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Old 25th March 2013, 11:48 AM   #31
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Quote:
Originally Posted by CopperTop View Post
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
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 ?

Quote:
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
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
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Old 25th March 2013, 11:53 AM   #32
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Originally Posted by DF96 View Post
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.
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. 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
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Old 25th March 2013, 12:18 PM   #33
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Quote:
Originally Posted by DF96 View Post
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.
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.
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Old 29th March 2013, 09:02 PM   #34
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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.

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Old 30th March 2013, 01:20 PM   #35
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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
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Old 31st March 2013, 07:10 PM   #36
DF96 is offline DF96  England
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Quote:
Originally Posted by CopperTop
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.
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.

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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