DC offset need help again :-( DC offset need help again :-( - Page 2 - diyAudio
Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

DC offset need help again :-(
DC offset need help again :-(
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
Thread Tools Search this Thread
Old 10th October 2004, 04:43 PM   #11
MikeB is offline MikeB  Germany
diyAudio Member
MikeB's Avatar
Join Date: Apr 2004
Location: GŁtersloh
Yes, i'm familiar with currentsources to diffamps, but this way q17
simply passes the current from the 12k to the diffamp, at least tries
to. So without q17 the same current is fed into the diffamp.
For feeding a diffamp a simple resistor is not too bad, but introduces
ripple from psu. The impedance compared to a ccs is no big problem
here, as the voltage across the 12k does not vary much.
The AKSA for example uses a simple resistor, but has a "stabilized"
voltagesupply to the frontend.

  Reply With Quote
Old 10th October 2004, 05:33 PM   #12
bocka is offline bocka  Germany
diyAudio Member
Join Date: Jul 2003
Location: Hannover
Hi djdamix,

change the 12k resistor nearby Q17 to 270 ohm. Add 2 diodes 1N4148 in series from base of Q17 to the negative side of the power supply and change R36 from 1k to 12k. This will fix your problem
  Reply With Quote
Old 12th October 2004, 07:47 AM   #13
djdamix is offline djdamix  France
diyAudio Member
Join Date: Jun 2004
Location: Lyon
I'have fixed the problem, The 100u capacitor was bad ... I've changed it and the offset disappear, as on my first amp about (30mV) ... strange ... Anyway as most of you say I'll change the current source (Q17) to something better.

Thanks for all your advices.
  Reply With Quote
Old 26th October 2004, 08:38 AM   #14
Duo is offline Duo  Canada
diyAudio Member
Duo's Avatar
Join Date: Jun 2002
Location: Victoria, BC, Canada
Send a message via ICQ to Duo
Definitely Bocka's idea is what I'd do.

With the base of Q17 going to 0V through a resistor and the collector loaded by the differential amp, the CB junction is nearly forward-biased as mentioned before.

Certainly changing in a 270ohm emitter resistor and adding the diodes forward-biased to V- and a 12k resistor will make a proper current source.
-- Duo, W1ngs, VA7MON, and lesser known handles. --
-- http://www.w1ngselectronics.com -- My Work and Projects --
  Reply With Quote


DC offset need help again :-(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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
What is DC offset? spooney Car Audio 16 9th September 2013 12:32 AM
DC Offset JannaCassandra Chip Amps 3 26th July 2008 03:20 PM
Help With DC Offset Sybex23 Chip Amps 8 15th November 2004 07:11 PM
GC offset jan.didden Chip Amps 4 3rd July 2004 08:10 AM
GC very low DC offset matjans Chip Amps 7 22nd September 2003 10:24 PM

New To Site? Need Help?

All times are GMT. The time now is 05:06 AM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio