Calling all SET fans

11-17-15: Swampwalker
YW, Schubert. Two watts normally would make no discernible difference but that's a 33% increase, so maybe so. IIRC, Atmasphere has pointed out that very important to get adequate power w an SET amp because because their distortion rises very rapidly as power output goes up. I have no independent knowledge of these kind of technical issues, so if I'm not remembering correctly, my apologies.

You're remembering correctly, Michael. Atmasphere has said in a number of past threads that to get the best sonic performance from a SET amplifier it should not be asked to supply more than a small fraction of its rated power (something like 25% if **I** am remembering correctly), because of the progressively increasing amounts of distortion SETs produce at increasing power levels (and the progressively smaller amounts of distortion they produce at decreasing power levels).

However, neither the Almarro A205A nor the Coincident Dynamo is a SET, as the EL34 and EL84 are not triodes. And based on their power ratings and on the schematic and comments shown in this review of the Almarro A205A MkII I'm pretty certain that neither amp is even operating those tubes in the so-called triode mode. Therefore I'm not certain of the degree to which Ralph's point might be applicable to those particular amplifiers.

Regarding the difference in power capability, the Almarro A205A MkII is rated by the manufacturer at 5 watts, with the review indicating 4.8 watts. The difference between 4.8W and the 8W rating of the Dynamo is 2.2 db, not a great deal but perhaps enough to be significant on some recordings. As we all know, though, specs commonly don't tell the whole story when it comes to subjectively perceived power capability, with distortion characteristics, power supply robustness, and other factors being involved.

The one other comment I would offer at this point is that the multiple mentions on the second page of the Almarro review of hum, buzz, and the need for a cheater plug would definitely give me pause. I say that in part because in the photos of the unit there and elsewhere, and also based on the schematic shown in the review, it appears to me that the ground shells of the RCA input jacks, and hence the circuit ground of the unit, are probably connected directly to the chassis (although I can't tell with total certainty). Which would inherently create a susceptibility to ground loop issues, that may or may not materialize depending on the grounding configuration and other characteristics of the component(s) it is connected to.

Best regards,
-- Al

Len, no, I was not implying that. My mention of the fact that the Almarro amp and the Dynamo are not SET (Single Ended Triode) amplifiers was to make the point that for them to perform at their sonic best, whatever that best may be, it **might** be LESS necessary to run them at a small fraction of their rated power than in the case of a true SET.

Best regards,
-- Al

The 6BM8 combines a triode section and a pentode section in a single tube. The triode section is much more limited in power capability than the pentode section, so the triode section is normally used to drive the pentode section, which in turn provides the amp's output power. But the pentode section is itself very limited in power capability, such that to achieve 8 watts I believe the EE integrated must be using two of them in push-pull.

So as might be expected there are many variables that distinguish the EE integrated from a 300B or other comparably powered SET. One being single-ended operation of the power tube vs. what is probably push-pull operation in the EE. Single-ended operation avoids "crossover distortion," which affects the zero-crossing of the signal and therefore becomes increasingly significant at low power levels. Another being use of a triode power stage in a 300B amp vs. a pentode power stage in the EE, with good triodes generally being considered to be more linear (at least when not pushed in terms of power delivery). Another being that the 300B, as well as the lower powered 2A3 and 45 tubes, being especially well regarded for their sonics in comparison to most other triodes. Another being that since the 300B, 2A3, and 45 tubes are relatively expensive, they tend to be used in amp designs that are less constrained by cost considerations than amps that would be designed around less expensive tubes.

So as might be expected many factors are involved, undoubtedly including others that I haven't thought of.

Best regards,
-- Al

Thanks, Jet. Yes, implementation of the phase splitter in a push-pull amp is certainly a critical aspect of the design. I can't offer any particular insight, though, regarding the tradeoffs between use of a transformer and use of a tube for that purpose.

I'd imagine, though, that as with many things in audio either approach can provide results that are either better or worse or similar to the other, depending on the specific implementation and the other aspects of the design.

Best regards,
-- Al

Way to go, Mapman!

A speaker that is a **true** 90 db/1W/1m/8 ohms driven by 8 watts should be able to generate SPL's in the mid-90's at a centered listening position about 10 feet from the speakers. Which would certainly seem likely to be adequate for the majority of chamber recordings. The problem that often seems to occur, though, as Duke mentioned early in the thread, is that the specs are inaccurate and/or misleading.

One commonly seen example of a spec being misleading even if it is accurate would be a spec such as 90 db/2.83volts/1m for a 4 ohm speaker, or for a speaker that is spec'd as having a higher impedance but which is more accurately characterized as a 4 ohm speaker. The 90 db in that situation corresponds to just 87 db/1W/1m, since 2.83 volts into 4 ohms is 2 watts rather than 1.

In this case, though, it would seem that the 90 db figure is an honest one.

Best regards,

-- Al