeed currently offering his own self-designed and built ESL speakers with his tube amps connected to them without output transformers. Anyone in the San Francisco Bay Area wishing to hear them can do so at Roger's new facility.

That's fantastic! For several reasons.  First, proves I don't make stuff up, which most readers think I do.  Next I am actually in the Bay Area so I'd love to.


I used a pair of Ralph's 60 watt mono blocks to drive my Acoustat Four's for a few years. Under powered for sure ... but oh my God, that mid-range!! To die for! 

The Atmosphere amps were on loan from a friend and I ended up using an ARC Classic 60 to drive those speakers. Still under powered with better bass. The speakers are long gone, and the Classic 60 is my spare amp ... just in case. :-)
Hi, I do have the Sl3 and used a Dared DV200 monoblocks and that speaker never sounded so good but the amp has to be re-tube every 1 ~1.5 years and it so painful because it uses 6 kt88 per monoblock. I still have it tho. I used the Krell FPB300 with no problem but a subtle inferior in the highs. There is nothing like a powerful tube amp on electrostatic speakers.

I  am running Martin Logan Spires with a Mystere tubed pre amp and Moscode 402 AU hybrid amp and am very happy with the sound.
I am running 2) Benchmark AHB2 in mono on my QUAD  ESL-2912s.  Love it!  Even 1 AHB2 in stereo did a super job but that bit more power puts it over the top.  Could be the best amp speaker combo I have ever heard.

Erik, Music Reference’s phone number is still the Santa Barbara one (805)687-2236, which will go to Roger’s voice mail. His email address is Wish I could join you! I miss the Bay Area, having grown up in Cupertino/San Jose, coming into San Francisco for gigs, and to go to The Fillmore and Tower Records. Very expensive to live there now! Is Village Records in Mill Valley still around? Used to be a great store for Roots Music.

Roger has opened an Audio Engineering school in Oakland (I believe, though it may be Berkeley), wanting to pass on his electronic expertise to younger designers and audiophiles. The Music Reference model (with prices) page on the website lists the ESL speakers, and a bunch of new, low-power amps. OTL’s, Single Ended, etc. Roger is a really creative and knowledgeable tube amp designer.

Thanks for the replies, guys, very helpful stuff.

Ralph, I’d still like to get your opinion on McIntosh amps with autoformers. Just in general, do you think they are a good sounding amp compared with other amps in their price ranges? Do they implement their autoformers well? Would they be a good choice for driving speakers with difficult impedance loads?  Theoretically, of course.  We all know that good sound depends on many factors in a given system.

Love my leak stereo 20 with my quad 63 using audio research pre. 
Then with my very efficient avant-garde garde duo omegas the transcendent minibeast otls as mono blocks with transcendent ground grid ore amp was mighty fine. 
I power my ML Electromotion ESLs with a Primaluna Dialogue Premium power amp (not the HP model) with KT-150 tubes (24 watts triode mode and 48w ultralinear) and it sounds great and I prefer triode mode. I also use the same amp to drive a pair of Spendor S2/3s (8ohm) and they sound great too. I don't care much about the tech specs, i just try the different ohm taps on the amp and whatever sounds best with the rest of my system is what I use. Sound is full, robust, detailed, natural, and I often get goosebumps. For me it is all about the music, but I like learning about the equipment, to a certain extent!! Lol. Interesting discussion, thank you!

One data point.

I use Martin Logan CLS (original) in one system and although I have auditioned tube amps with them, I have found that solid state amps with good power supplies work by far the best.  Mine are run with a stereo Classe DR3 VHC (a whopping 45 watts).

Not saying that the magic tube amp isn't out there, just that I haven't found it.
When I read all of the responses saying that tube amps will have problems driving Martin Logan speakers, I just had to make my first post on Audiogon.

I have 2 Audio Research VT100 Mk IIs bi-amping a pair of Martin Logan SL3s. These speakers have never sounded better. The sound is organic and natural sounding. If the recording has a lot of spacial information and depth, it is revealed in the presentation. If the recording is flat, that too is revealed. Cymbals sound the way they should. Vocals, including female, just sound right.

Before bi-amping the SL3s, I had one VT100 amp. The sound was similar but there was less depth and the stage wasn’t as wide. Also, large orchestral works just didn’t have the presence that they should have. This was the reason for a second amp. NOTE: I do not listen at high volume levels. The stereo is in a loft so the left and right speaker are not presented with the same wall configuration which just messes up the stage width and depth at high volumes. Plus, I want to be able to listen to my stereo for many years. ;)

BTW, my pre-amp is also tube based.

Recently, I wanted to get away from two amps and tubes. I read a lot about Pass Labs amps and purchased an X350.5. I liked some of what it did but ultimately the sound was just unnatural with overblown bass, etched highs and an odd midrange. Every time, I switch back to my VT100s, I found that I enjoyed the music more. I returned the Pass Labs amp.

I am now looking for a more powerful tube based amp so I can go to a single amp.

My experience for what it's worth.

Long time ML user since 1979. I've owned SL3's, Aries i's, ReQuests, CLS,  Monolith III's, and now Theos. 

I've been on Audiogon since 1997. There's always been a myth that ML's are "harder to drive." I drove SL3's with a lowly 35 watt Prima Luna. I drove CLS to satisfying levels with an 8 watt SET amp! Currently I'm using a Dennis Had Inspire firebottle KT88 SET to power Theos. 

Each individual has different audio needs. We each listen differently. I listen to jazz, in a smaller room now. But even when I had a larger room I drove ML's to very satisfying levels with Manley 450 mono's. In fact, I've never had a more satisfying audio experience than pushing a pair of CLS' with those Manley's. 

I'm big on tube amps for ML's....and I sewed my audio teeth on Pass, Threshold, Plinius, and too many other amps to mention.

It's not a one size fits all audio world. What works for me won't necessarily work for you. And that's as it should be. 

If I had a friend with a pair of SL3's I'd be wondering more about how much longer are those panels going to last, as that speaker went out of service in 2002?
McIntosh equipment and ML’s are both sold by the same retailers, is that the reason for the question? My friend was a huge, enthusiastic McIntosh dealer until they went with Magnolia/Best Buy. Due to his kindness I have tried various McIntosh amps on various electrostatics. I know that the McIntosh amps are not a good match for (full-range) electrostatics beginning with QUADs. The OP should find out if they offer another solid state amp with lots of current to drive the electrostatics. You might stay away from Levinson amps too.

Yes, the Classe’ 45 watt VHC amp should drive electrostatics well. Bravo with sticking with a great amp! Reich is a brilliant designer.

Unfortunately the Martin Logan’s "curvilinear" membrane is a fundamentally flawed design. That, among other reasons, is why they have to offer a 5 year warranty.

ivanj, I asked about McIntosh because I have read many threads where Ralph recommends Zero autoformers for hard to drive speakers and even for not hard to drive speakers. Since McIntosh makes amps with autoformers designed specifically for a particular amp, I thought they might be a good solution for speakers with very low impedances and wanted Ralph’s or anyone else’s opinion on that match. Is it a good one or are Macs just not a good match in spite of his recommendation of autoformers? I know some people just don’t like the sound of Mac amps and point to the autoformers as the reason.

Why do you say that the curvilinear design is fundamentally flawed?

Ralph, I’d still like to get your opinion on McIntosh amps with autoformers. Just in general, do you think they are a good sounding amp compared with other amps in their price ranges? Do they implement their autoformers well? Would they be a good choice for driving speakers with difficult impedance loads? Theoretically, of course.  We all know that good sound depends on many factors in a given system.
I was not aware that Mac was still making those; in the old days their autoformers worked quite well. But with those older amps I would not be asking them to drive anything much below 4 ohms.

The only thing difficult about the MLs is usually their impedance. Beyond that its my opinion that its a Bad Idea to make any amplifier work hard by making it drive a 'difficult load'. What happens is you get more distortion, usually of the type that make the resulting sound harsher and less detailed.

This is why I've recommended the ZERO so often in the past, as it allows the amplifier to drive an easier load.

I don't think the Macs have impedance taps below 4 ohms but usually they do employ a fair amount of negative feedback so they should work alright on ML loudspeakers if not pushed too hard.

McIntosh has autoformers in their solid state amps and specifies that the rated power of the amp remains the same into 8, 4 or 2 ohms. 

In the MC275 tube amp they call the output transformer an output transformer but in the specs they list it under Autoformer.  In stereo mode they say it outputs 75 watts into 4, 8 or 16 ohms, and in mono parallel mode, 150 watts into 2, 4 or 8 ohms.

If they have a 2 ohm tap I would expect them to work fine.
The Music Reference RM-200 Mk.2 does itself have a 2 ohm tap. Great amp.
What a wonderful thread,  I enjoy an education on audio any time, to all the contributors, thankyou,  as much experience I have with audio,  it is delightful to learn,  cheers gentleman.