preamp-cap-buffer

[udip]

Hi all!


In order to avoid dc at the output of preamps you have about 3 choices:
(I'm talking about preamps that can drive low impedance loads,
like 1k and below, and also has variable gain):

1) Use electrolitic capacitor at the output, and it has to be quite
big if you don't want some bass roll.

2) Use some king of a servo to null the dc at the output.

3) Design a perfect circuit with perfectly matched parts in
order to avoid dc from the beginning.

Well, I don't like options 1 and 2, and option 3 is quite difficult
to obtain (at least for me), specially when the gain is variable.
So I thought why not use a PREAMP-CAPACITOR-BUFFER circuit,
so the capacitor can be a high quality small value one (because
of the hign Z of the buffer), and the buffer is unity gain so
it can be easy to obtain zero offset for dc-coupled output.
I'm not trying to avoid capacitors at all, but just electrolitics.

I'm sure I'm not the first one who thought about that, but I haven't seen circuits using this method, so I wonder if it has shortcomings that I haven't thought of?


Udi.

[Leolabs]

Hi,is me again Your block diagram seems has appeared in some1's article on designing low distortion power amplifier,but i cant recall who's article.

Regarding your "PCB",have you consider the offset of the output buffer itself????

[Stocker]

use a buffer with a pair of DC-null pins?

[Bill Fitzpatrick]

?

http://home.c2i.net/semfielec/buffer/buffer.htm

[Leolabs]

As i expected,Bill,FET source follower with current sink loading Quite common but a good design indeed

[udip]

It's quite easy to design a buffer with zero offset, like the
schematic that Bill posted...


Udi.

[adason]

http://www.pha.inecnet.cz/macura/buffer_en.html

[adason]

http://focus.ti.com/lit/ds/symlink/buf634.pdf

[AudioWizard]

Why not 2)?