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Old 14th March 2013, 06:29 PM   #141
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Fifth edition, page 129, figure 5.9, type 2 , the Lender-Boberly circuit seems to have something wrong in it.

Maybe the sixth edition could have some comments on Samuel Groner's comments on Audio Power Amplifier Design Handbook by Douglas Self. I was so fascinated by Samuel's circuit, page 48, figure 56 that I built it. I worked as intended on the bench, but I did not yet measured it

By the way, I have a blameless amp since1994, the boards were available through Electronics World, I think. It's still working fine.
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Old 14th March 2013, 06:39 PM   #142
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Originally Posted by forr View Post
Fifth edition, page 129, figure 5.9, type 2 , the Lender-Boberly circuit seems to have something wrong in it.
Do you think you could be a bit more specific?

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Maybe the sixth edition could have some comments on Samuel Groner's comments on Audio Power Amplifier Design Handbook by Douglas Self.
It has more than comments on it. Samuel Groner's document is an absolutely first-class bit of work, and we have worked together to extend many aspects of it. All is revealed in the sixth edition.

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By the way, I have a blameless amp since1994, the boards were available through Electronics World, I think. It's still working fine.
Of course it is!
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Old 14th March 2013, 06:44 PM   #143
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Originally Posted by ivanlukic View Post
I think that it is wrong to reject and completely ignore CFA in your book....
.... CF amps simply sound much better than VF amps.
I absolutely do not accept this.
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Old 14th March 2013, 09:15 PM   #144
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Quote:
Do you think you could be a bit more specific?
Let's call Tr4 the PNP emitter follower and Tr5 the NPN common emitter of the following stage which forms the VAS.

The role of the Vbe of Tr4 is to compensate for the Vbe of Tr5 in order to get the same voltage at the base of Tr4 and at the emitter of Tr5.

If we suppose the current passing through Tr5 to be 10 mA, it should be equal to the current trough Tr4, due to the current mirror effect.

Then the voltage at the emitter of Tr4 is to be around 10 V (1 kohm * 10 mA) + 0.6 V (voltage drop across the diode) + 1 V (voltage across the degenerating resistor of the current mirror).

Then the emitter voltage of Tr4 would be approximately equal to positive ouput rail minus 11.6V. The circuit is not going to work for usual power supply voltages of amplifiers.

I think that the right schematics should have a constant current source or a high value resistor loading the emitter of Tr4 and a constant current source loading the collector of Tr5. And that the 4k7 in the emitter circuit of Tr5 should be of a much lower value.

Last edited by forr; 14th March 2013 at 09:43 PM. Reason: First phrase of the initial response removed
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Old 14th March 2013, 09:42 PM   #145
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Originally Posted by forr View Post
For a good balance in the input differential pair, voltage across each 4K7 should be equal, at around 2.35 V.
The configuration is dealt with very fully in the 6th edition, and input pair balance is a major theme.
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Old 14th March 2013, 10:23 PM   #146
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Originally Posted by DouglasSelf View Post
Never said I could, if you are talking about slew-rate etc.


I do, and it has no downside. But wide bandwidth can easily be an embarrassment, leading to destructive oscillation. Some of the "fast" Japanese amplifiers were notorious for this.


I do. Nobody wants an amplifier that hums like a beehive.


But why? The implication is that you want a very fast slew-rate, but as I said upthread, what is really needed is the optimal slew-rate- faster than required for audio by ten times, say, for a good safety margin, but no more, so that if HF oscillation occurs we are not left cringing under a shower of molten silicon.


It's good to talk...
You've taken everything to the extreme to try to prove your point. So, no open discussion, just stubborn assertions.

In discounting CFA, you are ignoring an important class of amplifier and painting yourself in a corner on this one. There are many fine CFA commercial products (Acuphase, Krell for starters) . . . and DIYers will continue to build CFA designs (JLH's great 10W singleton CFA class A amp is still getting built and raved about 40 years on).

For my part, I'll continue designing and building both.
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Old 14th March 2013, 10:52 PM   #147
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Originally Posted by Bonsai View Post
...So, no open discussion, just stubborn assertions...
On that topic, you never replied to this post.

Best wishes
David
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Old 14th March 2013, 11:06 PM   #148
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Default To discuss with a Master does not make you a Master

Just show you are trying to be recognized as one...and proving you are not

Call Self stuborrn is an untolerable arrogance.

Unbeliavable people discussing with this man.

To be under the spot light may be the main need.... ridiculous all that stuff... answer his questions only.

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Old 15th March 2013, 12:07 AM   #149
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Originally Posted by Bonsai View Post
(JLH's great 10W singleton CFA class A amp is still getting built and raved about 40 years on).
JL Hood never called his design a "current feedback" amplifier; that's because it is nothing of the sort.
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Old 15th March 2013, 12:24 AM   #150
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michaelkiwanuka,
Not to get in the middle of this disagreement but it does appear that both Bob Cordell and Doug Self have acknowledge the terminology for this type of amplifier. Though Doug does not seem to think that the topology is worth his time to add to his book he has obviously acknowledged that there is such an animal. You on the other hand don't seem to want to do that under any circumstances. Stop already, we get your point that you don't like the reference that is being used, but it most certainly has that title to the topology no matter your refusal to agree to the name.

That would be like me telling you that there is no such thing as fish and chips, they are obviously French Fry's and no matter what you want to say they are nothing but French Fried potatoes! Same kind of semantic argument you are attempting to put forward here.......
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