A transistor in isolation? No.
A transistor in a particular circuit, with particular DC voltages and signal voltages and sources and loads? Yes, maybe. Finding it is called 'design'.
People may try to tell you that a 2N12344 always works best at 8.1342mA. This is a signal that you can ignore what they tell you.
Once again, don't keep looking for simple answers to complex questions. How long is a piece of string?
A transistor in a particular circuit, with particular DC voltages and signal voltages and sources and loads? Yes, maybe. Finding it is called 'design'.
People may try to tell you that a 2N12344 always works best at 8.1342mA. This is a signal that you can ignore what they tell you.
Once again, don't keep looking for simple answers to complex questions. How long is a piece of string?
Ok but just one last question about linearity
What is the widely accepted test to assess the linearity of a circuit ?
is it the distortion test ?
Can we say that if a circuit has a high distortion is not linear ?
You can very well understand that one thing is to read a graph of distortion (like those in the Stereophile reviews for instance me too i understand that and found bad units ) another one is to be able to design an equipment (and this is not for everyone)
If this blessed distortion test is THE TEST everything is much simpler
Because then i would buy one sim SW and changing the parameter for just one bjt until i find a circuit with low distortion that then i will try to build
It could be the case that just a one bjt line stage optimized could have low enough distortion, at least for me
And i would leave with humble pleasure more complex topologies to talented designers
And moreover i think that to start a circuit with just one bjt is the best
Even at school they start with simple circuits I guess
If one is not able to understand this kind of circuit is better not to start completely
But still my main question is about the common test used to assess the linearity
Just think that I thought it were the frequency response test
Thanks again
Kind regards,
gino
What is the widely accepted test to assess the linearity of a circuit ?
is it the distortion test ?
Can we say that if a circuit has a high distortion is not linear ?
You can very well understand that one thing is to read a graph of distortion (like those in the Stereophile reviews for instance me too i understand that and found bad units ) another one is to be able to design an equipment (and this is not for everyone)
If this blessed distortion test is THE TEST everything is much simpler
Because then i would buy one sim SW and changing the parameter for just one bjt until i find a circuit with low distortion that then i will try to build
It could be the case that just a one bjt line stage optimized could have low enough distortion, at least for me
And i would leave with humble pleasure more complex topologies to talented designers
And moreover i think that to start a circuit with just one bjt is the best
Even at school they start with simple circuits I guess
If one is not able to understand this kind of circuit is better not to start completely
But still my main question is about the common test used to assess the linearity
Just think that I thought it were the frequency response test
Thanks again
Kind regards,
gino
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Linearity (or lack of it) is a circuit property. Distortion is the result of what non-linearity does to a signal. It can be measured by looking for harmonics or intermodulation. Distortion (almost) always varies with signal level, so a useful distortion measurement includes more than one signal level. Distortion often, but not always, increases with larger signals.
Frequency response is something different. It is caused by filters, intended or unavoidable. Both filtering and non-linearity can change the shape of a waveform, but on the latter causes distortion. People sometimes find this confusing, and claim that a filter has 'distorted' a signal. At some point in the ensuing discussion it usually emerges that they either don't understand, or don't believe, Fourier theory.
All of this is standard textbook stuff.
Frequency response is something different. It is caused by filters, intended or unavoidable. Both filtering and non-linearity can change the shape of a waveform, but on the latter causes distortion. People sometimes find this confusing, and claim that a filter has 'distorted' a signal. At some point in the ensuing discussion it usually emerges that they either don't understand, or don't believe, Fourier theory.
All of this is standard textbook stuff.
It could seem weird to you but this for me is extremely important, and i thank you sincerely
From day one i heard of this damned linearity and all the circuital tricks to improved the low intrinsic linearity of transistors
But i was confused about which test shows the non linearity
For me this becomes now a cornerstone, a reference to judge those circuital tricks
What i have found always at least strange of this distortion spectra is the fact that i send a single tone in the input and at the output i get the armonics
Other people by the way are very much less worried by this fact
So maybe it is a my problem
Anyway thank you. This was my dilemma
Perfect ! no more annoying questions
I will try to understand something from the book recommended me here
By the way i like very much the idea of sim SWs
My feeling is that they are an exceptional tool and a great point to start
If i am not wrong i can change parts in the circuit and the SW automatically can give a distortion spectrum,
This is for me now that i understand the importance of this test is amazing. I am honest.
I have just an observation
When i look at this distortion graphs on Stereophile I see that they are measured with pure resistive load (600, 10k, 100kohm etc.)
But from the spec of some amps i see also some capacitance at the input, in some case even more than 500pF
I wonder if this capacitance would impat on the distortion performances of a preamp
They should carry out the tests with a though load, like 10k+1000pF
Just to be on the safe side
Strangely i see this tests often shown in the datasheets of op-amps
Thank you sincerely
Kindest regards,
gino
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What i have found always at least strange of this distortion spectra is the fact that i send a single tone in the input and at the output i get the armonics
This is simply the result of representing a waveform in terms of Fourier analysis.
This says that a repeating waveform may be synthesised by adding together other waveforms at the correct frequencies, amplitude and phase. It can be shown that any waveform can be represented by a sum of sinusoids at multiples of the fundamental frequency i.e. sinusoids are elemental components of any repeating waveform.
If your circuit has a tendency to clip, then its output can no longer be represented by a single sinusoidal waveform. However, by Fourier synthesis you could sum sinusoidal waveforms at multiples of the fundamental frequency (i.e. harmonics), at the correct amplitudes and phase, and arrive at the clipped waveform exactly. Fourier analysis is the opposite of Fourier synthesis, and automatically finds the amplitudes and phases of these harmonics from the clipped waveform. The energy of these harmonics vs. that of the (desired) fundamental at the amplifier's output is the THD measure, basically.
Hello ! I am sorry but this is both extremely interesting and completely beyond my ability to understand
You mean that the distortion of a device can be predicted with math without measuring it ?
This is really fascinating.
I do not think that i would be able to calculate even a basic circuit
But i think i could be able to use one of these sim softwares
From what i understand a lot of audio designers simulate their designs before actually build them.
This at least for me could be a good point to start.
Simulate a very basic circuit, try to optimize it with the sim SW and then build it and ... listen
It would be better to measure it before listen anyway
I think I am done for now.
Minimalism and linearity ... now i have good answers to both this questions.
Thank you very much again.
Have a nice day !
Kind regards,
gino
Hello ! I am sorry but this is both extremely interesting and completely beyond my ability to understand
You mean that the distortion of a device can be predicted with math without measuring it ?
Hi ginetto
The main point was in answer to your question about how a sinusoidal input to a distorting amplifier circuit can give rise to multiple 'frequencies' at the output. They are only separate frequencies in the sense that they are harmonics i.e. integer multiples of the incoming frequency and locked in phase, so they do not sound like multiple signals, merely a change in the timbre of the waveform. Fourier analysis of the measured output would show that a sine wave clipped by an amplifier contains a number of harmonics, but on an oscilloscope it would show as a fixed repeating waveform - which it is. A computer simulation of the action of the amplifier based on the components' known characteristics would, indeed, predict the clipping, and thus the THD, without needing to measure it.
Audio electronics is a branch of electronics; in fact one of the simpler branches. Electronics is a branch of electrical engineering. Electrical engineering is a branch of applied physics. In physics understanding involves being able to make calculations using mathematics. Therefore circuit understanding involves being able to estimate its properties, including distortion. I say 'estimate' because we sometimes do not know the required parameters for a particular device in enough detail to make an accurate prediction. Fortunately audio design is usually sufficiently noncritical that an estimate is good enough.ginetto61 said:
So a circuit designer should be able to predict, roughly, things like gain, frequency response and distortion before he measures or simulates. The alternative is blindly copying others, or random fiddling (in reality or on a computer) until the circuit comes out right. Some people call this 'design', but it is not design in any serious engineering sense of the word.
I see, and this in some cases can be very pleasant even if not properly faithful to the original signal ?
Very interesting.
By the way i wonder how much it is possible to lower the distortion of just one bjt acting on its working conditions.
If this distortion is below the earing threshold why bother with more complex topologies ?
Is there really a need for them ?
And this is most interesting because it simplifies a lot the work
As i said i think that i should start with studying a sim SW and a pc based oscilloscope.
Just to start of course
Thank you very much indeed.
Kind regards,
gino
I see. It's Physics.
I wonder if circuits with same distortion spectra sound the same, indipendently from their complexity.
And as i said above how much low distortion we can get with a basic circuit.
If this distortion is low enough maybe it can be tolerated
Thank you very much again
Regards,
gino
You say this, but there are apparently sane, intelligent people spending multiple thousands of dollars on not amplifiers, but pieces of wire, and hearing "night and day" differences between them. To the average newcomer, it must make audio engineering look like a very complicated branch of electrical engineering indeed.
ginnetto,
you are asking good questions. these are the same questions that are asked every day even by those who have extensive training and education!
what you end up with are layers of complexity, from simple to extremely complex. at each level the "answer" looks similar but different. when you start, by default you need to find and use the "simplest" explanations. as one progresses along the way, one finds that even the most complex analysis is only a good approximation of reality. that approximation may be "good enough" or even more than good enough, but one realizes the limitations in everything.
audio, and most other things are exercises in compromise. you get one thing to be very very good, and maybe other things are "good enough" or even not good enough. so, you have a balancing act. the trick is to make the balance point high enough so that the weakness (the worst parts) are still very good.
there is no perfection. there are only various approaches.
you asked if there were two devices with identical spectra of distortion, if they would sound the same? darn good question. the "scientific' answer is that they sure as heck ought to! in reality they will likely sound the same or very very close.
of course, you have to realize that in saying something like this, practical devices, like amplifiers almost always will act differently into non-resistive loads, so different circuits are very likely to produce different spectra of distortion into non-resistive loads, even if they should for some reason be essentially indistinguishable driving a resistive load...
so, nothing is ever quite the same in audio... and by the same token the threshold at which things become indistinguishable is as unclear as the answer as to where that threshold lies.
today, there are really fairly fantastic tools to do simulations, but they are only as good as the models, and the models are imperfect... so you could do nice simulations, and learn a whole lot about how a circuit will behave. then when you build the circuit, you learn a whole lot about how real devices decide to behave on their own... and then what you can and can't hear, and what makes a difference when it shouldn't, and what doesn't.
all in all, it's great fun, frustration and never quite simple...
...that's why this is a very active forum.
No easy answers, lots to learn, lots to read, lots to do.
_-_-
you are asking good questions. these are the same questions that are asked every day even by those who have extensive training and education!
what you end up with are layers of complexity, from simple to extremely complex. at each level the "answer" looks similar but different. when you start, by default you need to find and use the "simplest" explanations. as one progresses along the way, one finds that even the most complex analysis is only a good approximation of reality. that approximation may be "good enough" or even more than good enough, but one realizes the limitations in everything.
audio, and most other things are exercises in compromise. you get one thing to be very very good, and maybe other things are "good enough" or even not good enough. so, you have a balancing act. the trick is to make the balance point high enough so that the weakness (the worst parts) are still very good.
there is no perfection. there are only various approaches.
you asked if there were two devices with identical spectra of distortion, if they would sound the same? darn good question. the "scientific' answer is that they sure as heck ought to! in reality they will likely sound the same or very very close.
of course, you have to realize that in saying something like this, practical devices, like amplifiers almost always will act differently into non-resistive loads, so different circuits are very likely to produce different spectra of distortion into non-resistive loads, even if they should for some reason be essentially indistinguishable driving a resistive load...
so, nothing is ever quite the same in audio... and by the same token the threshold at which things become indistinguishable is as unclear as the answer as to where that threshold lies.
today, there are really fairly fantastic tools to do simulations, but they are only as good as the models, and the models are imperfect... so you could do nice simulations, and learn a whole lot about how a circuit will behave. then when you build the circuit, you learn a whole lot about how real devices decide to behave on their own... and then what you can and can't hear, and what makes a difference when it shouldn't, and what doesn't.
all in all, it's great fun, frustration and never quite simple...
...that's why this is a very active forum.
No easy answers, lots to learn, lots to read, lots to do.
_-_-
Thank you very much indeed for your very helpful reply
To try to understand something i have to simplify
As at school the first circuit that they teach is the basic one, not the more complex one
Still the all issue remains complex this also i understand very well
Speaking of extreme distortion i have been amazed by this unit here
Profiler | Kemper Profiling Amplifier | KPA | Guitar Amplification Redefined
maybe one day it will be possible to have a Krell with the sound of a 300B ... just a little more powerful ?
Thanks a lot and kind regards,
gino
To try to understand something i have to simplify
As at school the first circuit that they teach is the basic one, not the more complex one
Still the all issue remains complex this also i understand very well
Speaking of extreme distortion i have been amazed by this unit here
Profiler | Kemper Profiling Amplifier | KPA | Guitar Amplification Redefined
maybe one day it will be possible to have a Krell with the sound of a 300B ... just a little more powerful ?
Thanks a lot and kind regards,
gino
Those who are aware of psychological issues such as suggestion and placebo are still subject to them. Those who deny them are even more subject to them.CopperTop said:
Men have, occasionally, been known to brag about their supposed skills in various physical or mental challenges or their bodily attributes (yes, I know this comes as a surprise to some of you!). A 'night and day' difference which disappears under controlled conditions might not be quite as large and obvious as is claimed.
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