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

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.

Lewinskih01, you are right on real balanced connection, that’s another parameter I’ve been considering. Let’s see what Ralph is going to suggest.
For subs, your comments sound very professional and I am sure you spent a lot of time on setting the subs. I wish I had your skills and patience. I came across this article which is very interesting. I changed my mind on Subwoofer size. I guess it’s better to move toward a 12” sub. I am not really obsessed with a lot of bass in the music. I do love attending live music performances and the thing I noticed is that the bass in live music does not shake the salon, classical music to Jazz/Blues and even semi-metal group like OM! A good compromise on bass and the whole setting is the key! Besides finding a good subwoofer especially built for music is another challenge, because most subs are made for HT!

http://www.soundstage.com/maxdb/maxdb200101.htm

Besides finding a good matching amp, my plan is to get one good sub and perhaps later on move toward a second sub. Rythmik subs looks nice and well-built. There is not too much reviews on those subs, I was wondering how do you compare Rel Storm vs. Rythmik subs? I mean uniquely for music usage.

Michel

The link didn't go through?!

http://www.soundstage.com/maxdb/maxdb200101.htm

Per the B&W web site the impedance goes down to 3 ohms. Power wise the M60 sounds like it would be fine. However, the 3 ohm impedance could be a problem. The way around this would be a Zero auto former (anti cables.com) which is placed between the speaker and amp and allows the amp to "see" a higher impedance with easily selectable choices of 2x, 3x and 4x the speakers impedance. So, as an example, if you choose the 3x option the M60 would see a speaker impedance of 9-24 ohms which on paper sounds about perfect but you can easily switch between the options and see which sounds best. It come with a 60 day in home trial so there's lots of time to find out which works best for you. Another benefit, the M60 will put out 80 watts/ch at 16 ohms up from the 60 watts/ch at 8 ohms.

It may sound strange to have an OTL amp only to have but a transformer between the amp and speaker but the Zero autoformer is not like the transformer in a traditional tube amp which has both primary and secondary winding. The Zero only has primary and just enough windings to do the impedance adjustment so it much more transparent than the typical output transformer
.
BTW, the Zero is not just for OTL's. Virtually all tube amps will sound better into a higher impedance. For instance, the MC275 mentioned by Lewinski above, IMHO, would benefit from the Zero by not having to play into the impedances below 6 ohms with lower distortion, better bass etc. Some of the biggest users of the Zero's are Magnepan owners with their 4 ohm impedance driving them with tube amps.

Check out anticables.com. Hope this helps.
BTW, my own setup has an Atmasphere S30 driving the 16 ohm Zu Superfly's.