F4 dc offset problem - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

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 15th February 2013, 05:19 PM   #1
rosario is offline rosario  Romania
diyAudio Member
 
Join Date: Jan 2011
Location: Timisoara
Default F4 dc offset problem

Hello everybody , i have a problem with my f4 amplifier.My right chanel the dc offset when i turn on i have -70mv and after 3 hours is near 0mv , but with my left chanel i have some problems when i turn on everytime i have different value and and goes up and down very fast and the las value was from 86mv to 120mv in 10 minutes.

Thx for help, greetings from Romania.
  Reply With Quote
Old 15th February 2013, 05:32 PM   #2
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
as I said in PM - post pictures

double check mounting of outputs on heatsink - are they tightly & evenly screwed on heatsink , check all solder joints (including all resistors in biasing network)

replace TL431 - it's cheap anyway

luckily - your problem isn't connected to input Jfets in any way
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa... by Mighty ZM
  Reply With Quote
Old 18th February 2013, 07:46 PM   #3
Dzius is offline Dzius  Poland
diyAudio Member
 
Dzius's Avatar
 
Join Date: Sep 2010
Location: Warsaw
I had similar problem caused by P2 trimpot (500 ohm). Change it then. Besides I noticed that it's very easy to set DC offset very close to zero within range of -3 to +3mV or smaller. If problem still exist replace TL431 as Zen Mod said.
  Reply With Quote
Old 19th February 2013, 01:49 PM   #4
rosario is offline rosario  Romania
diyAudio Member
 
Join Date: Jan 2011
Location: Timisoara
Thx for advice , i will try these days.
  Reply With Quote
Old 20th February 2013, 01:22 PM   #5
diyAudio Member
 
Join Date: Feb 2012
Location: Timisoara
I put an 500 ohm trimpot and the lowest voltaje was 1,516 volt. What can i do?
  Reply With Quote
Old 20th February 2013, 02:45 PM   #6
rosario is offline rosario  Romania
diyAudio Member
 
Join Date: Jan 2011
Location: Timisoara
And with an 2 kohm the lowest voltage was 478 mv, i will try with an 5 kohm tomorrow.
  Reply With Quote
Old 21st February 2013, 08:41 AM   #7
rosario is offline rosario  Romania
diyAudio Member
 
Join Date: Jan 2011
Location: Timisoara
After a new 5 kohm trimpot nothing change, i changed also the TL431 same problem.
What can i do , other changes?
  Reply With Quote
Old 21st February 2013, 09:25 AM   #8
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
pics
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa... by Mighty ZM
  Reply With Quote
Old 27th February 2013, 07:45 PM   #9
rosario is offline rosario  Romania
diyAudio Member
 
Join Date: Jan 2011
Location: Timisoara
The problem was TL431 , i change it and is working now. Thx people.
  Reply With Quote
Old 27th February 2013, 09:43 PM   #10
biju55 is offline biju55  India
diyAudio Member
 
biju55's Avatar
 
Join Date: Jul 2011
Location: Kuwait and India
Send a message via Skype™ to biju55
thx zen mod
  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
F4 DC offset drift performance question. gl Pass Labs 3 5th January 2010 04:44 PM
DC-offset problem Bootstrapper Solid State 12 6th October 2007 08:25 AM
DC offset problem whatsnew Chip Amps 17 2nd January 2007 08:26 PM
DC offset problem maxw Chip Amps 38 17th May 2006 02:31 AM
Is this DC offset problem. rs1026 Chip Amps 4 24th December 2004 12:02 AM


New To Site? Need Help?

All times are GMT. The time now is 08:24 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