Re: Transistor Junction Noise

Hello Allen,

-  I'll check further and report the results, and modify the paper based on
what I have heard  back so far - the design rational (at least)definite
needs expanding - an some of the respondents need to go back to transistor
theory 101 and see why "rules of thumb" can be bent and sometimes why they
should be bent, but some have been insightful  - if you could you could
flesh out you circuit with appropriate values it would make my life easier -
you could assume beta as 200 or 400.  That would be nicely in the range for
the common transistors I suggested.  Can you hunt around for a better
schematic package ?  I forget the one I used but it was public domain - it
is on my XP Partion and I'm now using win98 so I can't look up the name for
you - I'll get it next time.

I have been testing and collecting data from protoboard lash ups of
circuits - your circuit was on the board (without C1), I've put C1 in and
tested it - it didn't seem much improvement, but it was only a very first
and quick test - I will be more thorough before I jump either way.  have you
though of splitting R1 in half and adding C1 there (other have suggested
it) - this removes the AC feedback, and increases gain but at the cost of
making the circuit much more dependent on the transistor characteristics -
something someone has already criticised it for.

The one of the things I found most galling from this whole experience has
been the speed of criticism, without any checking or thought.  I put out a
paper which I thought was nicely laid out, photographed, diagrammed and put
on a nice web page.  All these things showed I took care and thought  with
what I do, but without building or testing anything came all these untested
opinions. that doesn't work / is wrong / this (unbuilt and untried mod) is
better.

Anyway an update is due in 5 - 10 days (this means of course 15 -20)


"Allan Herriman" <[EMAIL PROTECTED]> wrote in
message news:[EMAIL PROTECTED]
> On Thu, 27 Nov 2003 08:47:46 +1000, "David Eather" <[EMAIL PROTECTED]>
> wrote:
>
> >If you read the application notes I made you will see that designs
EXACTLY
> >like the one suggested and endorsed below were tested, AND rejected - in
> >that case because of low AC gain.
>
> Not EXACTLY.  Your PDF document shows that you tested one *without*
> C1, which is needed to increase the AC gain.
>
> >There is nothing wrong with the collector feedback bias design suggested
> >below except that it has lower gain  My design puts out -6db, but with
the
> >SAME TRANSISTORS in the collector feedback bias design below they put
> >out -38 db, very significant a drop of 32db.
>
> The collector feedback has no effect at frequencies above a few Hz.
> It stabilises the bias, without reducing the gain at audio
> frequencies.
> I suggest that if you measured a different effect, you were probably
> testing a different circuit.
>
> Please look at the circuit again.  Is it really the same as the one
> you tested?
>
> >> > Please use a fixed point font to view.
> >> >
> >> > #                         VCC
> >> > #                         +
> >> > #                          |
> >> > #                          |
> >> > #                         .-.
> >> > #                         | |R2
> >> > #                         | |
> >> > #                         '-'
> >> > #                          |
> >> > #                  R1      |
> >> > #                   ___    |        C3
> >> > #      +-------+---|___|---+
> >> > #      |       |           |        ||
> >> > #      |       |           +--------||-------
> >> > #      |       |           |        ||
> >> > #      |       |           |
> >> > #      |       |           |
> >> > #      |        <|       |/
> >> > #      |    Q1   |-------|   Q2
> >> > #      |        /|       |>
> >> > #      |       |           |
> >> > #      |                   |
> >> > #      |                   +-----+
> >> > #      |                   |     |
> >> > #      |                  .-.    |
> >> > #     --- C1              | |   ---
> >> > #     ---             R3  | |   --- C2
> >> > #      |                  '-'    |
> >> > #      |                   |     |
> >> > #      |                   |     |
> >> > #     ===                 ===   ===
> >> > #     GND                 GND   GND
> >> >                                                        .
> >> > created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de
>
> Regards,
> Allan.