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Amps Atma-Sphere M-60 Mono blocks OTL design

I just purchased a used OTL Atma-Sphere M-60 mono blocks that I have sent to Atma-Sphere to be upgraded to the current model 3.3 and I also added the option of a higher quality power supply and V caps.

I have sold my old trusted Eggleston Andra 2’s speakers and have built some monitors using Aurum Cantus ribbons (102db) and Aurum Cantus midwoofers (90db) that are both rated as 8 ohm nominal. I have a DEQX Premate and will be crossing over to (2) JL Audio F-113 subs at 80hz.

Currently I am using a solid state high power stereo amp (Pass Labs) that I used with the Andra 2’s.

The Atma-Sphere M-60 is rated at 60 watts class A and is said to work better with higher impedance loads.

It will probably be a few weeks until I get the M-60 and was hoping someone could provide opinions of what to expect.

I listen to late 60 early 70’s classic rock music mostly. Sometimes loud.

ozzy

128x128ozzy
charles1dad's avatar
charles1dad
10,250 posts
 
Ozzy,
Believe me I understand.  These two amplifiers are of such different design and topology and I'm always very interested as to what someone hears in comparison. 
Charles 
atmasphere's avatar
atmasphere
11,807 posts
 
I do not think the ZEROs will be useful on this speaker.

The ZEROs should always be regarded as a problem solver (and for any amplifier). The problem is that the amp sounds worse without them, in a nutshell. If the amp sounds better without them then it should be a no-brainer that you don't need them.

M-60s do quite well on an 8 ohm load- the only issue I question is whether 60 watts is enough power, but since this system also employs a subwoofer and crossover, I don't expect that to be an issue.
ozzy's avatar
ozzy OP
7,467 posts
 

atmasphere,

Thanks for the comments. My Pass Labs amp is rated at 350 watts A/B rms per channel but I think it only puts out 30 watts in class A. Supposedly, once the meter starts to move it is leaving class A for class B.

With my present DIY speakers, the needle does not budge, so I'm thinking I may be only using less than 30 watts.

ozzy

gdnrbob
4,445 posts
 
@ozzy 
The Atma-Sphere amps do get hot. In fact, they raise the temperature about a few degrees 2 feet away (I have to relocate my thermostat to the opposite side of the wall now). Though I have opted to mount them on the wall rather than a rack, so they get lots of air circulation.
Do they warm up the room, not really, but it doesn't get cold as fast as it used to.
Bob
almarg's avatar
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almarg
9,670 posts
 
The M-60 is spec’d as consuming 300 watts per monoblock, and since it operates in class A it will draw that amount of AC power all the time (when it is being operated, of course). And it will convert all of that power into heat, except for the amount of power it sends to the speakers, nearly all of which will be converted into heat by the speakers anyway.

So assuming the spec is reasonably accurate, which I’d expect since it is one of Ralph’s products, the amount of heat introduced into the room by the two amps will correspond to 600 watts. About the same as the heat that would be introduced into the room by six 100 watt incandescent light bulbs.

Best regards,
-- Al

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