Recommended Speaker List for Atma-Sphere OTL Amplifiers.

OK, I am not sure how many times this has been disscused but the information is found all over the forum. I would possible love to compile a list here.

I personally own the Classic Audio Loudspeakers T1.5

I am now looking to build a second room with the M60 Mono Blocks and MP-3 Pre-amp.

Would love fellow audiogon memebers posting any feedback with speakers they have used with these Amazing OTL sounding Amplifiers.
Note on these amps, although I've never heard these amps I think I saw one as a prop in a Frankenstein movie…possibly one of the most retro designs out there…cool. Also Atmasphere the person posts smart stuff here frequently.
I played a pair of Zu Union speakers with my MA-1's/MP-3, the results were incredible. They came close to my Vandy Treo's.
I don't have the M-60's but wonder if a pair of Zero's would allow you to use them with the Treo's?
In any case, Ralph makes a heck of an amp/preamp.
I use M60s and an MP-3 in my system first with Audiokinesis Jazz Modules and now Quad ESL 57s. I’m getting a pair of Spendor 1/2E speakers to use with them as well.

Dealer disclaimer.

I've been designing speakers with Ralph's smaller amps (S-30 and M-60) very much in mind for years, but my speakers tend to be bigger than average (though usually not "T-1.5 big").  I do horn speakers that hopefully don't sound like horns, well at least not in the negative ways that the word "horn" can bring to mind.   

In a fairly compact speaker, you might consider High Emotion Audio and Omega Loudspeakers. 

At what they do well the Quad 57s are just magnificent.  If you decide to do a stacked pair, contact me for a tweak suggestion.

Best of luck in your quest,




I did consider your speakers. Ralph always speaks highly about you. The issue with me was I was looking for something more exotic. I am still searching and planning to fly into the USA to have a a listen to a few speakers and may visit you if you dont mind.

I have had a number of people listen to my Jazz Modules. One in particular who is pretty well known in the audio world mentioned that they sounded better than the German and other exotic horns he has heard. If you do visit Duke and hear his speakers I'm pretty sure you'll drop that exotic requirement. I only sold my Jazz Modules because my bi-amped ESL 57 set up with multiple woofers in a "swarm" array (ala Duke) gave me the benefit of what the ESL 57 does best without the bass limitations and resonance issues of those speakers.

Thank you very much, Clio09. I don’t mind my Jazz Modules being replaced by Quad 57s + swarm! Very nice combination.

Dragon, thank you for having considered my speakers.

Cosmetically they certainly are not exotic, nor do they use any particularly exotic technology in the drivers, aside from optional Beryllium diaphragms for the compression drivers. I now have access to a master woodworker who has built T-7s for John Wolff, so I can offer excellent cabinetry on a custom basis, but he is not cheap.

Speaking of which, have you considered the T-7? Field coil motor, wizzerless fullrange cone, beautiful tonal qualities, and magnificent cabinetry.

I don’t know whether this would be "exotic", perhaps merely "unorthodox", but some of my models deliberately approximate the acoustic effects of being in a significantly larger room, which imo has psychoacoustic benefits.

If you are serious about hearing what I do, I would like to put you in touch with a colleague of mine who a) has more of my designs on hand than I do; b) has a much better audition set-up than I do; and c) has contributed ideas which have significantly improved my designs.  I spoke with him just a few minutes ago and he'd enjoy it very much.   


I have the M60s and MP3 and use Vandersteen Quatros. Sounds incredible with no zeros needed.
I use a pair of John Wolf's T3.3 Classic Audio Loudspeakers  with the field coil option with my Novacron's. 
The Atma-Spheres are amazingly transparent with a huge sound stage. I would go with speakers capable of producing a huge sound stage and ones that are transparent. 

I have used the M60's and the MP-3 with the older model Wilson Benesch Curves. Great sound. There is a pair of Audiogon right now.

At the risk of stating the obvious, they should have a high, relatively flat impedence curve for the most part, although as others noted, they are reported to mate well with Quads.  Also Soundlabs and Magnapans, IIRC.  I have used them successfully with Merlins, Hornings, and now with a DIY pair of open baffles with field coil mid/tweet and conventional mid/low bass units.  From personal experience, if you have the room, they are fantastic with the Classic Audio speakers, being able to reproduce live SPL rock music in a very large room with the M60s..  If you want to get an opinion about how they mate with a particular speaker, you should ping Ralph (Atmasphere screen name), if he doesn't show up here on his own.  You will get an honest opinion with, IMO, no marketing hype. 
I am well aware of the smaller inconvenience of owning OTL gear but in my honest opinion for this level of quality in enjoyment I am more then willing to compromise. Once the match of the speaker and amplifier is complete all you experience is pure magical bliss!

The T1.5 Classic Audio Loudspeakers are excellent and magical theirs nothing like it. Its just flows with music in a emotional way that sparks your deepest feelings so easily, I feel like I'm transported somewhere else. 

The speakers are full field coil. These are a keeper I would never part with them. Mines are paired with the New Atma-Sphere Amplifiers "Nirvana". A Super Regulated OTL Amps LOL The best Atma has developed till date I guess.

The OTL amps have been a revelation. I was more in to SET and certain push pull class A design but never experience this form of lucid feeling from a sound system.

Its going to be hard to find a speaker that can perform like a Classic Audio Field coil but in a smaller and less expensive package and designed for smaller rooms.

I have been considering smaller horn speakers or Single wider-band drivers too. Just not settle down yet and need to go out and listen to some of the manufactures that are based in the EU.

My ultimate goal was to build a smaller system with another set of Atma-sphere gears this time with the MP-3/MA60. Once you go OTL you cant go back :-)  Everything else just sounds slower and less transparent. I cant seem to enjoy my previous gear (for second system) and thus had to sell some of them off.

Good suggestions here, thank you all.

I remember Ralph telling me he used Bud Fried's loudspeakers when he developed his amplifier, and I'm not sure there's a better match for either.  The series crossovers and true transmission line couples magically with the OTL.  Even after a couple of attempts at revival, sad to say the brand has faded into the vapor.

For what it's worth, though still owning several other speakers, including several Frieds, after hearing the Quad ESL57, which Bud brought to the USA, I've stopped thinking about loudspeakers.  No other brings as much reality
Dragon-vibe.....can you expand on your statement....I know very little about OTL

"I am well aware of the smaller inconvenience of owning OTL gear "
 I hope Ralph (atmasphere) responds. If not, you can always PM him.
I own a pair of MA-1's and have found them to be the most remarkable amps providing unmatched sonics as well as reliable, trouble free performance.
Go to his website, he has some good pages on his design.
As far as OTL inconvenience, there were earlier designs (Futterman, I believe), that were known to be problematic. Ralph's design improves upon this and makes his amps essentially bullet proof.
With my Atma-Sphere M-60 Mk 3.3 I ended up making my own DIY speakers. I stayed with 8ohm hi sensitivity drivers. The cabinets were purchased from Parts Express and are High Gloss, they look very nice.

I used Aurum Cantus G1 Ribbons and ScanSpeak drivers. My DIY external crossover boxes were made using Mundorf SGO classic caps, Path Audio resistors and Janzen inductors and the speakers were wired internally with Cerious Technologies Graphene Extreme wire.

Recently, I thought that I should upgrade my amps and then speakers. I don't know why just had the itch I guess.

So, in the last few weeks I have heard Magnapan 3.7i's with Rogue Audio amps, (very disappointing IMHO) Focal Kantra 2's with Nagra $80,000 amps and today the Goldenear Reference speakers with some $$$ French amps.

To my ears, none of these amps/speakers combinations sounded as good as my Atma-Sphere M-60 3.3 with my DIY speakers.

Bigger and more expensive is not always better...

I agree with the praise for OTL, and Atma-Sphere. I own a pair of MA-1s and have not looked back. I tried with different speakers, and even if 8 ohm speakers sounded OK, the full benefit of the amps was evident only when I got Audiokinesis Dream Maker speakers (16 ohm). Very much recommended, if you have room for them.
How does Tannoy & atmasphere match up?  Especially in the bass department......
my Fall project may be a set of the Monobloc kits to run the Vandersteen Treo at the condo for coastal winter heat !!!!!

Proac3.8 or any other proac before they switched to a 4 ohm load,which they recently did, why I don’t know, but the earlier proactive speakers are madgic with the atma spheres!

The Eminent Technology LFT-8b is very well suited for the M60 in all regards save one, that of sensitivity/efficiency. The LFT is rather insensitive/inefficient (rated at 83-4 dB), so in a large room at high listening levels the M60 may not provide enough power to the speaker. But planars are known to sound louder than equivalently-rated dynamics.

In all other regards the LFT-8b is an excellent match for the M60. It presents an almost purely resistive 8 ohm load to the amp, the midrange/tweeter panel itself an 11 ohm load. Put a solid state amp on the dynamic woofer (180Hz down), the M60 on the m/t panel, and live happily ever after! Ralph Karsten says he has M60 owners successfully using the amp with the LFT-8b.

Contact Emerald Physics (sold direct) o see who has their 2.8s in your area

Very easy load   

2.8s received an Absolute Sound award

MSRP $9998, but they run specials,


I have their KCIIs with upgrades similar to their Pro model. One of the very best speakers I've owned, including Genesis Vs, Accoustat 2 + 2s, Nearfield Pipedreams, Magnepan 3.5Rs, Usher 6371s...

KCIIs < $2500     
I think that the impedance curve is more important than the sensitivity. The DeVore 0/96s are a superb match and this comment is based on hours of actual listening experience. A friend and myself built a pair of M60s and have never heard a better amp on the DeVores. We compared the M60s to VAC, Audio Note and Mastersound. 
Vandersteen 5 series, Quatro series, Treo's with Sub 3s  have an easy impedance for most any tube or OTL design.
The unique 100  HZ high pass unloads the heavy lifting for the main amp and allows the speakers internal solid state amp to take care of the bass frequencies, in room compensation adjustments takes out your room / placement issues dramatically improving transparency and clarity of the whole system.
 Vandersteen dealer
..and to pile on a bit, the Vandersteen way preserves the transfer function of the main amplifier, which is part of the point of this thread....

How does Tannoy & atmasphere match up? Especially in the bass department......
Very well is the short answer.
I have used the MA-1s amp with the Vandersteen Treos without subs and they sound great!
Dragon, it all depends on how and what you like to listen to. If you are a rocker and like to play loud than an efficient horn system like those mentioned above would be the way to go. But if you tend to listen to more acoustic instruments, jazz and classical at moderate levels then the mid range purity of a full range ESL would be best. Something like the Sound Labs 545. I am not crazy about ESL-57s because they are just too fragile and in all reality the Sound Labs is a much better all round speaker. It is much better in the mid bass and it's high frequency dispersion is much better as well as being tough as nails. Ralph also insists they match up with his amplifiers beautifully. The 545s are also a lot smaller than the big boys. I believe they are narrower and taller than the ESL-57s and would take up less floor space. They are less sensitive than a horn system and will not go as loud but still 8 watts will get you to 95 dB, a comfortably loud volume and theoretically you could hit 102 db with a 60 Watt amp, louder than most of us listen.
I’m a little late to this thread sorry.

 I’ve come across some older M60 mk2 amps a friends has at his audio shop the price is right so I’m seriously looking at them. Question is will they drive high efficiency horns like the current klipsch heritage line. I’ve currently been trying  some modded heresy 3s with the thought to move to the new Heresy 4, Cornwall 4. Or La Scala in the near future. 
I’m very new too OTL Amps but am quite versed in SET etc. I’m coming from SET 300b Amp. So tubes are not new just OTL. 
Also I read the amps can be run with less tubes at lower power is this correct? 
I am considering a trip to the shop for and update-recap-etc as required.  Probably new tubes as well as the ones in it are unknowns and miss matched. I suspect the previous owner pulled his good tubes when he traded it. 
Thanks I’m advance 

I believe you should have no problems running the M60s with the Klipsch line, if you are coming from the SET world where typically you manage less power than what this OTL can offer you should be fine. Yes you could run the amp removing tubes but I personally wouldn't, others have said and I have my subjective feeling and like many other cases that running with full capabilities will provide better sound at lower volumes with high efficient speakers than with same settings and tubes removed. I have MA-1s BTW and I run all 28 tubes all the time with high efficient speakers, the power tubes in the Atmas are very inexpensive and they last a long time because the way their circuit operates, the mk3 revision improves this as well if I'm not mistaken so it might be worth sending the amps to Ralph if you have the financial means of course to check them and reactivate the warranty and upgrade.

Which preamp are you planning on using?
How big is your room and how loud you listen to music?

My concern with Klipsch speakers would be possible dips in the impedance curves of each speaker. Efficiency is only part of the issue.

When we compared the M-60s to several SETs the results were significant. The M-60s were like water while the SETs like chocolate milk. The other thing that we found is that even the 20 watt parallel single ended amp ran out of steam very quickly and started to distort in a very obvious, albeit pleasant way. 

I personally was thinking mainly on impedance more than in sensitivity terms, you are correct impedance is big part of it, most of klipsch is usually 8 ohm nominal and above 93 sensitivity, I have P37f as secondary speakers and very easy to drive with the Atmas, mains are AudioKinesis which are 95 dB and 10 ohms.Anyway, could you recommend me an amp like bourbon? Not much into chocolate milk.
Joking aside, the preamp used could have a lot to do with your SET comparison but I have to ask which type 300b?

Actually we used an Audio Note 300B, an Audio Note Kit 300B parallel single ended, a Mastersound 32B (crushed the other SETs). VAC Phi 200 and Atmasphere M-60s. Preamps used were Essence Jasper, CAT, Audio Note, Thor Audio and an older VTL. The preamps universally sang the praises of the M-60s. To understand the inherent limitations of SETs you need to compare them with an OTL. You will instantly hear the limitations of the transformers, the inherent problems with the lower power and the quick clipping which sounds like the amp is producing power but it is really a bunch of gunk. The push-pull VAC did very well , but lacked the texture of the Mastersound and was completely outclassed in every way by the Atmasphere. Most of the listening was done on a pair of DeVore 0/96s which is a very easy OTL friendly load. 
Thank you, I asked because I can't comment on the 300B SET as I haven't had a chance to compare one on my system, I have a PSET in which I tried many different tubes combinations (not 300B) and when it starts clipping and distorting is not very pleasant, still better than a SS but obviously distorted. The Atmas on the other hand (and this is not apples to apples as I have MA-1s) are wonderful driving 10 ohm speakers.
If you are listening to low volume the PSET is pretty good.
thanks guys for answering in this older thread. 

luisma31 thank you for the tube quantity information. 

I believe the M60 Mk2’s i’m looking at have the mk3 upgrade already if not I’ll send them to Atmos for the upgrade. 

AudioTroy thanks for that quick comparison that makes sense to me after owning the Finale Audios 300b’s great amps, but they never left me with the feeling they were doing the speakers justice I had at the time (living voice speakers only 94db, I've since been experimenting with horns). 

I've owned and enjoyed a few ProAc models over the years as well so nice to know they are a good match. (older ones anyway). 

thanks all I've texted my friend and going ahead with the buy. consider me M60's owner. 

Now to decide if to keep my preamp or move to a balanced Pre. I have a completely redon Sansui CA 2000 that has every cap -diode - and various other things replaced. Its surprisingly good sounding now.  Its actually down right amazing now, with so much flexibility I forgot how much I missed some of the things old preamps had). 

But a simple Schiit Freya + may satisfy the balanced proposition on the short term as a reasonable cost alternative. I also have a balanced Schiit multi bit DAC Gumbi and Gold Note PH10 phono stage that's also balanced that may move me to a whole balanced system, well mostly my tuner isn't balanced. 

Cheers all

Keep in mind the m60 have 8 power tubes vs 14 on the ma1 so you are accounting for 60 percent or so of the ma1 power, which is IMO sufficient
Ask Ralph Karsten of atmasphere about your speakers, pre etc he is very helpful even on used equipment, my opinion is irrelevant here, if you like to listen to music at high volume the m60 might not be enough
Schiit products are simply not in the same league as your M 60s. Kind of like putting low octane in a performance car. I think you would be better served by Ralph's entry level preamp (only single ended) than anything made by Schiit.
I somewhat agree with the above comment, except to add that the Schiit Freya is certainly in a class by itself as an amazingly engineered and excellent sounding truly balanced tube (or not, your choice) preamp with more features and flexibility than anything out there. USA made and costing around 900 bucks. Designed by brilliant engineers. Classy.
Question is will they drive high efficiency horns like the current klipsch heritage line. I’ve currently been trying  some modded heresy 3s with the thought to move to the new Heresy 4, Cornwall 4. Or La Scala in the near future.

We've been showing with Classic Audio Loudspeakers for decades and they are pretty efficient; depending on the model 97dB to 105dB. The M-60s work great on most horn speakers and is probably the goto amp in that regard.Klipsch is no worries.

The amps can be updated with full warranty reactivation.

@wolf_garcia while the Shiit is certainly balanced, it doesn't support the balanced standard (like most studio and stage equipment does). Support of the balanced line standard is rare in high end audio. There are balanced tube preamps that do.
it doesn’t support the balanced standard
Hi Ralph, good to see you chimed in.
Just for education purposes when you say it doesn’t support the standard do you mean "it is not differential", aka duplicate stages + and -?Hope you are doing well

Whether the Freya supports the ’balanced line standard’ is kind of besides the point to me. I’ve had the Freya+ for about 4 months now, and it is so above the mid-fi equipment I’ve been using that it really is in a league by itself when you consider it’s lowly price.

Detail, imaging and musicality is better than anything I’ve experienced with my Totem Hawks. Yes, I’m sure there are preamps that are slightly better(we are way beyond the point of diminishing returns here), but you’re probably spending $3500 and up for them.

And if one wants that very last 3-4% and can afford the very top of the line, then go for it. For the rest of us trying to get as much bang for buck as we can, Schiit Audio has no equal at this point.  At least WRT their multibit dacs, the Freya+ and the Aegir Class A amp.
I’ve bought the M60s. It’s a rather different step then I was originally going to go but the opportunity to have some truly excellent amps was hard to pass by. I’m not a rich man being a retired military career man. I had originally got out of 300b amps they just didn’t do it for me that little power. I was going to play with vintage for a bit until I decided where I was going. The Atmos amps sort of fell into my lap so it’s changed my path somewhat.  
I only brought up the Freya as I thought it was a fully balanced peramp that could be a starting point. But I do have a totally rebuilt vintage Sansui CA 2000 I was planing for a vintage set up that’s actually quite good sounding but only single ended.

Obviously it’s a vintage preamp and not to the level of Ralph’s own preamps. But after spending money I didn’t really have on amps I’m not in a position right now to buy a preamp until I sell off the vintage gear I have. And let’s be honest my speakers are not going to show what they are capable of anyway at this point until I upgrade. 
Thanks for the advice my friends. Looks like my audio journey has taken a turn for the better.  I’ll be picking up the amps in a week or two once my friend reopens his shop.  Closed for cov19 at the moment.  From there I’ll buy a new tube set as they are questionable and mismatched brands. Actually any recommendations for tubes for that work well in the Atmos OTL would be helpful. 
Ralph thanks for the support. I believe these amps were sent to you in 2015 for the mark 3 update. I’ll check once I get them and if not arrange to have them sent to you. I can see one amps serial number in my picture it’s 236 I can’t make out the other amps. 
Exciting times in audio. 
Cheers my friends 

Glen  Newdick 

I’m sure you will enjoy the amps Glen, I believe you could use the Sansui with no issues except you will need to short pins 1 & 3 per the Atma manual (see below)
"If you use the RCA input connector, make sure a shorting jumper is installed between pins 1 & 3 on the XLR connector else a buzz may result"
The most important tubes for the sound are the driver tubes the 6SN7’s, I know you are not buying stock but the stock tubes that comes with the Atmas out of the box usually chinese Shuguang Brown Base 6SN7s are very decent, that said you could improve with NOS tubes or even some Chinese Boutique tubes, if you need more on the subject I can provide more details and I’m sure others will do as well.The power tubes "sonically" won’t provide much, not many options either, the Russian 6AS7G Svetlana’s 6H13C are very very stable, sound is magnificent and to me these are the tubes to go on this amps as far as power tubes is concerned. The NOS RCA’s 6AS7G could provide a little more power at the expense of reliability and headaches, and money too. I went that route and turned back, my MA-1’s do fine with the power offered by the Russian power tube the way Ralph designed it. If you need more details I will be happy to provide such but my advise if your speakers do fine with the Russian tubes don’t change them, I experience one of the RCA tubes heavy arcing, smoke came out of the amp (or tube) and it is very common with these tubes, IMO reliability is an issue. DO NOT USE 6AS7GA on that amp, the tube IS NOT COMPATIBLE, stay away from GE’s 6AS7G, you will run into problems.Let us know what tubes comes with the amp and I’m sure Ralph or someone else or myself will be able to help.Maybe I missed it but your speakers are sensitivity? and nominal impedance?
Just for education purposes when you say it doesn’t support the standard do you mean "it is not differential", aka duplicate stages + and -?
No- the balanced standard requires that the output not reference ground and otherwise is able to drive a low impedance. That is how cable immunity occurs- otherwise you’d have to pick your cables to get things to sound right and longer cables are out of the question.

Glen, if updated in 2015 then its a Mk 3.2 or possibly early Mk3.3; either way a good find! The plate on the front states the amp’s actual identity; the number after the dot is stamped in so will be a 2 or 3.
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