Myths That Plague Tube Audio © 2001 Alan Kimmel
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From the orginal TubeLabs site
Copyright © 2001 Alan Kimmel. All Rights Reserved
Myths That Plague Tube Audio
Tube Audio, more so than many other fields, is beset with myths, biases based on hearsay and "old husbands" tales, and unfounded criticisms of opposing viewpoints. The myths are fueled by bias and ignorance. Sometimes the believer of a certain myth has not thoroughly checked out the validity of his cherished belief. Or he made some little effort to do so but didn't do an adequate job. Either way, his cherished belief may be unfounded but he may think it is bullet-proof.
At the root of the myths you will find that the believer has chosen ONE belief, one paradigm, which he wants to believe is ALWAYS true. Some audiophiles, especially Tube audiophiles, desperately want some ONE THING to ALWAYS be true no matter what. There is no ONE magic thing which will always guarantee good sound. The sound of an amp is due to a combination of things.
The following are some of the myths that plague tube audio:
1. "The closer an amp is to Class A, the better it will sound.".
This myth says that Class B always sounds the worst, Class AB sounds better, and Class A always sounds best. I used to lean towards believing this one myself until my ears encountered a Class B amplifier (which uses transmitting tubes) that has more sonic purity than the majority of Class A and Class AB amps available. No, I'm not saying Class B is best. I'm saying the (operating) Class of a tube amp is not as important as how much "class" the amp has.
2. "Triodes always sound better than pentodes."
In some situations, even the opposite can be true. Triodes have the advantage that no matter how they are used they will usually sound good. Pentodes are more particular about how they are used. But if used properly pentodes can yield fabulous performance and superb sound.
3. "The simpler the better."
This myth says that the simpler an audio circuit is, the better it will sound. Einstein once said something very relevant to high end audio: "Everything should be as simple as possible, but not simpler."
Many feel that the Single Ended way is the best way to make an amplifier because SE is the simplest. But even the simplest SE amplifier is not as simple as it really could be. To be as simple as possible, there should be only ONE tube in the amp-- the output tube. Next, to be as simple as possible, your magnetic phono cartridge should be replaced with a crystal or ceramic type, because these put out a high enough signal level as to be comparable to Line level. This obviates the need for a phono preamp. If you want to be even simpler, obtain a speaker with an impedance of several thousand ohms so you can connect it directly to the tube, in place of the output xfmr primary, eliminating your output xfmr.
You now have a sound system that is truly the world's simplest, but how would it sound (even if it had enough gain) ?
Obviously it will not sound as good as a sound system containing one of the better magnetic phono cartridges. Also it may or may not have enough gain since the power amp has only one tube-- the output tube. Besides the fact that the better speakers are not available in the several thousand ohm category, the continuous DC current through the voice coil would probably push the voice coil out of its gap.
The point is, the simplest way is not always the best way. Instead of striving for things to be as simple as possible, the best thing to strive for is THE PATH OF LEAST RESISTANCE TO THE MUSIC. As shown above, the simplest path is not necessarily the best path. The simplest path is not always the path of least resistance to the music.
Now consider the human hearing system-- the ear, the eardrum, the middle ear, and the inner ear, etc. It's complex! But it was made just right. The Master Designer knew exactly what He was doing. Would you go to an ear surgeon and say, "Doctor, I think my hearing system is too complex. I want you to remove some of it so it will be as simple as possible." Even if the Dr. could do this without harming your hearing, who would actually go through with it? Obviously there is AN IDEAL LEVEL OF COMPLEXITY designed into your ear. If you get simpler than the ideal level of complexity you fall short. Or if you EXCEED the ideal level of complexity, again you fall short sonically.
To sum up my comments on this myth: Just as circuitry that's too simple can be a disadvantage, likewise circuitry that's too complex is also a disadvantage. There is, in any given situation, a happy medium-- an ideal level of complexity, which is dependent upon the topology and techniques used.
So I believe what Einstein said. I believe amplifiers should be as simple as possible, but not simpler, for the very best sound reproduction.
4. Regarding Single Ended (SE) versus Push-Pull (PP) topologies, there are two myths:
One says SE sounds best, while the other myth says PP sounds best. The truth: The sole fact that it is either SE or PP will not guarantee one topology to have superior sound over the other. Some SE amps sound better than some PP amps, while some PP amps sound better than some SE amps. Again, the final sound is dependent on a combination of many things.
5. Another myth: Tube amps always sound better than solid-state amps.
Actually, this myth is often true. But everyone knows that the best sounding solid-state amp sounds better than the worst-sounding tube amp. What the solid-state-only crowd won't entertain is that the best sounding tube amp may well sound better than the best sounding solid-state amp.
6. Many believe negative feedback (NFB) always sounds bad.
The truth is, it depends on a combination of things, namely, how it is used. Are you aware that every triode tube has (local) NFB built into it? The plate, with nothing to shield it from the grid, injects some NFB into the grid. This fact led to the development of tetrodes and pentodes because engineers were seeking a tube whose plate had no influence on the grid (i.e., no NFB). Hey all you Zero NFB fanatics, if you really want to be 100% true to your Zero-NFB fixation you must throw away your triodes and use only pentodes. But I don't recommend you do that because triodes are usually the best voltage amplifiers. Pentodes can excel at current amplification. So let's use triodes for voltage amplification and pentodes for current amplification. This fact about triodes shows us that the human ear LOVES local feedback.
AND there are other examples that show that local feedback is pleasing to the human ear. When you don't bypass the cathode resistor of a gain stage, you are using local feedback. When properly done, local feedback is definite plus.
What about "global" NFB? Anti-NFB audiophiles oppose global NFB most of all. But chances are they haven't heard a Futterman OTL, which relies on global NFB. If they do get to hear such an OTL they may well change their tune. All I'm saying here is that in some situations global NFB can be a plus.
There are other myths in tube audio but these are probably the main ones. These myths hurt the cause of tube audio because some of their proponents criticize other technologies within the tube audio field. One of the richest strengths of tube audio is the great diversity of technologies that are possible. Each technology has a certain advantage or set of advantages which may best meet the needs of the individual for his/her situation. Many times the best solution is to combine many of these technologies. The Key: HOW each of these things are used determines the sonic excellence (or lack thereof) of a design.
No one thing will always guarantee good sound. Let's stop looking for one magic truth to always be so. Clinging dogmatically to only one cherished paradigm cuts you off from the vast realm of possibilities that exist. Just because a device or an idea sounds bad when used one way doesn't mean it can't sound good used another way. The key to great sound is a winning combination of things. Let your ears be your guide and keep an open mind.