2. amps-preamps
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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.
128x128broadstone
broadstone's avatar
broadstone OP
310 posts
 
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.
tubegroover
2,320 posts
 
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.
broadstone's avatar
broadstone OP
310 posts
 
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.
pani
1,219 posts
 
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 ?
almarg's avatar
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almarg
9,670 posts
 
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
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