In article , Paul wrote:
http://www.thatcorp.com/datashts/AES...ic_Preamps.pdf
It's still very interesting reading.
Gary has been giving this presentation for several years in various forms,
and it gets better every year.
Most of it is common knowledge but some of it (like phantom fault protection)
really isn't very well-known in the industry at all.
I'm gonna assume they can't be too worried about
revealing too many trade secrets in an online document,
as reverse-engineering is very easy to do, and as we
all know, all companies hire engineers from their
competition anyways!
The people from THAT want people to be building as many mike preamps
as possible using their ICs, and they don't want those preamps to have poor
performance or poor reliability because that would affect the reputation of
their components. So it's in their best interest to teach designers how to
make the best possible preamplifiers that they can.
SECRETS DON'T STAY SECRET FOR VERY LONG!
And I'm sure all of this stuff is common
knowledge anyways.....
Some of it is... the whole long-tailed pair preamp topology has been around
in the audio industry since the 1970s when the Trans-Amp came out. But an
awful lot of engineers never got told about all the things that affect CMRR,
and I don't think any of us ever thought about having to protect from impulses
when the phantom power caps discharge. They aren't trade secrets by any means,
they're just things that nobody ever mentions in school.
But... you'll notice that just about everything discussed in the first half
of the paper.... CMRR issues, feedback resistor issues, DC bias issues,
and protection issues... all of them can be readily solved by dropping a
transformer in front. Of course, you get a whole other pile of problems
with the transformer but for that you need to read the Jensen app notes instead
of the THAT ones.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."