Atma-Sphere amps

226bw · « **on:** 22 Mar 2010, 05:31 pm »

Hi Duke,

This is the same Chris that has been in contact with you regarding your speakers. Rather than asking you more questions in private emails I thought I'd use the forum, with the thought that others may also be interested in your answers.

Before contacting you I had been contemplating purchasing an Audio Space Ref 1, either the KT88 or 300b version. However I notice that you may "voice" your speakers using Atma-Sphere amps. These are not available for audition in my part of the world, so I was wondering if you could give me an overview of the amps sound and why you like to use them for testing your speakers (if that is the case). The S-30 would be within my budget, the preamp might have to wait.

I'd also be interested in other forum members impression of the Atma-Sphere line.

(I listen primarily to blues and blues based rock)

Cheers,

Chris

Russell Dawkins · « **Reply #1 on:** 22 Mar 2010, 05:49 pm »

Hi Chris, welcome!

Good question - I'd be interested, too.

James Romeyn · « **Reply #2 on:** 22 Mar 2010, 08:04 pm »

My website has details on my 40 some year history as a hobbyist, musician, guitar hawker, pro and hobbyist, some recording work.

I've heard many of the best amps and on the right load (not too much if at all below 8 Ohms, moderately flat above 100 Hz) Ralph's amps may be in a singular class. After Duke made an impedance flattening device for my monitors, about 86-87 dB sensitivity, the amp just flat out did any and everything I could possibly expect it to do. It absolutely played about twice the power of my Plinius SA-50 Mk3, 50Wpc pure class A, not a slouch power wise, will drive 2 Ohm loads, up to then my favorite SS. The OTL 30W played any desired SPL in my 3200cf room. I've considerable experience with very good transformer coupled tubes, including what would otherwise be about $30k/pr custom 845 tubes built with the best Asian sourced custom transformers (trans about $3k ea).

The OTL musicality, spatiality and top to bottom purity may be in a class by itself. Before the EQ device the sound was still good but the 20 Ohm peak @ 2.2 kHz just skewed up the FR too much. My friend who built the above described custom tubes is familiar with every noteworthy tube design. He swears by the OTL on the right load, saying nothing may beat it including his own transformer designs. He compliments zero to few commercial designs of any kind. He owns the Cary 300B; I saw it underneath and he mocked the grotesquely bad work and parts (his opinion; one part was actually completely senseless and not even in the circuit!).

If/when finances allow I will get the 30W OTL from Duke. IMO on the right load the OTL would occupy permanent hierarchy in your chain of system quality. You'd never consider a speaker requiring a different amp.

For its balance of cost/SPL/sound quality nothing touches the OTL. Again, 30W powering 86-87 dB speakers in a 3200cf room seemed to have endless headroom, sounding more like a 200-400W brute. The monitors have only a single ported 6.5", so results are unknown powering something with significant back-EMF.

Duke · « **Reply #3 on:** 22 Mar 2010, 09:26 pm »

Hi Chris, good question!

The extent of the "voicing" you mention is actually only in the impedance curve. Briefly, the Atma-Sphere S-30 has an exceptionally high output impedance (low damping factor) so it is exceptionally difficult to find speakers for. Most speakers with a suitable impedance curve are well above the price category of the S-30. I figured that if my speakers worked well with the S-30 at one end of the spectrum, and a NuForce amp at the other end (those were the two I used in development of my first generation waveguide speakers), they'd also work well with just about everything in between.

Also, I thought the S-30 was such an elegant little amp that I really wanted to showcase it. From what I understand, S-30 sales have increased significantly since I've been using the amp at audio shows. Now in my opinion the M-60 is superior, but still the S-30 is pretty amazing in its price range when driving a suitable load.

So it's not that my speakers are voiced for OTLs but not SETs... I've also shown with SET amps from two different manufacturers (deHavilland and NTV). It's that the smooth, fairly high impedance curve works well with a wide variety of amps.

Now as far as "voicing" the speakers, there are two used-adjustable features that come into play. The first is the ability to change the port length, to account for room acoustics and/or amplifier interaction (the low damping factor OTL amps deliver considerably more power into the bass impedance peaks than a solid state amp would, so we lower the tuning frequency to compensate). Second, there is an outboard resistor in a terminal cup on the back of the speaker, and this resistor is bypassing a resistor in the crossover network. By changing the value of this external resistor we can adjust the tweeter's output. Actually the effect is partly shelving and partly tilting, such that the effect is greater at 10 kHz than at 2 kHz. This is a higher quality solution than all but the very best L-pads (which are over $130 each and only available as a custom-order item at 100 pieces minimum). And even then, an L-pad would function as a shelving-only control, with little or no tilting function.

zybar · « **Reply #4 on:** 22 Mar 2010, 10:43 pm »

Count me in as another huge Atma-Sphere fan and supporter.

I have owned/extensively auditioned some great tube and ss amps from the well known and little known vendors out there (Pass, BAT, Moscode, Plinius, VAC, Bryston, CI Audio, Audio Mirror, Bella Extreme, Jeff Rowland, McCormack, AVA, McAllister, and Rogue Audio to just name a few) and the Atma-Sphere MA-1's I am currently using with Vandertsteen 5A's are my favorite amps by far.

As Jim said above, the Atma-Sphere OTL design delivers musicality, detail, texture, and space in ways few amps can do. If you want an amp that gets you off the merry go round and just lets you enjoy the music, this is the amp for you. Check out the Atma-Sphere website and you read about all the accolades and awards. They didn't garner such universal praise by accident.

George

poseidonsvoice · « **Reply #5 on:** 22 Mar 2010, 11:01 pm »

Our very own TomS. has chosen the Atmasphere M-60 Mk III's as his reference amps for the Abbey's which are 95dB sensitive. He is completely smitten with them to put it lightly. I'm sure he'll chime in when he has the chance.

Anand.

TomS · « **Reply #6 on:** 22 Mar 2010, 11:10 pm »

Quote from: poseidonsvoice on 22 Mar 2010, 11:01 pm

Our very own TomS. has chosen the Atmasphere M-60 Mk III's as his reference amps for the Abbey's which are 95dB sensitive. He is completely smitten with them to put it lightly. I'm sure he'll chime in when he has the chance.

Anand.

Yes, what Anand and George said...

Zybar and Earflappin turned me on to the M60's (thanks!) and they are as good as anything I've ever heard. They don't really sound like whatever you may think of a "typical" tube amp. They have the harmonic richness and tone you definitely want, but the sheer clarity of them will startle you, without the nasty side effects that such high resolving power sometimes brings with it. Very simple design and Ralph's service is great as well. Highly recommended!

hmen · « **Reply #7 on:** 22 Mar 2010, 11:51 pm »

Since I got my M-60's five years ago I have not even thought about replacing them. How many of us can say that about ANY piece of equipment?

Brian Cheney · « **Reply #8 on:** 23 Mar 2010, 12:41 am »

We used MA 1 monoblocks in our live vs recorded demonstration at THE Show Las Vegas this past January.

The Atmasphere's drove the ribbon mid and treble sections of a single pair of RM50 speaker systems from 220Hz up, in a 28x32x9' ballroom outfitted with 30 listening chairs. With standees we had as many as fifty people on hand hearing a five piece band and two vocalists, recorded in hi-rez and DSD formats with two mics, no mixing board, and no signal processing. Playback was virtually an exact replica of the live performances.

I don't know what more can be expected of any amplifiers. I can tell you that a similar demo we held a year earlier, with all solid state electronics, did not come off as well.

So yes, I do think Ralph's electronics are the best I've heard in my 34 years of professional audio.

Brian Cheney
Pres VMPS Ribbon
www.vmpsaudio.com

Russell Dawkins · « **Reply #9 on:** 23 Mar 2010, 01:01 am »

Now I wish I needed an amplifier! I really would like to hear these.

Unfortunately, my speakers are internally tri-amped.

JoshK · « **Reply #10 on:** 23 Mar 2010, 01:07 am »

The only Atma-Spheres I've heard were Hmen's M60s driving the RM40s (mine until I sold them to him). I was amazed at the bass they could produce. Very clear sound. Not warm or euphonic at all.

I know as a philisophical design philosophy, I am not into the OTL topology due to the amount of feedback required, but those amps made me question my beliefs. Almost.

TomS · « **Reply #11 on:** 23 Mar 2010, 01:15 am »

Quote from: Russell Dawkins on 23 Mar 2010, 01:01 am

Now I wish I needed an amplifier! I really would like to hear these.

Unfortunately, my speakers are internally tri-amped.

Russell - Funny, I am listening to International Guitar Night II on my M60's as I type. The tapping on the second cut (Celtic Medley) is spooky...

poseidonsvoice · « **Reply #12 on:** 23 Mar 2010, 01:18 am »

Quote from: TomS on 23 Mar 2010, 01:15 am

Russell - Funny, I am listening to International Guitar Night II on my M60's as I type. The tapping on the second cut (Celtic Medley) is spooky...

Hmmm...Perhaps I should start looking through Audiogon for some used M60's that I can update. I was going to build a pair of GM70 SET's...

Anand.

JoshK · « **Reply #13 on:** 23 Mar 2010, 01:26 am »

Quote from: poseidonsvoice on 23 Mar 2010, 01:18 am

Hmmm...Perhaps I should start looking through Audiogon for some used M60's that I can update. I was going to build a pair of GM70 SET's...

Anand.

I have a feeling those are very different sounds. You might try to listen to a SET and an OTL. Those are as different as tube topologies can be. In theory/rule-of-thumb (which is broad generalizations that don't always hold), the SET will err on even harmonics, mostly H2 with little if any higher order harmonics. The OTL, via feedback will likely create less overall distortion but more higher order through IMD and due to PP canceling, err on the odd harmonics.

Pass has often said that in listening tests, people often pick the amp that sides on H3 over one that sides on H2. I think (this being my hypothesis) that the H3 (PP usually) amp typically sounds faster, more detailed, while the H2 amp sounds warmer more inviting. The truth will come in long term listening. I think I determined I prefer the amps that err on the H2 side, but I also believe it comes down to personal preference.

zybar · « **Reply #14 on:** 23 Mar 2010, 01:36 am »

Quote from: poseidonsvoice on 23 Mar 2010, 01:18 am

Hmmm...Perhaps I should start looking through Audiogon for some used M60's that I can update. I was going to build a pair of GM70 SET's...

Anand.

I'll be happy to sell you a pair.

George

Duke · « **Reply #15 on:** 23 Mar 2010, 02:09 am »

Quote from: JoshK on 23 Mar 2010, 01:07 am

I know as a philisophical design philosophy, I am not into the OTL topology due to the amount of feedback required, but those amps made me question my beliefs. Almost.

The S-30 has 2 dB of global negative feedback. The M-60 has 1 dB of global negative feedback. The MA-1 and MA-2 have zero global negative feedback. Other OTL amp manufacturers sometimes use higher feedback which results in higher damping factors, making their amps compatible with a wider range of speakers.

On a somewhat different subject, occasionally you'll see a negative comment about Atma-Sphere amps claiming that they're thin or bright or something. Inevitably this is due to the way the amplifier interacts with that particular speaker's impedance curve. If I hadn't tamed the impedance peak in Jim Romeyn's speakers, I'm pretty sure the combination would have sounded bright.

I can go into some detail if anyone is interested, but briefly most speakers are designed for the way a constant-voltage amplifier behaves into their impedance curves, which is not the way a low damping factor amplifier behaves, be it SET or OTL or something cooked up by Nelson Pass.

Atma-Sphere was the first amplifier line I became a dealer for, based on the performance of their big amps driving SoundLabs. So compatibility with Atma-Sphere amps was high on my list of priorities for my own speaker designs. As of a couple of years ago Ralph Karsten had the largest collection of Golden Ear Awards of any manufacturer, but even if he didn't have any it would still be an honor to be associated with him and his amplifiers.

Despite the difference in circuitry, I think that OTL and SET amps have more in common than not. Both have low global negative feedback, low damping factors, benign distortion envelopes, relatively benign behavior in the early phases of clipping, and no transformer hysterisis (the slight loss of low-level energy - and thus low-level detail - when the magnetic field in the output transformer is collapsed and then reversed as the waveform crosses to the negative phase of the signal; SET amps simply modulate the field but never collapse and reverse it, while OTL amps... you know...). The types of speakers that work well with one also work well with the other, assuming the amp is powerful enough. Philosophically I do like the coherence of having a single output tube per side, but I'm not sure there's a real-world issue there. Maybe one day I'll make a high efficiency 32 ohm speaker that can use a single-tube-per-channel OTL amp.

Which brings up another interesting feature of the Atma-Sphere amps: They can be run with less than their full complement of output tubes. I used to do that in the summer in New Orleans.

poseidonsvoice · « **Reply #16 on:** 23 Mar 2010, 02:41 am »

Quote from: JoshK on 23 Mar 2010, 01:26 am

I have a feeling those are very different sounds. You might try to listen to a SET and an OTL. Those are as different as tube topologies can be. In theory/rule-of-thumb (which is broad generalizations that don't always hold), the SET will err on even harmonics, mostly H2 with little if any higher order harmonics. The OTL, via feedback will likely create less overall distortion but more higher order through IMD and due to PP canceling, err on the odd harmonics.

Pass has often said that in listening tests, people often pick the amp that sides on H3 over one that sides on H2. I think (this being my hypothesis) that the H3 (PP usually) amp typically sounds faster, more detailed, while the H2 amp sounds warmer more inviting. The truth will come in long term listening. I think I determined I prefer the amps that err on the H2 side, but I also believe it comes down to personal preference.

And if cost is no object, might as well have both

Anand.

mgalusha · « **Reply #17 on:** 23 Mar 2010, 03:09 am »

Quote from: poseidonsvoice on 23 Mar 2010, 02:41 am

And if cost is no object, might as well have both

Or all three, SET, PP and OTL. All make me happy in various ways.

A friend has the Jazz modules and drives them with a Consonance Cyber 845 SET and the combination is really good.

James Romeyn · « **Reply #18 on:** 23 Mar 2010, 03:58 am »

Ditto all the accolades. Again, after Duke built the impedance EQ device, the OTL got out of the way more than anything I've ever heard. In that way it was most remarkable and noteworthy and the sound was not as I expected because I had no other reference for something with so little sonic footprint, except to convey the musical emotion, forget about everything else and let the music come forth. Staging/imaging was silly good, more 3D than ever before (some of the wrap around sound effect of properly setup MBL Radiahlstrahler omnis).

James Romeyn · « **Reply #19 on:** 23 Mar 2010, 04:00 am »

Quote from: mgalusha on 23 Mar 2010, 03:09 am

Or all three, SET, PP and OTL. All make me happy in various ways.

A friend has the Jazz modules and drives them with a Consonance Cyber 845 SET and the combination is really good.

You won't hear many contradictions to that! Are the Cyber 845s reliable?