The 300B World
Disclosure: I am not new to Aric Audio, but I am new to the 300B.
I took delivery of my Aric Audio 300B PSET a couple of months ago. Since then, every listening hour has been different than it would have been were I new to both. I want to know who is responsible for what I'm hearing. So, the overriding question every observation is passed through is simply "Was that the 300B or was that the 'Aric Audio Heft'?" Over the years I have purchased a number of different amps and preamps from Aric and have come to identify certain characteristics that can be expected from all of his builds. That's why I keep going back. Examples include the "dead black" background, the solid signal strength delivered by his preamps, the ease with which the soundstage can be mapped, and the raw power resulting from the overbuilt approach he takes in his design work: "The Aric Audio Heft." Knowing what I would get from any Aric Audio amp is instrumental in being able to appreciate the magic of the "show off tube."
I've heard it said that people who go to the 300B never really come back and I've been intrigued by that ever since. It invites critical listening across the broadest spectrum of music one can tolerate. It's here that observations are bagged and tagged, the first being the kind of music I listen to matters much less because I find myself listening differently and hearing so much more. One of my favorites is the leading edge of the lower frequencies and the way every beat reminds me that I'm listening to a 300B. The way I would characterize the sound profile would be to say it's as if the veil has finally been lifted and the distance between the performance and my listening chair closed. You know it immediately even if you can't quite define it yet and it commands your attention.
For some reason I'm surprised by how closely the tonal qualities of SET and PSET modes align. Somehow, I thought there would be more of a "sonic cost" for that extra power. I'm still cautious here though because the quad of tubes I'm using for PSET mode are not topflight tubes. So, the final analysis will have to wait until I can level the playing field. In SET mode I'm listening to a pair of Gold Lions, which I consider to be at least among the heavyweights. The question I'm presently grappling with is which tubes come next? I've done my due diligence researching the various offerings and think it will be a quad of Emission Labs XLS 300Bs. Any input around your experience with 300B tubes I would welcome. Yes, I have my wish list that starts with the Western Electrics (which I'm sure I'll own one day) but the guidance I'm seeking here is the step between now and then. What would be a suitable tube to take an already remarkable experience to a whole new level? Conversely, are there tubes that I should simply stay away from? My thanks to all. Happy listening.
As I explained earlier, the big challenge of SET OPT design is bandwidth. Its pretty easy to get bandwidth using a 45! Wider bandwidth means less phase shift, so the sound stage is recreated more accurately and there's less coloration at the bandwidth extremes (for example, phase shift in the bass region can rob it of impact, even if the transformer is flat to 20Hz). |
I think you'll find that the differences you hear have more to do with who designed and built the output transformers than anything else. How well the tube works with the transformer; how well the driver circuit and voltage amplifier circuits work all affect the sound. So it seems unlikely that anyone might be able to describe the sound of the different tubes given those variables! |
@tomcy6 Yes. I recommend the 8 Ohm tap. You'll need a sub to be convincing (IMO) since the speaker rolls off sharply below 50Hz.
Nothing, other than it was one of the first power tubes used for SETs when they made a comeback in the early 1990s (back then it it was them or the 211...). By the late 1990s, the 2A3 had eclipsed the 300b, which in turn by the mid 2000s was replaced by the type 45. But there really isn't any difference in the performance/sound of these tubes other than output power. The reason the smaller tubes sound better is the smaller output transformers, usually due to wider bandwidth. In any case you need a speaker with enough efficiency to take advantage of that power. The Klipsch La Scala has a good functional minimum for use with a 300b at 101dB in most rooms. Unless you are in a small listening environment, speakers with less efficiency will cause the amp to make too much power (and distortion) to really appreciate what its about. |
+1 If you really plan to use a 300b amplifier this is the best advice you can have. |
@charles1dad back in the 1980s the bit in your last sentence was true. But since the newer analyzer tools have become available, no longer. I’ve noticed though that such has little impact since people doing measurements often don’t do enough or the right ones; manufacturers don’t always publish them and finally, there’s not enough education in the field to be able to interpret what the measurements imply. But if the stars align then you can accurately predict how a circuit will sound, based entirely on the measurements.
To the first sentence, I’ve not found that to be the case, although with any kind of inductive coupling good iron is essential! Choke coupling is mostly an excuse to use an expensive inductor when a good resistor will do as well with wider bandwidth. Put another way, if more time was spent optimizing the operating point of the tube and less on fancy inductors that wind up (if you see what I did there) being mostly for show and tell, the circuit would exhibit the same positive attributes. Any circuit that is zero feedback will be affected by nearly everything in it since there is nothing to reject distortion, phase shift and the like. To this end, to avoid phase shift you need really wide bandwidth. To avoid distortion, you need good quality parts, each part of the circuit optimized for the operating point of the active device (since this issue applies to solid state circuits with zero feedback as well) and proper layout to avoid stability problems and noise pickup. |
This statement is incorrect. You can operate any tube using coupling capacitors just as linearly as using an interstage transformer. OTOH the trick with transformer coupling is making sure that the input and output impedances match the transformer properly to maximize bandwidth and yet prevent distortion due to the process of what is known as 'ringing' (which is when the output has an insufficient load). @charles1dad The issue with direct-coupling (Loftin-White) is that you can have signals that are below the LF bandwidth of the output transformer; this can cause saturation (distortion) of the transformer. You also need higher operating voltages to pull this off. If you choose your coupling caps carefully, you can reduce the LF saturation problem and of course the power supply voltage does not have to be so high. |
@jtgofish I don't think so- for teh last 65 years audiophiles have been hearing this problem despite the measurement camp touting its all 'expectation bias'; IMO/IME the measurement guys that think this don't have the engineering knowledge to understand why its happening. This in particular with solid state since its inception. It really doesn't seem to matter about the tweeter (tweeters with breakups will make it worse). IME this is why tubes are still in business 65 years on from being declared 'obsolete'. Fortunately class D is offering a solution; just in time since in the next 10 years tubes will get a lot harder to find. |
@jtgofish FWIW the kind of speaker in the simulation is rarely used with SETs. They are low power and so speakers used with them tend to higher efficiency; also designed to expect a higher output impedance of the amplifier, with no expectation that the amp behave as a voltage source! Most tube amps with zero feedback will act more like a power source than a voltage source. So the standard ’simulated speaker load’ is irrelevant if the user has his SET set up correctly. In @charles1dad ’s case, the speaker he is using was designed specifically for tube amps with higher output impedance and no feedback. For more on this topic see: The Voltage and Power Paradigms Since loudspeakers of all types typically have much wider frequency variation than amplifiers, the theory is that the tonality imparted by distortion figures more importantly than tonality induced by FR error. This is because the ear/brain system converts all forms of distortion to tonality and pays more attention to that as a result. SETs produce innocuous distortion so can be fairly neutral in this regard. The brightness and harshness of traditional solid state is an example of this: you can’t measure it on the bench in terms of FR error, since the brightness is caused by distortion interpreted as a tonality. Its really hard to get away from this problem with amplifiers using feedback, since what usually happens is the the distortion vs frequency starts to rise somewhere near 1KHz due to a lack of Gain Bandwidth Product. Ideally distortion vs frequency should be a flat line across the audio band, and with any zero feedback amplifier with sufficient bandwidth that’s exactly what you get. Alternatively this can be fairly easily accomplished with a self oscillating class D amplifier, since obtaining super high GBP values is fairly easy with them so feedback is properly supported across the entire audio band. See for more information. When distortion rises with frequency, its because the feedback is decreasing with frequency and so distortion is going up. This usually does not show in THD figures; in effect sweeping this problem under the rug. So the actual distortion at higher frequencies where the ear is more sensitive can be quite a lot higher than the THD values suggest! So while I’m not an SET fan by any stretch, picking on them due to FR errors due to output impedance is not the way to expose their real problems!
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This of course is what filter capacitors are for.
Actually if the design is competent, this can also be said of the filter capacitor at the output of the filter choke, assuming a capacitor input supply. |
In a traditional single-ended 300b amp the current draw is constant, from idle to full power. That means the voltage drop across the rectifier is constant too. If you are hearing differences, there can be only 2 causes; the first being that the amp isn't biased class A1 so at higher power levels the current varies (there is a class A2 and A3 operation where grid current is present at full power). The second reason is you are hearing the difference due different voltage drops across the rectifier tube itself. One advantage of tube rectifiers is that don't interact with the power transformer to create 'diode noise'. However, solid state rectifiers can be set up properly so the diode noise is properly taken care of; they can be as quiet as a tube rectifier. The nice thing about this is that they don't go downhill over time and hold up better. If this is done correctly it will outshine any tube rectifier. With DHTs you don't need to worry about cathode stripping since there's no cathode coating. |
