Gareth,
This is not at all an exhaustive answer.
Electrons move fast in vacuum (the emission of electrons is produced by heat). It means quick response to signal changes and very small time difference between input and output. The events happen more correctly in time promoting linear transfer.
This is not at all an exhaustive answer.
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Electrons do move fast in a tube, but they can also move quickly in a transistor. I don't think this is a limiting factor for audio and doesn't have a meaningful impact on linearity.
The limitation to linearity in a tube is actually the electrons themselves. Their presence in the vacuum distorts the electric field between the anode and cathode. The result is that the current flow is not a linear function of voltage. It can be approximated as a 3/2 power law. This is the basic linearity of a tube. It's closer to a straight line than the exponential curve of a BJT.
Static Induction Transistors operate in a similar fashion, the equations of their behaviour are therefore similar and they can be approximated with the same power law curve as a tube. This is partly why they have been of interest for audio. JFETs have a 1/2 power law curve and are similarly favoured by some for audio.
All of the devices have real transfer curves that deviate from the simple models we make for them. I read somewhere that tubes can become exponential at very low currents.
The limitation to linearity in a tube is actually the electrons themselves. Their presence in the vacuum distorts the electric field between the anode and cathode. The result is that the current flow is not a linear function of voltage. It can be approximated as a 3/2 power law. This is the basic linearity of a tube. It's closer to a straight line than the exponential curve of a BJT.
Static Induction Transistors operate in a similar fashion, the equations of their behaviour are therefore similar and they can be approximated with the same power law curve as a tube. This is partly why they have been of interest for audio. JFETs have a 1/2 power law curve and are similarly favoured by some for audio.
All of the devices have real transfer curves that deviate from the simple models we make for them. I read somewhere that tubes can become exponential at very low currents.
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embarassingly slow ? - the power BJTs we are using today have cut off frequencies that are way up there. Small signal BJTs can operate significantly faster than that.
a big problem ? - not that I can see.
2007
"Researchers at the United Kingdom's University of Southampton have produced bipolar transistors that are twice as fast as current devices. Using a standard silicon-bipolar-fabrication technique with fluorine implantation, the group has demonstrated transistors with a transition frequency (fT) of 110GHz."
a big problem ? - not that I can see.
2007
"Researchers at the United Kingdom's University of Southampton have produced bipolar transistors that are twice as fast as current devices. Using a standard silicon-bipolar-fabrication technique with fluorine implantation, the group has demonstrated transistors with a transition frequency (fT) of 110GHz."
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Why thank you
But what is driving it all... you have such strong views on amplifier design and topology.
While I agree speakers are hugely important... the qualities of differing types of amplifier can shine through even on lesser speakers... so I have found anyway... and get things right with really good speakers and you can just blow the competition away
So come on
what's pumping the amps around those Maggies ?Sounds like we have the speaker side of things somewhat in common, at least. I'm running Tympani IV's (slightly modded and significantly repaired) with a VMPS New Larger Sub handling 40Hz and below.
Amp-wise, it's a fairly modified PS Audio 200c for the T-IV bass panels, a bridged Adcom 555-ii for the VMPS, and a SUMO Andromeda II for the mid/high panels. Also old equipment; the SUMO is newest at about 1992.
I would agree that the Magnepans are a gentle load in terms of reactance, but they're relatively low impedance, and want a ton of power to really light up. They also benefit from high LF damping factors in order to better control the bass panels. Is this why you're not crossing them in until 80Hz? Tube amps and Maggie bass don't generally marry well....
There is not much to argue with because is just a commercial tips!
. If something has to be sold at many thousands of dollars, pounds or euros then is right working customarily (and honestly) for this target of price. Doing primarily the best engineering work as possible. Bills for stylist designers should came for second. Imho at least!
Piercarlo
PS - I wrote this things because I retain most experieced and well trained engineers perfectly able to cope with task proposed and, if seriously motivated and not jammed from marketing imperatives, perfectly able to find new way of solving problems if needed.
Often are just "audio guru" transplanted in many marketing or advertising offices that miss the essential: anyone should be left to do by itself his own job without not required advices, pseudo technical bullshits and so on. And this include the need of NOT obeying some marketing constrains of design first conceived for satisfying magazine benchmarks instead of really well breed equipments.
Engineers and technical departments have other task to do instead of sustaining the sicked credibility of marketing and advertising offices. If they like to support their "arguments" with "pleasurable, plausible and understandable" technical fallacies, invent hoaxes for best doing it is just their own job, not that of someone else...
Don't miss an usually untold because implicite thing: electrons move fast in vacuum tube because they are low in density and just moving in vacuum. If you try to enhance meaningfully charged carriers in tubes (as done in gas tubes) their mobility sink deeply into a slug speed region: intense as number of slugs but sloooow!
Piercarlo
PS - Have you some link to details of news about BJT with flourine implant?. I'm interested in
Maybe he listens to himself. That might explain why he has not heard your request.My dear Lumba.... please tell us all what you listen too... I have asked you many times
Sorry to be off topic, but most others have gone this route and degenerated a good thread into a mish mash of unanswerable argument.
Originally Posted by Mooly View Post #563
My dear Lumba.... please tell us all what you listen too... I have asked you many times
At best we start a new thread with the follow headline:
"A new Generation of Power Amplifier - Lumba's ultimate approach"
Maybe then we will learn more details about Lumba's preferred circuit topologies
My dear Lumba.... please tell us all what you listen too... I have asked you many times
At best we start a new thread with the follow headline:
"A new Generation of Power Amplifier - Lumba's ultimate approach"
Maybe then we will learn more details about Lumba's preferred circuit topologies
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If you Google for high speed BJT you'll find a lot of stuff, the one I quoted was here:
Bipolar transistors achieve speed record.(GLOBAL DESIGNER) - EDN Asia | Encyclopedia.com
Lumba: I fear it is time for you to fess up - you need to tell us about what amplifier(s) you use
Thanks!
No, he can't fess anything otherwise he should stop to make ourselves "fessi" (an italian word what mean "fool", in very colorful sense
)Hi
Piercarlo
Vacuum tubes dont have only disadvantages and a good push-pull triode amp can produce <0.1% THD.
