Atma-Sphere MA-1 amps

 

What 6SN7's and what location are people using in their MA-1's?

as noted...
 

I own a pair of MA-1 Mk.IIIs and an MP-1 Mk.III linestage+phono. I could tell you how much I enjoy this combo, but I'd just start gushing. Both are quite revealing of up and down stream componentry and both become even more magical with NOS 6SN7s. I've spent time with the M60s, MA-1s and MA-2s - there are differences across the members of the Atma-Sphere lineup, but within the same revision level, they share the same design, many of the same bits, and to my ears sound more similar than different. Reviews of the M-60 and MA-2 are a bit more prevalent and they should give you a pretty good word picture of the sound of the MA-1.

At present I'm using 4 Ohm Audio Physic speakers (Avantis) and the MA-1s drive them just fine. I've tried them with and without the Speltz Zero Autoformers, and while the Zeroes work as advertised they are not entirely without their own sonic signature. Different speakers yield different results, but in no way do I find the Zero mandatory on my 4 Ohm spkrs.
 
Tim
 

Thank you Rushton, Tom, Pbul57, Tvad, and others for your comments and insights. I really appreciate listening to others describe the same equipment I've heard. Imo, the Atma-Sphere circuit - whether in the amps or preamps - is highly revealing of virtually any change made to it. I finally grasp what RK means when he talks about 'listening to the circuit'.

Having heard the amps and preamps with and without V-Caps, I find increased tonal depth across the frequency range with the V-Caps. 'Tonal depth' being characterized as the sheer amount of harmonic and overtone information accompanying the fundamental. What I have not heard from the V-Caps is an increase in warmth, or put differently, an increase in pleasing second-order harmonic distortion that lends a sense of 'fullness' to notes. Lack of fullness is not lean tonality.

Because I presently use the amps and preamp as my review references, I've been round and round debating with myself how best to characterize their sound in contrast with other gears. Crudely put, 'thin', imo, means lacking information - one is not hearing all the harmonics and overtones available to be heard within ones audible range because they have gone missing - all else being equal, lost in the circuit. At this juncture I don't believe the Atma-Spheres are lean or thin in tonality.

Hopefully I'll solve this with a better vocabulary some day, but for now the way I parse things is to say the Atmas have plenty of tonal depth, but do not display the same tonal weight as some other components I've heard. And I cash *that* out not as sweet/dry or rich/lean, but as warm/cool, where warm suggests pleasing distortions and cool suggests a more analytical sound verging on displeasing distortions (more odd order). The Atmas are not 'cool', but they're not warm and I presumptively think that may be what some folks intend when they say they're thin or lacking tonal texture. In effect, texture is distortion. The Atmas do not convey less tonal information, they distort less, but its less of what turns out for us humans to be a pleasing distortion, and its absence is noticeable if that's how you like your music. I struggle with this, and don't mean to say any other person's characterization is incorrect; I just need a way to put consistently into words the similarities and differences i hear between the Atmas and other gear that will make sense.

Tim
 

Is it possible for you to characterise your experience with the Atma amps before, during (break-in) and after when the sound finally settled?

 
Thank you Tom.
 
I found the amps and preamp more similar than different across break-in. Out of the box there was plenty of resolution, but the sound was a little tight and closed-in. Relatively speaking, tonality had a wee bit of a greyish cast. During break-in, which I counted roughly at 120 hrs for the preamp, and a little more for the MA-1s, music gradually became relaxed and seemed to flow with a more natural pace. Tonal colors made something of a transformation towards the end of the break-in period - they really blossomed - all of which was rather startling. That final leap came over a few days for the preamp, and, say, over a weeks time for the MA-1.

The subsequent addition of the V-Caps to the MP-1 took things back a step before going forward two. Highs and the mid-bass got a tad edgy and a touch of the greyish tonality returned. Over roughly 6 weeks, things smoothed out and the tonal colors deepened. Sonic memory is difficult, but I'm confident that tonality eventually improved beyond where things had got to prior to the V-Cap upgrade.

Fwiw, I find both amps and preamp sound their best after being on for 1-2 hours - the hotter their tubes the better.

Tim
 

I swap tubes around every few months - there are many great combinations. NOS tend to last much longer than contemporary brands - or so everyone says - I haven't had a 6SN7 go south on me yet, so no direct experience.

MA-1 Mk.III ---
Driver: Sylvania GTA or RCA GTB
Tubes 2&3: VT-231 Ken-Rads (these positions have biggest influence on sonics, imo), RCA Grey Glass
Tubes 1&4: VT-231 Sylvania, RCA Grey Glass, or VT-231 Raytheon

I really like the VT231 Ken-Rads in the the amps. They're still out there but getting a bit (more) pricey.

Couple notes:
i) My Mark IIIs are in the traditional narrow chassis, so position may be different w/ the newer style. Driver is understood as position #5 at the edge of the chassis facing the output tubes.
ii) For NOS, the driver position requires a GTA or GTB - something that supports a higher 450VDC plate voltage; the other positions do just fine with other NOS (eg. GT or VT231).

The preamp is both challenging and fun because of the phono section, where it is harder to get good *quiet* tubes - but its definitely doable.

MP-1 ---
forwardmost 6SN7: VT-231 Ken-Rad
other 6SN7: Electro-Harmonix or stock Chinese
phono (12AT7s): CV4024 Mullards, '60's Siemens 12AT7s, 6201 Sylvania Gold Brand

I put Herbies Tube Dampers on 3 of the 5 6SN7 per channel and 3 of 4 12AT7s per channel. The dampers work well.

check this out:
The Reference 6SN7 Thread

The gear is incredibly revealing of tube changes (for that matter any change) and tube rolling becomes lotsa fun. Good section matching w/in a tube is v. important.
 
Tim
 

 
So... what are you trying and whattya like?