I said push-pull VAS.
I'm sure I've seen Class B or AB VAS stages but they are few & far between. Please post links to such (mythical?) beasts if you sight one.
As for "Blameless" ... [deleted 2 pgs of semantic, pseudo pedantc rant ... ]
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In a push-pull Vas that runs, say, 10mA standing current, the top device can source much more into the load than 10mA. The bottom device can sink much more than 10mA from a load.
Just drive it harder and the sky is the limit, current-wise.
P-P can always be driven into class B.
SE can only exceed the standing current, ehhh, single ended, as Andrew explained. P-P can exceed the standing current bipolarly, so it can easily move into class B territory on both polarities.
jan
Just drive it harder and the sky is the limit, current-wise.
P-P can always be driven into class B.
SE can only exceed the standing current, ehhh, single ended, as Andrew explained. P-P can exceed the standing current bipolarly, so it can easily move into class B territory on both polarities.
jan
Arrrgh! You are referring to the dreaded symmetrical IPS amps like on CFAs.
Alan
D.Self has his own site.
In there he has lot's that is very worth reading.
He also has an early article from WW that I think pre-dates his books.
Most of the pre 4th edition of his "The Audio Power Amplifier Design Handbook" is in this page
Distortion In Power Amplifiers
"Blameless" means you can't blame the amplifier if you attend to all 8 distortion creating "errors".
The list is now up to "Distortion Eleven".
6th edition is expanded in many areas and new additions. It is well worth buying.
I like JLH, D.Self & R.Cordell. They are all very different and I consider they complement each other by the different ways they approach the problems and solutions.
D.Self has his own site.
In there he has lot's that is very worth reading.
He also has an early article from WW that I think pre-dates his books.
Most of the pre 4th edition of his "The Audio Power Amplifier Design Handbook" is in this page
Distortion In Power Amplifiers
"Blameless" means you can't blame the amplifier if you attend to all 8 distortion creating "errors".
The list is now up to "Distortion Eleven".
6th edition is expanded in many areas and new additions. It is well worth buying.
I like JLH, D.Self & R.Cordell. They are all very different and I consider they complement each other by the different ways they approach the problems and solutions.
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Hi engrlvtn,
It sounds like you have little experience. That is OK. Everyone needs to start somewhere. I suggest you get a copy of Doug Self's amplifier book and/or my book as a start. There is also a lot of material on the web that can help. I also urge you to start small. Start with a 50 or 100w amplifier to get some initial experience.
Cheers,
Bob
thanks, I will try and do that. I have tried some before but I lost the schematic. I am learning and I will go with your advise. thanks once again
Ah!!! I finally broke down. I just bought the Audio Power Amplifier Design by Self.........All.......thanks and no thanks to you!!!!
Thanks
Hi Jan, I disagree with your definition of what a Blameless amplifier is. First, if we go with what you reasonably claim was the original intent of the term, every well-engineered amplifier would be a Blameless amplifier. That definition is so overly broad as to be useless. The term Blameless is indelibly associated with Doug Self, and even he would not claim that the term should be used to describe all amplifiers in which the distortion sources he discussed have been minimized.
The Blameless amplifier is a Lin topology that has been refined with good engineering that reflects Doug's design philosophy. Perhaps it should be called a Simple Well-Engineered Low Distortion Amplifier (SWELDA). Or maybe it should be called a Well-Engineered Lin Topology (WELT). Yes, I like that even better.
Would you refer to a CFA as a Blameless, even though it is technically just as blameless as a Blameless? Would you call a MOSFET power amplifier a Blameless, even though Doug eschews MOSFETs? Would you call an amplifier with a push-pull VAS Blameless just because it is even more blameless than a Blameless? The list goes on.
Perhaps these other amplifiers should all be called Selfless
.In my view the Blameless (WELT) is a topology that includes:
- A BJT LTP with emitter degeneration
- a current source for the tail of the LTP
- a current mirror load for the IPS
- A single-ended Darlington VAS
- a current source load for the VAS
- Miller compensation
- 2T output stage that complies with the Oliver biasing criteria
As Doug and all of us have learned over time, Doug's Blameless has evolved and improved since he first coined the term Blameless - for example the addition of a Triple output stage. So the meaning of the term becomes fuzzier over time.
The simple topology described above what was most linear IC designers cut their teeth on in the 70's or sooner. Even back then, most op amps quickly evolved to something more sophisticated, one reason being that this topology would latch up in a unity gain configuration.
Cheers,
Bob
Well, Bob, the definition is what Douglas coined it to be. I don't think anyone can 'disagree' in that context with a definition.
I agree that since Douglas appears to use overwhelmingly a specific topology, that topology got associated with the term 'blameless'. But I can imagine that someone would design a very different topology, with diamonds and CFA and what have you, and check off all the various distortion causes as are mentioned in the original article and end up with a 'blameless' amp to the original definition, with a completely different topology.
Hasn't happened, true, but that doesn't change the concept.
Jan
I agree that since Douglas appears to use overwhelmingly a specific topology, that topology got associated with the term 'blameless'. But I can imagine that someone would design a very different topology, with diamonds and CFA and what have you, and check off all the various distortion causes as are mentioned in the original article and end up with a 'blameless' amp to the original definition, with a completely different topology.
Hasn't happened, true, but that doesn't change the concept.
Jan
Bob Cordell said:
Could both you gentlemen explain in simple terms why this is the case?
Or is this just an observation?
Certainly this PNP i/p topology, first seen in Raytheon 4136 and used later by many including Motorola, appears very problem free if not quite 1ppm THD20k.
Today, NJM use it et nauseum for everything from very low noise to huge current delivery with great success.
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Hi Mr. Cordell
I have a question about slew rate. What is the minimum requirement of slew rate of the power amp to get lower distortion at 20KHz? I used SR=Vpeak X 2 pi X fc to calculate for 100KHz Vpeak = 50V to get SR=31.4V/uS. But some people want to push beyond 100V/uS. What is the requirement for a given Vpeak?
Also, have you thought about the question is post 5121 in page 513 of this thread?
Thanks
Alan
I have a question about slew rate. What is the minimum requirement of slew rate of the power amp to get lower distortion at 20KHz? I used SR=Vpeak X 2 pi X fc to calculate for 100KHz Vpeak = 50V to get SR=31.4V/uS. But some people want to push beyond 100V/uS. What is the requirement for a given Vpeak?
Also, have you thought about the question is post 5121 in page 513 of this thread?
Thanks
Alan
Back in post #4404 I discussed the Sansui diamond design and Bob commented on what he thought of it.
I put the sim in this thread.
http://www.diyaudio.com/forums/soli...ifferential-pa-simulation-possible-build.html
I put the sim in this thread.
http://www.diyaudio.com/forums/soli...ifferential-pa-simulation-possible-build.html
Only 3 posts ... ??
I went "all the way" with this ...(Kypton V2) -
here's the final perfected input stage (with anti-parallel diodes in first stage).
http://www.diyaudio.com/forums/solid-state/248105-slewmaster-cfa-vs-vfa-rumble-108.html#post4126276
Post 5384 has all you need to build it.
Thimios scoped the "non- diode (clamped)" version 2 (below)
"Sticking" on saturation until we clamped the 1st stage with anti-parallel
diodes.- then it was quite good.
Post 5282 on .... this ips was perfected.
Vzaichenko's "tubesumo" is also this topology with a 12au7 valve for first
stage.
OS
Attachments
Hi Waly,
I don't recall anyone making op amps back then with PNP input stages, since virtually all junction-isolated processes back then had only lateral PNPs to use. They had current gain often less than 5. They were infinitely crappy. I hated designing with them. I think their ft was about 1 MHz. At that time (early 70s) Bell Labs was developing the full complementary junction-isolated process that included vertical PNPs. Once we got to use those, we never looked back. We came out with an op amp with a full-complementary diamond buffer output stage in the mid-late 70s (those op amps also used TPC, which we called T compensation at the time). If my memory serves, Analog Devices used this process for their first vertical-PNP-equipped op amps.
I think there was one exception to the lateral PNP matter. That was Harris Semiconductor, who I think was doing a diectrically-isolated process. I believe they were quite expensive and often used in space/military et al applications. They were rad resistant.
Cheers,
Bob
And I used Raytheon 4136 in 1977 as probably the first OPA which I thought would be blameless in a DBLT with +/- 15V rails .. with suitably band limited signal of course
DON'T LAUGH!4136 topology probably outnumbers even 5532/4 in audio today cos all the NJM parts.
Hi Waly,
Thanks for pointing that out. I had forgotten the LM324. Not sure how they got such good performance with lateral PNPs, but the darlington connection maybe gave them enough current gain.
The more sophisticated evolution from the simple NPN LTP topology I was referring to in my earlier post was the 741, where they used NPN input transistors whose emitters were connected to lateral PNPs to get downward signal transmission.
Cheers,
Bob