B&W 804s + Atma-Sphere M60 MkIII.2

Michel,

Never heard the Atma-Sphere, nor know much about it. I can say, though, my 804S driven by my McIntosh MC275 sounds great. It's rated at 75W per channel, and some claim these versions deliver closer to 90W, but clearly not a lot of power. At the time I bought this amp, I also tried these speakers with an MC252 Mc SS amp, and preferred the tubes - to me the added Watts weren't key. Larger B&W indeed need a lot of power. I think the 804S are a great match with tubes. BTW, my pre is also tubed.

Atma-Sphere might chime in here. If they don't, go ahead and post the question to them.

Re sub, I run two Rythmik subs and I'm very pleased with the setup. Setup is tricky, but I learnt a lot in the process. If you go down that road let me know and I can share more on the way I approached it.

Let us know how it goes.

Call Ralph at Atmasphere. He has heard his amps on most speakers out there and will give you the straight poop. One of the real good guys in this field.

Swampwalker, thanks, I called Atmasphere and Ralph was not available. I talked to someone there and he said B&W804+MA-60 would be a good match but he was not so sure! I need to drop an e-mail to Ralph himself to find out about it.

Lewinskhil01, thanks for sharing your experience. I had 804D and 804S(!) driven by Mc402 which was excellent in term of details and sound-staging! However I felt B&w804D was a little bit bright, especially with AQ-SKY cables! I thought to incorporate some Tube Pre-amp to the loop. I added a MC2300 which resolved the problem, the brightness was gone. Finally I sold my 804D and for Tannoy Canterbury. The Canterbury has too much forwarding sound which becomes kinf o tiring after a while, I am not really proud of this last choice! I have to say B&W are excellent speakers for their comparative price range.
This 804s setup is for a second audio room (vacation house) and I am using my McIntosh Mx-135 as pre-amp. It is an excellent preamp-processor with a wonderful MM phono that I used it with a SUT for MC cartridges. I don't want to go crazy on spending too much money for this second set-up, my wife wouldn't allow that!?! I Heard Mc275 at dealer driving Martin-logan and Sonus Faber speakers. I was very pleased with its sound, it has a lot authority and details. Besides when I heard ATMA MA-60, I was so overwhelmed, perhaps there is something magic about OTL amps. Of course it was not a same setup and it is not an objective comparison! I try to find out more about ATMA MA-60 and matching issues with B&W804s. Otherwise I will go with McIntosh MC275, which is also kind of my wife’s favorite stylish amp! In the mean time I use my Denon POA-A1HDCI.
Lewinskih01, Regarding Subwoofer, I was planning to get one of those Velodyne EQ-Max10”. I read too much about one sub vs. two subs! Obviously, two subs resolving is more obvious. Besides there is a lot of challenges of incorporating 2 subs, placement, added distortion etc... I don’t know how much improvements I can get with 2 subs instead of one sub!? 20%, 30% of improvement or more?! Have you done this experience with just one sub? It seems placing subwoofer in the middle would be a good compromise!?
Cheers,
Michel.

Michel,

I think Atma amps are outstanding, from what I read. Zero feedback, OTL, fully balanced. BUT...your MX135 is not fully balanced, I believe, despite having XLR connectors. Make sure you tell Ralph about this.

Buying a used 275 is certainly an option if you want to minimize expenses. Mine is a mk.IV and I have no desire to upgrade to newer ones - besides, I really dislike the green leds under the small tubes the new 275 has.

Subs: big deal! But you have to be willing to invest time in setting them up. 1 sub vs 2, don't know how to quantify the improvement but it's definitely a lot more than 30% in my case. I'm not running stereo subs playing both the same frequencies and same settings. Google Earl Geddes approach for setting up multiple subs. It made a huge difference for me.
I chose Rythmiks for having a reputation of very clean sound, not overly expensive, and have very many variables you can set up in the plate amp. BTW, my two 12" Rythmiks replaced a single REL Storm III. Nice sub, but didn't have the flexibility I wanted. BTW, my Rythmiks are DIY boxes, quite heavy and heavily braced. Each sub weights 100 lbs, for a 56 liter box.
Experimenting with placement of subs is crucial in Geddes approach. Each sub has pa different setting for crossover, slope, volume, phase (a critical feature), and amplifying/damping a certain frequency/bandwidth.
I use a measuremnt mic, an outboard USB card for the mic, and REW software. These are absolutely needed for setup. I wish I could post graphs here. With only the 804 playing you see the lowest frequencies missing as you would expect, plus the room interaction at the lower frequencies. Add one tunned sub and the lowest frequencies are boosted, but I still get huge peaks and valleys in response. Add the second tunned sub (tunned t work with the other sub) and the response gets smoothed significantly.

One of my subs ended up right in between my speakers, while the other one is tugged in a corner.

Sorry I get long winded. I did enjoy learning through this setup process!

Lewinskih01- you make a good point, although many people report excellent results running them single-ended either w a conventional RCA termination (w shorting pin in the XLR jack) or w an XLR-terminated (aka pseudo-balanced) connection.
Not to get too far off point, but can you tell us whether you are running stereo subs or dual mono subs. If the latter, do you think that the same "rules" apply to stereo subs.