2nd the Pass.
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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"
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
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.
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).
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):
This means nothing to me but I would like your thoughts on the MA2-Mk2.3 driving these lovely speakers.
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.
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 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.