Looking for great tube integrated for Martin Logan Summit X speakers

I've had upgrade fever every since I added bass traps and acoustic panels to my listening room and wondered why I didn't do that years ago.  So I've decided to change my Plinius Hautonga integrated and make the plunge to tubes. I want that sound, and the thought of tube rolling appeals to me.  I was leaning toward the Primaluna Dialogue HP integrated, but after doing more reading, I'm concerned that it won't have adequate power due to the Summit's impedance needs.  I'm admittedly a novice with tubes, so seeking help from the forum.   My room is about 12x15, with the area behind my listening position open for an additional eight feet.  I don't listen at high volumes at all, and my favorite music is female jazz, smooth jazz, Nora Jones type vocals.  Music comes from SACDs and Tidal exclusively - I have no analogue gear.

The rest of my gear:
  • Gustard x20u DAC modified by Rick Schultz
  • Oppo 103D for SACDs modified by Rick Schultz
  • Bryston BDP-1 music streamer
Will I be happy with the Primaluna, or do you have other suggestions in the $5,000 range?  Or should I stay away from tubes for these speakers?

Appreciate your opinions!

There are a lot of people who say MLs sound best with tubes but my experience is that they do better with lots of power.  I never tried them with tubes.

I had Summit Xs powered by Pass XA30.8s and they sounded great to me.  The 30.8 I believe puts about 100 watts into 8 ohms and increases into 4 and 2 but doesn't double down.

I decided to see what a muscle amp would sound like and got a D'Agostino Classic Stereo.  300 watts into 8 ohms 1,000 into 2 ohms.  It was a great improvement in every way.  The Summit Xs really came to life with more power.

So that doesn't answer your question, but that was my experience.
I owned Martin Logan SL3s for many years and used a BAT VK500 ss amp....the Stat panels dip real low in impedance. I also heard the those Logans with a 35 watt tube amp and the sound staging was surreal so I guess it depends on the damping factor of the amp?? Those with the big tech knowledge could probably explain exactly what kind of tube rig would have synergy with your speakers 
I've had my PL HP for 4 years. 

ML stats have been on my radar among many others.

I found them to sound fantastic with the PL.

Using sealed floorstanders/sub, and just looking for something different.

IMO, a subjective decision that only your ears can decide.

You won't know until any speaker is in your room.

This review mentions tube/SS performance with the Summit X

If more power is needed, you could drop KT120 or 150's to replace the EL34's. Other than visceral DEEP bass, I didn't hear anything lacking with the EL34's. Subs would take care of this.
This is just my personal taste, someone else may find it okay without a sub. 
The Rogue Cronus Magnum II/III has plenty of grunt. Not the quietest integrated out there but probably the most powerful under $5K. I prefer it to many pricier amps I've heard. In use, it sounds like it has muscle comparable to a 300 watt SS unit, but retains the euphonic tube blossom. After rolling the preamp tube, its bass can put many SS integrateds to shame. 
+1 to

After changing 12Ax7 with Telefuken and 12au7 with Brinmar NOS tube it is a very good amplifier to drive your speaker.
All you have to do is look at this impedance curve, with a 4ohm load and and negative 65 degrees of - phase angle at 3.5khz you have an amp busting load that would seem to be blow 2ohm!!! EPDR.
Then again at 5khz to 20khz it goes from 2ohm down to 1ohm.

No tube amp will get the best from these speakers, unless it has lots of global feedback is over 100watts and has an output transformer specifically designed to be 2ohms.

The best amp to get the very best out of these are solid state and ones that can "almost" double their wattage from 8ohm to 4ohms and then from 4 ohms to 2ohms.

Cheers George

Forgot to mention, also at 250hz there’s a 4ohm -60 degree phase angle load which will equate to around 2ohms EPDR ( equivalent peak dissipation resistance ), that will also be hard for a tube amp to drive.
This is the power region, which will give good "body" to lower/mids if driven correctly.

Cheers George
My advice is that you have to audition them in your own home. I did that just last night. I had my checkbook out prior to the test, fully convinced that I was going to be the proud owner of a PrimaLuna HP integrated amp. Also in the mix was a 400 watt Anthem STR integrated amp. 

Although I loved the stage presence of the PrimaLuna, unbelievably, it didn't have the power to run my hungry AR 910 TSW's. The sound could be phenomenal if I ran mono blocks, but I wasn't ready to shell out that kind of money. 

Next up was the Anthem. It had power in spades, but lacked the depth and warmth. 

I then re-auditioned my 1980's NAD 2600's and to my great surprise that system had the best over all sound. Richer, full and more stage presence than the Anthem, and better bass control than the PrimaLuna. 

The reason for the want to upgrade is that I have a intermittent static somewhere in the system. It has been to the repair place twice and no help. Suggestions??? 
@georgehifi brought up some good points. I didn’t bother to look up the real-world efficiency specs of these speakers.

If you want tube sound from a solid-state integrated, look into the newer Yamaha MOSFET-based amps. I’ve yet to encounter any others that come near as close to emulating the lush midrange and 3D-holographic soundstage of a tube amp - not even the tube/SS hybrids. I’ve compared my A-S1100 back-to-back with my CMII, which is fitted with NOS tubes, and the Yamaha manages at least 90% of the tube character, but with greater detail.

These integrateds are 2-ohm stable, run cool (at least, they do with 4-ohm nominal speakers), and have very large power supplies. They’re also dead-quiet in operation. A lightly-used or demo A-S3000 would probably fall within your budget.
Thank you for all your comments.  I am definitely a novice here, so please excuse these questions.

My listening position is about 8 feet from the speakers.  I never listen loudly, and I prefer chamber music jazz, blues, Nora Jones, Diana Krall, and similar.  So I definitely don't stress the speakers at all.  Knowing that, should I still be concerned about impedance levels?  The Primaluna has very large transformers.  They also say that Martin Logan used their equipment at shows a few years back.  The Summit X speakers have a sensitivity of  91 dB/2.83 volts/meter.

@georgehifi, that Yamaha looks like it might be a good option.

smills59 OP
@georgehifi, that Yamaha looks like it might be a good option.


I’d look at a s/h John Curl designed Parsound Halo Integrated Hint, or it’s successor the Parsound Halo Integrated Hint 6, both have ESS Sabre32 Reference DAC in it and phono stage.
These will drive the Summits fine, as they are bjt output and can give good current 45 amps into those nasty impedance’s of the Summits.

I wouldn’t bother the the Prima Luna on these speakers it will act like a tone control.

Cheers George
smills, There is a Martin Logan Owners website and forums:


Try your question there.  Here's a link to a search for tube amp:


The problem with tube amps is that MLs are very hard for an amp to drive and most tube amps can't put out the current (or voltage?) to drive them properly.  People use tube amps anyway and like the sound.  I wish I could give you an easy answer, but I can't.  
Not sure where you live but worth trying to find a dealer that either has your speakers in their shop or will let you home demo the amp.  I owned ML Monolith IIIx for 15 years, different from the Summit but similar in that the woofer is driven by a separate amp.  I used tubed amps on the panels and they have the same challenges as the Summit panels.  ARC D125 which had rated power of 110 watts per channel into 16 ohms (obviously way less into the panel) and then VAC PA160III monoblocs which I generally ran triode so 60-80 watts per side depending on output tube.  Both of these amps had more than enough power to drive the panels in a room that is 12x25 with a cathedral ceiling.  As for tube rolling, it's fun but can be distracting.  Since sold the MLs and went with a BAT VK3000SE integrated, tube input and SS output.  Works well with my current speakers and I just enjoy the music.  Have fun with the speakers, I do miss the air those panels can move!
I strongly suggest you reconsider whether you really must have a tube integrated amplifier. I suggest you instead consider either A) a used Innersound Electrostatic Amplifier (yes, there really was an amplifier with that name), B) a CODA amplifier, with similar capabilities or C) one of Roger Sanders Magnatech amplifiers (look for Sanders Sound Systems website). Any of these amplifiers will transform your experience with the Martin Logans. 
Here's what Harry Pearson wrote about the Innersound: The Absolute Sound, August 2000, Harry Pearson, reviewer
Editor's Choice: Mid-Year Edition

I'm not about to steal my own thunder here, I hope, by letting you in on a secret. InnerSound's new solid-state amplifier, designed specifically to drive the weird loads posed by electrostatic speakers, brings out a degree of performance - and loudness - I never expected to get from the Quads. With the assistance of a Carver subwoofer (rolled off above 40 Hz), I managed to play the entirety of the soundtrack from "Gladiator" without so much as a blown fuse and, in Music Room 2, with enough volume to replicate the movie's dramatic effect. Not only did I get greater dynamic range from the speaker, but seemingly wider frequency response as well.  

Sans woofer, the Quads went deeper into the bass (they held up into the 40 Hz region) than I'd heard. And at the other end of the spectrum, they reached higher more comfortably. I believe in an ordinary (no, not large) room, like No. 2, I could, with the exception of certain Telarc Kunzel potboilers, play almost any composition of musical interest at something approaching a concert-hall dynamic range, especially with the Carver sub thrown in for reinforcement of the bottom octave (below 40 Hz).

Given the peculiar nature of an electrostatic load, sez the well-written explanation (for a look-see, check out the website www.innersound.net/eslamp.htm), such an amp must produce not only voltage, but prodigious amounts of current as well. And check out the claim that the InnerSound "can deliver a staggering 135 amps of current with a combined power rating of 4500 watts per channel." And "it can drive loads below one ohm without damaging its output transistors." And "since it has so much voltage and current capability that it never clips, it doesn't exhibit any transistor sound." From my limited experience, thus far, with the system, I can attest to the seeming lack of any high-frequency clipping with the Quads, which gives the speaker a top-end airiness and openness I've never heard from them before.

I wish we had more electrostatics on hand to assess the befores and afters of the InnerSound mating. But we only have the Dutch Audiostatic panels, which we can't get the company to take back, and these are severely limited in terms of their excursive abilities, and even with the InnerSound, can't be played to anywhere near soul-satisfying loudness. Yep, they played better and with a stitch more volume and with some of the most perfectly "pure" sound you'll ever hear, but not on any music I'd care to live with, long haul. We also tried, in preliminary evaluations, the InnerSound with normal speakers, and found them neutral, wideband reproducers, minus most, if not all, solid state artifacts. Perhaps they are not - and only further listening will tell for sure - as exquisitely and honestly musical as the Danish Gamut amp, but running sans electrostats, they are lovely and musically satisfying. (Consider this a sneak preview and forgive the lack of detailed commentary - that will be coming.)

For some unknown reason, I’m focused on tubes. I called Kevin and Upscale Audio and he talked me into ordering a Dialogue HP Integrated which arrives Tuesday. he also offered me $2500 for my Plinius Hautonga integrated, which seems fair. He said at my listening levels and room size, the HP will be perfect.  I will try the PL HP for a few weeks before I decide. I do understand the impedance issue, but maybe at 65 I cant hear those frequencies anyway. :) I read on their website that Martin Logan used PL amps at a few shows a few years back, so maybe they will be what I want. If not, I’ll send it back and keep my Plinius and investigate something like the BAT VK3000SE or similar. I know the best option is probably to have a tube preamp and SS amp or mono blocks but not in my budget to go separates. I could get the PL preamp and use the Plinius amp by hooking up to the HT input until I can afford a better amp...Hmmm? What do you guys think about that?


Steve -
There's nothing wrong with tubes, but I commend to your attention Roger Sanders' excellent white paper on "tubes vs. solid state" which can be found on the sanders sound systems website. I found it to be very helpful in understanding why some folks insist on tubes while others prefer solid state.
All I can say is "WE TRIED" and the sales pitch won out.

Cheers George
Well, not completely.  I'm also going to order the Saunders ESL amp and use my Plinius as preamp while I compare the two.  I read the article that markusthenaimnut referred me to on their website and it was also very , convincing.  In that article he does say that the roll off at high frequencies is probably not noticeable (maybe more so for us older folks), and that power is very important.  He uses a large transformer, as does the PL.  It will be interesting to compare them both.  The Summitt x bass is powered, so the amp will only power the panels.  

I appreciate everyone's comments and suggestions.  This is a great hobby with many opinions, all of which are certainly valid.  That's what makes it fun!
Let us know  which amp you end up with.  Enjoy!
Sorry to say save your money, the Prima Luna will be a big failure on these, look at the black wavy line, that’s it’s deviation from the ideal flat line!!, and that’s it driving a "very easy simulated Kantor speaker load".
Your Summits will make it look 2 to 3 times worse!!.

Cheers George
Just spoke to Roger at Sanders.  I ordered the ESL Mk II since my Summits have powered bass units.  Really looking forward to the test next weekend.  Going to play all weekend long!  I will update with my thoughts as I play each one, and compare them to the Plinius.

Thanks everyone!
Should be an interesting shootout.

Technical specs/graphs may indicate absolutes, but it won't guarantee what your ears like.

The PL certainly will equal, if not best the Sanders in build quality/detail.

Just spoke to Roger at Sanders. I ordered the ESL Mk II

Sanders amps are a great anmps and match for his ESL's which is said are not as hard to drive as the Summits.

Read this owner with one, that keeps popping fuses with the ML Montis which are a little easier to drive compared to your Summits. 


Cheers George
Looking forward to the results.

I agree with tablejockey, graphs are meaningless if you don't like the sound. I've owned/auditioned my share of flat-measuring gear that sounded lifeless and uninspiring. 

Whichever amp has you jonesing to fire up your system each night is the one you should pick.
graphs are meaningless if you don’t like the sound

True, but all graphs and measurements are the basis for a good product They save a lot of time if you can understand them selecting the good from the bad. And can save you a lot of time knowing what will be compatible electronically with what, instead of wasting money and time on things that have no chance of being compatible.   
Knowing if they have a good Electronic Engineering design to start with, and are not just a poor design that’s someone has thrown together in a nice glitzy box without any regard for measurements or testing.

Cheers George
well, the Primaluna arrived and I set it up last night.  It needs about 100 hours to break it in, but of course I couldn't resist and started listening to music right away.  Mind you, the Plinius is a great Integrated, but man was I blown away by the imaging, sound, and control of my Summit X speakers.  It was absolutely beautiful.  As though my speakers came alive.  This is a HUGE step up for me.

George and others, what should I listen for that will show me the limitations of tubes with my speakers?  Is there specific music that will make this apparent to me?  I want to make sure I grasp the effect of the impedance shortfall of tubes before I listen to the Sanders.

I also received the Sanders ESL amp today.  Going this route will be more expensive because I would have to buy a preamp eventually.  I plan to use the Plinius as a preamp initially if this is the route I go.

I will listed to the Primaluna for about a week, then move to the Sanders.  Setup takes time to move back and forth, so I'll probably spend about a week or so with each and then make a decision.

Thanks everyone!
Congratulations. Your experience demonstrates the well known fact that there are many variables in play to predict an outcome with any degree of certainty. Instead of trying to find the shortcomings of the tube circuit, I think you should listen to familiar music and decide for yourself if you can hear anything missing. If anything, you “might” hear a slight roll-off at extreme high frequencies due to the inherent very low impedance of the ESL panel. Enjoy.
I have owned a Primaluns Dialouge 1 Intergrated in the past . It drove my KingSound King Electrostatic pretty good in a smaller room . My speakers should be harder to drive than you ML . I now own a Primaluna Premium HP amp . It works great with Electrostats . Have no idea what graph would indicate a poor match with stats . Enjoy the amp !
I have owned a Primaluns Dialouge 1 Intergrated
 It drove my KingSound King Electrostatic pretty good in a smaller room .
My speakers should be harder to drive than your ML .

No sorry it’s the other way around.

King sound

Cheers George
"George and others, what should I listen for that will show me the limitations of tubes with my speakers? Is there specific music that will make this apparent to me? I want to make sure I grasp the effect of the impedance shortfall of tubes before I listen to the Sanders."


It's great, having the experience/wisdom of SOME qualified members here, but trust your own ears. As mentioned earlier, white papers with graphs and specs certainly are necessary to establish a baseline "good," but it ain't gonna ensure what YOUR ears like.

Your favorite music will sound more convincing on one of the two. 

Happy listening!

"George and others, what should I listen for that will show me the limitations of tubes with my speakers?

As I said above a tube amp that’s a good design, but doing it hard into this load of the Summits.

The hard load is at:
At 5khz to 20khz may show a distant subdued high frequency.
And again at 3.5khz this may soften the presence area of the mids

You may "characterize" this as sweet and euphonic at first listen. Then after a while, even a week or two you may understand that it’s not what it should be, and that "the life" is missing from the music, detail, attack, presence and harmonic decay are waning.
Saying all this is with a tube amp that behaves itself in the top end.

But the Prima Luna has an odd peak up there, that says to me output transformers are ringing (oscillating).
This "could" counter to a degree the statements I make above but in a very crude way.

Cheers George
The amp now has about 50 hours of break in and I have listened now for about 15 hours.  I have to say, it's still amazing.  I'm pretty new at this, but I'm not hearing what George is referring to.  Not saying he is incorrect, just that I'm thoroughly enjoying this amp.  Break in for this is about 100 hours, so it should be in it's prime Monday night.

I have the Sanders and my old Plinius action as preamp ready to power up mid-week.  Question: should I plug in the Sanders to let it begin breaking in?  Do I have to have speakers attached if it's on?

Do I have to have speakers attached if it's on?
Solid state amps can be powered without any load on them.
But tube amps need to see a load, as there is the possibility without a load they can damage the output transformers if they go into oscillation.

Cheers George  
George, I hate to say it, but I'm really liking the PL HP integrated.  But you have me concerned about what I may be missing due to the impedance of my speakers.  I actually had a hearing test done recently and I can hear as slow as 133 HZ, and as high as 8400 Hz.  I'm not sure I'm reading the charts you referenced above correctly, but it appears the PL will work fine for these frequencies.  Am I reading this right?

Also, does the high power transformers of the PL help with this?  Would moving up power tubes to KT-120 help?

Sure appreciate the advice!!!
As I said before these are the two areas the PL would have trouble with

"The hard load points are at:
At 5khz to 20khz (a 2 octave spread) may show as distant subdued high frequency.
(But the Prima Luna has an odd peak up there, that says to me output transformers are ringing (oscillating).
This "could" counter to a degree that problem, but in a very crude way.)

And again at 3.5khz this may soften the presence area of the mids"

Cheers George
Glad to hear you like the Primaluna . Maybe now we can stop hearing how it is a mismatch with stats.. That would be nice . Getting into the kt150's will bring it up another level as well . 
smills, Would you give us a little more information about how the two amps compare on your Summit Xs?
tomcy6, I definitely will.  I've been snowed in, in Oregon for the past five days and unable to get home to hook up the Sanders ESL, but I'm heading there today and will spend the weekend with it.  It has lots of power, soit will be interesting to hear the difference.

maplegrovemusic, those KT150s are expensive!  Not sure I would put another $800 into the PL, but KT120s might be possible.  Any suggestions?  Or is it better to replace the two gain tubes fIrst?

This hobby is awesome!
"Not sure I would put another $800 into the PL, but KT120s might be possible. Any suggestions? Or is it better to replace the two gain tubes fIrst? "


Experimenting with the 2 inner gain tubes can fine tune the overall characteristics of whatever power tubes are in the amp.
The EL34’s have great mids and highs. You might hear the KT88,120 as more solid in the bass, but less refined mids. The KT150’s are reported to have the best of the EL34 mids and KT88’s low end.

I had a feeling you would be pleased with the performance of the ML’s/PL. I have a PL HP, and thought ML’s sound great thru it.

As mentioned earlier, your own ears are the best judge.

Still wondering what your impressions are of the Sanders, compared to the PL. I’m guessing the Sanders may subjectively, catch your attention in some areas, but wont sound as organic as the PL. That of course, is just my subjective opinion. You may prefer the Sanders.
Waiting to hear an update on this.  There have been a few similar threads recently on tubs vs SS for Martin Logan.  I am in the SS camp but admit I have not tried tubes with the MLs.  Also smills59, what speaker cables are you using?
Still listening to them, but here is a quick update:

No doubt this amp has the power and also is beautiful to listen to.  I would say that is is much more detailed and refined, bringing out every sound with more clarity than the PL.  There are no negatives to it, except for the price to me.  I started out looking for an integrated amp to replace my Plinius, but the Sanders would require a preamp, which is not in my budget right now.  I could make it work, but is the Sanders $2500 better than the PL?  Or do I like it that much more than the PL?  That's the question I'm trying to answer right now.

Primaluna Dialogue HP Integrated:
I do love the PL.  Like tablejocky above, I don't hear an impedance issue like georgehifi warns about above - and I do appreciate the warning.  I read more about the PL, and they claim that the power is ample for the ML Summit X because they are relatively efficient, and that their "massively overbuilt output transformers produce more than enough juice for" my speakers.  To me, they seem to be correct.  I would say that the PL has more punch than Sanders, the sound is more intense, while the Sanders is more laid back.  I'm pretty sold on the PL except for one element that is bugging me:

Listening to some tracks, there seems to be a "crackle" or overly expressed crackle when the artist uses a "T" as in Vermont, or a "C" in some pieces.  The Sanders did this too, but it was not as pronounced as in the PL.  It's not a BIG issue, but now I'm focused on it.  This happens in triode or linear modes, and really only when listening to SACD, which I do a lot.  It's almost as if the Sanders presented this less loud and in more detail, and the PL because they are tubes, can't do that.  The PL now has about 125 hours of operation, so should be fairly broken in.I don't think this is the impedance thing showing its ugly head, but perhaps someone else can offer an opinion.

Anyone have an opinion about this?



Perhaps. imperfection of the recording. Just as you may hear exaggerated "S"
in others?

I notice this occasionally in my system. I have confirmed it being the recording, by playing suspect record at a show/dealer, at it’s heard on the "$$$SYSTEM"

The best systems seem to only distract you because of everything else being so good.

I’ve heard plenty of speakers with the PL.
ML’s to me,sound amazing to me. Same goes for horns, also many of the
usual suspects talked about here. It’s really a personal preference, since the PL will mate with just about every speaker on the market.

Notice I didn’t write ALL.

If you keep the PL, fine tuning is achieved thru the inner gain tubes, power tubes and power cable. The power cable thing is yet another contentious subject which
starts wars here.

smills59...if you decide to go w/ the Sanders ESL, I am getting ready to sell a Parasound P3 pre.  It will definitely not bust your budget.
"T"  "C"  "S" are all sibilant sounds, as I said in a link  above the hard areas for an with the Summits are 5khz to 20khz (the sibilance area)  and again 3.5khz (presence area of the mids).
And the Prima Luna has a very odd high frequency boost in the top end which I believe to be output transformer oscillation which could very well exaggerate "sibilance".

Cheers George
Here is a review of the Summit X by Absolute Sound's Noel Keywood.  In the measured Performance section he states, " Valve amps with a 4 ohm output tap are a good choice..."

Here is a review of the PL Dialogue HP Integrated by Stereophile's Robert Deutsch.  He states, " Ever since I reviewed PrimaLuna's ProLogue Premium, for the June 2012 issue, it has been the model I would turn to when I wanted a moderately priced integrated amplifier to try with a new speaker. It never disappointed me, and never seemed outclassed, even when the speaker was the Martin Logan Montis ($10,000/pair)."   The Montis has an impedance of .5 ohom at 20khz.  And the HP version has more output transformers that the standard Premium model. 

Here is the Montis impedance chart:

Listening to the amp with my Summit X speakers, it is indeed very nice.  

The only problem you say your getting, is with "T" "C" "S" sounds

I have a friends with Summits, both series 1 and 2 "X" None of them experience any sibilance at all, in fact they are all very transparent and delicate in the highs, as are my own Monolith III’s with the newer Neolith panels. If I ever had to get rid of the huge Monoliths, the Summit’s are what I would get instead. the speaker is innocent, look at what driving them.

Here is what John Atkinson said about the strange HF peak which starts it's rise at 8khz in the measurements.
" Note the peak between 30 and 50kHz in fig.1. This peak was at its highest from both taps into 8 ohms and higher impedances, but disappeared when the load impedance was well below the nominal transformer-tap value. But with the tap matched to the load, this peak was associated with a significant amount of overshoot on a 1kHz squarewave (fig.2), though a 10kHz squarewave revealed that the consequent ringing was critically damped (fig.3), the amplifier maintaining its stability."

Cheers George
The guy still wants to argue a point he thinks a graph will prove.look at the words spoken by the reviewers george. 

They were John Atkinson words sunshine, he knows more in his little toe than you’ll ever know. https://forum.audiogon.com/posts/1701980
I decided to call Rogue Audio this morning and ask them about their Chronow Magnum III integrated, and how it would do with Summit X speakers.  The gentleman I talked with was very knowledgeable and helpful.  He said that they have a massive linear power supply and not to worry about impedance.  They have many customers with challenging speakers like the Summit X with impedances that go down to 1 ohm and have no issues.  The Magnum III weighs 55#.  The PL HP has more tubes and weighs 66#.  They both claim massive output transformers.  
I decided to call Rogue Audio this morning and ask them about their Chronow Magnum III integrated