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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.

Cheers
Che
che13
mapman's avatar
mapman
22,811 posts
 
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.
rushton's avatar
rushton
2,445 posts
 
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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audiofeil
4,011 posts
 
>>How does the # of tubes affect the ability to match the impedance curve?<<

OTL amplifiers have no output transformer.
mapman's avatar
mapman
22,811 posts
 
"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.
pubul57
3,712 posts
 
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.
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