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Old 13th December 2012, 03:18 PM   #31381
Bonsai is offline Bonsai  Taiwan
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Quote:
Originally Posted by john curl View Post
"All quiet on the western front." I guess we can move forward again. Unfortunately, what I am now working on, (improvements to power amps) is confidential, but I will say that I am sticking with the complementary differential jfet input that I have used for so many decades, now.
If anything, I think that RFI buffering is more important than ever. Heavy Class A operation is VERY IMPORTANT, as well.
I still have not found any IC that I would use in replacement for good discrete design.
They are just too compromised in idle current (too low) for me to be comfortable with them.
People are always asking me for cheaper and easier to build designs. Unfortunately, I don't have any. It is not what I do. I try to make the best, most elegant designs I can think of, in respect to the price point that I must work to. I'll leave IC's mostly to mid-fi, where people suppose that everything sounds the same, anyway, as they have been told by others. '-)

Bias the opamp output stage into class A. Very easy to do. Then you can have the pick of any VFA or CFA topology device you care to try. And, plenty of choice on te JFET front as well.
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Old 13th December 2012, 04:34 PM   #31382
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Still not good enough. Regarding JFETs, no good P-parts available.
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Old 13th December 2012, 05:32 PM   #31383
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PMA is correct. Remedies to help the 'starved' output stage can help, but they are not a whole solution, as complementary jfets do not appear to be yet practical for IC design.
We, therefore, have to revert to good but not necessarily the best topologies to get anything done.
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Old 13th December 2012, 05:56 PM   #31384
Waly is offline Waly  United Kingdom
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Originally Posted by john curl View Post
complementary jfets do not appear to be yet practical for IC design. We, therefore, have to revert to good but not necessarily the best topologies to get anything done.
You seem to assume that complementary JFETs are the one and only option for what you call "high end". Is this correct, or is this just another excuse to avoid (good) opamps?
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Old 13th December 2012, 06:06 PM   #31385
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as complementary jfets do not appear to be yet practical for IC design.
There are several processes that would support them but there is no compelling reason to spend the money for the extra layers. In the real world fashion architectures don't have much value. Also for reasons mentioned before they are complementary in only the grossest sense.
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Old 13th December 2012, 06:14 PM   #31386
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No perfect devices yet available, and no known ways exist to make them true complementary, if your religion requires strictly symmetrical design. Even push-pull stages with transformers can't be strictly symmetric because transformers contain coils that have beginnings and ends.
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Old 13th December 2012, 06:31 PM   #31387
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You know what is funny, Scott. I thought that the same thing would happen with complementary bipolar topologies, and that nobody would ever build a complementary symmetry bipolar topology, BUT Harris did! Mil requirements seem to allow for advanced topologies. By the way, your AD797 topology appears to be derived from an earlier Harris topology. However, it would seem, and I will try to find the evidence, that complementary different cmos or mosfet topologies are coming of age. What do you know? '-)

Last edited by john curl; 13th December 2012 at 06:39 PM.
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Old 13th December 2012, 06:38 PM   #31388
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The basic idea behind complementary differential input stages, whether bipolar or jfet, comes from the desire to have a BALANCED SECOND STAGE. This can only be easily done with a complementary differential input stage. A 2 piece complementary jfet input stage is also possible, and POSSIBLY an improvement over the jfet complementary differential input stage, but is is difficult to get the offset out. I abandoned it in 1973, for the full complementary differential jfet input stage, because of this.
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Old 13th December 2012, 06:49 PM   #31389
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Originally Posted by john curl View Post
You know what is funny, Scott. I thought that the same thing would happen with complementary bipolar topologies, and that nobody would ever build a complementary symmetry bipolar topology, BUT Harris did! Mil requirements seem to allow for advanced topologies. By the way, your AD797 topology appears to be derived from an earlier Harris topology. However, it would seem, and I will try to find the evidence, that complementary different cmoss or mosfet topologies are coming of age. What do you know? '-)
CMOS has complementary in its name so they were on to it in 1967 (for different but related reasons), Harris just applied the same logic to bipolar (pun intended).

Don't waste your time I only moved the take off for the output when I noticed it enabled the crossover nulling. You won't find that, on the surface it's illogical since it removes one stage of buffering the output now needs to be a triple.
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Old 13th December 2012, 07:50 PM   #31390
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With IC's, one rarely knows the application it will be put towards. So All specs are important to get to be their best. BUT, in audio line level stages or power amps, there can be a laxing of the input for lowest noise in the whole wide world. And, if you dont rely primarily on gnfb to make the thing linear as possible, the good complimentary jFEts issue subsides and can be made to work very well with more local degeneration and modest gnfb used for excellent results. This was my thought and implimentation of desired complimentary jFET topologies for line level amps. - Thx RNMarsh

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