Advice re the use of OTL amps vs others


In my recent transition from solid state to vacuum tube amplification I'm learning a little about the various types of circuitry designs available. I'm currently using the Cary Rocket 88R amp mostly in Triode mode, and Peachtree Audio Nova as a preamp. The warmth I gained is extremely satisfying but I'm not sure if this is attributable specifically to the Rocket or simply as a result of transitioning to this setup vs solid state Peachtree to Martin Logan ESL's.

I'm impressed with what I hear about the Atmasphere amps and would like to consider them but have some concerns. What I've read is that the OTL amplifiers supposedly present the best of both worlds between a solid state and valve amp sound. In one way of thinking, using the Peachtree pre and the Rocket amp, I have somewhat the same thing now. I know it's not that simple but that's why this thread. I'm not concerned about overall sound quality with the right OTL but am that I might loose some of the warmth or "roundness?" I've found with the Cary.

Therein lies the question. I have no way that I know of to locally (33064) audition the Atmasphere S30 which is the one I'm leaning toward based on my research so far. The speakers which I'm now using and intend to keep are the original Reference 3A MMC Serie having an efficiency rating of approx 85dB and 8 ohms impedance.
broadstone
Talk to Atmasphere. I think 30 watts from an OTL may not be enough
Alan
the S-30 is one of my all time favorite amps, and Ralph is one of my all time favorite guys to deal with in this crazy hobby. Give him a call or send him an email - he'll give you honest advice on what he feels will work best, not just what he wants to sell you. he's really one of the good guys. you also might want to look into the zero autoformers.
Agree with Alan the S30 might not be enough power but it depends on several other factors. How big a room you have? How loud you listen? If the 3A MMC speakers dip below 6-7 ohms them you should also consider the ZERO Autoformer. A better match would be a speaker that has an impedance of 12-16 ohms for the S30. But again it's best to contact Atmasphere directly they can tell you if this will work or not.
Thanks. What you're saying regarding power and speaker impedance are the specific issues that I'm concerned about. The fact that I'm having success with the present setup has given me a sense of optimism regarding potential use of the S30. I have received and used advice from AtmaSphere and agree that he's the person I need to contact but haven't found the way to do so using these forums. So, maybe my question here should be how to talk to him directly.
Broadstone concerning your query as to whether an Atma-sphere S30 is enough, I DO recall a thread regarding their use with the MM Decapo with some saying yeah others nay, not enough power. Given your room size I think you are on the fringe, it again would depend on your musical tastes and levels that you that you require. I do recall that Ralph mentioned that many of his customers use the S30 with Decapos which are essentially the same design and probably the same electrical characteristics or close at least. I would think 30 watts is pressing it and would go for the mono 60 watt amps if considering an OTL.

So far as the characteristic sound of your Cary vs a an OTL in general very different presentation. In my experience, I've owned 2 OTL amplifiers, that when mated with the right speaker they are certainly worthy of consideration, heat factors aside. The transients and rise time on an OTL are more like real music, very fast and dynamic. You are not going to get that added warmth that the Cary delivers. I feel OTLs can get closer to the sound of real music but it DOES take care in selection of matching ancillaries. The added transparency can work against you if this is not addressed properly. And yes, they can present the best of both worlds whereas cheaper SS designs have a tendency towards dryness and a 2 dimensional character there is a wide variation in the presentation of tube amps as well. So far as an OTL there is no substitute for listening for yourself. btw, the Atma-sphere amps I've listened to, always in unfamiliar systems, have just been superb in every way.
Broadstone, If you are getting enough power with the Cary (which is about 40 watts to my understanding) then the S-30 with a set of ZEROs will do the job- it will make about 45-50 watts in that situation.

BTW, all you have to do to contact Atma-Sphere around here is to talk to me- I work there.
Thanks, Tubegroover. That's exactly the kind of information I was looking for. Being new to tubes, what I've found and most appreciate is the warmth provided that I've not been able to find in solid state, at least in a price range that I'm able to justify. This is something so important to me, mostly because of age related hearing issues, that I don't want to lose it even if I have to give up tack on realism.

What you said about the relative lack of warmth with the S30 was my main concern and even though I'm not considering changing speakers, I'm not giving up on the OTL route Just yet. Also, I recently promised myself in earnest that I won't buy another major component until I audition it in my home so that's going to be a factor.
Broadstone I don't want to give the impressions that OTLs lack warmth but that some tube amps ADD warmth that isn't really there as appealing as it may be. Bottom line is that you have to decide for yourself again there is no substitution for listening.

My caveat about the S30 would be relative to your room size, I speak from experience on this matter. About 15 years back I was using a 25 watt OTL that worked quite well that is until I moved my set-up into a larger room. Room size fyi was/is 20X18X10 opening into a 12X8X10 adjacent area. Not enough power for some music. I also purchased a Speltz zeroformer to help deal with this issue but found the only satisfying setting at the lower multipliers changing the multiplier upward greater than 2X the sound became more SS like and lost much of the harmonics and texture that I liked about the amp in the first place. Bottom line is while I liked the amp a lot without the autoformer it just wasn't enough power for me. Just something to consider.
Tubegroover. Thanks I didn't take it in any way other than honest advice based on your experience. My concerns in that direction were already formed anyway, based on several other sources that I've been reading. The response by Atmasphere confirms my thinking that if I'm already having success with the current setup, the possibility exists that I might expect to have good experience with the S-30. I'm keeping my options open and hope to find some way to audition them locally.
Adding a ZERO which is after all a transformer after the otl ? Does it not defeat the whole purpose and sonics of otl in the first place ? How much of the otl sound remains after that ?
Pani's question is a logical one, but the answers to it that are provided in the FAQ at the zeroimpedance.com site are good ones IMO:
12) What is the difference between the ZEROs autoformer and a typical tube amplifier's transformer?

The ZEROs have a few advantages over "typical" tube amp transformers:

A) The music comes out on the same winding wire that it goes in on so the music does not have to pass from a primary winding to a secondary winding.

B) There is no DC current to contend with. When a transformer is made to accommodate a DC field, its audio transparence is compromised.

C) The impedance ratio is very small (16 ohms to 4 ohms, compared to a few thousand ohms to 4 ohms). This simply means that it is much easier to achieve things like, frequency response extremes, than with a "typical" tube amp transformer. The ZEROs sport a frequency response of 2 Hz to 2 MHz.

13) Doesn't adding the ZEROs to my Output-Transformer-Less (OTL) Amplifier defeat the benefits of the OTL design?

The ZEROs were originally designed to maximize the full benefits of the OTL amplifier by changing the speaker's load impedance to the Maximum Power Transfer Region of the amplifier being used.

The ZEROs are not an amplifier fix, they are a speaker fix. It is a great disfunction to music loving audiophiles for speaker manufactures to be making 4 ohm speakers with 3 or 2 ohm impedance dips, and then expect amplifiers and speaker cables to be able to transfer music into a load approaching a dead short. The ZEROs simply multiply the impedance of the speaker in use, and do it so transparently they provide greater benefits than the "penalty" of an added component.
From a technical standpoint, and aside from a couple of spelling errors, that all makes perfect sense to me.

Great comments by Tubegroover, as can be expected. I would just add that the Transcendent OTL amplifier with which he did not experience good results using Zero ratios greater than 2X was vastly different in design than Ralph's OTLs, including in numerous respects involving both the topology and the tube types used in the output stage. See this reference on what I presume is either the same or a similar Transcendent model.

Best regards,
-- Al
Followup questions for Ralph:
1) Doesn't the 85db rating suggest that the M60s would be necessary for adequate power?
2) Perhaps I'm oversimplifying, but doesn't the 8ohm impedance tell us that zeros shouldn't be necessary?

For OP, as former owner of Cary Rocket 88(older version, not R), Atma-Sphere M1 and Berning ZH270, among other tube amps IMHE:
1) You've already received numerous great comments here characterizing the sound of the Cary vs OTLs
2) For me the OTLs portray much more realism vs the more old school tubey sound of the Rocket, which did tend to smooth things over with a lack of transparency and lack of dynamic jump
3) In limited experience with zeros, I found they blanched the sound in ways that I couldn't live with. I personally wouldn't choose any solution requiring them, although YMMV.
4) Ultimately my suggestion is to commit to your speakers (or not) and then go OTL only if the speaker is a good match for the OTL under consideration without autoformers.
Cheers,
Spencer
Thanks Al for your comments. With regard to the autoformer and the Transcendent amplifier you very well may be right, different topologies and tubes used. Interestingly enough, the gentleman I sold the autoformer to was using an Art Audio tube amplifier with 6c33 outputs. It too was recommended to him because of power issues. Never did find out out it worked out in his application. I really wanted to like it as I spent some time making several purpleheart cases for the autoformer for myself and another autoformer owner and invested in some nice edison price posts to easily change the turns settings. The things sat around for years before I finally sold them as the cases were so pretty.
Spencer, my impression is that Ralph generally doesn't post on weekends, so while we await his response I'll mention the following, regarding your second question specifically:

First, the S30 which Broadstone is asking about, at least in its most recent version, is spec'd at a considerably higher power rating into 16 ohms (45 watts) than into 8 ohms (30 watts). Using the 2X tap of a Zero would, of course, result in the amp seeing a nominal load of 16 ohms with his nominally 8 ohm speakers.

Second, the output impedance of the S30 is spec'd at a rather high 7 ohms, which when used in conjunction with a nominally 8 ohm speaker without a Zero would probably have significant and somewhat arbitrary effects on tonal balance due to the interaction of the 7 ohms with how the speaker's impedance varies as a function of frequency.

If Zeros are not used, the M60s' considerably higher 8 ohm power capability (60W) and lower output impedance (4.1 ohms) figures to provide much better results with Broadstone's speaker than the S30, as I see it.

Best regards,
-- Al
Al, I disagree with the 2nd sentence to the last paragraph:
..."It is a great disfunction {sic} to music loving audiophiles for speaker manufacturers to be making 4 Ohm speakers with 3 or 2 Ohm impedance dips, and then expect amplifiers and speaker cables to be able to transfer music into a load approaching a dead short."...
Some of the popular and most accurate audiophile loudspeakers ever made have such impedance plots, and many, many amplifiers and most speaker cables work quite well with them.
4 ohm not a big deal for many amps 2 ohm or less separates the men from the boys.

It takes an amp and speakers to make good sound. Does not matter really which one carries a bigger load as long as the two can work together well as designed.

Granted an easy load makes choice of amp easier. But it isn't the end of the world if it is less than perfect which most all speaker designs are in some way regardless.
Hi Unsound,

Yes, I for one would agree with your disagreement with that statement. While my own preferences have evolved such that I favor tube amplification and speakers having benign impedance characteristics, it seems abundantly clear that many audiophiles have assembled very fine systems with opposite approaches.

As is usual in audio, a multitude of different approaches can each provide good results, bad results, or results at various points in between, depending on many factors.

Best regards,
-- Al
Whatever "accurate" is eh Unsound? I too love the Sonus Faber "Extrema" and Apogee Scintillas as examples but that "nebulous" of terms "accurate" as applicable to an audio system is well....nebulous, which is to say, seems like an accurate way of describing it, at least to me. I only find accurate in the concert hall and would have to trust the mixing engineer to tell me that a given monitor is accurate in reproducing what he hears in a recording studio. Some are better than others so who do you trust? You can only trust what you hear. Hearing is unique among the senses in that we all perceive and value things differently and most importantly those values, judgements and perceptions more often than not can't be measured. So what we're left with is reconciliation of the measurements with what we hear. Better to keep it simple to my way of thinking, I personally don't want to be limited to a speaker design that is limited to amplifier choices because of its electrical characteristics which isn't to say it may be viable for others.
^IMHO, this is an example of what accurate is (at least by current standards):
http://www.stereophile.com/content/dunlavy-audio-labs-signature-sc-vi-loudspeaker-specifications
http://www.stereophile.com/content/dunlavy-audio-labs-signature-sc-vi-loudspeaker-measurements
http://www.stereophile.com/content/dunlavy-audio-labs-signature-sc-vi-loudspeaker-measurements-part-2

One could also take the other view; that choosing some particular amplifiers disqualifies some speaker choices. I am of the opinion that it is better to choose amplification for speakers rather than speakers for amplification.
Wow!! Unsound. I never heard Dunlavy speakers, but on paper they are quite impressive. Are they time coherent? If so, add them to the short list of 3 or so other brands that are.
Potentially accurate. If the speakers were perfect, what would you be listening to?
Bifwynne, yes.
Csontos, More accurate than many, if not most, but not perfect. LOL!
Answer; all that proceeded and followed the speakers.
Thanks Al. I use a Tenor OTL 75. It is one amp that I dont want to let go. Lets see if zeroimpedance has a home demo scheme, I would love to give it a try.
Adding a ZERO which is after all a transformer after the otl ? Does it not defeat the whole purpose and sonics of otl in the first place ? How much of the otl sound remains after that ?

IMO/IME there is a simple rule of thumb: the ZERO should help and not hinder. So if its doing the job all the transparency and speed that OTLs are known for will be intact- after all, the ZERO has wider bandwidth than the amp itself- usually with tube amps the transformer is the bandwidth limitation.


1) Doesn't the 85db rating suggest that the M60s would be necessary for adequate power?
2) Perhaps I'm oversimplifying, but doesn't the 8ohm impedance tell us that zeros shouldn't be necessary?

A lot depends on room size, how lively it is, how close one is to the speakers and personal listening habits. Given those numbers I would be more likely to go with the M-60s, but in a smaller room there might be no point. The impedance does suggest that the M-60s would be fine without a set of ZEROs.


Al, I disagree with the 2nd sentence to the last paragraph:
..."It is a great disfunction {sic} to music loving audiophiles for speaker manufacturers to be making 4 Ohm speakers with 3 or 2 Ohm impedance dips, and then expect amplifiers and speaker cables to be able to transfer music into a load approaching a dead short."...
Some of the popular and most accurate audiophile loudspeakers ever made have such impedance plots, and many, many amplifiers and most speaker cables work quite well with them.

All amplifiers, tube and solid state, make more distortion into lower impedances. While it is true that many solid state amps drive low impedances with power, making them do so is not the same as saying they are sounding their best. Generally speaking all amps will sound better (meaning: smoother and more detailed with greater authority) driving a higher impedance.

I have a set of Classic Audio Loudspeakers at home. They are 16 ohms, 98 db 1 watt/1 meter, go to 20Hz no worries and have no breakups in the audio passband (owing to a pure beryllium diaphragm with a Kapton surround in the midrange unit, which handles most of the range of the speaker)- they are very smooth and detailed. They had to beat out a lot of speakers in order to find their way into my home. Dunlavys are nice but these are better. Not as cheap though...

As I mentioned before, its a Bad Idea to make an amplifier work hard; tube or solid state. It might surprise some people here that OTLs can make as much current as a solid state amp, and when you think about it the reason why is obvious- they have to do the same work. But if you want to get the best out of them you present them with a reasonable load and then the magic happens. Because OTLs can be just as fast or faster than a solid state amp (the output section risetime of our amps is around 600V/microsecond) and lacking the odd ordered harmonics that plague solid state designs, they can be quite beguiling as you can simply hear details that other amps seem to miss.

The idea is just the same as if you have a fine car, motorbike or bicycle- it will handle better and be more confidence inspiring if it has good quality tires. Inappropriate tires will not allow you to realize the performance that is possible.