Does anybody know if the OptimMOS is an older or newer design
than those in Sloanes book? I understand it appeared in a
magazine in 1999, but the book was also published that year.
The puzzling thing is that the OptiMOS goes against some of
his own "design rules" in the book, so I wonder if he
changed his mind before or after writing the book and how
this amp compares to the "optimal" one in the book?
jgwinner,
what do you mean by 'a unique type of "nested feedback" system incorporated into the VA stage'? I can't find any such
feedback, unless you are referring to the two-pole compensation
network.
I haven't read Selfs book, so I am interested in how his and
Sloanes conclusions differ regarding BJT vs. MOSFET. Would it
be too much to ask for a brief summary of this?
than those in Sloanes book? I understand it appeared in a
magazine in 1999, but the book was also published that year.
The puzzling thing is that the OptiMOS goes against some of
his own "design rules" in the book, so I wonder if he
changed his mind before or after writing the book and how
this amp compares to the "optimal" one in the book?
jgwinner,
what do you mean by 'a unique type of "nested feedback" system incorporated into the VA stage'? I can't find any such
feedback, unless you are referring to the two-pole compensation
network.
I haven't read Selfs book, so I am interested in how his and
Sloanes conclusions differ regarding BJT vs. MOSFET. Would it
be too much to ask for a brief summary of this?
jgwinner,
I take back the question on VA-stage feedback. I had another
look at the diagram an found I had missed it. I thougt he was
ony using ordinary cascoding as in many of his other designs.
This is even more strange, however, since he argues very strongly
against nested feedback loops in his book.
I take back the question on VA-stage feedback. I had another
look at the diagram an found I had missed it. I thougt he was
ony using ordinary cascoding as in many of his other designs.
This is even more strange, however, since he argues very strongly
against nested feedback loops in his book.
Reading Randy Sloane's book I am left with the impression
that while published in 1999, it was written in the late 80's.
This from his references to topologies and available devices.
This is not intended as a criticism of the book, but rather
a potential explanation why his 1999 design might incorporate
some slightly different ideas.
that while published in 1999, it was written in the late 80's.
This from his references to topologies and available devices.
This is not intended as a criticism of the book, but rather
a potential explanation why his 1999 design might incorporate
some slightly different ideas.
Maybe, but why it should take ten years to publish the book...?
Anyway, I don't think the OptimMOS is really a more modern
topolgy. All the principles he uses are mentioned in his book
as possible solutions, some of them even used in particular
cases. However, he seems to have changed his mind about
which is the best solution for certain things, now using the
ones he dismissed as inferior or pointless in the book. For
instances he spent many pages praising current mirrors but
said that there was not much point in cascoding a BJT
diff pair. Now uses a cascode, but no current mirror. He did
not like nested feedback, but now uses it. He seemed to prefer
CFB output stages to emitter followers, while now using the
latter, although this was somewhat arbitrary also in the book,
varying from design to design. As for old components, well
he use som new devices for the diff pairs, otherwise it is
exactly the same ones as he uses in the book.
Of course, anyone is free to change his/her mind whenever
it seems appropriate, and I am sure Sloane has some reason
for it. Perhaps, he tried to make a somewhat cheaper version
of the "optimal" amp in the book, and concluded that doing
things the other way would be better in this particular case.
Still, having recently read his book I can't help being curious
about this change of mind.
BTW Nelson, would you label the OptiMOS as more modern than
the designs in the book or was it just that you considered those
in the book old-fashioned?
Anyway, I don't think the OptimMOS is really a more modern
topolgy. All the principles he uses are mentioned in his book
as possible solutions, some of them even used in particular
cases. However, he seems to have changed his mind about
which is the best solution for certain things, now using the
ones he dismissed as inferior or pointless in the book. For
instances he spent many pages praising current mirrors but
said that there was not much point in cascoding a BJT
diff pair. Now uses a cascode, but no current mirror. He did
not like nested feedback, but now uses it. He seemed to prefer
CFB output stages to emitter followers, while now using the
latter, although this was somewhat arbitrary also in the book,
varying from design to design. As for old components, well
he use som new devices for the diff pairs, otherwise it is
exactly the same ones as he uses in the book.
Of course, anyone is free to change his/her mind whenever
it seems appropriate, and I am sure Sloane has some reason
for it. Perhaps, he tried to make a somewhat cheaper version
of the "optimal" amp in the book, and concluded that doing
things the other way would be better in this particular case.
Still, having recently read his book I can't help being curious
about this change of mind.
BTW Nelson, would you label the OptiMOS as more modern than
the designs in the book or was it just that you considered those
in the book old-fashioned?
It's not a question of old-fashioned, just an observation
of the probable date it was written. We should expect
designers to change their opinions.
Both Sloane's and Self's designs are conventional. I
personally think that the Opti-mos is more mature
simply because it has a simpler gain path, in spite of
the cascoding and output limiting circuits.
When I started out, I put everything but the kitchen sink
into my circuits, but over the course of 30 years I have come
to have a better appreciation of what you can get done
simply, either from the objective or subjective viewpoint,
and I would be interested to see if other designers mature
in a similar way.
I find both dogmatic in their views, particularly with regards
to the subjective side of audio. To be sure, there are plenty
of excesses in the subjective side, but that's not a good reason
to dismiss subjectivism entirely.
of the probable date it was written. We should expect
designers to change their opinions.
Both Sloane's and Self's designs are conventional. I
personally think that the Opti-mos is more mature
simply because it has a simpler gain path, in spite of
the cascoding and output limiting circuits.
When I started out, I put everything but the kitchen sink
into my circuits, but over the course of 30 years I have come
to have a better appreciation of what you can get done
simply, either from the objective or subjective viewpoint,
and I would be interested to see if other designers mature
in a similar way.
I find both dogmatic in their views, particularly with regards
to the subjective side of audio. To be sure, there are plenty
of excesses in the subjective side, but that's not a good reason
to dismiss subjectivism entirely.
I agree that Sloane represents the conventional, or even
conservative, school. I haven't bothered so much about
audio electronics for over 20 years, except for listening to
music, of course, but in the past year I have started to get
interested in the area again. I bought Sloanes book by impulse
and found it interesting. On the one hand the designs
seemed familiar from what high-end used to look in the 70s,
but I got the impression that there is a much more rigid
understanding nowadays of how the conventional topologies
work and what are important design criteria (within the
conventional paradigm, that is). My idea was to build one of
Sloanes amps, or something similar, but first read up and
polish off the rust from my old knowledge in the area.
I have been very sceptic towards most other design schools,
but following disussions here and in other places I have
realized that there are at least a few of you minimalists, if I may call you so, who seem to have a more well-founded and
nuanced (maybe thats swenglish?) view of what you are
doing, being not only extreme subjectivists but also relating it
to sound engineering principles. I must say I am becoming
increasingly curios to study your designs closer than I have done
so far. It may end up that I build both a conventional amp and
one of yours. We'll see. One reason that I am reconsidering
my view on minimalistic and even valve (tube) designs is that
I am fan of historical recordings and it surprises me more and
more how good the sound can be in the best of the
old recordings. Sometimes I wonder if much has happened
since 1930. Amplifiers were probably very straightforward
and simple then, often without feedback. Yet it can still sounds
so good, with more realistic acoustics than most modern
recordings. There must have been something they were doing
right back then.
Having followed this forum for some time I must say that my
respect for you Nelson has been constantly growing, just
because of the sound views you just put into words yourself
in the previous post. You represent one design school, but you
are not dogmatic and seem quite happy to discuss and
appreciate other types of designs in an relatively unbiased way.
Having that combination of experience and open mind that you
show is a quite rare human quality, in my experience.
conservative, school. I haven't bothered so much about
audio electronics for over 20 years, except for listening to
music, of course, but in the past year I have started to get
interested in the area again. I bought Sloanes book by impulse
and found it interesting. On the one hand the designs
seemed familiar from what high-end used to look in the 70s,
but I got the impression that there is a much more rigid
understanding nowadays of how the conventional topologies
work and what are important design criteria (within the
conventional paradigm, that is). My idea was to build one of
Sloanes amps, or something similar, but first read up and
polish off the rust from my old knowledge in the area.
I have been very sceptic towards most other design schools,
but following disussions here and in other places I have
realized that there are at least a few of you minimalists, if I may call you so, who seem to have a more well-founded and
nuanced (maybe thats swenglish?) view of what you are
doing, being not only extreme subjectivists but also relating it
to sound engineering principles. I must say I am becoming
increasingly curios to study your designs closer than I have done
so far. It may end up that I build both a conventional amp and
one of yours. We'll see. One reason that I am reconsidering
my view on minimalistic and even valve (tube) designs is that
I am fan of historical recordings and it surprises me more and
more how good the sound can be in the best of the
old recordings. Sometimes I wonder if much has happened
since 1930. Amplifiers were probably very straightforward
and simple then, often without feedback. Yet it can still sounds
so good, with more realistic acoustics than most modern
recordings. There must have been something they were doing
right back then.
Having followed this forum for some time I must say that my
respect for you Nelson has been constantly growing, just
because of the sound views you just put into words yourself
in the previous post. You represent one design school, but you
are not dogmatic and seem quite happy to discuss and
appreciate other types of designs in an relatively unbiased way.
Having that combination of experience and open mind that you
show is a quite rare human quality, in my experience.
It's hard to read Self on subjectivists view (takes up most of the first chapter of both his books) without hearing a note of fanatism in his comments.Nelson Pass said:
I imagine when I get old and cranky I'll probably sound about the same.
Phil
Christer said:
I was forced to look in a dictionary, never heard of nuance before. Christer means "nyanserad" and my book has also "shade of meaning". What do you say really, well-balanced point of view?
Mr Pass is a man with deep insight.
Maybe I will get tired of my overloaded designs and join the minimalistic club 🙂My contribution to this thread is RT75 based on Matti Ottala's ideas in the 70's about low feedback and low open-loop gain.
The swedish magazine Radio & Television (later Elektronikvärlden) had articles about this new thinking which was really new at that time. If you check my homepage you can catch a glimpse of it.
http://home5.swipnet.se/~w-50719/hifi/rt75/index.html
Many people built this amp (>1000) inlcuding myself (when I was 16). This amp (you can see the pictures) works still! The basic design needed some development which was published later.
Per-Anders,
I remember the RT75. There was quite a lot of talking about it
here in Sweden when it was new, and I remember a friend of
mine building one. Since you still have one up and running,
do you have any opinion on how it performs compared to
modern amps of the conventional school? Just curious to know.
And yes, although I usually try to avoid making up english
words without checking, I thought making an adjective out
of "nuance", as we do in swedish, would be straightforward
enough to be understood. Still don't know if the word exists in
english, though. I checked this morning, and it's not in my
Oxford and I don't have my Webster at hand.
I remember the RT75. There was quite a lot of talking about it
here in Sweden when it was new, and I remember a friend of
mine building one. Since you still have one up and running,
do you have any opinion on how it performs compared to
modern amps of the conventional school? Just curious to know.
And yes, although I usually try to avoid making up english
words without checking, I thought making an adjective out
of "nuance", as we do in swedish, would be straightforward
enough to be understood. Still don't know if the word exists in
english, though. I checked this morning, and it's not in my
Oxford and I don't have my Webster at hand.
You have to get "Prisma" dictionary from 2000!
The RT75 had an outout stage with gain (3), rather odd and also not easy to handle. I omitted that in my QRO amp.
RT75 is soundwise OK but it lacks off some basic "stability". It's easy to break it with short power interruptions. Turn off and turn on fast, don't do that! = Fried output transistors!
The QRO amp was designed to have a well-controlled startup procedure. Smooth and easy. I have the same thing in my monster designs, headphone and phono amps (which adds up complexity a bit).
The RT75 also had no over current protection, fuses don't do the job in a BJT stage. Easy tho break the transistors with a short circuit. My QRO had MOSFET's much more reliable in that respect. MOSFET's can take a short circuit with only fuses and zener at the gates. I hate foldback current limitation! Bad with "difficult" speakers at high volume of course.
The RT75 had an outout stage with gain (3), rather odd and also not easy to handle. I omitted that in my QRO amp.
RT75 is soundwise OK but it lacks off some basic "stability". It's easy to break it with short power interruptions. Turn off and turn on fast, don't do that! = Fried output transistors!
The QRO amp was designed to have a well-controlled startup procedure. Smooth and easy. I have the same thing in my monster designs, headphone and phono amps (which adds up complexity a bit).
The RT75 also had no over current protection, fuses don't do the job in a BJT stage. Easy tho break the transistors with a short circuit. My QRO had MOSFET's much more reliable in that respect. MOSFET's can take a short circuit with only fuses and zener at the gates. I hate foldback current limitation! Bad with "difficult" speakers at high volume of course.
QRO
Peranders
Why didn't you put more inforamtion on the QRO on your site?
Diagram, pcb, etc.
Carlos
Peranders
Why didn't you put more inforamtion on the QRO on your site?
Diagram, pcb, etc.
Carlos
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