What amp should I buy to power Martin Logan Esl's?

I currently have the Martin Logan ESL's and I am have a two channel set-up. They are currently being powered by a PeachTree Audio Nova 125. I am debating selling the Nova 125 and replacing it with something. What is the best Amp/setup to power these two speakers as a two channel? Is the Nova 125 sufficient for this task, or should I replace it? Thanks for your thoughts-
You should replace the peach tree as the power amp for the ML. Job (amazon) makes a nice cheap amp. Use the proper cables on that and you will have a nice system.
Not sure if this in your price range but when I had Martin Logan Requests I had Clayton amps with a tubed pre and it was an amazing transformation of sound. Expensive amps but highly worth it in my estimation...
read up on what an ESL looks like as a load to a power amp (you'll find that it looks like a massive capacitor). You can read this on Wikipedia & Sanders Sound Labs website. Once you assimilate this info, get an amp that can drive a huge capacitor & not go unstable (i.e. break out into oscillations). Your choices will be limited & will consist of expensive amps (hey, that the physics of an ESL!! don't want to deal with the expense? Don't get an ESL!). Also make sure that you buy low capacitance cables - they don't have to be expensive necessarily but they need to have low capacitance.
Bombaywalla, how do tube amps mate with ESL/capacitive loads? I kinda' recall that tube amps "generally" like resistive loads with positive/inductive phase angles. Come to think about it, I'm not so sure that SS amps particularly like super-low impedance loads with large negative phase angles.
08-05-13: Bifwynne
Bombaywalla, how do tube amps mate with ESL/capacitive loads? I kinda' recall that tube amps "generally" like resistive loads with positive/inductive phase angles. Come to think about it, I'm not so sure that SS amps particularly like super-low impedance loads with large negative phase angles.
In general, tube amps do not mate very well with ESL/high capacitative loads.
Tube amps, generally, have a much higher output impedance (as you now know) & together with the ESL looking like a big capacitor, the combination acts like a low-pass filter with a low(er) frequency -3dB frequency. This will have the tendency to roll-off the high frequency content of the music signal.
Now, tube amps can be used with ESL speakers but, if you notice, these tube amps are physically large units. Examples are Tube Research Labs products, Wolcott Presence amps, large VTL monos, CAT JL2/JL3, etc. These large tube amps have many parallel output tubes thereby reducing the overall output impedance & widening the bandwidth of that low-pass filter created by the amp o/p imp & the ESL capacitor.
So, this is from the impedance point-of-view.
Another point-of-view is the ability of the power amp to generate power into a low(er) impedance load. Tube amps have a higher output impedance & when you consider the voltage-divider effect, as the ESL impedance goes down, the tube amp cannot generate sufficient power into that low impedance thereby giving you anemic sonics. Per Ralph Karsten's constant-power theory, the tube amp will change voltage output swing & current output swing such that the product of voltage & current will equal the max power rating of the tube amp. So, if the ESL impedance goes down, the current delivery will go up & the voltage swing will go down such that the product of increased current & decreased voltage will equal the max power rating of the tube amp. Most tube amps do not double their output power as the load impedance halves (like s.s. amps) so power delivery over varying load impedance is mostly fixed. OTOH, s.s. power amps have a much lower output impedance & will deliver much more power into a lower impedance (within the limit of their power supply/transformer). Thus higher current delivered into a lower impedance mostly makes up for the lower voltage swing that would have resulted from a lower impedance ifff there wasn't an ability to deliver enough current. IOW, ability of a s.s. amp to deliver more current into a lower impedance gives a higher voltage swing. And, this means you will get more robust sonics because pk-pk voltage swing generated in the speaker directly xlates to driver pistonic action (which is what creates sound).
Power delivery into a low(er) impedance matters a lot when we have a highly capacitative load because the phase angle of a capacitor is negative & the effect of this ph angle is to reduce the real part of the music waveform (when a music signal goes thru a capacitor, it becomes a complex waveform meaning that the waveform now has a real & imaginary part. the real part is what's of meaning to us as it gets converted to sound energy. the imaginary part is the instantaneous power dissipated in a reactive/capacitative element. Average power thru a capacitor will be zero but it will have instantaneous power dissipation). So, when the real part of the music waveform is reduced, you need to pump more power from the power amp to compensate (or submit to listen at a lower volume/an anemic or less dynamic signal). This is where tube power amps eventually come up short/run into their output power limit. Big/huge tube power amps fare much better & of course, s.s. power amps also fare much better.
you are correct in stating that speaker loads with low(er) phase angle shifts are much easier to drive & the power amp (tube or s.s.) is much happier in that sort of condition.
Thanks Bombaywala -- very good explanation. After breaking big rocks with a sledge hammer, courtesy of Ralph and Al, I'm starting to better understand speaker/amp electrical matching. Of course, I've also come to better understand that speaker and amp designs are often the result of engineering/technical compromises. I believe Al and others made that point as well many times.

One such compromise that comes to mind is the benefit and cost associated with using negative feedback. Ralph and Al have spoken about many of the costs, such as TIM distortion and odd ordered harmonic distortion. They have also mentioned some important benefits, such as lower overall distortion, increased bandwidth and lower output impedance.

Case in point: I believe that ARC uses NF in most (if not all) of its tube amps. For example, the somewhat new ARC Ref 150 tube amp uses 14 db of NF and has approximately 1.1 ohm output impedance off the 8 ohm tap and about 60% of that value off the 4 ohm tap. See Stereophile/John Atkinson Ref 150 bench test last year.

Not sure if that turns a low impedance/high capacitance ESL speaker into vanilla ice cream for the Ref 150. Not even sure if the Ref 150 likes ice cream. But I wonder how well tube amps that use NF fare with ESL loads.
08-06-13: Bifwynne
Thanks Bombaywala -- very good explanation.
thanks for your kind words Bifwynne.

But I wonder how well tube amps that use NF fare with ESL loads.
I would think that tube amps using large amts of NF would fare quite well with highly capacitative loads from a purely electrical interface point-of-view. As mentioned by you in your post, NF would make the power amp measure really well on the testbench. I would think that you would get pretty decent sonics from a high-NF tube amp but what would be missing would be the soul of the music. I think that a high NF tube amp would never truly 'sing' to the music - it would have many of the audiophile attributes but would sound very clinical & non-engaging.
I forgot to write in my prev post - comments from other members who have experience with tube amps driving highly capactitative loads are most welcome. Hopefully I'm the person with the least amount of knowledge on this topic. Thanks.
Bombaywalla, not sure what constitutes "large amounts of NF," but the ARC Ref 150 uses 14 db of it. Perhaps somewhat responsive to the issue of tubes and ESLs, ARC reports (and Atkinson confirms) that output regulation is approximately +/- .5 db off the 4 ohm tap. So ... maybe the amp may add a touch of "flavor" to the acoustic presentation, but who said life is perfect.

Can't say that I recall reading comments that the Ref 150 doesn't sing to the music, but I'm tone deaf. What do I know??

I suppose we still don't know for sure what all the techno-babble means in real life. So I echo Bombaywalla's request that folks who have matched tubes and ESLs report their real-life experiences. Kinda' an interesting topic.
In my post I did not intend to single out the ARC Ref150 (which I understand is of personal interest to you due to your ownership). I was referring to the tube amp-ESL match in general so as to not hijack the OP's thread. Thanks.
Bombaywalla -- you're right ... the Ref 150 is of personal interest to me. But not because I own it, but rather because I want to own it. ;>')

Having said that, if there is any validity to my thesis that tube amps using NF may (??) perform SS-like, and therefore may (??) be able to drive ESLs, does go to the OP's thread about ESL-amp matching.

In short -- I don't know the tech answer to whether a particular tube amp will match well a particular ESL. Perhaps the best way to answer the Q is to ask the manufacturer. Of course, a live audition, if possible, would be great.
FWIW tube amps can work extremely well with ESLs. The problem you run into sometimes (one that is common with ML ESLs) is that the impedance of the speaker has really been set up to favor transistor amps (i.e. are set to a lower impedance) more than tube amps.

So tube amps can have a tough time on ML ESLs as a result.

There is however a fairly simple solution, which is to get a set of ZEROs to go between the amp and speaker. I have seen this work quite well with our amps; I have one customer who has run that combination for over 20 years (he has one of the first sets of CLS-2s, which were notoriously hard for tube amps due to the overall low impedance).

FWIW an ESL is not by definition a low impedance speaker. Two good examples are the Quad ESL 57 and 63 which are moderate loads for smaller tube amps, as are certain Acoustats and certain AudioStatics. The more recent Sound Labs have become a lot easier to drive as well. It is the choice of the designer as to whether they are trying to make the speaker work with transistors or tubes- if transistors the impedance will be quite low (perhaps only 0.5 ohms at 20KHz!).
Best ML sound I have heard was off a Krell integrated amp about 4 years ago. I also heard a pair of Focal Profile 918s on the same system and both sounded very good. It was a very lively and decent sized Twitter listening room. Holography was off the scale with both.
Best ML sound I have heard was off a Krell integrated amp about 4 years ago.
funny as that was my experience as well. the best M-L sound I heard was Krell FPB600 monos driving the M-L Statement E2 speaker. Krell CDP & Krell preamp. MIT cables. That was in the Sound Advice showroom when Gail Martin Sanders himself was touring the country doing these demos.
I still remember the sound today-absolutely fantastic! I wanted to run out & buy that exact system right there & then! Alas, when I was presented the bill I saw that it was in unobtainium land....;-0
Source on that system was a krell CD player as well. ICs and speaker wires were all Audioquest I am pretty sure.
I wouldn't discount tube amps in regard to driving ESL hybrids such as Martin Logan or a pure ESL such as Quad. The combination can be quite magical as a matter of fact. In years gone by I used a nominally 40 wpc (probably more like 25 wpc in actuality) Class A single ended parallel pentode 5881/6L6 amp to drive ML Aerius speakers and it sounded simply wonderful if a little lacking in dynamics at times. Switched to an EL34 push/pull amp from the same company putting out 100wpc and the Aerius speakers gained in dynamics if a bit less detail. I've driven Quad 989s with both 70 wpc and 140 wpc conrad-johnson tube amps (Premier 11A and Premier 140) and they both made beautiful music with the Quads.

Granted, as a previous poster stated, the Quads are a more benign load than the ML. However, just because a certain pairing may look great or not so great on paper isn't always an indication of what it's actually going to sound like. So much of it is system dependent and a matter of personal taste that blanket statements may be misleading.

Just my 2¢ naturally.

I just took a look at your Peachtree online, which I should have done first. :) It seems like a very nice, versatile unit. Why are you considering something else?
Why ask if the Peachtree is sufficient when you can try it and draw your own conclusions?

And the best advice in this thread is from Joe_appierto who wrote "just because a certain pairing may look great or not so great on paper isn't always an indication of what it's actually going to sound like."
This is a really good question since ml ESL speakers (and stats in general) are hard to find good amps for. They are a challenging load, and difficult to drive. They are revealing to a fault, almost. This can be a great or a terrible thing!

The solid state amps I have that will _work_ with them that I have tried are Aleph 60 Monoblocks (bedroom system), mine were Rawson built and run quite hot, hotter than my VTL Monos do... Love these. A great combo! The speakers are Ascents.

In my (tiny!) office, I have shoehorned a pair of ReQuests. They are powered by a Van Alstine FetValve 500hc. This amp does a decent job powering them, and the gain stage has two 12ax7's in it, which makes it tubey and nice, however the Aleph 60 Monoblocks are better, IMO.

Tubes are a _really_ good idea for these. This is the true sweet spot. vtl MB-450 or MB-300 are awesome. My ARC vm220 monos are great as well.

I know Atma is completely awesome, but I've never tried them...