Amps Atma-Sphere M-60 Mono blocks OTL design

It's been quite a while since I've been on the 'gon and even longer since I've posted anything.  Hello Charles, hello Ralph. Hope all is well with you and yours?

Seems like I purchased my MP-1 and MA-1 Mk 3's not long after SoundStage did a review of them in 2007. Gee, has it been that long? After owning CJ, VTL, CAT and a gaggle of other highly regarded "audiophile approved" offerings, I rolled the dice and went with something a bit different; OTL's.  Actually, the MP-1 isn't an OTL but it is a revelation compared to what I'd owned previously.

I actually purchased the MP-1 first. I really like Ken Stevens and have owned many of his preamps over the years but honestly, brand new out of the box, the MP-1 was in a different league than my CAT Ultimate Mk 2. Immediately, the music was more relaxed, smoother and more refined. Transparency and detail were off the charts yet not in your face like some audiophile gear. A slight edge to the sound that I had suspected all along was revealed by the MP-1 and was gone.

Enough blather, bottom line, the MP-1 was so good, I had to go with the MA-1s. I also went with all upgrades in both components except for the "power supply boost" which it seems like Ralph said wasn't necessary with my set-up.

Like others in this post, my speakers are DIY with separate satellites powered by the MA-1's and subs that are self powered using some really nice Rythmik Class A/B amps. I mention this because anyone with such a set-up should consider a second pair of outputs on your line stage; one for your amp/amps, the other for your subs.

Ten years or so later, no regrets. Matter of fact, last Saturday night my system sounded so good, I didn't get to bed til 4:00 am. Bet you haven't done that in a while Charles?

As Ralph explained, a short break-in of the 6AS7 power tube is the way to go and will extend life and reliability. When mine first arrived, I do recall one died early on but Ralph had included a few extras so no problem. Years later, they're still operating perfectly. Ditto for the MP-1. 

Tube rolling, don't get me started. I'm of the opinion, the larger 6SN7 type tube is far superior for audio than the miniatures like  6922/6DJ8's or 12AX7. I know Ralph uses 12AT7's in the phono but a different application than a line stage or driver in an amp. 

I've accumulated so many Telefunkens, Tungsols(1940's/50's) and other beauties from the past, I shudder to think what I've got tied up in tubes. Many of the oldies like the RCA red base 5962 can last 10,000 hours or more. Not so with the mediocre stuff coming from Asia and Russia. Sound quality, no comparison. Like all manufacturers, Ralph has to use  what's readily available but after a good break-in, I'd experiment. 

I notice with concern, the MP-1 now uses only two 6SN7's per side instead of five. Hopefully we're not losing any of the good things valves bring to the table. Besides lower noise, what's your thinking Ralph? Cheaper to re-tube? Just kidding! Hey, what about tube rolling? Have all my NOS jewels suddenly become worthless?

 A pair of MA-1's with 14 power tubes per amp, 28 glorious tubes glowing in my dimly lit great room and I really don't notice the heat. Actually, nicer than a fire place and cheaper if you consider what some people spend on good hard wood to burn.

I barely notice those red and amber lights either. Must be all the glowing 6AS7's. See, if you'd gotten the MA-1's instead of the M-60's, you wouldn't have a problem. Just kidding, we're all on a budget.

I really shouldn't have read this thread. I probably won't sleep well tonight as I toss and turn thinking about "upgrading" to 3.3's. 

Ok Ralph, after all this high praise,  I expect some special consideration when I call.

Finally, read the manual. This isn't rocket science. First, toggle up the amber side. Let them warm up five minutes. Then you toggle up the red side. Wait a few more minutes then crank it up. DC offset, I adjusted mine when I first got them, about 10 years ago, and haven't touched them since. I suppose if I ever have to replace a tube I'll check offset and that's about it. Not so complicated!

Well, time for bed.  Live long and prosper y'all.

Hi Bob (rfogel8),
It’s good to see your post and I’m glad to know you and your family are doing well, life is precious. I can’t say that I am up until 4 am but I still listen to music pretty much the same as always. Roughly 3 to 4 hours (sometimes longer) 4 or 5 days a week.

I still very fondly recall my SET amplifier with your easily driven DIY speakers and your MP-1 preamplifier, it was really a fun and memorable evening, natural, engaging and relaxed. Wow, the years fly by 😊. I am happy that you are finding the time to enjoy your wonderful system. Music is good stuff to spend time with and appreciating its charms. 
Charles

I notice with concern, the MP-1 now uses only two 6SN7's per side instead of five. Hopefully we're not losing any of the good things valves bring to the table. Besides lower noise, what's your thinking Ralph? Cheaper to re-tube? Just kidding! Hey, what about tube rolling? Have all my NOS jewels suddenly become worthless?

Ha! Actually the MP-1 uses three 6SN7s per channel. In the Mk3.3 version, prior to its release we had spent two years working on a Constant Current Source (CCS) circuit that could outperform the one in the earlier preamps (and amps). In the amps the old CCS drifted about 17 parts per million over an AC input voltage range from 100V to 126V. This in turn assured that the voltage amplifier performance stayed the same over the same range. In the preamp the same circuit was used but the preamp has severely regulated supplies so it was a bit more immune. At any rate, the new CCS is performing at about an order of magnitude greater performance so we were able to improve the differential effect in the voltage amplifiers of the amps and preamps; in the case of the MP-1 this meant that two 6SN7s got eliminated in each channel as they were CCS circuits. But the actual signal path tubes are the same.

To remove the bulb on one of our amps: unscrew the lens (lenses of other colors and texture are available). The bulb is an old-school bayonet mount and so you push on it and twist it 90 degrees counterclockwise and it pops out of the holder. To reinstall is the reverse process. The stock bulb is a type 47 which is a 6V lamp (we run it at 4.5V for greatly extended life and to dim it a bit); a 12V lamp can be installed.