Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

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 22nd March 2011, 12:58 AM   #1
diyAudio Member
Join Date: Mar 2011
Default LM4780 oscilation with reference PCB


I just build a LM4780 amplifier, using the reference PCB from national.com. The sad thing is that it goes into oscillation after 30-60 seconds after powering it on. Sometimes even faster with the source in. The oscillation occurs with source in or without it.
The only thing I changed from the difference layout were the Ci1 and Ci1, because I was unable to find 68uF, I used 47uF, but I don't think this is the problem.
Any advices are appreciated.
  Reply With Quote
Old 22nd March 2011, 01:27 AM   #2
Join Date: Jan 2008
Blog Entries: 2
How do you know it's oscillating? Is it low frequency (motorboating) or high?

The 47uF shouldn't make a significant difference. If it's a reference design (is it the one in the datasheet?) the chances are you've built it wrong. If this is the case it can be very hard to find your error, you check it and check it but you don't see it.

  Reply With Quote
Old 22nd March 2011, 08:18 AM   #3
diyAudio Member
Join Date: Mar 2011
here's the sound:

So you are telling me the reference design is wrong ? To be honest, I used press and peel, but it wasn't that good, so I have to aid it with a marker. If it's the PCB to blame, I will post pictures soon.
This makes me very sad, first time I tried using a strip-board, and it was a failure. This is the second attempt...
  Reply With Quote
Old 22nd March 2011, 09:42 AM   #4
AndrewT is online now AndrewT  Scotland
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders
He is saying you have probably assembled it incorrectly. Not that the design is wrong.
regards Andrew T.
  Reply With Quote
Old 22nd March 2011, 09:52 AM   #5
diyAudio Member
Join Date: Mar 2011
meaning that I put the wrong parts in the wrong places, I will check, but I really don't think so.
  Reply With Quote
Old 22nd March 2011, 12:32 PM   #6
diyAudio Member
Join Date: Mar 2011
yeah, my bad. Rg and Rsn 2.7k not 2.7ohm. Going to the store
  Reply With Quote
Old 22nd March 2011, 12:56 PM   #7
diyAudio Member
Join Date: Feb 2011
Dou You have a picture of the built panel?
Did you electricaly isolate the IC from heatsink ?
(my TDA amp did funy things without it)

and how does Your PSU look like?

The bad resistor value should solve Your problem, if not then the above information might help us a fair bit.
  Reply With Quote
Old 22nd March 2011, 01:16 PM   #8
diyAudio Member
Join Date: Mar 2011
I will post pictures, as soon as I replace the resistors
  Reply With Quote
Old 24th March 2011, 05:37 PM   #9
diyAudio Member
Join Date: Mar 2011
so, after I changed the resistor, the amp works ok, .... )) maybe wonderful is the right word, I just love how it sounds. And I am using some not so good Sony speakers (can't wait to change the tweeters) but still it sounds wonderful.
Yesterday I spent many hours with making the case. It lacks the upper part and left, but I have some perforated metal, and I will install it soon. Here are the pictures:


I also have to paint it, or cover with some textile don't know
  Reply With Quote
Old 25th March 2011, 02:44 PM   #10
diyAudio Member
Join Date: Feb 2008
Location: Jackson,michigan
Glad to see this this report as I still have five of them that I haven't done anything with yet. jer
  Reply With Quote


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
LM4780 PCB akira Chip Amps 31 23rd January 2011 04:24 AM
Adding caps to prevent oscilation in AF 5687 ervinl Tubes / Valves 9 22nd May 2010 06:27 PM
Amplifier oscilation Diogo Solid State 15 15th October 2008 11:44 AM
yet another LM4780 pcb zdr Chip Amps 7 24th September 2008 08:29 PM

New To Site? Need Help?

All times are GMT. The time now is 08:46 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