Atma-sphere M60 II.3-Any good for 4 ohm speaker?

Guys, I like the idea of trying OTL, but, in looking at the mfg. web page, I see the power rating going down to 40 watts for 4 ohm load, and going up to 80 watts for 16 ohm load. I am receiving my speakers next week, and they are 95DB with a 3.8-4 ohm load(Reimer Tetons)What do you think of these amps with a 4 ohm speaker. Also, why does the power go down, not up?

Thanks in advance
711smilin, against conventional wisdom, my Atmas have sounded great with a 4 ohm speaker - Frieds. Actually, they are the best amps I have come across for Frieds.

Now, understand that the series crossover (presenting a resitive load) might be the reason, but since your sensitivity is high enough, you might want to give it a shot. The other thing is that a lot of loudspeakers specify a nominal impedance of say, 8 ohms, but the actual curve shows them to be quite demanding. I hear the Reimers are a kind load to an amplifier.

Incidentally, have you bought a pair of Atmas yet? I have an ultra modified pair that I might be able to give you a really good deal on (not yet sure that I was going to sell them). They are MKII.3, plus A LOT of upgrades, such as the 12SX7 (instead of 6SN7 driver - better than any 6SN7), and some other unique things.
Trelja, I have not bought them yet, I was thinking of buying the pair for the tsunami auction, for a good cause, and a write off. Email me about yours if you would. I just sold my pair of cardinals, and received the DK today. I also have my VRD's kt88 mono's. But am obsessive with this journey. Call me an audiophool, if you will. I do.
711smilin, I might be the guy you should be talkin' to :-)

Brian, good suggestion, why did I not think of it.
Can anyone tell me the difference between the new Rendition Audio Monitor 60 and, the Atmasphere M60?

The Monitor 60 is one beautiful piece. I am assuming both these amps were designed by Ralph.

711, an auto-transformer will solve the 4-ohm issue. I used an Atmasphere MA-1 on my Magnepan 3.6's with the auto-transformer with excellent results.

But that Monitor sure is nice looking....
Ralph is back!

Many of you may not be aware of the fact that Ralph Karsten has returned to Atma-sphere, along with his proven track record of product development, customer service, quality, and integrity. The other parties who were briefly running Atma-sphere during Ralph's "departure" in 2004 are no longer affiliated, in any manner, with Atma-sphere. I don't wish to comment further concerning details, since I don't want to see this thread closed. In short, Atma-sphere is back to the same high quality operation for which it has been known for the past 25(?) years!

711smilin, call Atma-sphere (Ralph or Bill) since they will be able to best help you with your decision. And forget about the tax write-off, which only comes into play for an amount OVER the fair market value of a charity item!

Trelja, I would check with Atma-sphere regarding the 12SX7 tube mods. I was lead to believe that this mod was not good for transformer longevity, but I may be mistaken. I was discussing several issues about my amps, and could have misinterpreted or confused information about the 12SX7 mod.
As you suggest, the Rendition Audio Monitor 60 is designed by Ralph Karsten; it's styling goes back to the earlier Atma-Sphere M-60 styling that Ralph always liked. The circuit is very close to the current M-60 MkII.3 but in a different chassis.
711Smilin, what you see in the power output specifications of the M-60 into different impedance loads (power goes down as impedance goes down and up as impedance goes up) is characteristic of OTLs. (As contrasted to solid state where the reverse happens.) It's one of the reason OTLs traditionally do a good job with electrostatic speakers which can have dramatically rising impedances in the top end.

I don't doubt Trelja's description of his experience with 4-ohm Frieds. But the "conventional wisdom" is not just "urban myth", there's a lot of solid reality to it. Trying to drive 4-ohm speakers with M-60s will be an iffy proposition, and not just due to the reduced power. There will be increased challenges around controlling the woofers effectively due to the impedance mis-match of the M-60 to the 4-ohm speaker load. With certain specific drivers, the matching may work; apparently it does so with Trelja's Freids, but I'd be very hesitant drawing broad conclusions from a single specific example (which I think is an exception). You may get a similar result with your Reimer Tetons, but you may not.

The greater number of output tubes in the MA-1 make it a much more suitable match to a benign 4-ohm impedance curve than the M-60. The increased number of tubes in the MA-1 lowers the output impedance of the amplifier by half (compared to the M-60) and makes for better power transfer into the lower impedance load and better control over the drivers. It's not just a function of the MA-1 having higher rated power output: it's also a function of better controlling the low impedance speaker's driver.

The Zero autoformer can help. But it's not a panacea, and while there are reports from many folks who have been very pleased with the results obtained with the Zeros in their systems, there are also reports from people who not positive about the reulting sound quality.

The best way to get advice about the compatibility of the M-60s with your Reimer Tetons is to call the factory and ask Bill or Ralph: 651-690-2246 If they've had any experience with your speakers, they'll give you a straight answer about compatibility.

Thanks for clarifying that "Ralph is back!" It is good to have him available at A-S once again to talk with.

As to the 12SX7 mod, I haven't heard about this creating any problems. The main considerations for Ralph when I asked about this mod are: (1) increasing cost of the 12SX7 on the vintage tube market; (2) significantly decreasing availability and no "new" production; (3) much better availability of the 6SN7, including great sounding vintage stock (although the vintage is also getting more costly). In short, he's not a fan of this mod and doesn't recommend it for these reasons even though many people report liking the sonic change.
Rushton may I be honored to say friend, There is a peculiar phenomena when it comes to the supply of old tubes. They come out of every nook and cranny when the demand goes up.
That doesn't address the issue of a low impedance speaker with an OTL sans autoformer. I have heard high powered ones with Avalons on a couple of occasions with excellent results. I have heard Ralph's reputed personal favorite the 60s with the undeniably true Frieds do a great job with the resistive load of the Real thing but have also heard tell of the 30s failing to power a demanding load due a less "benign" impedance load.
Thus get the power and/or make sure your impedance is very firm or will tend to rise before it drops.
711Smilin, your heart is in the right place. You should buy the pair on auction here for the tsunami victims. I offer my personal debt of gratitude to you and Ralph for making this happen.

I actually spoke to Ralph about them this week. They will be built soon, and have the MKII.3 circuit, with the switch to choose Class A or AB. It is his way of giving back, he and I are big believers in kharma. Ralph feels forever endebted to us for taking a stand for him. I feel that we could never pay him back, even if we did what we did a million times, for all of the good the man has done in his life.

I have ZERO idea why anyone would want to run their Atmas in Class AB. Well, yes, I do. They will throw off a lot less heat, as well as using less electricity. But, as the sound will surely take a step down, in my opinion, those interested in Class AB should look elsewhere. Ralph doesn't agree with running them in Class AB, it was a design of the non Ralph regime, and he has told me new designs will forego it in the interest of offering the best sound, at a lower cost (less circuit complexity).

The 12SX7 mod causes no damage to the amp whatsoever. Ralph and I have spoken at length about it, and while he concedes that the tube offers superior sound to any 6SN7, it does not meet his 20 Year Rule, as the tube is no longer in production. One of the reasons Ralph is such a prince is that he wants his customers to be sure that their purchase will still be viable in 20 years.

I think that if prodded, he would do the mod, as it is simple (you just run off of one of the other transformer taps) and easily reversible for anyone who would ever go back (you just switch the wire back to the other tap).

Personally, I disagree with the rationale for not running the 12SX7 - cost. I just bought 8 NOS 12SX7 tubes for $100 last Saturday. I now have more than 2 full sets in reserve. I don't know how long 6SN7 tubes last, but it should be a minimum of 10 years in most tube amps, and probably a lot longer. With the set in my amp, plus two in reserve, I'm probably OK even if I use the amps when I'm 80 years old (I'm 35 now). And, remember, if need be, I could always go back to the 6SN7 after moving just one wire.

Going along with the feelings of everyone I have talked to, including Ralph, that the tube DOES eclipse any 6SN7, tell me where you are going to get a tube that sounds this good for $8 - $30 per tube? Heck, the cheap Sovtek 6SN7s are $10 - $20 each. I know when I was buying good 6SN7 tubes for my last pair of Atmas, I could never find anything for these prices. Yes, they have spiked in price, and it is solely due to Atma Sphere owners such as myself buying them up, but the price is still a fraction of a Sylvania, RCA, or KenRad 6SN7.

Finally, because a tube is no longer in production does not mean it will not go back into production. ElectroHarmonix recently began producing KT90 tubes, which were only produced by Ei in the past and were thought to be soon extinct (NATO destroyed the factory in the 1998 bombing of Yugoslavia). Why did EH start making the tube? Demand, of course. There is money to be made there. If tube amp manufacturers try the 12SX7 and feel it to be superior to the 6SN7 (I hear more and more people talking about the 12SX7) we will start seeing them use it (Denis Had of Cary uses a lot of out of production tubes in his Cary and AES products), and some company like EH, JJ, or Shuguang will begin producing it once again (look at all the tubes that have gone back into production because of Dennis Had). It Economics 101. And, we will be taking audio to a higher plane. Some people focus on problems, I try to live my life by focusing on solutions. It's a glass half empty - glass half full thing.
Oh, one issue I forgot to address are the chassis of the M60 MKII.3.

There are currently THREE different chassis available.

The old style, with the tubes in the front, transformers in the back, and the squared off transformer covers. This is the classic M60 design.

The "other regime" style, with the transformers running longitudinally down the middle of the amps, with tubes on either side. It looks like the S30 and MA1. I believe Ralph is not a fan of this design and it will be going by the wayside.

The third style is the Rendition, which returns to the classic M60 layout, updated with rounded transformer covers and a stainless steel plate in front of them. It's a takeoff on the original design.

To my eyes, the Rendition looks like the 1940's (streamlined - aerodynamic), whereas the other design looks like 1950s (modernist - contemporary). I like them both. Which do I prefer? I don't know, I keep going back and forth...

While 4 ohm speakers are not kind to the M60s, a lot of people use Reimers with low powered and SET tube amplifiers. I would at least try it. And, regarding the Zeroes, Ralph knows I find they detract from the sound (you lose the AtmaSphere magic). Atma means "soul", and I guess I would just call them Spheres at that point. Still, a lot of people are fans, so you might want to give them a try and see where you stand.
The Atma-Sphere M60 can be ordered in any of the three styles Trelja describes. The Rendition Audio M60 looks pretty much the same, one exception being the meter which functions as a VU meter on the Rendition.
Trelja, your NOS 12SX7's that you bought, are you talking about USA or EU brands, or Chinese, Russian, or Yugo brands? I'm not sure, since you say that the 12SX7's are not being produced, so all tubes would technically be considered NOS. What are the sonic advantages of the 12SX7's over the 6SN7's? I just sent my M-60 Mk. 2.2's back for circuitry upgrades (but no A/B mode for me, thank you very much!) Hopefully, you are also using an Atma-sphere pre-amp, as well. And what are you using for speakers?

711smilin, I agree with Trelja. You will be buying a great product, while helping people who are definitely in need and badly hurting. I didn't mean to sound callous concerning my comment about a charitable tax deduction; I just didn't want you to get a big surprise from your "Uncle Sammy"!
Fatparrot, the tubes I picked up last week were just about all grey glass RCA 12SX7 tubes. I think that two of them were General Electric as well.

By the way, my favorites so far are a pair of RVC (RCA Canada) grey glass I picked up in the fall. They have the RCA 6SN7 grey glass kind of sound, which is a really fat midbass, lending some welcome (for me) warmth to the sound, in addition to a whole lot of slam. I use them in position V1, which is where I like them best.

It is kind of hard for me to describe their superiority over 6SN7, as the amps that I have that use them came that way. I was never able to listen to them with the 6SN7 tubes. It is a unique pair, and probably one of the finest sets of M60s in existence. They're certainly superior to my former pair, which needed the power supply upgrade as a start.

I will say that the sound of this pair is extremely liquid, relaxed, and natural sounding. Yet, at the same time revealing of astonishing detail, with a good bit more powerf in the bass. This particular pair has a lot of advantages over my former amps - better passive parts (teflon film/foil caps, etc.), a big bump in the power supply, and no negative feedback. There are a few other things with this pair of amps, such as test jacks on each output tube to measure it, the B+ supply has been modified with voltage regulation(I have no idea...) and a "pi filter" has been added to the driver stage power supply. Basically, they were sent in with the mandate to do every possible upgrade known, and that was that.

From other people who are more familiar with the before and after of the 6SN7/12SX7 with their pair of M60s, they are considered a super low distortion tube. I have heard that they take a lot of the best traits of the RCA (big time bass) and the Sylvania (superb midrange and treble) and put them into one tube. Hopefully, someone who has done the surgery can chime in with their opinions here, as I am beginning to drive past my headlights in this post. It's probably also time for Ralph to put me in my place...
Fatparrot writes:
711smilin, call Atma-sphere (Ralph or Bill) since they will be able to best help you with your decision. And forget about the tax write-off, which only comes into play for an amount OVER the fair market value of a charity item!
Thanks for the clarification on the tax issue.

Guys, Thanks for your honest responses, I TT Brian, essential audio and he told me to look elsewhere. I am really thinking about buying another pair of Cardinals, cause I already am missing the 300B magic again. This will be my third pair in 6 months. Nutty hobby, huh? When I receive my speakers, I will start the search again. I have enough new equipment on the way, I guess.
What speakers are you getting "711"? I thought you had the Reimers. Are you changing these or, just adding some "furniture" to another room?
I have 3 pair of Cornwalls(modded)now, the Reimers will be here in 2 weeks or so. I only have 1 room to play, so I combine 1 rack for HT, 1 Rack for 2 channel. Mucho eq in and out on a constant basis, hopefully to stop soon. Revolving door getting to time consuming to enjoy the MUSIC.
Does anyone have any experience with MA-1 11.3 and Dunlavy SC-4a speakers? They are also 4 ohms, 91db and pretty stable.
Jwin, I've not heard this combination, but they might work depending on the minimum impedance, how smooth the impedance curve is, and the characteristics of the bass driver. Adding a "Zero" autoformer might be useful. The best answer would come from Atma-Sphere. If you call or email Ralph, he can tell you if he has customers using this combination successfully.

What I can say is that the Atma-Sphere MA-1 Mk.II is a stunning amplifier in its neutrality, transparency, speed and (with complementary speakers) tremendous bass control and impact. This is coupled with exceptionally truthful rendering of harmonic overtones and an overall musicality that is instantly addictive. Good Luck!
Thanks Rushton. The impedance of the Dunlays is pretty flat. It ranges from 3 ohms to 7.5 ohms max. Wouldn't a zero autoformer put a transformer in the circuit of the OTL design?