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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
 
Pass Labs vs Atma-Sphere,  two thoroughbreds,  should be quite interesting. 
Charles 
bigboltz
55 posts
 
gdnrbob,

I'll get my MP-3 this week. I was wondering if yours has the phono stage and if so, what do you think? What others have you had for comparison?
atmasphere's avatar
atmasphere
11,793 posts
 
Where's a good source for Russian and Chinese 6AS7?  
We stock both and both are available on ebay.

Usually when we ship a set of amps we precondition the tubes first and then play them. In this case since the amp was used it came with its own tubes. So we tested them and played them. Its not quite the same...

At any rate, over the years we've been researching how the tubes fail. Most of them fail immediately after shipment or else when they reach the end of their service life (which can often be 10,000 hours or more). The 'after shipment' part is what concerns us most.

What we've been finding is that most of the tubes fail due to arc-over and subsequent damage to the internal elements. It appears that the mechanism is the cathode coating, which is very much like a paint applied to the cathode (but in this case improves the cathode's ability to emit electrons; this is true of all tubes). The cathode coating can flake apart just like old house paint and if the tube is conducting the tube can arc as the flakes are conductive. Since many of these tiny flakes can be loosened during shipment, if the tube is subsequently subjected to a prolonged heating cycle most of the flakes that are occurring can fall harmlessly to the bottom of the tube and then the tube can provide normal service after that.

This applies to any in-directly heated power tube and is nothing unique to the tube we use. IOW running the amp in Standby for a few hours is a good practice anytime its been shipped, assuming the amp has a Standby function.
gdnrbob
4,444 posts
 
@bigboltz, sorry I have no phono stageon my preamp. I found streaming music and am hooked.
ozzy's avatar
ozzy OP
7,459 posts
 

Well, though the Fed Ex truck broke down, I finally got the M-60’s.

A Couple of Questions:

The ember and red lights are way too bright compared to the tubes. I have put some electrical tape over them to dim them. Is there a more elegant way to do this?

The term putting the amp in standby is confusing. I assume this means both switches are on and full power is applied just nothing is playing?

Is the screw next to the center switch the DC offset Null adjustment?

almarg,

You were right about the need to rebalance the DEQX. The M-60’s do not have the same gain as the Pass Labs which caused a big difference in the main speakers and the JL-Audio Subs levels. I have increased the gain through the DEQX for the main speakers, and I will do a complete DEQX setup later.

I will hold my comments about sound quality until I have more time using them.

ozzy


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