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.
broadstone

Showing 3 responses by almarg

almarg's avatar
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
almarg's avatar
almarg
9,670 posts
 
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
almarg's avatar
almarg
9,670 posts
 
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
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