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  #1   Report Post  
David Grant
 
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Default preamp design

I hope this is an appropriate news group to post this (I apologize if not)

Well first of all I'll say a bit about myself... I'm an electrical
engineering student with an interest in audio electronics. In the third year
of my program we covered basic amplifier design, which I loved, and I've
been considering a career in this field since.

At the moment I'm particularly interested in microphone preamplifiers since
I'm a poor student who has his own project studio, but doesn't own (and
can't afford) a nice preamp like the Great River.

I'm having a good bit of trouble finding any info on design strategies that
are specific to microphone preamps. I've found some schematics on the net
but there's rarely any very detailed explanation given about why they were
designed the way they were, and what considerations were made. I understand
all the basic principles like CMRR, slew rate, etc... but there seems to be
some sort of understanding gap, and I'd like to bridge that gap. I realize
it's probably something I'm not going to be able to grasp over night, I'm
just looking for some kind of direction.

If anyone knows of any resources that would help me, I'd appreciate it.

Thanks,

Dave


  #2   Report Post  
P Stamler
 
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At the risk of blowing my own horn, I've written several articles on preamp
designs, both solid-state and vacuum tube based, in what is now audioXpress
magazine (the solid-state series was published in 1996, when the magazine was
called Audio Amateur). In the articles, I talked about some basic principles of
design which apply to microphone preamps in general, not only to these designs.

Peace,
Paul Stamler
  #3   Report Post  
Pooh Bear
 
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David Grant wrote:

I hope this is an appropriate news group to post this (I apologize if not)

Well first of all I'll say a bit about myself... I'm an electrical
engineering student with an interest in audio electronics. In the third year
of my program we covered basic amplifier design, which I loved, and I've
been considering a career in this field since.

At the moment I'm particularly interested in microphone preamplifiers since
I'm a poor student who has his own project studio, but doesn't own (and
can't afford) a nice preamp like the Great River.

I'm having a good bit of trouble finding any info on design strategies that
are specific to microphone preamps. I've found some schematics on the net
but there's rarely any very detailed explanation given about why they were
designed the way they were, and what considerations were made. I understand
all the basic principles like CMRR, slew rate, etc... but there seems to be
some sort of understanding gap, and I'd like to bridge that gap. I realize
it's probably something I'm not going to be able to grasp over night, I'm
just looking for some kind of direction.

If anyone knows of any resources that would help me, I'd appreciate it.


The first thing you need to know with mic pre-amps is how to design with
discretes. Has your course covered that in any depth ? Relatively unlikely I'll
guess.

That's the first hurdle. A good understanding of differential circuitry,
feedback methods and noise calculations takes you further. Then you get into
understanding device parameters. Does rbb mean anything to you for example ?

Graham

  #4   Report Post  
Chris Hornbeck
 
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On Mon, 1 Dec 2003 18:02:05 -0500, "David Grant"
wrote:

If anyone knows of any resources that would help me, I'd appreciate it.


There's also some excellent general info at:
http://www.rane.com/library.html

Good fortune,

Chris Hornbeck
"That is my Theory, and what it is too."
Anne Elk
  #5   Report Post  
David Grant
 
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"Pooh Bear" wrote in message
...
David Grant wrote:

I hope this is an appropriate news group to post this (I apologize if

not)

Well first of all I'll say a bit about myself... I'm an electrical
engineering student with an interest in audio electronics. In the third

year
of my program we covered basic amplifier design, which I loved, and I've
been considering a career in this field since.

At the moment I'm particularly interested in microphone preamplifiers

since
I'm a poor student who has his own project studio, but doesn't own (and
can't afford) a nice preamp like the Great River.

I'm having a good bit of trouble finding any info on design strategies

that
are specific to microphone preamps. I've found some schematics on the

net
but there's rarely any very detailed explanation given about why they

were
designed the way they were, and what considerations were made. I

understand
all the basic principles like CMRR, slew rate, etc... but there seems to

be
some sort of understanding gap, and I'd like to bridge that gap. I

realize
it's probably something I'm not going to be able to grasp over night,

I'm
just looking for some kind of direction.

If anyone knows of any resources that would help me, I'd appreciate it.


The first thing you need to know with mic pre-amps is how to design with
discretes. Has your course covered that in any depth ? Relatively unlikely

I'll
guess.


We've never used the term "discrete" anywhere, but am I correct in assuming
it means "not in IC form" (i.e BJT amps versus op amp ICs)? If that's the
case then we've done a good bit.


That's the first hurdle. A good understanding of differential circuitry,
feedback methods and noise calculations takes you further. Then you get

into
understanding device parameters. Does rbb mean anything to you for example

?

We've covered differential BJT amps, cascode configuration, some frequency
response, feedback (shunt/series sampling) and some stability. I remember
some stuff on calculating CMRR if that's what you mean by noise
calculations. As for the device parameters, I'm not sure. Rbb sounds like
the symbol one of my proffs used to denote the base resistance used for
biasing a BJT, but otherwise it doesn't mean anything to me.

We did all the derivations of gain, in/out resistance for most of the amps
we discussed in class, and usually everything simplified down to something
neat and tidy. I've tried to do small signal analysis on some of the mic-pre
schematics I've looked at, but I always end up with huge long expressions
that turn very messy. I also never end up with the quoted specs in the end!
It seems like there must be some simplification that I'm missing. Common
mode gain control for example... what on earth is that (apart from a gain
control)?

Maybe I just need more experience with this stuff, but I'm not sure where to
find that.

Thanks for the help

Dave

Graham





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Arny Krueger
 
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"David Grant" wrote in message



If anyone knows of any resources that would help me, I'd appreciate it.


I think a reasonable first step would be to figure out how to reliably and
relevantly determine the effectiveness and performance of a mic preamp. Both
technical tests and listening tests seem relevant. Tests with various
microphones and microphone techniques and/or simulations of them seem
relevant.

Then, apply those evaluation techniques to a number of commercial products
at various price levels, as well as various technological implementations
(tubes, discrete solid state, ICs).

Identify good things, bad things, peculiarities, foibles, desirable
features, and good baseline performance in terms that are comparable across
products and implementations.

Then, design, build and evaluate a mic preamp that maximizes as many of the
high priority desirable properties as possible.



  #8   Report Post  
Wilfried Adam
 
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David Grant wrote:

I'm having a good bit of trouble finding any info on design strategies that
are specific to microphone preamps. I've found some schematics on the net
but there's rarely any very detailed explanation given about why they were
designed the way they were, and what considerations were made. I understand
all the basic principles like CMRR, slew rate, etc... but there seems to be
some sort of understanding gap, and I'd like to bridge that gap. I realize
it's probably something I'm not going to be able to grasp over night, I'm
just looking for some kind of direction.

If anyone knows of any resources that would help me, I'd appreciate it.



Hi Dave,

you may be interested in an article I wrote for, and which was published
in Electronics and Wireless World – June 1989, p628, about designing low
noise audio amplifiers or more specifically: designing for low audio
front-end noise with real semiconductor devices.
Reprints of this article which includes numerous references are
available from http://www.softcopy.co.uk.

Enjoy!


Wilfried Adam

  #9   Report Post  
Scott Dorsey
 
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Default preamp design

David Grant wrote:
That's the first hurdle. A good understanding of differential circuitry,
feedback methods and noise calculations takes you further. Then you get

into
understanding device parameters. Does rbb mean anything to you for example

?

We've covered differential BJT amps, cascode configuration, some frequency
response, feedback (shunt/series sampling) and some stability. I remember
some stuff on calculating CMRR if that's what you mean by noise
calculations. As for the device parameters, I'm not sure. Rbb sounds like
the symbol one of my proffs used to denote the base resistance used for
biasing a BJT, but otherwise it doesn't mean anything to me.


Okay, your typical preamp is a differential BJT amp, with something after
it to give it a little bit more gain.

OR, it's a transformer with some single-ended gain stages.

We did all the derivations of gain, in/out resistance for most of the amps
we discussed in class, and usually everything simplified down to something
neat and tidy. I've tried to do small signal analysis on some of the mic-pre
schematics I've looked at, but I always end up with huge long expressions
that turn very messy. I also never end up with the quoted specs in the end!
It seems like there must be some simplification that I'm missing. Common
mode gain control for example... what on earth is that (apart from a gain
control)?


Basically you throw out all the small terms.... the input stage noise floor
is so high that it swamps everything else. There was a paper by Marshall
Leach in the JAES a decade ago which went through all the noise floor math
for a dozen different preamp configurations, in a clear and concise way.
You need to read it. Everybody needs to read it.

Maybe I just need more experience with this stuff, but I'm not sure where to
find that.


Go to your school library, get old copies of the JAES, and read through
them. Also get the RCA Radiotron Handbook, which is thoroughly obsolete
and talks about tubes, but the math is the same and the circuits can generally
be stolen outright and implemented with FETs.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
  #10   Report Post  
David Satz
 
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Default preamp design

David Grant wrote:

I'm having a good bit of trouble finding any info on design strategies that
are specific to microphone preamps. I've found some schematics on the net
but there's rarely any very detailed explanation given about why they were
designed the way they were, and what considerations were made. I understand
all the basic principles like CMRR, slew rate, etc... but there seems to be
some sort of understanding gap, and I'd like to bridge that gap. I realize
it's probably something I'm not going to be able to grasp over night, I'm
just looking for some kind of direction.

If anyone knows of any resources that would help me, I'd appreciate it.


John Hardy has an excellent literature package that he sends out on
request; some elements of it are available for download as PDFs on
his Web site at http://www.johnhardyco.com/products.html--see in
particular the PDF about the 990 discrete op amp--but make sure
to request the whole package.

Also be prepared (not at all with John Hardy, but with some other product
lines) to see a fair amount of mysticism and hand-waving that parades as
engineering--but you probably noticed that already.


  #11   Report Post  
Arny Krueger
 
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Default preamp design

"Scott Dorsey" wrote in message


Basically you throw out all the small terms.... the input stage noise
floor is so high that it swamps everything else. There was a paper
by Marshall Leach in the JAES a decade ago which went through all the
noise floor math for a dozen different preamp configurations, in a
clear and concise way. You need to read it. Everybody needs to read
it.


That would probably be:

Noise Analysis of Transformer-Coupled Preamplifiers 746047 bytes (CD aes5)
Author(s): Leach, Jr., W. Marshall
Publication: Volume 40 Number 1/2 pp. 3·11; January 1992
Abstract: Noise analyses of input stages of typical transformer-coupled
preamplifiers are presented. Conditions are derived for which the
transformer improves the signal-to-noise ratio of the circuits. Examples are
presented which are typical for microphone preamplifiers


Also relevant:

Designing Low-Noise, High-Linearity and High-Speed Preamplifiers for
Magnetic Transducers 409166 bytes (CD aes10)
Author(s): Ogwang, D. Okel
Publication: Preprint 1829; Convention 70; October 1981
Abstract: An ultra-low-noise preamplifier front end configuration is
determined through the analysis of the noise behaviour of a bipolar
transistor, current mirror and an FET in relation to the noise performance
of various preamplifier configurations. A design for Hi-Fi performance, in
accordance with the demand for a low-noise, high-linearity and high-speed
preamplifier for use with a magnetic transducer, is then presented.


  #12   Report Post  
Arny Krueger
 
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"David Satz" wrote in message
om

John Hardy has an excellent literature package that he sends out on
request; some elements of it are available for download as PDFs on
his Web site at http://www.johnhardyco.com/products.html--see in
particular the PDF about the 990 discrete op amp--but make sure
to request the whole package.


Also be prepared (not at all with John Hardy, but with some other
product lines) to see a fair amount of mysticism and hand-waving that
parades as engineering--but you probably noticed that already.


This one seems to be highly informative and purely orthodox:

http://www.johnhardyco.com/pdf/990.pdf .


  #13   Report Post  
David Grant
 
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"Arny Krueger" wrote in message
...
"David Grant" wrote in message



If anyone knows of any resources that would help me, I'd appreciate it.


I think a reasonable first step would be to figure out how to reliably and
relevantly determine the effectiveness and performance of a mic preamp.

Both
technical tests and listening tests seem relevant. Tests with various
microphones and microphone techniques and/or simulations of them seem
relevant.

Then, apply those evaluation techniques to a number of commercial products
at various price levels, as well as various technological implementations
(tubes, discrete solid state, ICs).


I assume I'd need to know how the commercial products I'm comparing are
designed for this to be of most benefit. Are there schematics available
somewhere for commercial units (I wouldn't expect there to be) or is it
practical to reverse engineer their design?


  #14   Report Post  
Harvey Gerst
 
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Default preamp design

David Grant wrote:

I'm having a good bit of trouble finding any info on design strategies that
are specific to microphone preamps. I've found some schematics on the net
but there's rarely any very detailed explanation given about why they were
designed the way they were, and what considerations were made. I understand
all the basic principles like CMRR, slew rate, etc... but there seems to be
some sort of understanding gap, and I'd like to bridge that gap. I realize
it's probably something I'm not going to be able to grasp over night, I'm
just looking for some kind of direction.

If anyone knows of any resources that would help me, I'd appreciate it.


I'm not really touting myself, but recently on my forum, there was an
interesting discussion among a lot of the leading preamp designers. Take a look
he

http://recpit.prosoundweb.com/viewtopic.php?t=7774

Harvey Gerst
Indian Trail Recording Studio
http://www.ITRstudio.com/
  #15   Report Post  
Arny Krueger
 
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Default preamp design

"David Grant" wrote in message

"Arny Krueger" wrote in message
...
"David Grant" wrote in message



If anyone knows of any resources that would help me, I'd appreciate
it.


I think a reasonable first step would be to figure out how to
reliably and relevantly determine the effectiveness and performance
of a mic preamp. Both technical tests and listening tests seem
relevant. Tests with various microphones and microphone techniques
and/or simulations of them seem relevant.

Then, apply those evaluation techniques to a number of commercial
products at various price levels, as well as various technological
implementations (tubes, discrete solid state, ICs).


I assume I'd need to know how the commercial products I'm comparing
are designed for this to be of most benefit. Are there schematics
available somewhere for commercial units (I wouldn't expect there to
be) or is it practical to reverse engineer their design?


The schematic publication policies of equipment manufacturers range from
high levels of secrecy to easy disclosure .

Here's some examples of easy disclosu

http://www.johnhardyco.com/pdf/990.pdf

http://www.rane.com/pdf/ms1bsch.pdf

http://www.rane.com/pdf/dms22sch.pdf

http://www.rolls.com/data/mp13man.pdf

You've got google, right?

;-)




  #16   Report Post  
P Stamler
 
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It might also be useful to get hold of the Jensen transformer data book,
including all of the application notes. That'll give some insight into the
design problems to be solved.

Peace,
Paul
  #17   Report Post  
Ben Bradley
 
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Default preamp design

In rec.audio.pro, "David Grant" wrote:

I hope this is an appropriate news group to post this (I apologize if not)

Well first of all I'll say a bit about myself... I'm an electrical
engineering student with an interest in audio electronics. In the third year
of my program we covered basic amplifier design, which I loved, and I've
been considering a career in this field since.

At the moment I'm particularly interested in microphone preamplifiers since
I'm a poor student who has his own project studio, but doesn't own (and
can't afford) a nice preamp like the Great River.

I'm having a good bit of trouble finding any info on design strategies that
are specific to microphone preamps. I've found some schematics on the net
but there's rarely any very detailed explanation given about why they were
designed the way they were, and what considerations were made. I understand
all the basic principles like CMRR, slew rate, etc... but there seems to be
some sort of understanding gap, and I'd like to bridge that gap. I realize
it's probably something I'm not going to be able to grasp over night, I'm
just looking for some kind of direction.

If anyone knows of any resources that would help me, I'd appreciate it.


As others here have indicated, there's some good info out there,
you just have to dig a bit for it. Arny posted some commercial
schematics - the Rane uses the INA163 - I've used it as well as the
older (and slightly better and available in DIP thru-hole package)
INA103. Get the datasheets for these at http://www.ti.com. I've got
a design using it on my website.
These are 'basic' chips - Analog Devices have similar ones in there
SSM line. To get better performance (lower noise) requires discrete
transistors on the input, as I'm sure you know. The LM194/LM394
datasheet has a "High performance instrumentation amplifier"
schematic. I don't know how good it would be for a mic pre, though
with three of these devices for one amp, it looks like it's designed
to sell a large quantity of LM194's.

There's this Usenet post from John Hardy concerning the LM194 as
used in the 990:

http://groups.google.com/groups?q=+%...tbi.com&rnum=1

or:

http://makeashorterlink.com/?M2E8222B6

I've yet to ask him for his "data package," I suppose I should.

Thanks,

Dave


-----
http://mindspring.com/~benbradley
  #18   Report Post  
Scott Dorsey
 
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Default preamp design

Arny Krueger wrote:
"Scott Dorsey" wrote in message


Basically you throw out all the small terms.... the input stage noise
floor is so high that it swamps everything else. There was a paper
by Marshall Leach in the JAES a decade ago which went through all the
noise floor math for a dozen different preamp configurations, in a
clear and concise way. You need to read it. Everybody needs to read
it.


That would probably be:

Noise Analysis of Transformer-Coupled Preamplifiers 746047 bytes (CD aes5)
Author(s): Leach, Jr., W. Marshall
Publication: Volume 40 Number 1/2 pp. 3·11; January 1992
Abstract: Noise analyses of input stages of typical transformer-coupled
preamplifiers are presented. Conditions are derived for which the
transformer improves the signal-to-noise ratio of the circuits. Examples are
presented which are typical for microphone preamplifiers


This is later than the paper I am thinking of, I think. But this is also
well worth reading.

Designing Low-Noise, High-Linearity and High-Speed Preamplifiers for
Magnetic Transducers 409166 bytes (CD aes10)
Author(s): Ogwang, D. Okel
Publication: Preprint 1829; Convention 70; October 1981
Abstract: An ultra-low-noise preamplifier front end configuration is
determined through the analysis of the noise behaviour of a bipolar
transistor, current mirror and an FET in relation to the noise performance
of various preamplifier configurations. A design for Hi-Fi performance, in
accordance with the demand for a low-noise, high-linearity and high-speed
preamplifier for use with a magnetic transducer, is then presented.


Wow, I don't remember this at all. I'm going to have to go look it up now...
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
  #19   Report Post  
Scott Dorsey
 
Posts: n/a
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David Grant wrote:

I assume I'd need to know how the commercial products I'm comparing are
designed for this to be of most benefit. Are there schematics available
somewhere for commercial units (I wouldn't expect there to be) or is it
practical to reverse engineer their design?


Until about 1985 or so, everything came with schematics in the manual.
And a lot of products still do.

Without the schematics, you can't fix it. I won't buy anything I cannot
fix.

For a good adventure, get out the schematics for the Mackie 1202, the
1202 VLZ, and the latest generation, and compare them. The successive
refinements are very interesting.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
  #20   Report Post  
Eric K. Weber
 
Posts: n/a
Default preamp design

Have a look at:
http://www.forsselltech.com/schematics.htm

for some usefull information.....

Rgds:
Eric Weber
www.webermusic.com




  #21   Report Post  
Pooh Bear
 
Posts: n/a
Default preamp design

David Grant wrote:

"Pooh Bear" wrote in message
...
David Grant wrote:

I hope this is an appropriate news group to post this (I apologize if

not)

Well first of all I'll say a bit about myself... I'm an electrical
engineering student with an interest in audio electronics. In the third

year
of my program we covered basic amplifier design, which I loved, and I've
been considering a career in this field since.

At the moment I'm particularly interested in microphone preamplifiers

since
I'm a poor student who has his own project studio, but doesn't own (and
can't afford) a nice preamp like the Great River.

I'm having a good bit of trouble finding any info on design strategies

that
are specific to microphone preamps. I've found some schematics on the

net
but there's rarely any very detailed explanation given about why they

were
designed the way they were, and what considerations were made. I

understand
all the basic principles like CMRR, slew rate, etc... but there seems to

be
some sort of understanding gap, and I'd like to bridge that gap. I

realize
it's probably something I'm not going to be able to grasp over night,

I'm
just looking for some kind of direction.

If anyone knows of any resources that would help me, I'd appreciate it.


The first thing you need to know with mic pre-amps is how to design with
discretes. Has your course covered that in any depth ? Relatively unlikely

I'll
guess.


We've never used the term "discrete" anywhere, but am I correct in assuming
it means "not in IC form" (i.e BJT amps versus op amp ICs)? If that's the
case then we've done a good bit.


That's academia for you - lol. Been ages since I heard anyone use the term
Bipolar Junction Transistor. Had to stop and think.

Real engineers just call the bipolars as opposed to mosfet etc. :-)

Most op-amps have bjt inputs btw - they're just 'invisible' to the user.



That's the first hurdle. A good understanding of differential circuitry,
feedback methods and noise calculations takes you further. Then you get

into
understanding device parameters. Does rbb mean anything to you for example

?

We've covered differential BJT amps, cascode configuration, some frequency
response, feedback (shunt/series sampling) and some stability. I remember
some stuff on calculating CMRR if that's what you mean by noise
calculations.


Nope. CMRR is purely rejection of signal.

A thorough understanding of noise sources and how to add them is required. Are
you familiar with the equation for thermal noise for starters ?

En ( the noise voltage ) = sqrt ( 4.K.t.R.Bw) K=Boltzmann's constant (
1.37.10^-23), t = absolute temp in Kelvin, R=the resistor whose noise you want
to know, Bw=bandwidth of interest ( 20kHz for audio )

It's also helpful to know about things like flicker noise (some transistors are
better than others).

Remember to sum noise sources as RMS !

As for the device parameters, I'm not sure. Rbb sounds like
the symbol one of my proffs used to denote the base resistance used for
biasing a BJT, but otherwise it doesn't mean anything to me.


Damn close, it's the 'intrinisic' base resistance of the transistor itself and
appears in series with the source, degrading the noise performance. Select a
transistor with low Rbb. Same is true for Ree too, but I've never seen that on a
datasheet, prolly to low to be of interest., although the dynamic emiiter
impedance is very important. Most mic stages don't run input transistors at
around 2.5mA Ic by accident.


We did all the derivations of gain, in/out resistance for most of the amps
we discussed in class, and usually everything simplified down to something
neat and tidy. I've tried to do small signal analysis on some of the mic-pre
schematics I've looked at, but I always end up with huge long expressions
that turn very messy.


Yeah, what they teach you is over-complicated. You need to strip it to the bare
essentials and concentrate on what's important. I saw the light when I read a
series of articles in the UK's Wireless World about 30 yrs ago. Written by a
lecturer who wanted to make to topic of transistor amplification understandable
on a practical level.

For example - a simple 'common emitter' single transistor gain stage with a
collector load R and an un-bypassed emitter R. Theory would have you go into
untold complexities. For all practical purposes though, the voltage gain =
collector load R / emitter R.

I also never end up with the quoted specs in the end!
It seems like there must be some simplification that I'm missing. Common
mode gain control for example...


I've no idea where you would see that in practice. Where did you come acros it ?

what on earth is that (apart from a gain control)?

Maybe I just need more experience with this stuff, but I'm not sure where to
find that.


Experience is the key. Keep at it.


Graham

  #22   Report Post  
Pooh Bear
 
Posts: n/a
Default preamp design

Scott Dorsey wrote:

Arny Krueger wrote:
"Scott Dorsey" wrote in message


Basically you throw out all the small terms.... the input stage noise
floor is so high that it swamps everything else. There was a paper
by Marshall Leach in the JAES a decade ago which went through all the
noise floor math for a dozen different preamp configurations, in a
clear and concise way. You need to read it. Everybody needs to read
it.


That would probably be:

Noise Analysis of Transformer-Coupled Preamplifiers 746047 bytes (CD aes5)
Author(s): Leach, Jr., W. Marshall
Publication: Volume 40 Number 1/2 pp. 3·11; January 1992
Abstract: Noise analyses of input stages of typical transformer-coupled
preamplifiers are presented. Conditions are derived for which the
transformer improves the signal-to-noise ratio of the circuits. Examples are
presented which are typical for microphone preamplifiers


This is later than the paper I am thinking of, I think. But this is also
well worth reading.

Designing Low-Noise, High-Linearity and High-Speed Preamplifiers for
Magnetic Transducers 409166 bytes (CD aes10)
Author(s): Ogwang, D. Okel
Publication: Preprint 1829; Convention 70; October 1981
Abstract: An ultra-low-noise preamplifier front end configuration is
determined through the analysis of the noise behaviour of a bipolar
transistor, current mirror and an FET in relation to the noise performance
of various preamplifier configurations. A design for Hi-Fi performance, in
accordance with the demand for a low-noise, high-linearity and high-speed
preamplifier for use with a magnetic transducer, is then presented.


Wow, I don't remember this at all. I'm going to have to go look it up now...
--scott


Lol !

On the commercial front, there's some good stuff too from some of the
semiconductor manufacturers. It doesn't go into 'ultra low-noise' applications,
but the theory is identical and you get some worked examples.

The 'Bifet Design Manual' from Texas is still available I think and I also found
National's 'Audio Handbook' useful - not sure of that's still around though.

Blow me ! It's been re-issued ! Not hard to see why.
http://www.audioxpress.com/bksprods/books/bkaa59.htm

TI have an excellent site actually - literally stuffed with info. Check out their
'knowledgebase'. Although most of the stuff is about ICs, the noise theory ( and
other stuff ) is universal.

If you are planning a career in audio, get TI's 'Op amps for Everyone'. Available
online as a pdf. Publication # SLOD006B. A mere 464 pages !

Also, do a google on SSM2019 and get the data sheet. See how an integrated mic
pre is made. You can do better with a discrete front end though.


Graham


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