Zero DC Offset - 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 5th January 2005, 08:17 PM   #1
nitin is offline nitin  India
diyAudio Member
 
nitin's Avatar
 
Join Date: Aug 2004
Location: NEW DELHI
Send a message via ICQ to nitin Send a message via MSN to nitin Send a message via Yahoo to nitin
Default Zero DC Offset

I'm newbie in electronics(Doing Mechanical Engg. ) but gainclone seem to be so interesting that i decided to try some soldering .

I made a gainclone based on LM3886tf in non-inverting(bob's scm.)with 27db gain with only 6.78k after 1k to sgnd as against 19.8k.

The problem is i get DC Offset that range from +20 to -35mv on multimeter during obsv. is this caused by improper power bypassing or is source is to blame. so point is that how should DC Offset ibe made zero.

Dc offset(-20mv) is lower without speaker lead connected.Also no capacitor is connected after 1k resistance to SGND it is optional as in datasheet fig. or essential and is 47uf ok for bookshelf spkrs.

Thanks in advance.
  Reply With Quote
Old 6th January 2005, 06:51 AM   #2
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
Less than 50 mV is not a problem.
__________________
/Per-Anders (my first name) or P-A as my friends call me
  Reply With Quote
Old 6th January 2005, 02:38 PM   #3
Jontie is offline Jontie  United Kingdom
diyAudio Member
 
Join Date: Jun 2004
Location: Nottingham, England
Per-Anders is quite correct. If you think of it from the point of view of speaker dissipation, 50mV output offset represents a dissipation of about 313 micro-watts into 8 ohms. An offset of even 10 times this still only gives a dissipation of 31.35 mW (at current of 62.5 mA). Only a delicate tweeter is likely to be distressed by this, and wouldn't see it when decoupled by a capacitor, which is almost always the case.

IMHO, the importance of output DC offset is often overplayed, usually in the cause of specmanship.
  Reply With Quote
Old 6th January 2005, 06:28 PM   #4
nitin is offline nitin  India
diyAudio Member
 
nitin's Avatar
 
Join Date: Aug 2004
Location: NEW DELHI
Send a message via ICQ to nitin Send a message via MSN to nitin Send a message via Yahoo to nitin
Thanks
So the ~-30mV is not big to worry about,also upto what level in mV there is no harm to speakers as i'm not using crossover.

I have seen 47uf in many scms. after 1k and that of non-polar type possiblely to reduce DC offset but i am not using any capacitor after 1k so the 1k goes straight to SNGD w/o any capacitor in b/w and my speakers are sounding good w/o it. does i need it or it is optional comp. or what value is going to be fine 47uf or 33uf for bookshelfs.

i want to make buffer based on OPA627BP for my gainclone. Do you guys can pls point to some good scms.
  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
What is DC offset? spooney Car Audio 16 9th September 2013 01:32 AM
DC Offset JannaCassandra Chip Amps 3 26th July 2008 04:20 PM
Help With DC Offset Sybex23 Chip Amps 8 15th November 2004 08:11 PM
GC offset jan.didden Chip Amps 4 3rd July 2004 09:10 AM
GC very low DC offset matjans Chip Amps 7 22nd September 2003 11:24 PM


New To Site? Need Help?

All times are GMT. The time now is 03:31 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