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