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Jon Kirwan
Guest
Guest
Tue Feb 09, 2010 10:20 pm
On Tue, 09 Feb 2010 14:07:27 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:
Quote:
On Tue, 09 Feb 2010 12:59:01 -0800, Jon Kirwan
jonk_at_infinitefactors.org> wrote:
On Tue, 09 Feb 2010 08:33:45 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:
snip
Useless nonsense....
Are you talking about my comments, those of others here, or
the link you posted below?
http://home.comcast.net/~mercerd/MobileStudioProject/Activity_6_zero_gain_amp.pdf
I'll take a look, today.
Thanks,
Jon
The link. Do the math, it's a hoax, good only at one current and
temperature pair... besides being Beta sensitive.
...Jim Thompson
jonk_at_infinitefactors.org> wrote:
On Tue, 09 Feb 2010 08:33:45 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:
snip
Useless nonsense....
Are you talking about my comments, those of others here, or
the link you posted below?
http://home.comcast.net/~mercerd/MobileStudioProject/Activity_6_zero_gain_amp.pdf
I'll take a look, today.
Thanks,
Jon
The link. Do the math, it's a hoax, good only at one current and
temperature pair... besides being Beta sensitive.
...Jim Thompson
Ah! Thanks! I can use lessons like this, too! If I can see
what you see there, then that means something. Very good way
to teach. Will keep your points in mind as I read it.
Jon
Phil Allison
Guest
Guest
Tue Feb 09, 2010 10:46 pm
"Tim Williams"
Quote:
The general idea is to put the Vbe transistor on the same heatsink as the
outputs, if not glued to a transistor directly.
Unfortunately, for widely mismatched current densities, this doesn't work.
** Huh ??
More gobbledegook presented as fact.
Quote:
http://webpages.charter.net/dawill/Images/Ampere.gif
Quote:
In this boringly typical circuit, the 2N3904 Vbe mult. doesn't have enough
tempco to compensate the far beefier (= lower current density??) output
darlingtons.
tempco to compensate the far beefier (= lower current density??) output
darlingtons.
** Proof by assertion and an isolated example known only to the poster.
Gotta love that on usenet.
..... Phil
Tim Williams
Guest
Guest
Tue Feb 09, 2010 10:48 pm
"Bob Monsen" <rcmonsen_at_gmail.com> wrote in message
news:1265746051.657782_at_sj-nntpcache-3.cisco.com...
Quote:
On a related note, there was an article in a recent EDN about a self
biasing preamp which was kinda cool. Instead of trying to track the
difference using diodes or a multiplier, it used a couple of transistors
and an opamp to set the correct values at the bases of the pass
transistors. It was so novel (at least to me) that I typed it into
LTSpice. Here it is:
biasing preamp which was kinda cool. Instead of trying to track the
difference using diodes or a multiplier, it used a couple of transistors
and an opamp to set the correct values at the bases of the pass
transistors. It was so novel (at least to me) that I typed it into
LTSpice. Here it is:
Could you take a screenshot of the schematic?
Tim
--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Jon Kirwan
Guest
Guest
Tue Feb 09, 2010 11:08 pm
On Tue, 9 Feb 2010 14:05:32 -0700, "bg" <bg_at_nospam.com>
wrote:
Quote:
snip
Your circuit is an example of collector feedback. Collector feedback does
not work well with large signal swings and it lowers the input impedance. A
lower input impedance means that the drivers will also need a lower output
impedance. The bottom line is that you will not see this bias method used in
a power output stages. Another option is to use emitter feedback but for the
emitter resistors to be effective, they will drop alot of signal output and
waste power, which explains why those resistors are usually very low values,
They have very little effect unless the emitter current is large. At the DC
bias current level, they don't do a thing.
Local feedback (emitter feedback or collector feedback) both create more
problems then they solve for stabilizing the power output stage bias point.
To keep the output stage bias point stabilized, the use of overall feedback
is the standard practise. A simple typical amplifier might have a
differential input stage, followerd by a voltage amplifier, followed by the
power output stage. The output from the power stage is fed back to the
differential input stage. High open loop gain with large feedback is the key
to better stabilization of the operating points. Fix it with feedback is a
term to remember.
Your circuit is an example of collector feedback. Collector feedback does
not work well with large signal swings and it lowers the input impedance. A
lower input impedance means that the drivers will also need a lower output
impedance. The bottom line is that you will not see this bias method used in
a power output stages. Another option is to use emitter feedback but for the
emitter resistors to be effective, they will drop alot of signal output and
waste power, which explains why those resistors are usually very low values,
They have very little effect unless the emitter current is large. At the DC
bias current level, they don't do a thing.
Local feedback (emitter feedback or collector feedback) both create more
problems then they solve for stabilizing the power output stage bias point.
To keep the output stage bias point stabilized, the use of overall feedback
is the standard practise. A simple typical amplifier might have a
differential input stage, followerd by a voltage amplifier, followed by the
power output stage. The output from the power stage is fed back to the
differential input stage. High open loop gain with large feedback is the key
to better stabilization of the operating points. Fix it with feedback is a
term to remember.
This point is made, again and again, so it must be true! And
if it weren't true, why else would opamps have been such a
successful building block?? So I completely buy the idea.
I am still trying to study each part, though. At some point,
I will raise my head a bit above that level and take a larger
look. But I'm not yet prepared for it, as the pieces
themselves are still too fuzzily understood. I want to
quantify those, in detail, before expanding my view. In
doing so, I hope to have a somewhat better understanding of
opamps, themselves, too. Not just from a large scale view,
but also in understanding problems within them and how to
choose among various approaches when struggling with a
specific application in mind.
I take your point. But it doesn't change, at all, my
interest in seeing what can be reasonably done with at teh
Vbe multiplier level to accomodate variations in current.
That remains interesting in and of its own right.
Quote:
The typical bias chain using diodes can be made with resistors as well, but
diodes have the advantage of dropping the bias voltage while having a lower
impedance to the signal.
diodes have the advantage of dropping the bias voltage while having a lower
impedance to the signal.
That makes sense.
Quote:
Sometimes you will see those bypassed with a large
cap if the impedance causes to much signal loss.
cap if the impedance causes to much signal loss.
I had thought of that, as well. Though, of course, I hadn't
put values to it.
Quote:
Diodes can also offer temperature compensation.
Their Eg and N would seem to suggest some difficulties with
curve matching, but I agree broadly.
Quote:
In any case, an output stage will have way more
current flowing in that bias chain than is actually needed as base bias
current.
current flowing in that bias chain than is actually needed as base bias
current.
This seems to argue with something I read John L. saying, but
I didn't accept it (or reject it), yet. I will need to get
there in due course. But I'm still taking pieces one at a
time.
Quote:
The voltage drops developed in the bias chain will not be greatly
affected by changes in the base emitter junction because the base bias
current is small compared to the current in the bias chain.
affected by changes in the base emitter junction because the base bias
current is small compared to the current in the bias chain.
I read this sentence a few times to try and make sure I
followed it well. If I do, and I may not, I think I
addressed this when I tried to calculate the R_ac figure.
The numbers I come up with for a 5mA "bias chain" current
with 1mA in the base bias current and 4mA in the collector,
come out as around 15 Ohms, or so. If I'm right about that,
it seems almost certain that there is _some_ response to even
modest variations in current through it. A 500uA change
yields a 7.5mV change. When I LTspice it, I get a simulation
that matches what I calculate, too.
Quote:
And remember,
that " Fix it with feedback " applies here too.
that " Fix it with feedback " applies here too.
Yes, the mantra is slowly deepening within me.
Quote:
So variations in the power
supply have a very reduced effect on the bias point. The feedback signal is
a voltage, and enough feedback will compensate to keep the output voltage
offset at zero. It will not compensate for for excessve collector currents
or power dissaption if the offset voltage remains low.
supply have a very reduced effect on the bias point. The feedback signal is
a voltage, and enough feedback will compensate to keep the output voltage
offset at zero. It will not compensate for for excessve collector currents
or power dissaption if the offset voltage remains low.
Good point for me to remember!! Thanks.
Quote:
That is why temperature compensation is used too.
I begin to see, better. Thanks, again.
Quote:
In the early years of transistors, it was common to see transistor stages
using many of the techniques used with vacuum tubes. Dc coupled amplifiers
were rare, because any bias shift was amplified in further stages. Feedback
was applied locally, and overall feedback had no effect on the DC operating
points.
using many of the techniques used with vacuum tubes. Dc coupled amplifiers
were rare, because any bias shift was amplified in further stages. Feedback
was applied locally, and overall feedback had no effect on the DC operating
points.
I seem to recall that vacuum tube amplifiers even let the
consumer modify the global NFB. But, as you say, since it
wasn't so critical to the design that was probably why it was
allowed in the first place. With BJTs, it seems now to me
that global NFB is _so_ important that such things cannot be
left as "tweeks" by some consumer playing with a knob!
Quote:
The trend now is to stabilize everything with feedback. It works,
and it works well. Unless you are a purist and have some religious reason to
avoid this technique, there is no sense in reinventing the wheel.
and it works well. Unless you are a purist and have some religious reason to
avoid this technique, there is no sense in reinventing the wheel.
It's not a religious reason, unless _learning_ is a religion,
I suppose. I don't mind being told that "one day when you
are ready, you will use global NFB to take care of this." I
can gather and accept it, of course. But I also cannot
believe an amplifier can be designed with bags of random
bolts tossed together and "fixed with global NFB" in the end.
There are parts in there and they need to perform some
intended function to some reasonable approximation. And I am
still working on understanding each piece as well as some
thoughts about various approaches at that level to improve
the ideas.
For example, it's important to understand not just vaguely,
but quantitatively on various scores, how a diff-amp behaves
and why I may want to have a current mirror on the tails. I
don't want to just hear "put a current mirror there" and
learn nothing then about why. Later on, when I'm looking
globally at an amplifier, I can look backwards and say, "Hmm.
That Wilson mirror is great, but I really don't need it. The
bog standard 2-BJT mirror is fine enough." But I want to say
that from _understanding_ the details, not from others merely
assuring me about it.
See the difference?
Meanwhile, I'm still interested in seeing if my quantitative
analysis was correct (or wrong) and if there are some other
topologies for it, other than the two I mentioned, that may
be interesting to look at.
Thanks,
Jon
Jon Kirwan
Guest
Guest
Tue Feb 09, 2010 11:30 pm
On Tue, 9 Feb 2010 15:48:42 -0600, "Tim Williams"
<tmoranwms_at_charter.net> wrote:
Quote:
"Bob Monsen" <rcmonsen_at_gmail.com> wrote in message
news:1265746051.657782_at_sj-nntpcache-3.cisco.com...
On a related note, there was an article in a recent EDN about a self
biasing preamp which was kinda cool. Instead of trying to track the
difference using diodes or a multiplier, it used a couple of transistors
and an opamp to set the correct values at the bases of the pass
transistors. It was so novel (at least to me) that I typed it into
LTSpice. Here it is:
Could you take a screenshot of the schematic?
news:1265746051.657782_at_sj-nntpcache-3.cisco.com...
On a related note, there was an article in a recent EDN about a self
biasing preamp which was kinda cool. Instead of trying to track the
difference using diodes or a multiplier, it used a couple of transistors
and an opamp to set the correct values at the bases of the pass
transistors. It was so novel (at least to me) that I typed it into
LTSpice. Here it is:
Could you take a screenshot of the schematic?
I'll include an ASCII version here:
Quote:
: R2
: +V = 12V ,------/\/\---------------------,
: | 1k |
: | +V |
: | | |
: | \ |
: | / R1 |
: | \ 1k5 |
: | / |
: | | +V |
: C2 | ,----+ | |
: || 10uF R4 | | | 2N3904| |
: ,------||------/\/\---------+ | | | |
: I| || 100 | | Q4 e>| |/c Q3 |
: N| | | |-------| |
: | | | c/| |>e |
: | | C1 --- | | |
: --- | 10uF--- |2N3906 | |
: - V2 | | | | |
: --- SINE(0 .2 1k) | | | | | C3
: - | C5 | | | | || 470uF
: | | || 10p| | +----+-||----,O
: | +V +---||----+ | | || |U
: | | | || | | | |T
: gnd | | | | | \
: | | | |2N3904 | / R5
: \ ,-------, | | | | \ 8
: / R3 | | | +V | Q1 c\| |<e Q5 /
: \ 1k | +V | | | 2N| |-------| 2N3906 |
: / | | | | |\| | e<| |\c |
: | | |\| | '-|-\ | | | |
: | '--|-\ | | >----+----' | gnd
: | | >-+-----|+/ |
: +-------|+/ |/| LT6234 |
: ,-----+ |/| LT6234 | gnd
: | | | gnd
: --- C4 \ gnd
: --- 1uF/ R9
: | \ 1k
: | /
: | |
: gnd gnd
: +V = 12V ,------/\/\---------------------,
: | 1k |
: | +V |
: | | |
: | \ |
: | / R1 |
: | \ 1k5 |
: | / |
: | | +V |
: C2 | ,----+ | |
: || 10uF R4 | | | 2N3904| |
: ,------||------/\/\---------+ | | | |
: I| || 100 | | Q4 e>| |/c Q3 |
: N| | | |-------| |
: | | | c/| |>e |
: | | C1 --- | | |
: --- | 10uF--- |2N3906 | |
: - V2 | | | | |
: --- SINE(0 .2 1k) | | | | | C3
: - | C5 | | | | || 470uF
: | | || 10p| | +----+-||----,O
: | +V +---||----+ | | || |U
: | | | || | | | |T
: gnd | | | | | \
: | | | |2N3904 | / R5
: \ ,-------, | | | | \ 8
: / R3 | | | +V | Q1 c\| |<e Q5 /
: \ 1k | +V | | | 2N| |-------| 2N3906 |
: / | | | | |\| | e<| |\c |
: | | |\| | '-|-\ | | | |
: | '--|-\ | | >----+----' | gnd
: | | >-+-----|+/ |
: +-------|+/ |/| LT6234 |
: ,-----+ |/| LT6234 | gnd
: | | | gnd
: --- C4 \ gnd
: --- 1uF/ R9
: | \ 1k
: | /
: | |
: gnd gnd
(This was auto-generated from my LTspice to ASCII program.)
Jon
Ban
Guest
Guest
Tue Feb 09, 2010 11:38 pm
"Jon Kirwan" <jonk_at_infinitefactors.org> schrieb im Newsbeitrag
news:8te2n5llb72tgv03g653ajqjf360m3mc06_at_4ax.com...
Quote:
On Mon, 8 Feb 2010 18:23:16 -0800 (PST), "miso_at_sushi.com"
miso_at_sushi.com> wrote:
Okay. I'll do that if folks here aren't interested at all in
talking about it.
BS, a couple of good answers have come.
miso_at_sushi.com> wrote:
Okay. I'll do that if folks here aren't interested at all in
talking about it.
BS, a couple of good answers have come.
Jon, you should read this book, bit torrentwise
Audio Power Amplifier Design Handbook, 4th Ed. - (Malestrom)
by Doug Self, one of the deeper going but still very practical publications,
you'll love it.
Ban
Jim Thompson
Guest
Guest
Tue Feb 09, 2010 11:42 pm
On Tue, 09 Feb 2010 14:30:54 -0800, Jon Kirwan
<jonk_at_infinitefactors.org> wrote:
Quote:
On Tue, 9 Feb 2010 15:48:42 -0600, "Tim Williams"
tmoranwms_at_charter.net> wrote:
"Bob Monsen" <rcmonsen_at_gmail.com> wrote in message
news:1265746051.657782_at_sj-nntpcache-3.cisco.com...
On a related note, there was an article in a recent EDN about a self
biasing preamp which was kinda cool. Instead of trying to track the
difference using diodes or a multiplier, it used a couple of transistors
and an opamp to set the correct values at the bases of the pass
transistors. It was so novel (at least to me) that I typed it into
LTSpice. Here it is:
Could you take a screenshot of the schematic?
I'll include an ASCII version here:
: R2
: +V = 12V ,------/\/\---------------------,
: | 1k |
: | +V |
: | | |
: | \ |
: | / R1 |
: | \ 1k5 |
: | / |
: | | +V |
: C2 | ,----+ | |
: || 10uF R4 | | | 2N3904| |
: ,------||------/\/\---------+ | | | |
: I| || 100 | | Q4 e>| |/c Q3 |
: N| | | |-------| |
: | | | c/| |>e |
: | | C1 --- | | |
: --- | 10uF--- |2N3906 | |
: - V2 | | | | |
: --- SINE(0 .2 1k) | | | | | C3
: - | C5 | | | | || 470uF
: | | || 10p| | +----+-||----,O
: | +V +---||----+ | | || |U
: | | | || | | | |T
: gnd | | | | | \
: | | | |2N3904 | / R5
: \ ,-------, | | | | \ 8
: / R3 | | | +V | Q1 c\| |<e Q5 /
: \ 1k | +V | | | 2N| |-------| 2N3906 |
: / | | | | |\| | e<| |\c |
: | | |\| | '-|-\ | | | |
: | '--|-\ | | >----+----' | gnd
: | | >-+-----|+/ |
: +-------|+/ |/| LT6234 |
: ,-----+ |/| LT6234 | gnd
: | | | gnd
: --- C4 \ gnd
: --- 1uF/ R9
: | \ 1k
: | /
: | |
: gnd gnd
(This was auto-generated from my LTspice to ASCII program.)
Jon
tmoranwms_at_charter.net> wrote:
"Bob Monsen" <rcmonsen_at_gmail.com> wrote in message
news:1265746051.657782_at_sj-nntpcache-3.cisco.com...
On a related note, there was an article in a recent EDN about a self
biasing preamp which was kinda cool. Instead of trying to track the
difference using diodes or a multiplier, it used a couple of transistors
and an opamp to set the correct values at the bases of the pass
transistors. It was so novel (at least to me) that I typed it into
LTSpice. Here it is:
Could you take a screenshot of the schematic?
I'll include an ASCII version here:
: R2
: +V = 12V ,------/\/\---------------------,
: | 1k |
: | +V |
: | | |
: | \ |
: | / R1 |
: | \ 1k5 |
: | / |
: | | +V |
: C2 | ,----+ | |
: || 10uF R4 | | | 2N3904| |
: ,------||------/\/\---------+ | | | |
: I| || 100 | | Q4 e>| |/c Q3 |
: N| | | |-------| |
: | | | c/| |>e |
: | | C1 --- | | |
: --- | 10uF--- |2N3906 | |
: - V2 | | | | |
: --- SINE(0 .2 1k) | | | | | C3
: - | C5 | | | | || 470uF
: | | || 10p| | +----+-||----,O
: | +V +---||----+ | | || |U
: | | | || | | | |T
: gnd | | | | | \
: | | | |2N3904 | / R5
: \ ,-------, | | | | \ 8
: / R3 | | | +V | Q1 c\| |<e Q5 /
: \ 1k | +V | | | 2N| |-------| 2N3906 |
: / | | | | |\| | e<| |\c |
: | | |\| | '-|-\ | | | |
: | '--|-\ | | >----+----' | gnd
: | | >-+-----|+/ |
: +-------|+/ |/| LT6234 |
: ,-----+ |/| LT6234 | gnd
: | | | gnd
: --- C4 \ gnd
: --- 1uF/ R9
: | \ 1k
: | /
: | |
: gnd gnd
(This was auto-generated from my LTspice to ASCII program.)
Jon
What in the world ?
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Jon Kirwan
Guest
Guest
Tue Feb 09, 2010 11:50 pm
On Tue, 09 Feb 2010 15:42:48 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:
Quote:
What in the world ?
View in fixed-spaced font. And it's a rendition of the
schematic that Bob Monson had posted, earlier, from EDN. He
wrote, "On a related note, there was an article in a recent
EDN about a self biasing preamp which was kinda cool. Instead
of trying to track the difference using diodes or a
multiplier, it used a couple of transistors and an opamp to
set the correct values at the bases of the pass transistors.
It was so novel (at least to me) that I typed it into
LTSpice."
I merely re-arranged it in LTspice to be a little more to my
taste and then passed it through a program that generates
ASCII from that.
Jon
Jon Kirwan
Guest
Guest
Tue Feb 09, 2010 11:52 pm
On Tue, 9 Feb 2010 23:38:06 +0100, "Ban" <bansuri_at_web.de>
wrote:
Quote:
"Jon Kirwan" <jonk_at_infinitefactors.org> schrieb im Newsbeitrag
news:8te2n5llb72tgv03g653ajqjf360m3mc06_at_4ax.com...
On Mon, 8 Feb 2010 18:23:16 -0800 (PST), "miso_at_sushi.com"
miso_at_sushi.com> wrote:
Okay. I'll do that if folks here aren't interested at all in
talking about it.
BS, a couple of good answers have come.
Agreed. We are past that question.
Quote:
Jon, you should read this book, bit torrentwise
Audio Power Amplifier Design Handbook, 4th Ed. - (Malestrom)
by Doug Self, one of the deeper going but still very practical publications,
you'll love it.
Ban
Audio Power Amplifier Design Handbook, 4th Ed. - (Malestrom)
by Doug Self, one of the deeper going but still very practical publications,
you'll love it.
Ban
I just received a copy of the 5th edition, today. I'll
start, though the author says that it assumes a certain level
of prior training. And skimming through, I agree.
Jon
Jon Kirwan
Guest
Guest
Wed Feb 10, 2010 12:01 am
On Tue, 09 Feb 2010 14:52:02 -0800, I wrote:
Quote:
On Tue, 9 Feb 2010 23:38:06 +0100, "Ban" <bansuri_at_web.de
wrote:
"Jon Kirwan" <jonk_at_infinitefactors.org> schrieb im Newsbeitrag
news:8te2n5llb72tgv03g653ajqjf360m3mc06_at_4ax.com...
On Mon, 8 Feb 2010 18:23:16 -0800 (PST), "miso_at_sushi.com"
miso_at_sushi.com> wrote:
Okay. I'll do that if folks here aren't interested at all in
talking about it.
BS, a couple of good answers have come.
Agreed. We are past that question.
Jon, you should read this book, bit torrentwise
Audio Power Amplifier Design Handbook, 4th Ed. - (Malestrom)
by Doug Self, one of the deeper going but still very practical publications,
you'll love it.
Ban
I just received a copy of the 5th edition, today. I'll
start, though the author says that it assumes a certain level
of prior training. And skimming through, I agree.
wrote:
"Jon Kirwan" <jonk_at_infinitefactors.org> schrieb im Newsbeitrag
news:8te2n5llb72tgv03g653ajqjf360m3mc06_at_4ax.com...
On Mon, 8 Feb 2010 18:23:16 -0800 (PST), "miso_at_sushi.com"
miso_at_sushi.com> wrote:
Okay. I'll do that if folks here aren't interested at all in
talking about it.
BS, a couple of good answers have come.
Agreed. We are past that question.
Jon, you should read this book, bit torrentwise
Audio Power Amplifier Design Handbook, 4th Ed. - (Malestrom)
by Doug Self, one of the deeper going but still very practical publications,
you'll love it.
Ban
I just received a copy of the 5th edition, today. I'll
start, though the author says that it assumes a certain level
of prior training. And skimming through, I agree.
Okay!!! It has a great section on Vbe multipliers under
Chapter 15 on Thermal Compensation!! This is helpful. And
it includes a discussion on that collector resistor there and
in Chapter 7, where a chart is presented with various values
for my R3 shown and the curves over current. Nice!! It also
appears, on first glance, to confirm my impressions!! This
is very good.
Jon
Jim Thompson
Guest
Guest
Wed Feb 10, 2010 12:08 am
On Tue, 09 Feb 2010 14:50:50 -0800, Jon Kirwan
<jonk_at_infinitefactors.org> wrote:
Quote:
On Tue, 09 Feb 2010 15:42:48 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:
What in the world ?:-)
View in fixed-spaced font. And it's a rendition of the
schematic that Bob Monson had posted, earlier, from EDN. He
wrote, "On a related note, there was an article in a recent
EDN about a self biasing preamp which was kinda cool. Instead
of trying to track the difference using diodes or a
multiplier, it used a couple of transistors and an opamp to
set the correct values at the bases of the pass transistors.
It was so novel (at least to me) that I typed it into
LTSpice."
I merely re-arranged it in LTspice to be a little more to my
taste and then passed it through a program that generates
ASCII from that.
Jon
To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:
What in the world ?:-)
View in fixed-spaced font. And it's a rendition of the
schematic that Bob Monson had posted, earlier, from EDN. He
wrote, "On a related note, there was an article in a recent
EDN about a self biasing preamp which was kinda cool. Instead
of trying to track the difference using diodes or a
multiplier, it used a couple of transistors and an opamp to
set the correct values at the bases of the pass transistors.
It was so novel (at least to me) that I typed it into
LTSpice."
I merely re-arranged it in LTspice to be a little more to my
taste and then passed it through a program that generates
ASCII from that.
Jon
Burr-Brown was famous for using bias compensation like that in the
front ends of some of their operational amplifiers, but I doubt its
efficacy in power output stages.
The Burr-Brown scheme is similar to a discussion here a few (seven
years ago...
http://analog-innovations.com/SED/IB-Cancellation-WithTwoOpAmps.pdf
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Jon Kirwan
Guest
Guest
Wed Feb 10, 2010 12:17 am
On Tue, 09 Feb 2010 16:08:22 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:
Quote:
On Tue, 09 Feb 2010 14:50:50 -0800, Jon Kirwan
jonk_at_infinitefactors.org> wrote:
On Tue, 09 Feb 2010 15:42:48 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:
What in the world ?:-)
View in fixed-spaced font. And it's a rendition of the
schematic that Bob Monson had posted, earlier, from EDN. He
wrote, "On a related note, there was an article in a recent
EDN about a self biasing preamp which was kinda cool. Instead
of trying to track the difference using diodes or a
multiplier, it used a couple of transistors and an opamp to
set the correct values at the bases of the pass transistors.
It was so novel (at least to me) that I typed it into
LTSpice."
I merely re-arranged it in LTspice to be a little more to my
taste and then passed it through a program that generates
ASCII from that.
Jon
Burr-Brown was famous for using bias compensation like that in the
front ends of some of their operational amplifiers, but I doubt its
efficacy in power output stages.
jonk_at_infinitefactors.org> wrote:
On Tue, 09 Feb 2010 15:42:48 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:
What in the world ?:-)
View in fixed-spaced font. And it's a rendition of the
schematic that Bob Monson had posted, earlier, from EDN. He
wrote, "On a related note, there was an article in a recent
EDN about a self biasing preamp which was kinda cool. Instead
of trying to track the difference using diodes or a
multiplier, it used a couple of transistors and an opamp to
set the correct values at the bases of the pass transistors.
It was so novel (at least to me) that I typed it into
LTSpice."
I merely re-arranged it in LTspice to be a little more to my
taste and then passed it through a program that generates
ASCII from that.
Jon
Burr-Brown was famous for using bias compensation like that in the
front ends of some of their operational amplifiers, but I doubt its
efficacy in power output stages.
I am still struggling to understand it. There are very
obvious parts that I completely understand. For example, the
divider for a "center" voltage followed by a unity gain
buffer for drive current compliance. I would guess that the
gain is determined by the NFB resistor divided by the input
impedance, which is mostly R4 in this case... so 10. I see
an opamp looking like an integrator, but I'm frankly
unfamiliar with the 4-BJT arrangement structure and need to
think about that one.
Quote:
The Burr-Brown scheme is similar to a discussion here a few (seven
years ago...
http://analog-innovations.com/SED/IB-Cancellation-WithTwoOpAmps.pdf
years ago...
http://analog-innovations.com/SED/IB-Cancellation-WithTwoOpAmps.pdf
I'll download it now and look when I get a moment to engage a
little thought.
Thanks,
Jon
Jon Kirwan
Guest
Guest
Wed Feb 10, 2010 12:20 am
On Tue, 09 Feb 2010 15:17:24 -0800, I wrote:
Quote:
snip
I'm frankly
unfamiliar with the 4-BJT arrangement structure and need to
think about that one.
snip
I'm frankly
unfamiliar with the 4-BJT arrangement structure and need to
think about that one.
snip
I do "see" the emitter followers of Q3/Q5 on the schematic,
of course. It's the R1/Q1/Q4/C1 parts that I'm assuming is
the bias compensation and is the part I don't follow. The C5
looks like a very lightly applied integrator cap, which I
take is needed to avoid oscillation. And that's about where
I'm stuck.
Jon
Jim Thompson
Guest
Guest
Wed Feb 10, 2010 12:21 am
On Tue, 09 Feb 2010 15:17:24 -0800, Jon Kirwan
<jonk_at_infinitefactors.org> wrote:
Quote:
On Tue, 09 Feb 2010 16:08:22 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:
On Tue, 09 Feb 2010 14:50:50 -0800, Jon Kirwan
jonk_at_infinitefactors.org> wrote:
On Tue, 09 Feb 2010 15:42:48 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:
What in the world ?:-)
View in fixed-spaced font. And it's a rendition of the
schematic that Bob Monson had posted, earlier, from EDN. He
wrote, "On a related note, there was an article in a recent
EDN about a self biasing preamp which was kinda cool. Instead
of trying to track the difference using diodes or a
multiplier, it used a couple of transistors and an opamp to
set the correct values at the bases of the pass transistors.
It was so novel (at least to me) that I typed it into
LTSpice."
I merely re-arranged it in LTspice to be a little more to my
taste and then passed it through a program that generates
ASCII from that.
Jon
Burr-Brown was famous for using bias compensation like that in the
front ends of some of their operational amplifiers, but I doubt its
efficacy in power output stages.
I am still struggling to understand it. There are very
obvious parts that I completely understand. For example, the
divider for a "center" voltage followed by a unity gain
buffer for drive current compliance. I would guess that the
gain is determined by the NFB resistor divided by the input
impedance, which is mostly R4 in this case... so 10. I see
an opamp looking like an integrator, but I'm frankly
unfamiliar with the 4-BJT arrangement structure and need to
think about that one.
The Burr-Brown scheme is similar to a discussion here a few (seven
years ago...
http://analog-innovations.com/SED/IB-Cancellation-WithTwoOpAmps.pdf
I'll download it now and look when I get a moment to engage a
little thought.
Thanks,
Jon
To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:
On Tue, 09 Feb 2010 14:50:50 -0800, Jon Kirwan
jonk_at_infinitefactors.org> wrote:
On Tue, 09 Feb 2010 15:42:48 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:
What in the world ?:-)
View in fixed-spaced font. And it's a rendition of the
schematic that Bob Monson had posted, earlier, from EDN. He
wrote, "On a related note, there was an article in a recent
EDN about a self biasing preamp which was kinda cool. Instead
of trying to track the difference using diodes or a
multiplier, it used a couple of transistors and an opamp to
set the correct values at the bases of the pass transistors.
It was so novel (at least to me) that I typed it into
LTSpice."
I merely re-arranged it in LTspice to be a little more to my
taste and then passed it through a program that generates
ASCII from that.
Jon
Burr-Brown was famous for using bias compensation like that in the
front ends of some of their operational amplifiers, but I doubt its
efficacy in power output stages.
I am still struggling to understand it. There are very
obvious parts that I completely understand. For example, the
divider for a "center" voltage followed by a unity gain
buffer for drive current compliance. I would guess that the
gain is determined by the NFB resistor divided by the input
impedance, which is mostly R4 in this case... so 10. I see
an opamp looking like an integrator, but I'm frankly
unfamiliar with the 4-BJT arrangement structure and need to
think about that one.
The Burr-Brown scheme is similar to a discussion here a few (seven
years ago...
http://analog-innovations.com/SED/IB-Cancellation-WithTwoOpAmps.pdf
I'll download it now and look when I get a moment to engage a
little thought.
Thanks,
Jon
Study up on writing loop and nodal equations and either solving by
simultaneous equations or matrix manipulation.
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Jim Thompson
Guest
Guest
Wed Feb 10, 2010 12:24 am
On Tue, 09 Feb 2010 14:30:54 -0800, Jon Kirwan
<jonk_at_infinitefactors.org> wrote:
Quote:
On Tue, 9 Feb 2010 15:48:42 -0600, "Tim Williams"
tmoranwms_at_charter.net> wrote:
"Bob Monsen" <rcmonsen_at_gmail.com> wrote in message
news:1265746051.657782_at_sj-nntpcache-3.cisco.com...
On a related note, there was an article in a recent EDN about a self
biasing preamp which was kinda cool. Instead of trying to track the
difference using diodes or a multiplier, it used a couple of transistors
and an opamp to set the correct values at the bases of the pass
transistors. It was so novel (at least to me) that I typed it into
LTSpice. Here it is:
Could you take a screenshot of the schematic?
I'll include an ASCII version here:
: R2
: +V = 12V ,------/\/\---------------------,
: | 1k |
: | +V |
: | | |
: | \ |
: | / R1 |
: | \ 1k5 |
: | / |
: | | +V |
: C2 | ,----+ | |
: || 10uF R4 | | | 2N3904| |
: ,------||------/\/\---------+ | | | |
: I| || 100 | | Q4 e>| |/c Q3 |
: N| | | |-------| |
: | | | c/| |>e |
: | | C1 --- | | |
: --- | 10uF--- |2N3906 | |
: - V2 | | | | |
: --- SINE(0 .2 1k) | | | | | C3
: - | C5 | | | | || 470uF
: | | || 10p| | +----+-||----,O
: | +V +---||----+ | | || |U
: | | | || | | | |T
: gnd | | | | | \
: | | | |2N3904 | / R5
: \ ,-------, | | | | \ 8
: / R3 | | | +V | Q1 c\| |<e Q5 /
: \ 1k | +V | | | 2N| |-------| 2N3906 |
: / | | | | |\| | e<| |\c |
: | | |\| | '-|-\ | | | |
: | '--|-\ | | >----+----' | gnd
: | | >-+-----|+/ |
: +-------|+/ |/| LT6234 |
: ,-----+ |/| LT6234 | gnd
: | | | gnd
: --- C4 \ gnd
: --- 1uF/ R9
: | \ 1k
: | /
: | |
: gnd gnd
(This was auto-generated from my LTspice to ASCII program.)
Jon
tmoranwms_at_charter.net> wrote:
"Bob Monsen" <rcmonsen_at_gmail.com> wrote in message
news:1265746051.657782_at_sj-nntpcache-3.cisco.com...
On a related note, there was an article in a recent EDN about a self
biasing preamp which was kinda cool. Instead of trying to track the
difference using diodes or a multiplier, it used a couple of transistors
and an opamp to set the correct values at the bases of the pass
transistors. It was so novel (at least to me) that I typed it into
LTSpice. Here it is:
Could you take a screenshot of the schematic?
I'll include an ASCII version here:
: R2
: +V = 12V ,------/\/\---------------------,
: | 1k |
: | +V |
: | | |
: | \ |
: | / R1 |
: | \ 1k5 |
: | / |
: | | +V |
: C2 | ,----+ | |
: || 10uF R4 | | | 2N3904| |
: ,------||------/\/\---------+ | | | |
: I| || 100 | | Q4 e>| |/c Q3 |
: N| | | |-------| |
: | | | c/| |>e |
: | | C1 --- | | |
: --- | 10uF--- |2N3906 | |
: - V2 | | | | |
: --- SINE(0 .2 1k) | | | | | C3
: - | C5 | | | | || 470uF
: | | || 10p| | +----+-||----,O
: | +V +---||----+ | | || |U
: | | | || | | | |T
: gnd | | | | | \
: | | | |2N3904 | / R5
: \ ,-------, | | | | \ 8
: / R3 | | | +V | Q1 c\| |<e Q5 /
: \ 1k | +V | | | 2N| |-------| 2N3906 |
: / | | | | |\| | e<| |\c |
: | | |\| | '-|-\ | | | |
: | '--|-\ | | >----+----' | gnd
: | | >-+-----|+/ |
: +-------|+/ |/| LT6234 |
: ,-----+ |/| LT6234 | gnd
: | | | gnd
: --- C4 \ gnd
: --- 1uF/ R9
: | \ 1k
: | /
: | |
: gnd gnd
(This was auto-generated from my LTspice to ASCII program.)
Jon
Did something get lost in the ASCII? Otherwise collector-to-collector
as in Q1-Q4 is a no-no... one of those devices will saturate.
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
elektroda.net NewsGroups Forum Index - Electronics Design - Maintaining a Vbe Multiplier's bias value
