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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
gdnrbob
4,444 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
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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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ozzy OP
7,466 posts
 

gdnrbob, Al,

Thanks for the additional information.

Looking at my Pass Labs X350.5 specifications, it  lists power consumption at 600 watts temperature 53C.

ozzy.

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almarg
9,670 posts
 
Hi Ozzy,

I wouldn’t infer too much from that 600 watt number. The amp only operates in class A up to "40 watts peak," and beyond that output power level its AC draw will presumably vary with the dynamics of the music. Also, given the amp’s power ratings of 350 watts/channel into 8 ohms (700 watts total output) and 700 watts/channel into 4 ohms (1400 watts total output), obviously it would be drawing considerably more than 600 watts from the wall outlet when supplying anything approaching its rated output to the speakers.  (It can’t put out more power than it takes in, or anything even close to what it takes in given that it is not class D).

Given your earlier mention that your use of the amp has been such that it has rarely if ever left class A, FWIW my rough guess is that the amp has probably been introducing something like 300 to 400 watts into the room.

Best regards,
-- Al

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almarg
9,670 posts
 
BTW, Ozzie, I suspect that the X350.5 spec of "40 watts peak" for the point at which it leaves class A operation is equivalent to only 20 watts based on the usual conventions for defining amplifier power (corresponding to volts x amps with each defined on an "RMS" (root-mean-square) basis, rather than a peak basis).

So you’ve probably been using very little of that amp’s power capability.

Regards,
-- Al

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