Atma-Sphere MA2 Mk2.3 / Krell KSA 250 / Passlabs?

Good Evening Fellow Audio Heads!

I'm upgrading my amps (will be a big step up from my NAD S200) which I still love dearly.

The amps that I have the choice to purchase second hand are:

Atma-Sphere MA2 Mk2.3 - AUD $9000
Pass Labs X250.5 = AUD $6995
Krell KSA 250 = AUD $3000

Now the Krell and Atma-Sphere are class A. The Pass labs A/B. Front End will be a Atma-Sphere MP1 Mk3. Speakers are the unfriendly Dynaudio Confidence 5 (no intention of changing these lovely speakers)

Can you please advise your thoughts on what amp would sound best in this situation. Music Reggae / soul / female vocals. What amp listed is the best value? I would say either the Atma-Sphere or the Krell. I have only heard the Pass-Labs in person and that sounded nice and smooth. I like detail in my music.

Many thanks for all your help as it's impossible to do A/B comparisons.

I know first hand that the Atma-Sphere MP-1 preamp matches well with Pass Labs amplification. Since the Dyns are unfriendly, I'd suggest the Atma/Pass combo.

If the speakers were friendly...the answer would be obvious. However, I suspect you will very much like the Pass Labs on the Dyna speakers.

I have never heard Krell.
2nd the Pass.
If speakers are not OTL friendly, then Pass is the way to go.
Forget Krell and add Ayre to your list.

Better sonics and value.
The technical specifications of the Coincidence 5 seem quite suitable for the Atma-Sphere MA-2 amplifiers:

"phase correct, 6 dB per octave first-order crossover network"
Impedance, Nominal: 4 ohms
Impedance, (20-200 Hz): 4.6 - 9.2 ohms
Impedance, (200-20 kHz): 5.0 - 7.7 ohms

I must be missing something in a big way to not understand why you describe these speakers as "unfriendly." I'd encourage you to contact Ralph Karsten at Atma-Sphere to confirm, but on the surface it seems to me that the MA-2 amps would have no trouble driving these speakers. If that's indeed the case, the Atma-Sphere MA-2 would be a no-brainer choice for me.

Disclaimer: Atma-Sphere MA-2 owner
Rushton, do you think an impedance curve ranging from 4.6 to 9.2 ohms is

No agenda. Just wondering.

As I recall, most of the speakers recommended by Atma-Sphere have a
smaller spread between the low and high impedance spec, which would result
in a more balanced tonal presentation.

At least this is what I thought I had learned from Ralph. Maybe I need to go
back to class.

My Silverline Sonata III have a similar impedance curve to the Confidence 5,
and the Atma-Sphere M-60 amps did not match well. Perhaps the MA2 are
different than the M-60.
Tvad, I don't think that spread would phase an MA-2 in the slightest, provided the quoted phase swing is not a problem (on which Ralph could opine) and the curve is not too abrupt and steep.

The technical description on the web site shows the minimum impedance is above 4 ohms. My Eidolons have a minimum impedance of 3.6 and the MA-2s match exceptionally well with those speakers. The Sound Labs have a much wider spread of impedance values than quoted for the Coincidence, and, with some limited exceptions where Sound Lab went crazy low in the impedance curve to better match to ss amps, the MA-2 amps have always worked well on them.

Keep in mind that the larger number of tubes in the MA-2 significantly lowers their output impedance compared to an MA-1, let alone an M-60. You are exactly correct that both of these A-S models require more careful matching. But, the MA-2 is far more tolerant and Ralph has told me that they can drive most speakers on the market provided the minimum impedance doesn't go below the mid-3 ohms range and provided there aren't crazy steep dips and rises in the curve.

Perhaps Ralph will weigh in here and help us.
I think that Ralph is already on the road, headed for the Rocky Mountain Audio Fest.

I'm getting ready to leave myself and don't have time to try to find measurements online of the Dynaudio speakers. The MA-2 will have sufficient power, but I'd want to look at the impedance curve and frequency response curve of the speaker before voicing an opinion on that match-up.

Pass Labs and Ayre are in my opinion quite worthy contenders in solid state amplification.


>>Perhaps the MA2 are significantly different than the M-60.<<

Indeed they are.

The MA-2 will drive almost anything.
10-07-08: Audiokinesis
The MA-2 will have sufficient power, but I'd want to look at the impedance curve and frequency response curve of the speaker before voicing an opinion on that match-up.
Impedance match was my only concern as well.
FWIW, rumour has it that despite claims to the contrary, the Krell KSA 250 is probably more of a high bias class A/AB amp than a pure class A amp. It still might be the best value according to your list.
I overlooked the last line of the specs Rushton posted:

"Impedance, (200-20 kHz): 5.0 - 7.7 ohms"

That is very encouraging, and I think his assessment that the MA-2 would work fine is correct. Worst case scenario, I think the frequency response will deviate by less than 1 dB from what Dynaudio was getting with a solid state amp (presumably what they designed the speakers primarily for, but that smooth impedance curve makes me think there was a tube-lover involved).

The MA-2's for sure from what you've listed. I had a pair of MA-2's driving Soundlab A-1's for many happy years of listening and the Soundlabs are one of the hardest loads out there. Good luck! By the way the MP-1 with the MA-2's is a hard combo to beat at any price.
It would be nice to run the two Atmas pieces together if the tube amp could handle the load on the Dyns, but I do not see how that would work. Assuming this, you'll need a SS amp, either the Krell or Pass, not sure which would be better though.
I own the MA-2s and have owned Krells (KMA 160s) and have heard the KSA 250s: the AS MA-2s are, in my opinion in a different league. Furthermore, they easily drive my SP Tech Revelations, 4 ohm impedance, without any difficulty. I would grab the Atma-Spheres with both hands. You wont be sorry.
10-07-08: Springbok10
...they easily drive my SP Tech Revelations, 4 ohm impedance.

The pertinent (missing) information here is the impedance curve. Nominal impedance doesn't tell the complete story. Perhaps the Revelations have a flat impedance curve that does not vary substantially from the 4 ohm nominal specification.

It'd be hugely beneficial if manufacturers gave impedance curve specifications rather than only the nominal impedance spec. IMO, nominal impedance can be misleading and does not apply to speakers across the board.

I'm not questioning Springbok10's experience with his speakers and the Atma amps, but I'm using his speakers as an example to illustrate the point.
FWIW the MA-2s can handle a load like this easily. Customers have reported excellent results. Being a much larger amplifier than the M-60s they are not nearly so sensitive to load and there is a much longer list of speakers that they will play with ease.
10-07-08: Atmasphere
FWIW the MA-2s can handle a load like this easily.

What makes the MA2 able to handle larger impedance swings than the M-60 can handle, and how can a consumer evaluate this?
What makes the MA2 able to handle larger impedance swings than the M-60 can handle, and how can a consumer evaluate this?

More tubes= lower output impedance
m-60 4.1 ohms
ma2 1.75 ohms.

would be my guess.
The number of tubes!

How does the # of tubes affect the ability to match the impedance curve?

If it can drive the big Dynaudios I'm thinking it could also drive larger Ohms. I have not heard where there is a tube amp out there that is a good fit prior though.
>>How does the # of tubes affect the ability to match the impedance curve?<<

OTL amplifiers have no output transformer.
As Ralph has explained it to me (and I'm paraphrasing), the greater number of tubes in the MA-2 lowers the output impedance of the amp relative to an MA-1 or an M-60 (see Rwjp' post above). This lower output impedance allows the MA-2 to drive more easily a broader range of speakers (i.e., be less speaker sensitive) than many other OTLs.

One still needs to be cautious about the speaker's MINIMUM impedance (e.g., probably not less than the mid-3 ohms range) and still to seek speakers that have reasonably smooth impedance curves (no steep drops or spikes) without a lot of crazy phase shifts going on.

Ralph maintains the MA-2 can drive most speakers on the market, but there will always be some designs that simply won't be a good match. So, best to check.
"One still needs to be cautious about the speaker's MINIMUM impedance (e.g., probably not less than the mid-3 ohms range) and still to seek speakers that have reasonably smooth impedance curves (no steep drops or spikes) without a lot of crazy phase shifts going on. "

The Dyn Confidence 5's meet this criteria?

I suppose the only way to know for sure how it will sound would be to try it and compare if possible without taking a loss if things did not pan out.

I understand how a lower output impedance opens up more possibilities regarding speaker matches, but I still wonder how to determine anything reliably up front in lieu of more detailed impedance curve info for a particular pair of speaks.
If the Atma's can drive them fine - an awful lot of tubes though. I think you should take a look at the Pass XA-160s up for sale for less than $6,000 - I would choose the XA over X if and when money is not a consideration. 160 Class A watts should be enough, just not sure what problems the XA versus XA.5 (more current into lower impedances) might have with that impedance swing - seems like a good deal me though. I imagine Audiofeil would have some insight here.
Thanks everyone for the input.

This tech stuff has gone way above my head, but the phase shifts according to Dynaudio are as follows:

Impedance, Phase Shift (20-200 Hz):
-19.6º - +18.7º
Impedance, Phase Shift (200-20 kHz):
-5.1º - +15.1º
Impedance, HF (200 kHz):
5.4 ohms

This means nothing to me but I would like your thoughts on the MA2-Mk2.3 driving these lovely speakers.

Thanks again.

Che13, your best source of advice will be to call Ralph and talk to him about this match. Now that RMAF is over, you should be able to catch him via email or phone. His contact information is on the A-S web site.
I'm rooting that the Atmas amp works out.

Good luck!
Thanks All,

Ralph thinks they will drive them easily. I beleive him, just after other opinions before I down lay the $$$.

Thanks all for the input.

By the way looks like I will have to run them with my MP3 until the Australian dollar improves :(

Thanks all for the friendly advice.

Good luck Che13, when the Atma can drive a speaker, they are pretty hard amps to beat. I most recently had the CAT JL2 and Pass XA30.5, both wonderful amps, but I kept the Atma-spheres -- of course, my speakers are a great match for the M60s.
FWIW there is a general rule of thumb that you can follow regarding MA-2s and MA-1s. That is: if the speaker is known to work with tubes, it will be OK.

IMO there is a myth that a speaker has to be 'OTL friendly' (for example in the case of the MA-2, Manaplanars are 'OTL friendly') before any OTL can drive that speaker. IME what is needed is more like a 'tube friendly' speaker. see

for more information.

What you get from this is that a zero-feedback transformer-coupled tube amplifier, or a zero feedback **transistor** amplifier will have similar load requirements.
Well I got the Ma-2's and they EASILY drive the 2 ways about it. I also tried them them on Proac Response 8 Sigs (mini monitors) and they drive the C5 just as easily as a book shelf. Plenty of sound and all controled.

Ralph, that is good point made some time ago, it really isn't about being OTL friendly, but tube friendly - pretty much the same requirements. I get that now.
Che13, welcome to the family of happy Atma-Sphere MA-2 owners. I can't imagine living with any other amp in my system.
Anyone tried the MA 3 yet ?
For what it's worth, Ralph saved me over $5,000 by pointing out that the MP-1 and MA-2 are so well matched that he defied me to tell the difference between $100 Mogami Neglex i/cs and my very expensive Purist Dominus i/cs. I tried them and he was right. There was zero, zilch difference, so I sold the Dominus and am equally happy with the balanced Mogamis. You may want to try them. Obviously that does not apply to speaker cables. Just an FYI.
I use the same ICs, a bit cheaper than the Cardas I use with my other amps:) One really should take that into account with thinking about the price of the Atma-sphere gear. Rushton, I agree with you, I've not hear a better amp with my Merlins (very tube friendly).
I did the Mogami Neglex w/ Neutriks experiment too, using a 20ft run between my MP-1 and MA-1s. The Mogami yielded better than expected results though it wasn't long before a 5m pair of Shunyata Antares went back in place. The Mogami's bass was potent with more weight, though less tonal articulation. Around 1kHz on up, notes were softer and the overall presentation more diffuse than I cared for. But those are my ears. In the midrange and on the value scale, Mogami made a strong case for itself.
Jtimothya, you might want to try that experiment again while using a 600-ohm termination at the input of the amplifier. The MA-2 is equipped with a switch that allows you to set that termination if the preamp supports it (the MP-1 does).

If there is no termination you may still hear differences in the cables. They go away with the termination- that is what it is for. This is how the recording studios have done it in past decades and is why you run into so many recording engineers that tell you that 'cables don't make a difference'. Its not because they don't have the resolution to hear it, its because they use low impedance terminations with their equipment.