Sorry, Marakanetz, that explanation is not correct. First off, not all tube amps have output transformers. Mlsstl put his finger on the issue- odd ordered harmonics.
Smooth clipping is less odd-orders. Music is a very transient sort of waveform- when the transients clip the amp (even though the rest of the waveform does not), this will be a major factor in what separates the tubes from the transistors, **not** low frequency bandwidth. Odd-ordered harmonics are used by the ear/brain system as loudness cues; the transistor amp overloading on transients will be sounding very loud, whereas a tube amp might still seem to be asking you for more, without the associated harshness.
This is why guitar players prefer tubes as well.
BTW the difference between 250 watts and 100 watts in only about 4 db- not that much to the human ear. |
Marakanetz, not to be on your case or anything but while we do go for as much performance as possible at the same time we take advantage of the vintage look to keep the overall cost down, making our amps affordable against similarly-powered tube amps.
The idea that larger woofers are harder to control is pure mythology and a common one at that. My speakers at home have dual 15" woofers per side and our little S-30 can put plenty of excursion on them.
The amount of excursion a speaker has can be extremely variable as all speakers have different damping requirements. IOW it is not the case that the higher the damping factor the better- in fact there are no known examples of any speaker needed more than a damping factor of 20:1, yet there are cases of speakers that need damping factors as little as 0.1:1 (usually these are designs intended for open baffle).
If the amplifier under-damps the speaker, you actually get excessive excursion rather than too little, and vice versa if the the speaker is over-damped. |
Br3098, try it, you never know- for sure it will work with a pair of ZEROs... |
Br3098, I appreciate the humor but seriously, the heat of our amps is quite manageable. Up here in Minnesota we see the highest dewpoints recorded anywhere worldwide and our amps are easy to live with even in the summer. However the heat comes from being class A, not the number of tubes. You can run the amp in Standby all day and at the end of the day, put your hand on the tubes without fear of burns. But from stone cold, within a minute the tubes are way too hot to touch because they are conducting.
IOW a solid state amp of the same power that is also class A will heat up your room in much the same way- it will make about 85% of the same heat. The real issue is, what do you want the system to sound like? Real music? If so, you are going to have to go class A- all other classes of operation are performance compromises.
Now it may be that you can find nice-sounding amps that are not class A, in fact they abound. But the very best, the ones that stand apart- they will be class A. |
Unsound, for your answer: http://www.atma-sphere.com/papers/paradigm_paper2.htmlTubes will not drive all speakers 'correctly' and of course there are speakers that cannot be driven by transistors. However I am pretty sure that this thread is assuming that the speaker in use is not a variable for the purposes of this conversation. |
Br3098, they can be excellent help if the load impedance is too low! |
Orpheus10 and Mapman, the reason tubes seem more powerful has to do with the way we perceive sound and the different ways that tubes and transistors make distortion. I would look at some of Arthur's comments above- they are right on the money.
I think I also had some of this explained above too- if I need to clarify it just let me know. |
Orpheus10, the reason it seems subjective is only because the industry as a whole really does not want to talk about the science. For that I point you to the writings of Norman Crowhurst regarding feedback and its effects, also to http://www.atma-sphere.com/papers/paradigm_paper2.htmland if you have the time, I recommend reading 'Chaos' by James Gleick. Inside that book (a good primer for Chaos Theory) you will see some interesting waveforms, some of which you have seen before if you have spent any time around audio gear. BTW, Norman Crowhurst actually has charts of the strange attactors that govern the behavior of audio amplifiers using loop negative feedback, although he had no idea at the time that years later those charts would be associated with strange attactors. General Electric also proved some fundamental rules of human hearing the mid-60s, which for the most part was totally ignored by the audio industry (how we perceive volume through the presence of 5th,7th and 9th harmonics). This work has been extended in the 21st century by Dr. Herbert Melcher, a noted neuro-chemist, who has discovered that as an audio reproduction system violates human hearing rules (too much of the wrong distortions, too slow, stuff like that) that the processing of sound moves from the human limbic system to the cerebral cortex- and for this he actually has hard numbers! IOW there is plenty of science, much of it on-going, to support why tube power seems more powerful; like I mentioned before, its not about the power, its about how the technologies distort. |
Mapman, that is as succinct an explanation as I have ever heard. Well done. |
Unsound, what is meant by offense is not really a matter of taste. Back in the 1960s, GE did a test where they played music and test tones for people and gauged the response.
What they did was to introduce two types of distortion- even lower orders, and higher odd orders, in two tests. What they found was that people will tolerate without objection up to about 30% distortion if its all lower orders, but tiny amounts of odd orders, less than 0.1% was highly objectionable!
IOW, what they found out was that the human ear listens for the 5th, 7th and 9th harmonics in order to determine the volume of a sound and that we are sensitive to distortions as low as 0.001%, where we really don't care about lower orders (the 2nd,3rd and 4th).
This is also the difference between tubes and transistors as far as distortion goes. I myself do not like what many have come to call the 'tube coloration' and I have found that with careful design there is no reason to have to tolerate it either. Nor do I like transistor coloration, but its a lot harder to design transistor amps that lack it; all of them that I have heard that lack transistor coloration are all also zero feedback class A designs, I think not out of coincidence.
I don't fault anyone for disdaining the typical distortions that are easily heard in a lot of gear- I feel the same way. |
Unsound, the point of my post was in fact that all humans do indeed use the exact same perceptual rules- that is what the research (science) has proven. Taste is something else entirely and not on the table here.
As Joe and Arthur point out, timing is everything. What tubes bring to the table is the ability to build a low-distortion amplifier without loop feedback. With no loop feedback, time-domain distortions are 100% eliminated. With feedback, time-domain distortions become the name of the game. |
I've only seen snipets but its easy to prove if you have some very basic test equipment.
All you need is a sine/square wave generator, a small amp of any type, a VU meter and a speaker.
Set up the sine to drive the amp, which is in turn driving the speaker. Put the VU meter across the speaker terminals. Obviously you don't need a lot of power for this test. Set the sine wave to read 0VU on the meter. Now switch to the square wave and set it **without looking at the meter** to the same apparent sound pressure level.
What you will find is that with the square wave you are setting it somewhere in the neighborhood of -20 to -30 db to get the same sense of volume- less than 1/100th of the original power!
Square waves are composed of only odd-ordered harmonics. This is a very simple test, but it illustrates the issue very clearly. |
Unsound, seriously, just try the test I outlined above. It will eliminate any doubts you may have. When GE did their tests they found that people would not object to up to 30% THD- if it was all 2nd harmonic. But less than 0.1% of odd orders and they objected quite a lot. |
Unsound, its not. Almost any service shop would have such gear though, you could easily set up this test at almost any one of them simply because the speaker and the amp really are of no consequence in the test- the results are that profound.
How the human ear detects volume is a fundamental rule of human hearing- the 5th, 7th and 9th harmonics are the cues that tell us how loud a sound is. If these cues are distorted (enhanced) even by slight amounts, we hear it. Bright, hard, sheen, clinical, brittle, etc. are all words that audiophiles use to describe enhancement of these harmonics by very slight amounts; 1/100th of a percent is easily heard. |
Unsound, sounds like right here is the point where you are going to have to try this out yourself rather than relying on other's input. I've only been offering the 'why' behind the experience. |
Unsound, well, not vehemently at least :)
All the things I have looked at in the last 35 years or so point to tubes more closely obeying the rules of human hearing than transistors, mostly due to better linearity. So for the most part, I would build a system around the amplification, and look for a speaker that matches, rather than the other way 'round. It seems to me that this is an easier path to a system that sounds like real music. |
Here are some speakers that are not well driven by transistors: ESLs (too bright, no bass unless the speaker is only a foot or two from the wall), horns (usually very shrill, due to the reactive nature of the drivers), full-range high efficiency drivers (similar to horns), any box speaker wherein the designer was expecting a power response from the amplifier rather than a voltage response. An example of the latter is the Wilson Watt/Puppy, which had a resonance in the tweeter. This was controlled by a trap filter set at the frequency of the resonance. This caused a 2 ohm impedance at that frequency (2KHz). Tube amps, encountering that impedance, do not make much power and everything is good. Transistors dump power into that load, resulting in brightness. This is why you see such conflicting opinion on that speaker. for more info see: http://www.atma-sphere.com/papers/paradigm_paper2.htmlSo IME, since I prefer the reduced coloration of tubes, it makes sense to me to choose a speaker that works with that, rather than one that requires a transistor amp to sound right. IOW, that's why you choose the amplification first, then the speaker. Otherwise you can flush some big money down the loo. |
Unsound, if they disagree, its only because they have not been studying what happens that is different between tubes and transistors with respect to how they drive a load. Roger Sanders and I already went around on this one, and if you ask Roger West, he'll tell you that a lot of his customers use our amps... and Nelson Pass has different nomenclature as he uses Voltage Paradigm terms and I don't, but he and I are on the same page here. Just look at his articles about 'current source' amplifiers. You might also look at a great article written by the chief engineer of EV http://paulspeltz.com/tomcik/index.htmlWhat you get from this article is that there are no known examples of speakers needing over 20:1 damping factors, but that there are speakers that need damping factors of 0.1:1. IOW, the Voltage Paradigm does not work for all drivers. Sorry for the OT- this really deserves a different thread. |
Unsound, you are right, a lot of ESL designers do work with solid state. I am of the opinion that they have a particular challenge- break out of the niche that they are in by coming up with an ESL that actually works with transistors...
The problem is two-fold. First, the impedance decreases as frequency increases, meaning that a transistor amp will make more power, causing brightness. Bass is an issue, as there can be some pronounced impedance peaks in the impedance curve. This prevents a transistor amp from making power. This is why a 200 watt tube amp can keep up with a 600 watt transistor amp on a set of Sound Labs, as the 600 watt amp may only be able to make 75 watts in the bass, where the tube amp can be capable of nearly full power.
The second is of course that the impedance curve has nothing to do with driver or box resonance, something that is fundamental to the operation of the Voltage Paradigm. In fact ESLs prefer to see flat power response out of the amp rather than flat voltage response.
To limit these issues a lot of ESL guys keep the speaker impedance very low- 4 ohms in the bass and 0.5 ohms at 20KHz is common. You still have the 8:1 change in impedance, but many transistor amps cannot make much in the way of additional power into 0.5 ohms and at that impedance, the speaker cable itself is a huge limiting factor. Its a band-aid approach, and when you see this its an ESL manufacturer that wants to cash in on the extra market share that they see in transistors.
You may have noticed that this is an entirely different example of how a tube amp with less power can be more powerful than a transistor amp; whenever you are dealing with high impedances this can be the case. Sound Labs have a peak of over 40 ohms in the bass. The 600-watt transistor amp above driving that peak might only make 75-100 watts. |
Koegz, I read that paper some years back, but I have not seen it on the web. Do you know of a link to it? |
Pubul57, Kirkus has been right on all his points but one- I've not really talked a lot about the DC coupling issue, even though I am a proponent of OTLs (the two are not always the same thing).
In a nutshell though, I think true DC coupling from input to output to be a bad thing, because every power supply has a low frequency pole, and if you exceed it (which a true DC coupled amplifier can) then you can modulate the power supply with audio from the amp, and that's bad- it gobbles bass impact and adds distortion.
So a frequency pole somewhere in the amp that limits it to a point at least an octave above the low frequency pole of the power supply is a good idea. We take it a step further by having a separate power supply for the driver, which is part of where we get our low IM distortion numbers from.
A few years ago I looked all over the web trying to see if anyone had scanned or posted that GE study, but so far it exists in print form only, no web. |
Kirkus, Shadorne, and Unsound, I really appreciate your input over the years. Inside of what I call the Voltage Paradigm, yours can usually be counted on to be accurate comments, and always done with decorum :)
I want to point you to Duke's comment about the port tuning dated 04/12. Here Duke is pointing out how the port is set up differently depending on whether you are using Voltage rules or Power rules. Its not the only thing I have seen in speaker designs, as in crossovers I have seen capacitive or inductive shunts used to get the right power response out of the amp so that the driver will roll off at the right frequency.
I guess what I am getting at here is that the Voltage rules are not the only game in town, and this has always been the case. However I find that if I am dealing with an individual who is educated with Voltage rules, that they will generally assume that there are no **other** rules. So I am interested in you thoughts regarding Duke's post. |
Unsound, I think the 'harm' comes in when the speaker requires that the amp use a lot of feedback to work right with the speaker. Since our ears use the 5th, 7th and 9th harmonics as a means to perceive sound pressure, and since negative feedback is known to audibly enhance (distort) these harmonics, the result is something that sounds more like electronics and less like music.
This harmonic distortion contributes to the amp sounding 'loud' or 'shouty', even though it might be nowhere near clipping. Now we get back on-topic: tubes, which generally use less feedback, tend to have more *usable* power as they tend to sound less 'shouty', and thus encourage you to turn the volume control up higher without stress. This assumes, of course, that the tube amp is able to drive the same speaker that the transistor amp can, for any kind of reasonable comparison.
IME if the speaker is has reasonable efficiency, and lacks weird phase angles and the like (IOW is not demanding of the amplifier), that **all** amps driving that speaker will sound better. BTW this is a strong argument for higher impedances, since even though a transistor amp might be able to drive a 3 or 4 ohm load without strain, that is not the same thing as saying it is sounding its best while doing so. |
In the last 20 years the use of SETs has really increased a lot. It has resulted in a lot of speakers that were simply not available 20 years ago. So these days its ten times easier to find a speaker that works with 'current source' amplifiers than it used to be.
Unsound, I can think of three speakers that if you put a tube amp on them, the result will be shrill, and all for the same reason: the amp will not double power as impedance is halved (or conversely, cut the power to 1/2 as the impedance doubles): the B&W 802, the Avalon Isis and the mbl101e. So if you are working with speakers that have similar impedance curves, I can totally see where you are coming from.
BTW the speakers on that short list are all examples of Voltage Paradigm technology, and its been my experience that when you mix Voltage and Power technologies, you will get a tonal aberration; 'shrill' is a common resulting aberration. Several others have been mentioned above, such as the 'wooly bass' that Duke was commenting too. |
I think they do. It would be really tricky to build a zero-feedback transistor preamp. With tubes you can do three stages of gain between the LOMC phono input and the line out, I doubt that the same can be said of transistors, at least, I've not seen any so far.
I have an additional comment about distortion that Joe mentioned- that of, shall we say, 'dynamic distortion'. Its my opinion that we need some sort of distortion test that uses a non-repeating waveform similar to what you see in real music. What Chaos Theory is saying about this is that sine waves represent a stable state in an amplifier circuit that might otherwise have chaotic response. BTW Norman Crowhurst pointed this out 50 years ago in his writings about negative feedback. Chaos Theory really seems to point to the idea that negative feedback is a destabilizing factor in amplifier circuit design, in fact, going so far as to call it non-linear.
This seems to fly in the face of traditional theory, where negative feedback occurs as something to increase linearity. But what we find by its application is that the energy of the distortion (nice calculus segue here BTW) is not changed at all- it is instead spread over the spectrum as a harmonic noise floor injected into the circuit's output. In addition, in-harmonic distortions are created due to inter-modulations at the feedback node.
The way the ear deals with this is interesting- our ears can penetrate natural noise floors like hiss or the wind blowing by about 20db, but can't do the same with this harmonic noise floor, which thus masks detail that exists below it. This is one reason why zero feedback circuits tend to be more spacious. |
Myles, the mbl has an impedance peak of about 8-9 ohms in the midrange driver. The designer is expecting the amp to reduce power by 3 db through this range. An amplifier with feedback will do it, one without will not. A good number of tube amps tend to sound shrill on this speaker even though otherwise they have plenty of power. So Michael was probably using an amp with a lot of feedback.
The problem here is that IMO, amps with feedback sound somewhat shrill out of the box, IOW its my opinion that a speaker that requires this will never sound like real music.
Kirkus, I know about the TIM articles but obviously amps designed to overcome that 'issue' were horrendous.
IMO the issue with feedback boils down to open loop propagation delay in the amplifier- IOW its a timing issue. The feedback signal simply does not arrive back at the input in time to make the correction. With a steady-state signal, the amp locks in pretty well over a few iterations, but with a constantly-changing waveform the amp will be chaotic. This is an interesting subject and I agree- a topic for another thread. |
Emorrisiv, I've heard the Acoustats sound great with a set of M-60s and a set of ZEROs. The guy that had them also had an ARC Classic 60, and he had to use the ZEROs with that amp also. They seemed to otherwise present a challenging load for a tube amp, but my guess is that they were doing what a lot of ESL manufacturers do, which is to set the impedance low to try to get transistors to work with them.
At any rate Acoustats and tubes are a great combo if you can overcome the impedance issue, and ZEROs do that quite well. |
Yes, just as they also made a dedicated tube OTL-powered speaker. |
