lt cdr data said:I would love to see D. Self extend his book, and offered him some suggestions, like discussing symmetrical amps,..........he was not keen on the idea...thought it would take an age
Well i have written a sort of extension to Self's work...if only i can get it published.....
http://www.diyaudio.com/forums/showthread.php?s=&threadid=63038
I tried to build several full complementary diff amp with c mirrors and cascoded & darlington buffered vas... it never seems to work!
what i encounter most :
1. the Iq in the VAS is very high or it is nihil. last time it was around 200mA !! Needless to say i can only test it for some minutes before cooldown... whats more : when i touch one of the input stage transistors the Iq goes heavily up or down...
2. i have oscillations... even when i feedback 100% no amplifying thus.
it is a periodic signal between 20Khz and sometimes 400kHz... it is not a sinewave but periodic yes (no rnd noise). this trace is visible on every node __ on the rails, gnd, whatever point on the pcb! always the same trace... maybe interesting to tell : when i touch one of the input transistor by hand the frequency of the trace slightly changes... one more thing about is : the trace is near the size of the rail supply !!! how can this be with 0dB amplifiying??????? i think it must be a local problem not a closed loop problem.......
hope this helps someone ... maybe someone can help to point out my problem too...
very interesting thread, to say the least...
i did experiement with a complementary differential using current mirrors,
and it was stable and has very good specifications...
in short, it worked as good a the basic topology...
i encountered almost none of the problems noticed here, safe some
things that were in fact due to unsufficent knowledge at the time...
still ,i didn t retain the topology, as it s more complexe and in my tries,
it didn t significantly outperform the basic schematic without current mirrors..
i can only aknowledge that using a cascoded vas is not really a great idea,
unless we restrict to theorical advantages, in practice, it bring little, and it s a rather
a loosy trade off...
nowadays, i ll publish the schematic next month, for information purposes...
i did experiement with a complementary differential using current mirrors,
and it was stable and has very good specifications...
in short, it worked as good a the basic topology...
i encountered almost none of the problems noticed here, safe some
things that were in fact due to unsufficent knowledge at the time...
still ,i didn t retain the topology, as it s more complexe and in my tries,
it didn t significantly outperform the basic schematic without current mirrors..
i can only aknowledge that using a cascoded vas is not really a great idea,
unless we restrict to theorical advantages, in practice, it bring little, and it s a rather
a loosy trade off...
nowadays, i ll publish the schematic next month, for information purposes...
no problem, lumba, you seems to have enough knowledge
to know exactly about the holdings and borderings of this subject..
that s why i didn t even bother to contradict your "no" with
technical arguments..
true that it s an efficient technic to make
one justify endlessly that he s right with force technical details..
to know exactly about the holdings and borderings of this subject..
that s why i didn t even bother to contradict your "no" with
technical arguments..
true that it s an efficient technic to make
one justify endlessly that he s right with force technical details..
wahab,
maybe we can talk about this issue later. The design of this thread is just slightly exciting, but I will heavily criticize your design.
lumba, i count on you,
i m just about to publish this kind of design, a complementary
differential which in the way it was designed will doubtlessly
bring vast amounts of critics...
your critics are not only welcomed, but fully mandatory...
to calm down your hunger the time i tweak some components values,
, you can vociferate on this one...
http://www.diyaudio.com/forums/solid-state/155993-awb50-simple-power-amp.html
, you can vociferate on this one...
http://www.diyaudio.com/forums/solid-state/155993-awb50-simple-power-amp.html
as you know, lateral power fets of hitachi have higher THD with no
NFB than bjts..these latter have the advantage of decreasing distorsion
with increased bias current...
the only way to correct the non linearity of the fets is to apply some
NFB, and the profet (zenotron) has not enough open loop gain..
moreover, as it s a push pull, the third harmonic is way higher than the
second one, not talking of the higher order harmonics that are also
at a high value...this make the amp sound bright, which can be pleasing to
some ears...
to add insult to injury, the lateral fet don t need a high bias current
to reach their optimum..
that s why i abandoned the design to return to the complementary
differential using these same output devices..
with careful design, it s simple and the sound is neutral and sound
to my ears as having more dynamics...
i designed this latter at odds with commonly accepted ideas,
and it proved to be more musical , as there s ZERO compensation
caps, yet, it s stable even on a 8R + 100 uF load..(yes 100)....
NFB than bjts..these latter have the advantage of decreasing distorsion
with increased bias current...
the only way to correct the non linearity of the fets is to apply some
NFB, and the profet (zenotron) has not enough open loop gain..
moreover, as it s a push pull, the third harmonic is way higher than the
second one, not talking of the higher order harmonics that are also
at a high value...this make the amp sound bright, which can be pleasing to
some ears...
to add insult to injury, the lateral fet don t need a high bias current
to reach their optimum..
that s why i abandoned the design to return to the complementary
differential using these same output devices..
with careful design, it s simple and the sound is neutral and sound
to my ears as having more dynamics...
i designed this latter at odds with commonly accepted ideas,
and it proved to be more musical , as there s ZERO compensation
caps, yet, it s stable even on a 8R + 100 uF load..(yes 100)....
right, but as you (surely?) guessed ,i tested the full range from 1nF to 100 uF....
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