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

ozzy

jond, bigboltz,

I have tried several times to post but each time I’ll get almost done, then I edit (on Audiogon) and I lose the entire post! What a pain! So, I am using Word and the old cut and paste method.

Anyway, I have had several issues, some related to the Atma-Sphere and some not.

First off, as Almarg alluded to several replies back that with using the DEQX preamp settings that were adjusted to the Pass Labs amps output / impedances there would be an imbalance between the main and the subs. He was right and I set about to re-DEQX with the Atma-Spheres. If you have never used a DEQX unit it can be quite laborious to complete the process.

Then, the next day there was no sound from one channel. All the tubes were lit but no sound whatsoever. I re-checked all of my connections and could find no reason. I thought the worse that something failed internally in the M-60. I called Atma-Sphere and Ralph answered the phone. He suggested that I check the main output fuse. I thought, why, all the tubes are lit? But, when I pulled out the fuse it was blown. Replacing it brought back the sound in that channel. A day later while trying to use the M60 with my home theater, again no sound from the other channel, and that was also a blown fuse. Ralph, suggested that it was probably caused by one of the tubes arching since they have been moved around a lot during shipping and some flaking internal in the tube must have occurred. I concur somewhat, but I also did try to play the M60 extremely loud to test its limits.

I had a problem related to my Grand Prix amp stands and with my external crossover boxes. I used a short jumper to connect from the M-60’s to the crossover. When playing music the sound was dull. I thought for sure it was due to the Atma-Spheres. What I found was that the stiff 12 gauge silver/copper wire used as the jumper was actually under the shelf and was supporting the Grand Prix shelf thus preventing the shelf from floating on their own cushy pads.

To add to this, HiFidelity sent me one of their new Reveal XLR interconnects for trial and that has been another variable. Placing this interconnect behind my main component rack near the bottom, underneath other connections, was another real pain! The XLR ends are bulky and the cables are not flexible. As much as others are singing the praises of these interconnects I found them dull and limited in the frequency extremes. So, I tried to DEQX again with these cables and I just couldn’t get the sound right. So, I removed the Reveals to eliminate that variable and went back to re-setting the DEQX.

To make a long story short, my initial thought on the Atma-Sphere M-60’s is that they have real potential. But I notice that I don’t have a real good center image. This could mean they have a wider soundstage and the need for speaker reposition including toe in / out. So, I really do think it is too early to critique much more until I put more time on the M-60’s.

ozzy

Sorry to hear of your posting and other troubles ozzy and thanks for the update. Obviously you've put together a very complicated system there with many moving parts. I am guessing it would take substantial time and tinkering to get it sounding the way you want after dropping something as monumental as new amps into the mix. Not to mention you said the speakers themselves are recently completed and probably need some further running in time. So good point no need to critique now just take your time to get it all sounding right and remember it's a marathon not a sprint, you'll get there eventually!
+1 to Jon's wise counsel.

Ozzy, regarding the DEQX calibrations, to be sure it's clear I was envisioning that in addition to the effect of the amp change on the balance between the main speakers and the subs, the DEQX measurements (and the resulting calibrations/corrections) of the DIY mains themselves might change.  The reason being differences in impedance interactions between the mains and the very different output impedance of the M-60 vs. the Pass amp.

It sounds, though, like you're intending to re-do the entire DEQX measurement & calibration/correction process, which of course would address this.

Continued best of luck.

-- Al
 

Just found out why the center image was missing. I had a wire reversed on one of the jumpers to my external crossover. I must have done it while repositioning it on the amp stand. It did sound like it was out of phase.

I just posted some pictures of the amps and the external crossover on my systems page.

ozzy

Ozzy

Ive had my M60s for about 7 months. I bought them used and they came with a ton of the Chinese power tubes. The seller didnt indicate which ones were good or not. So it took and evening of swapping ( and a box of fuses) to get them up and running and holding the DC offset.  Since then, I've had 2 tubes fail. Each took out the fuse by the power cord.  Otherwise, they have been rock solid. I play them at least a few hours each evening and sometimes all weekend long.  Dont get discouraged.   I plan on re-tubing with the Russian variety soon.  

Soundwise, I swapped them out with a pair of Quicksilver monos( which are great amps in their own right) and it was quickly apparent how special they really are.  The Quickies seemed slow and veiled by comparison.