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

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
http://www.dynaudiousa.com/products/archive/conf5/conf5spec.htm

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

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.
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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.
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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.

Che13, welcome to the family of happy Atma-Sphere MA-2 owners. I can't imagine living with any other amp in my system.
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