Hi darkfenriz,
I could answer your question philosophically, with..
When they (the musicians) add distortion it's music, when we do it it's incompetence!
THD steady state into resistive load is a good starting point, then reactive load THD testing, square wave testing, slew rate testing, stability, .....
These are all lab tests readily available to us to hone a design. Once passed to within a set error regime or budget, then start further tests as perceived desirable or necessary.
Cheers
Greg
I could answer your question philosophically, with..
When they (the musicians) add distortion it's music, when we do it it's incompetence!
THD steady state into resistive load is a good starting point, then reactive load THD testing, square wave testing, slew rate testing, stability, .....
These are all lab tests readily available to us to hone a design. Once passed to within a set error regime or budget, then start further tests as perceived desirable or necessary.
Cheers
Greg
amplifierguru said:
These THD measurements wont tell you much about how the amp
will sound... unfortunately. This is not to say I don't strive for
good measurements, they just don't tell a complete story IME.
I recommend listening to the amp on as many systems as possible
with known recordings or better still, listen to the amp whilst
playing back a recordingwhilst done, in a recording or mastering
studio.
Playback direct off (original) analog tape is always an eye opener.
TCD
carlos-
"Well, Dr. Self made his book, but this do not make it better researcher than another one that do not wrote a book."
Mr self is alright,pity he is not here to chat with him, like we
do with Mr nelson pass
carlos-
"In my opinnion, low bias is not a good idea, as real world constructions shows that components are not easy to match."
good point,however to get precision out of component
mismatch you vary the components that control the mismatch
cheers
"Well, Dr. Self made his book, but this do not make it better researcher than another one that do not wrote a book."
Mr self is alright,pity he is not here to chat with him, like we
do with Mr nelson pass
carlos-
"In my opinnion, low bias is not a good idea, as real world constructions shows that components are not easy to match."
good point,however to get precision out of component
mismatch you vary the components that control the mismatch
cheers
mastertech ,
i think you dont succeed well in your saying because there are too many apprehensions involved that are viable in the coherence of mismatch of semiconductors ... high biasing doesn't help to eradicate the artifacts, it sometimes even make the things worse than before....
kanwar
i think you dont succeed well in your saying because there are too many apprehensions involved that are viable in the coherence of mismatch of semiconductors ... high biasing doesn't help to eradicate the artifacts, it sometimes even make the things worse than before....
kanwar
Nelson Pass said:
I'm sure Mr Pass doesn't need my help, but as researched by Self, it appears that the Vt which is the voltage across the Re as a result of a particular Ibias, is determining the point of least non-linearity of the output stage. That means that if you vary Re, you should keep the same Vt, so the Ibias will vary with Re. The optimum Vt is also different for a CFP or a CE stage. That again means that for minimum non-linearity, the CE and CFP stages have quite different Ibiases. (Don't remember the values but they are somewhere in this thread upwards).
Jan Didden
Oh mastertech ,
you are scientist with philosophy a.k.a perfectionist overkiller....dont mind
Are you single or multiple personality.....asking because you are refering yourself as "us" may be i dont know[may someone know here on this forum]
Ok regarding apprehensions......i did like to say they are too many to talk about them here......for a while...yeah you definately succeed welll in your......Hi-fi....perfection...no doubt....
Kanwar
you are scientist with philosophy a.k.a perfectionist overkiller....dont mind
Are you single or multiple personality.....asking because you are refering yourself as "us" may be i dont know[may someone know here on this forum]
Ok regarding apprehensions......i did like to say they are too many to talk about them here......for a while...yeah you definately succeed welll in your......Hi-fi....perfection...no doubt....
Kanwar
Hi Workhorse,
Jan was quoting (or paraphrasing) Self.
But Self was referring to minimising distortion. In this respect it is an objective measurement that he is recommending not subjective.
Many writers criticise Self BECAUSE he only considers objective results possibly to the detriment of subjective evaluation.
Jan was quoting (or paraphrasing) Self.
But Self was referring to minimising distortion. In this respect it is an objective measurement that he is recommending not subjective.
Many writers criticise Self BECAUSE he only considers objective results possibly to the detriment of subjective evaluation.
Hi Andrew,
i know that Jan was quoting Self...Thats why i had written acc to you[i think it is misinterpreted]
I want to know what are the views of Jan , sure objectively if he is comfortable with it only.....the subjective was choosen just to casulize the posting comment...
Now in new Form,
What are the parameters which effect the Vt for a given Re?
K a n w a r
i know that Jan was quoting Self...Thats why i had written acc to you[i think it is misinterpreted]
I want to know what are the views of Jan , sure objectively if he is comfortable with it only.....the subjective was choosen just to casulize the posting comment...
Now in new Form,
What are the parameters which effect the Vt for a given Re?
K a n w a r
Vt and Re´
Since I have been away from the forum, I didn't read this thread until today, and maybe nobody cares anymore. Anyway, I am surprised that the question about Vt has gone unanswered for so long, since I am fully convinced that most people know the answer. However, since nobody answered the person asking about it (or I missed that post) I'll try to answer him. (In all fairness, a partial answer has been given, stating that Vt is device independet so the question about Vt for JFETs and MOS is moot).
Vt
----
It seems obvious that Vt is used in this thread to refer to the thermal voltage, which is what Vt commonly denotes. This is a value which is a basic definition in semiconductor physics, and it is indepent of particular devices. Actually, it is just a shorthand notion where
Vt = k*T/q
where k is Boltzmanns constant, T the temperature in K and q is the charge of the electron. That is, Vt depends only on the temperature, since k and q are physical constants. At room temperature, Vt is approximately 26 mV.
Since this expression appears in the fundamental formula in the transport model for the BJT, it tends to reappear in many other expressions derived from it. A much simplified but very useful model for the BJT is the expression
Ic = Is*e^(Vbe/m*Vt)
where Is and m are device dependent. Since m is between 1 and 2, it is often ignored. Shuffling things around, we get the inverse
Vbe = m*Vt*ln(Ic/Is)
We can also derivate the first formula to get gm, since gm is defined as dIc/dVbe at the Q point. Hence we get
gm = dIc/dVbe at Q = Icq/(m*Vt)
that is, the only device dependent parameter is m. It is often assumed that m=1, which gives that gm = Icq/Vt = 40*Icq (last equality approximate).
Similarly, the dynamic base-emitter resistance, hie, is defined as dVbe/dIb at the Q point. Since Ic = hfe*Ib, we get
hie = dVbe/dIb = hfe*dVbe/dIc = hfe/gm= hfe*m*Vt/Icq.
In this case we have two device dependent parameters, m and hfe.
Sorry if this was too mathematical but I am afraid it is hard to give an answer that is more intuitive than this.
Re´
----
This puzzles me. First, there is hardly any unviversally agreed definition of this symbol. As a general rule, all symbols having a prime in them tend to be local definitions used only in a particular book or paper, or just within a single proof of a theorem. It is not clear to me from this thread where the symbol stems from. Maybe from Self, but it is not on his quite comprehensive web site at least (I don't have has book, unfortunately). Somebody gave a definition of Re´, but as far as I can see, that was exactly the definition of hie, that is the same as the definition of hie I gave earlier in this post. This does not correlate well with some subsequent poster adding Re´with Re, which is hardly meaningful for any purpose. As far as I can see, there is no concesus in this thread on what Re´is supposed to denote.
Since I have been away from the forum, I didn't read this thread until today, and maybe nobody cares anymore. Anyway, I am surprised that the question about Vt has gone unanswered for so long, since I am fully convinced that most people know the answer. However, since nobody answered the person asking about it (or I missed that post) I'll try to answer him. (In all fairness, a partial answer has been given, stating that Vt is device independet so the question about Vt for JFETs and MOS is moot).
Vt
----
It seems obvious that Vt is used in this thread to refer to the thermal voltage, which is what Vt commonly denotes. This is a value which is a basic definition in semiconductor physics, and it is indepent of particular devices. Actually, it is just a shorthand notion where
Vt = k*T/q
where k is Boltzmanns constant, T the temperature in K and q is the charge of the electron. That is, Vt depends only on the temperature, since k and q are physical constants. At room temperature, Vt is approximately 26 mV.
Since this expression appears in the fundamental formula in the transport model for the BJT, it tends to reappear in many other expressions derived from it. A much simplified but very useful model for the BJT is the expression
Ic = Is*e^(Vbe/m*Vt)
where Is and m are device dependent. Since m is between 1 and 2, it is often ignored. Shuffling things around, we get the inverse
Vbe = m*Vt*ln(Ic/Is)
We can also derivate the first formula to get gm, since gm is defined as dIc/dVbe at the Q point. Hence we get
gm = dIc/dVbe at Q = Icq/(m*Vt)
that is, the only device dependent parameter is m. It is often assumed that m=1, which gives that gm = Icq/Vt = 40*Icq (last equality approximate).
Similarly, the dynamic base-emitter resistance, hie, is defined as dVbe/dIb at the Q point. Since Ic = hfe*Ib, we get
hie = dVbe/dIb = hfe*dVbe/dIc = hfe/gm= hfe*m*Vt/Icq.
In this case we have two device dependent parameters, m and hfe.
Sorry if this was too mathematical but I am afraid it is hard to give an answer that is more intuitive than this.
Re´
----
This puzzles me. First, there is hardly any unviversally agreed definition of this symbol. As a general rule, all symbols having a prime in them tend to be local definitions used only in a particular book or paper, or just within a single proof of a theorem. It is not clear to me from this thread where the symbol stems from. Maybe from Self, but it is not on his quite comprehensive web site at least (I don't have has book, unfortunately). Somebody gave a definition of Re´, but as far as I can see, that was exactly the definition of hie, that is the same as the definition of hie I gave earlier in this post. This does not correlate well with some subsequent poster adding Re´with Re, which is hardly meaningful for any purpose. As far as I can see, there is no concesus in this thread on what Re´is supposed to denote.
Steven said:
OK, so Re´= hib = hie/hfe then. Maybe I misread the earlier post that I took to define Re´as hie.
I would however recommend against using Re´since it is hardly any standard notation that is agreed on, while hib is perfectly well defined in the literature. But as long as we all know what we are talking about, any notation works.
High or low bias in Class AB?
As low as maintains forward path gain, allowing feedback to work as advertised. Many amps (e.g. DC300A....) would switch off the output stage killing off Gm and forward path gain thus rendering feedback largely ineffective. Often, users will turn output stage bias OFF for reliability with high power sub amps causing a sharp discontinuity in the forward path rendering the feedback ineffective through a 'dead zone' on every cycle - at the crossover between upper and lower halves of the output stage occurring anywhere in the cycle depending on the load phase (zero crossing for resistive).
My amps typically run at 40-50mA per device causing minimal quiescent heating (<10W) while maintaining forward gain.
Cheers,
Greg
As low as maintains forward path gain, allowing feedback to work as advertised. Many amps (e.g. DC300A....) would switch off the output stage killing off Gm and forward path gain thus rendering feedback largely ineffective. Often, users will turn output stage bias OFF for reliability with high power sub amps causing a sharp discontinuity in the forward path rendering the feedback ineffective through a 'dead zone' on every cycle - at the crossover between upper and lower halves of the output stage occurring anywhere in the cycle depending on the load phase (zero crossing for resistive).
My amps typically run at 40-50mA per device causing minimal quiescent heating (<10W) while maintaining forward gain.
Cheers,
Greg
Hi,
I think the Re and Vt that is being asked about is the simple one, external to the devices.
Re is the emitter resistor of the emitter follower output devices. or
Re is the output resistors of the CFP/driver combination.
Vt is the voltage across Re during quiescent conditions.
Just my tupence worth.
I take that all back, just looked up Self - Fig 5.36 shows the total voltage across both emitter resistors as Va not Vt.
I think the Re and Vt that is being asked about is the simple one, external to the devices.
Re is the emitter resistor of the emitter follower output devices. or
Re is the output resistors of the CFP/driver combination.
Vt is the voltage across Re during quiescent conditions.
Just my tupence worth.
I take that all back, just looked up Self - Fig 5.36 shows the total voltage across both emitter resistors as Va not Vt.
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