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Old 17th March 2013, 11:06 AM   #231
FoMoCo is offline FoMoCo  United States
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Originally Posted by owdeo View Post
... the accountants who "manage" them like to reduce costs by sacking admin staff and expecting the lecturers to do their work as well as their normal teaching and research. So give the academics a break I say!
Obvious this is spoken by someone who is not paying $400 a credit for "education." At that price I expect a professor to do more than half-*** read me a poorly written textbook for lecture.

But, we are getting off-topic. And, it seems I started that.
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Old 17th March 2013, 06:08 PM   #232
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Default Well dear friends... come on

These gentlemen, Self and Cordell, were designing amplifiers when your mother and father began dating, and you were not even a future project, we now discuss these issues they've reflected on it at that time, decades ago ... do not think that you guys are so smart and that our teachers are mentally retarded ....... perhaps the opposite may be possible .... not dare to teach our masters, sit in the chair, answer the questions of your teachers and pay attention boys.

You mum maybe were using orthodontic appliances that time when they discussed some subjects you now trow to them.

Old folks does not become old...they become wise...they do not loose memory, the memory is selective...they remember the date

Powder without smoke was discovered long, long time ago, and now you discuss with Chinese (the inventors) why not to put the smoke back again.

regards,

Carlos
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Old 17th March 2013, 06:13 PM   #233
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Originally Posted by Kindhornman View Post
Sy,
Are those Ebers-Moll's the same ones who dig in my backyard, I thought they were just ground squirrels.........
That's not Ebers, I think it is Albert, See Albert Mol - Wikipedia, the free encyclopedia
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Old 18th March 2013, 12:08 AM   #234
owdeo is offline owdeo  Australia
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Originally Posted by destroyer X View Post
These gentlemen, Self and Cordell, were designing amplifiers when your mother and father began dating, and you were not even a future project, we now discuss these issues they've reflected on it at that time, decades ago ... do not think that you guys are so smart and that our teachers are mentally retarded ....... perhaps the opposite may be possible .... not dare to teach our masters, sit in the chair, answer the questions of your teachers and pay attention boys.
Agreed, well said Carlos! Mr Self published his seminal preamp design in 1976, which just happens to be the year I was born And while I was at uni in my EE classes, he published the now famous series on Distortion in Power Amplifiers which forms part of the book in question and which taught me far more about amplifier operation than any of the theory taught at my uni at the time.

I think it's perfectly reasonable to disagree or question their work, as they have no doubt questioned other's before them - this is part of learning and potentially advancing the science/art. Nobody has all the answers. But it needs to be done with humility and respect (qualities which they both clearly display I might add), and not driven by inflated egos... that way the potential for learning is preserved. We are fortunate indeed to be able to discuss our favourite subject with these masters so let's make it worth their while to be a part of this and not potentially drive them away with negativity and disrespectful comments.
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Old 18th March 2013, 12:25 AM   #235
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It's called debate. What started out by someone as a simple request to include a very popular topology was dismissed out of hand as being inferior, despite plenty of anecdotal and commercial evidence that suggests something quite to the contrary.

I will continue to buy their books - and Jan Didden's now that I have a Paypal account, if he will let me - but they are not infallible.
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Old 18th March 2013, 01:10 PM   #236
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Default TMC

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Originally Posted by DouglasSelf View Post
How about Transitional Output-Inclusive Miller Compensation? TOIMC?
Hi Douglas,

First, apologies for the late response (due trouble with my PC*).
As for TOIMC, admittedly, that would be a more exact description, though it's still ambiguous. As David pointed out, there are also other transition schemes possible: Transitional Input Miller Compensation (TIMC), for example. But that's not the only one. Also a combination of the two is possible: input AND output inclusion. How we call that? Also TOIMC or TIOMC? And what about the combination two pole compensation (TPC) and TMC: TTMC?
Anyhow, most of us know what is meant by TMC, so let's keep it that way.

Quote:
At what date did you invent it?
The idea was born somewhere in the mid-nineties, when I was thinking how to make Cherry's output inclusive compensation more stable.

Quote:
I do keep all my emails, but I have to admit that finding one that is eleven years old would be a bit of a mission, so I hope you will permit me to rely on my memory.
I sent you the emails around February 2002. Perhaps this helps to find them again.

Quote:
I recall that the correspondence was about an example of Output-Inclusive compensation that was published by Michael McLoughlin as a Letter to Electronics World in April 1992. I sent in my comments on his plan in August 1992. Firstly it used an under-biased output stage that created big crossover spikes. Secondly it used only small-signal transistors, with Cherry-type non-transitional Output Inclusion, (I gave the 1982 Cherry NDFL reference) and I already knew that it could not be scaled up to use power output devices without the certainty of oscillation. Nonetheless I built an improved version and did manage to demonstrate some reduction in distortion, but the amount was indeed not exciting, and other matters took priority. I am surprised to hear that I did not respond to two emails, and I am sorry you are not happy about that. I try to be meticulous in answering enquiries, as I feel that courtesy is so important in technical debates.
We have never discussed a letter to the editor. Maybe you confuses it with another letter (see picture below, a shortened version). That was about input inclusive compensation. But also in this case we didn't have any discussion about this subject, though you know about it, as you have listed it on your website.

Anyhow, it was you who told me that TMC was already invented by Baxandall. By then, you were the only one who know this. So no one else could have told me about Baxandall. This leaves no other possibility than our emails were about TMC.

Quote:
Well at least two of them weren't, because their despairing constructors asked me to fix them. (this was the April 1983 ETI design) All the component values were correct but stability was not to be had; I think using that Butler amplifier stage was a mistake. I entirely accept that these examples may have been outliers but they were built independently by two different people, so I suppose it is at least a data point to note.
Much depends on minor circuit details and how it was built. Too long traces/wires to the output devices for example, will be devastating. Also notice that Cherry applied output inclusive compensation in conjunction with shunt compensation by putting (small) capacitors between the base of the drivers and the supply rails. I guess without the latter has amp will also be unstable.

Quote:
But I would like to know when you invented it. I think we should try to record the history of audio as it happens.
When? As I said, somewhere it the mid-nineties.
Hope you will find back the emails.

Cheers,
E.

*PS: I still have PC troubles. Just bought an Z77 Asrock motherboard. Regrettably, this MB doesn't work together with my PCI sound cards (a Lynx L22 and Waveterminal 192X). I get a lot of dropouts. It's due to the fact the chip set on this MB does not support (good ol') PCI. Instead, the PCI slots are connected via a flaky interface chip to the PCIe bus. Hence the dropouts. So anybody who's using PCI sound cards, be warned! When upgrading your PC, make sure PCI is supported sufficiently.
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Old 18th March 2013, 01:57 PM   #237
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My own suggestions (refering to the 5th edition),
I would like to read some more words on :

Page 119 Figure 5.4f
Bootstapping VAS load R using an emitter follower
I rarely met this configuration but I found its simplicity rather smart.
It seems a very simple enhancement to buffer the VAS and may provide the same advantage as a triple output stage without the drawback for the bias of having six Vbe to compensate.

Page 356, Figure 12.12 (circuit of the class G amplifier)
A resistor of 2.2 kOhm (R11) is insterted in the Constant Current Source (Q6) for the input differential pair.
Some amplifiers have a resistor (1 kOhm or so) in this place, most of them have not. I never saw many explanations on its role.
Here, wiht high voltage power supply rails, one aim is certainly to lower the heat dissipation in Q6 wich is about 6 mA * 50 V = 0.3 W without it.
Has it any other effect ? I think of a compensation of the not purely resistive behaviour of the CCS at high frequencies.
Its presence may also help to control the CCS output current when debugging or repairing.

Amplitude and frequency distributions
Amplitude and frequency distributions wanted
For me, it's worth of more investigations.
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Old 18th March 2013, 01:58 PM   #238
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Originally Posted by Edmond Stuart View Post
...
As for TOIMC, admittedly, that would be a more exact description, though it's still ambiguous. As David pointed out, there are also other transition schemes possible: Transitional Input Miller Compensation (TIMC), for example. But that's not the only one. Also a combination of the two is possible: input AND output inclusion. How we call that? Also TOIMC or TIOMC?...
Yes, that's why I wanted to use TIMC and TOMC - to keep I for Input and O for Output so that TIOMC was clear
I have started to analyse the entire family but don't have much on TIOMC yet.
I am happy to use TMC as the default when there is no risk of confusion.
Like JCX, I am unaware of any systematic name convention and some of the schemes (mostly in op-amp literature) are very wordy.
The obvious way is to specify the admittance matrix or similar network analysis matrix. Can't see that catch on!

Best wishes
David
or If TMC is short for TOMC then
Dave

Last edited by Dave Zan; 18th March 2013 at 02:00 PM.
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Old 18th March 2013, 02:51 PM   #239
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Originally Posted by Edmond Stuart View Post
Hi Douglas,

First, apologies for the late response (due trouble with my PC*).
As for TOIMC, admittedly, that would be a more exact description, though it's still ambiguous. As David pointed out, there are also other transition schemes possible: Transitional Input Miller Compensation (TIMC), for example. But that's not the only one. Also a combination of the two is possible: input AND output inclusion. How we call that? Also TOIMC or TIOMC? And what about the combination two pole compensation (TPC) and TMC: TTMC?
Anyhow, most of us know what is meant by TMC, so let's keep it that way.

Doug,

I really hope you will stick with TMC in your upcoming edition. No three letter acronym is a perfect, unambiguous description, including TPC. Edmond deserves credit for popularizing it and giving it a pretty descriptive name, and I followed suit by using the term Transitional Miller Compensation in my text (which I believe is the first text to describe it, and where due credit is given to Edmond). To have two competing names for TMC would just add to the confusion. I urge you to stick with TMC.

Cheers,
Bob
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Old 18th March 2013, 05:33 PM   #240
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Default weak-inversion

Hi Douglas,

Forgive me if I say it a bit bluntly, but you for ask additions and/or improvement on the 5th edition: Chapter 14 on MOSFET output stages should be rewritten, completely.
The simulations of the (vertical) MOSFETs doesn't take into account the so called weak-inversion (or sub-threshold conduction). This has far reaching consequences, not just regarding the the graphs, but also with respect to your conclusions about MOSFETs. The point is that they perform much better then you and your simulator might think.

In this chapter, you stated:
"However, the most important difference may be that the bipolar gain variations are gentle wobbles, while all FET plots seem to have abrupt changes that are much harder to linearize with NFB that must decline with rising frequency. The basically exponential Ic/Vbe characteristics of two BJTs approach much more closely the ideal of conjugate (i.e. always adding up to 1) mathematical functions, and this is the root cause of the much lower crossover distortion.

A close-up examination of the way in which the two types of device begin conducting as their input voltages increase shows that FETs move abruptly into the square-law part of their characteristic, while the exponential behavior of bipolars actually gives a much slower and smoother start to conduction."


Well, the truth is that at low currents, that is, in the transition region (sorry for using the T-word again ) MOSFETs show a similar exponential behavior. So the X-over between the two output devices isn't that abrupt. Admittedly, WRT to BJTs, the gain 'wobble' is higher, but equally important, it is also wider. That means that the spectrum of harmonics from this wobble is smaller (i.e. less HF). Consequently, it's easier to linearize it by means of feedback.

Actually, I'm surprised that you didn't revise this chapter already in the 5th edition, as Marcel van de Gevel pointed this already out in 1996, see below.

Cheers,
E.

PS: You really don't like MOSFEts, do you?
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