Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Chip Amps Amplifiers based on integrated circuits

My_Ref Fremen Edition - Build thread and tutorial
My_Ref Fremen Edition - Build thread and tutorial
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 3rd January 2018, 10:39 PM   #3611
lehmanhill is offline lehmanhill  United States
diyAudio Member
 
lehmanhill's Avatar
 
Join Date: Jan 2008
Location: Chelsea, Michigan
Quote:
Originally Posted by Mark Whitney View Post
Most common cause for negative rail on the output is R11 going open. This should have been fixed by now.
A good guess. I put sockets in at the R11 position so that I could compare an old to new BOM. Sockets are a less reliable connection, so an open R11 could have been an issue, but I checked this and the connection is good.

To answer Spartacus' question, I only added the 20 pF and retested only the bad board.

After checking R11, I checked again. The result is a little different than I reported earlier. Measuring the output to input negative terminal (0V on the schematic) I find that the DCV is oscillating from -27 to +28 VDC on a period of about 1 seconds. When I flip over to ACV, I get various readings from 1 to 30 VAC. It looks like adding the 20 pF cap made things worse, but I still have no clue what's going on.

Jac
  Reply With Quote
Old 3rd January 2018, 10:59 PM   #3612
Spartacus is offline Spartacus  United Kingdom
diyAudio Member
 
Join Date: Jan 2002
Location: Gloucestershire
RF oscillation will mess up DC and AC volts. Adding a cap between pins 2 and 6 should improve stability, not worsen it, my only thought at the moment is that there is either a soldering error or a component is faulty. Could you show a photo of your work?
  Reply With Quote
Old 3rd January 2018, 11:38 PM   #3613
lehmanhill is offline lehmanhill  United States
diyAudio Member
 
lehmanhill's Avatar
 
Join Date: Jan 2008
Location: Chelsea, Michigan
This is the board with the DC offset issue. V1.2 boards. As mentioned, I am using sockets for several resistors to be able to compare BOMs. Right now the components are from the old BOM circa 2012. I also have faston tabs for C9 and C13 so that I can use the same components on both sets of boards. I removed the caps for the photo because they block the view of the other components.

Photos below.
Attached Images
File Type: jpg P1031162_lzn.jpg (237.5 KB, 246 views)
File Type: jpg P1031161_lzn.jpg (294.1 KB, 241 views)
File Type: jpg P1031163_lzn.jpg (338.7 KB, 232 views)
File Type: jpg P1031164_lzn.jpg (339.5 KB, 235 views)

Last edited by lehmanhill; 3rd January 2018 at 11:40 PM.
  Reply With Quote
Old 4th January 2018, 12:23 AM   #3614
sq225917 is offline sq225917  United Kingdom
diyAudio Member
 
Join Date: Jun 2004
Location: sheffield
Send a message via MSN to sq225917 My_Ref Fremen Edition - Build thread and tutorial
Check d3, 1st pic looks like splatter
__________________
Paradise Pre-reg PSU PCBs
  Reply With Quote
Old 4th January 2018, 12:37 AM   #3615
lehmanhill is offline lehmanhill  United States
diyAudio Member
 
lehmanhill's Avatar
 
Join Date: Jan 2008
Location: Chelsea, Michigan
Thanks sq. It was definitely worth checking, but it seems fine at 0.7 Vf.

Jac
  Reply With Quote
Old 4th January 2018, 01:08 AM   #3616
Joseph K is offline Joseph K  Hungary
diyAudio Member
 
Join Date: Dec 2004
Location: gran sasso
Wish a happy New Year to all!

Jac, I see a very nice build..
And don't see errors.

Just some note: A load would be nice to be in place, while experimenting.
Do You have anything from 4 to 10- 15 ohm, 5 -10 - 20 W resistor..?

5W for seconds only..

May I ask had you checked the zone of LM3886 compensation, 3,3k-1nF, R37 C3x, for good contact? The same way, good continuity at the input zone, 100k; 3,3k (R12);
Finally, a smaller feedback cap would not hurt, (pin2 - pin 6, from -IN to OUT) though probably OK. (like 4,7pF)

Assume all PS are OK?

Ciao, George
  Reply With Quote
Old 4th January 2018, 01:12 AM   #3617
Joseph K is offline Joseph K  Hungary
diyAudio Member
 
Join Date: Dec 2004
Location: gran sasso
If there would be contact problems at R10, 390ohm -- that would drive into instability, too
And C9 (if no continuity)

Last edited by Joseph K; 4th January 2018 at 01:27 AM.
  Reply With Quote
Old 4th January 2018, 01:19 AM   #3618
Joseph K is offline Joseph K  Hungary
diyAudio Member
 
Join Date: Dec 2004
Location: gran sasso
It is hard to judge from the photo: all 47k bridge components are having good contact?
  Reply With Quote
Old 4th January 2018, 05:56 AM   #3619
Mark Whitney is offline Mark Whitney  Netherlands
diyAudio Member
 
Mark Whitney's Avatar
 
Join Date: Feb 2013
Location: Netherlands
Any break in any of the feedback loops will cause this. The gain will then be very high (open loop).

R11, C9, R10, R7, R3 and the connections to the IC1-3 IC2-3 are a good place to begin.

Some of the soldering topside does not look good. You want to have the solder flow on the pads and pins on both sides of the board.
__________________
Regards Mark.
  Reply With Quote
Old 4th January 2018, 07:26 PM   #3620
lehmanhill is offline lehmanhill  United States
diyAudio Member
 
lehmanhill's Avatar
 
Join Date: Jan 2008
Location: Chelsea, Michigan
Thanks guys. Problem solved. Now a nice steady 2 mVDC offset.

I checked continuity in all the places George suggested. I touched up the soldering on several places, especially the LM3886 as Mark had suggested. I also found that I had bent the legs the little Caddock in R13 (100k) and I guess that it had developed a weak point at the bend. When I went to remove it, one of the legs came off. I'm not sure what fixed it, but if I had to guess it was either the Caddock or the soldering on the LM3886.

I appreciate the help.

Jac

PS That 2 mV was without a cap from 2 to 6 on the opamp, so the fast JFET opamps still have a pretty good record for stability.
  Reply With Quote

Reply


My_Ref Fremen Edition - Build thread and tutorialHide 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
My_Ref Fremen Edition - Beta build/Fine tuning ClaveFremen Chip Amps 1526 8th October 2017 04:03 PM
My_Ref Fremen Edition RC - Build thread ClaveFremen Chip Amps 1273 4th July 2016 07:21 PM
My_Ref Fremen Edition - need help on PCB evaluation ClaveFremen Chip Amps 450 23rd October 2013 04:38 PM
My_Ref Fremen Edition Interest/Group Buy ClaveFremen Group Buys 348 25th June 2013 10:58 PM
Last My_Ref Fremen Edition RC boards for sale ClaveFremen Swap Meet 3 4th December 2012 02:04 PM


New To Site? Need Help?

All times are GMT. The time now is 02:11 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki