preamp-cap-buffer - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 22nd February 2005, 12:53 PM   #1
diyAudio Member
 
udip's Avatar
 
Join Date: Oct 2004
Location: Israel
Default preamp-cap-buffer

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.
Attached Images
File Type: jpg 1.jpg (16.4 KB, 248 views)
__________________
"Things should be as simple as possible, but no simpler"
Albert Einstein
  Reply With Quote
Old 23rd February 2005, 03:16 AM   #2
Leolabs is offline Leolabs  Malaysia
diyAudio Member
 
Leolabs's Avatar
 
Join Date: Dec 2004
Location: Bukit Mertajam
Send a message via MSN to 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????
  Reply With Quote
Old 23rd February 2005, 04:14 AM   #3
Stocker is offline Stocker  United States
diyAudio Member
 
Join Date: Dec 2003
Location: Austin
use a buffer with a pair of DC-null pins?
__________________
Jesus loves you.
  Reply With Quote
Old 23rd February 2005, 04:51 AM   #4
diyAudio Member
 
Bill Fitzpatrick's Avatar
 
Join Date: Jun 2001
Location: Eugene, OR
?

http://home.c2i.net/semfielec/buffer/buffer.htm
  Reply With Quote
Old 23rd February 2005, 07:25 AM   #5
Leolabs is offline Leolabs  Malaysia
diyAudio Member
 
Leolabs's Avatar
 
Join Date: Dec 2004
Location: Bukit Mertajam
Send a message via MSN to Leolabs
As i expected,Bill,FET source follower with current sink loading Quite common but a good design indeed
  Reply With Quote
Old 23rd February 2005, 04:48 PM   #6
diyAudio Member
 
udip's Avatar
 
Join Date: Oct 2004
Location: Israel
It's quite easy to design a buffer with zero offset, like the
schematic that Bill posted...


Udi.
__________________
"Things should be as simple as possible, but no simpler"
Albert Einstein
  Reply With Quote
Old 23rd February 2005, 04:54 PM   #7
adason is offline adason  United States
diyAudio Member
 
adason's Avatar
 
Join Date: Nov 2004
Location: Maryland
http://www.pha.inecnet.cz/macura/buffer_en.html
  Reply With Quote
Old 23rd February 2005, 05:42 PM   #8
adason is offline adason  United States
diyAudio Member
 
adason's Avatar
 
Join Date: Nov 2004
Location: Maryland
http://focus.ti.com/lit/ds/symlink/buf634.pdf
  Reply With Quote
Old 23rd February 2005, 07:35 PM   #9
diyAudio Member
 
Join Date: Feb 2005
Location: Southern France
Why not 2)?
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
buffer/preamp? TheDriver41 Chip Amps 2 3rd October 2004 09:40 AM


New To Site? Need Help?

All times are GMT. The time now is 03:29 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2