The thermal distortion could be perceived? If so, how would we distinguish it from another type of distortion?
When the characterization and level of distortion of a sound system are relatively acceptable and the irremediably departing from the ideal signal forms are small and close to the floor of perception of human hearing, all attempts may be justified. to minimize it?
Could an amplifier in class A and with a very low excursion of the signal in relation to the maximum possible value given by Vcc, have a low thermal distortion?
Best regards
When the characterization and level of distortion of a sound system are relatively acceptable and the irremediably departing from the ideal signal forms are small and close to the floor of perception of human hearing, all attempts may be justified. to minimize it?
Could an amplifier in class A and with a very low excursion of the signal in relation to the maximum possible value given by Vcc, have a low thermal distortion?
Best regards
Power dissipation on gain transistor should be constant. If that is the case, both responses, with and without thermal model in example c.), are virtually the same. So introducing ..
I first met the Rush circuit in the Ed Cherry's NDFL amplifier published by Electronics Today International in August 1983.
If it has any relevance, the main origin of thermal modulation in a simple non-inverting configuration is the voltage variations across the emitter-collector of the input stage. If we reduce these variations, we should reduce the thermal modulation.
If we use an inverting configuration, the voltage variations become much smaller and there should be a lot less of thermal/memory distortion.
It is easy to compare the two configurations by ear.
I looked at (measured) thermal modulation of bias in an output stage. I could measure it, but found it only a few % of the bias current, and on the distortion measurement I didn't see anything at all.
Jan
Jan
Attachments
Similar set of measurements (with/without constant PD) performed on voltage gain device, like VAS transistor, would give quite more than only few percentages in THD differentiation (OLG mode) caused by thermal distortion. 0 dB voltage gain buffer is obviously more resistant to thermal distortions, especially in CLG mode, like your test case was.
If it is easy to distinguish, how would you distinguish by ear from an increasing distortion towards low frequencies caused, for example, by a capacitive coupling?
The characterization of such distortion I intuit that it should not be easy to distinguish, since it usually presents with temporary delay to the electrical disturbance that gives rise to it. Suppose the case of a strongly damped signal, followed by a significant period of silence, where the change of parameters in the active elements could occur only later during the period of absence of the signal (in this case, I think, it would be very difficult to distinguish the effect).
Dear Diego,
Why ask these questions when you can easily test if the recommended mods by Lavardin (or Peufeu) do improve sound quality???
Personally, I don't care if the improvement that I hear on my 3 modded amps an 1 DAC output comes from "ThMD" or from other mechanism(s), but I am inclined to think that it is indeed the former. I'll explain...
Apart from many improvements (which I won't detail here), the most striking for me was the exaggeration of transient sounds, like string plucking, bow attacks on stringed instruments, percussion on drums or piano, and even accidental noises. then I perceived that the amps sound more dynamic, as in more powerful even at the same volume levels. All these contribute to a more natural representation of the music and has a relaxing effect.
Then I stumbled across this interesting lectures:
MQA: Questions and Answers Tutorial: Temporal Errors In Audio | Stereophile.com
...which made me realize that the improvements I hear might be more related to time domain increased accuracy (alike reducing jitter in digital format) than in %THD or other.
The energy of the musical content, including its "envelope" and other, is better reproduced, better "concentrated", in the time domain so the brain has less processing to do to recognize the origin as music emitted from a musical instrument, from a human voice or from a fallen pencil...
The hearing system is much better and complex than we use to think...
For now I stopped experiments while I learn how to use LTspice since, due to the extraordinary (and additive; DAC-->amp) effect that replacing a simple PNP differential pair for a cacoded-CFP pair had on my musical experience, I want now to mod my output to a cascoded-CFP one and hear what happens.
Good luck,
M.
PS: Amnesis amp thread--> The AMNESIS amp: a good amplifier, like a gentleman, has no memory.
Dear Diego,
Why ask these questions when you can easily test if the recommended mods by Lavardin (or Peufeu) do improve sound quality???
Personally, I don't care if the improvement that I hear on my 3 modded amps an 1 DAC output comes from "ThMD" or from other mechanism(s), but I am inclined to think that it is indeed the former. I'll explain...
Apart from many improvements (which I won't detail here), the most striking for me was the exaggeration of transient sounds, like string plucking, bow attacks on stringed instruments, percussion on drums or piano, and even accidental noises. then I perceived that the amps sound more dynamic, as in more powerful even at the same volume levels. All these contribute to a more natural representation of the music and has a relaxing effect.
Then I stumbled across this interesting lectures:
MQA: Questions and Answers Tutorial: Temporal Errors In Audio | Stereophile.com
...which made me realize that the improvements I hear might be more related to time domain increased accuracy (alike reducing jitter in digital format) than in %THD or other.
The energy of the musical content, including its "envelope" and other, is better reproduced, better "concentrated", in the time domain so the brain has less processing to do to recognize the origin as music emitted from a musical instrument, from a human voice or from a fallen pencil...
The hearing system is much better and complex than we use to think...
For now I stopped experiments while I learn how to use LTspice since, due to the extraordinary (and additive; DAC-->amp) effect that replacing a simple PNP differential pair for a cacoded-CFP pair had on my musical experience, I want now to mod my output to a cascoded-CFP one and hear what happens.
Good luck,
M.
PS: Amnesis amp thread--> The AMNESIS amp: a good amplifier, like a gentleman, has no memory.
In relation to the possible existence of this distortion mode in discrete amplifiers I have not yet seen verifiable measurements that distinguish it from other types of distortions already known. What I have been able to find are only opinions of a subjective nature (including those of Peufeu himself), which raises doubts in being able to affirm if it is truly a new form of distortion different from those already known.
The effect caused by the tested stages and their proposed improvements is well known, but it must be borne in mind that a system functions normally in feedback to produce predictable and controllable responses. A system thus constituted (with all the stages associated and in feedback) is the one that I have not yet seen objectively measured yet.
A stage in cascode is an interesting tool, which minimizes the action of the Cbc parasitic capacity in one of the transistors to favor a more extended frequency response and achieve a comparatively greater and more linear gain than a simple stage without this implementation.
I think that a thermal modulation could occur mostly in integrated circuits and only be verifiable at frequencies well below the useful content of the audio band. It could represent problems only when the frequency of the thermal modulation is comparable to that of a useful signal. Since everything has thermal inertia and it is comparatively larger in relation to the speed of change of the lower audio signal, I do not think it represents a problem to be addressed.
Best regards
Furthermore, in case some effect creeps in the audio band, feed back removes it completely.
Why "mostly in integrated circuits" ?
Well, this is not the way that science works...almost all I read are experts' opinion on the form of "our present model, our present understanding of the problem predicts that there will be no effect whatsoever in this or that measurement of distortion". I contrast, most advances in human ascent are made when someone says -"now, that's interesting" or when one asks -"what if?" and then starts his own experiments to reject the hypothesis. Because, for example, what if we are measuring the wrong parameters?
The improvements I hear (clear, in the case of cascoded-CFP; possible, in the case of cascoded-VAS) might well be in the time domain...somehow...I don't know, apart the putative extension in frequency response. The articles which I linked above emphasize that the human hearing system is better than measurement gear in time resolution and that "sound envelope" is very important in sound recognition.
The brain is excellent in pattern recognition. Positive recognition is almost instantaneous. When the brain achieves it, it relaxes on the subject...
The mods, IMHO, produce a more dynamic reproduction of music, even at low volumes, with enhanced attacks, with less energy in the treble ("darker" presentation with predicted extended frequency response) and more in the midrange and midbass (one feels more the bodies of instruments), but with enhanced low level detail, so a different distribution of energy both in time domain and in perceived frequency output, in a relaxed manner, in the way that I am nearer to listening to a string quartet playing in my living room than listening to packaged, uninteresting music...
I am sort of amazed that skilled DIYers won't take the time to explore this most interesting topic. You can take any "blameless" type amp and do the organ graft in a couple of hours. Even if this mod has nothing to do with TMD I suspect that you will like the effect. For me it is a no way back mod, though I am still in the listening tests... a "how could I live without this all these decades" type of mod
please try it and tell me if I am crazy or not. I attach the diagram for the sub-circuit that I use to replace the input differential amplifier. I added another resistor which gave me negligible offset. I am no expert so you will probably make better decisions regarding position and value of the Rs. Feel free to advice.
Best wishes,
M.
Attachments
You mean by personal listening test when making the changes? That has no value to speak of.
Jan
Well, this is not the way that science works...almost all I read are experts' opinion on the form of "our present model, our present understanding of the problem predicts that there will be no effect whatsoever in this or that measurement of distortion". I contrast, most advances in human ascent are made when someone says -"now, that's interesting" or when one asks -"what if?" and then starts his own experiments to reject the hypothesis. Because, for example, what if we are measuring the wrong parameters?
The improvements I hear (clear, in the case of cascoded-CFP; possible, in the case of cascoded-VAS) might well be in the time domain...somehow...I don't know, apart the putative extension in frequency response. The articles which I linked above emphasize that the human hearing system is better than measurement gear in time resolution and that "sound envelope" is very important in sound recognition.
The brain is excellent in pattern recognition. Positive recognition is almost instantaneous. When the brain achieves it, it relaxes on the subject...
The mods, IMHO, produce a more dynamic reproduction of music, even at low volumes, with enhanced attacks, with less energy in the treble ("darker" presentation with predicted extended frequency response) and more in the midrange and midbass (one feels more the bodies of instruments), but with enhanced low level detail, so a different distribution of energy both in time domain and in perceived frequency output, in a relaxed manner, in the way that I am nearer to listening to a string quartet playing in my living room than listening to packaged, uninteresting music...
I am sort of amazed that skilled DIYers won't take the time to explore this most interesting topic. You can take any "blameless" type amp and do the organ graft in a couple of hours. Even if this mod has nothing to do with TMD I suspect that you will like the effect. For me it is a no way back mod, though I am still in the listening tests... a "how could I live without this all these decades" type of mod
I attach the diagram for the sub-circuit that I use to replace the input differential amplifier. I added another resistor which gave me negligible offset. I am no expert so you will probably make better decisions regarding position and value of the Rs. Feel free to advice.
Best wishes,
M.
This is a technical forum and, as such, a scientific method should be applicable to demonstrate quantitatively any change that is supposed to happen.
Then, only as a complement to this scientific method could there be subjective correlates or favorable qualitative opinions about the improvements that can be verified.
But the subjective opinion alone is insufficient, since it could be conditioned by a lot of situations that nothing could have to do with the supposed improvements that are attributed.
Douglas Self and other very respectable and objective members have not been able to find perceptible changes of improvement in relation to this issue in discrete systems.
The ability to faithfully reproduce the attack segment of a signal lies in the ability of the circuit to follow signals of a certain initial growth rate, partly compatible with the slew rate limitation for high frequency signals and partly compatible with the limitation imposed by the values of the capacitors (if any) to couple the signal between the different stages for low frequency signals.
The enhancement in the low level details are favored with a great rejection to the ripple of the power supply and with a lower noise floor of the system. This evolution would have to be analyzed in relation to the frequency or the bandwidth intended for listening. I have not seen analyzed or measured how that is finally in the proposed systems.
Best regards
Dear Jan,
I always listen to music in a subjective way...I do not know any other form of doing it.
I also chose my partner in a subjective way.
Best,
M.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.