Lm3886 problem - diyAudio
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
Reply
 
Thread Tools Search this Thread
Old 26th August 2014, 05:07 PM   #1
diyAudio Member
 
Join Date: Aug 2014
Default Lm3886 problem

Hello all,

I've built my proto type lm3886 on a bread board and after a testing it out I've come across an issue. When I turn up the volume the sound cuts off and on. Now I've built the basic schematic from the datasheet and haven't included the "optional components" as I'm still testing. So in regards to the issue my thoughts are that my amp may be clipping upon increased volume or it might have to do with my unregulated power supply. The reason my power supply isn't regulated is that I haven't found a way to regulate 45 volts as of yet.

My transformer is a toroidal 250va 30 + 30 with about 10,000 uf per rail.

Any thoughts or advice would be appreciated.
  Reply With Quote
Old 26th August 2014, 05:28 PM   #2
djoffe is offline djoffe  United States
diyAudio Member
 
Join Date: Oct 2008
Here's a quick guess. You don't have a big enough heatsink for the 3886's. So, when you drive them hard, they warm up, and the thermal cutout triggers, stopping the sound.

Update My Dynaco

Akitika GT-101 Audio Power Amplifier Kit
  Reply With Quote
Old 26th August 2014, 05:35 PM   #3
diyAudio Member
 
Join Date: Aug 2014
Quote:
Originally Posted by djoffe View Post
Here's a quick guess. You don't have a big enough heatsink for the 3886's. So, when you drive them hard, they warm up, and the thermal cutout triggers, stopping the sound.

Update My Dynaco

Akitika GT-101 Audio Power Amplifier Kit
Interesting guess as you might be correct. I do have an undersized heat sink that I had to use because its on the bread board. I have a fan blowing on it as well to reduce the heat, and it did reduce the cutoffs but they still occur sometimes. I also made a small speaker burn as I was testing the cutoffs at high volume...

How long are the typical cutoffs? Mine are for a second or two before playing again and then repeating the process.

Last edited by chasebank; 26th August 2014 at 05:41 PM. Reason: forgot something
  Reply With Quote
Old 26th August 2014, 06:49 PM   #4
diyAudio Member
 
Join Date: Sep 2004
Location: Minneapolis, Minnesota, USA
The power supply voltage is too high, the "optional components" in most cases are not truly optional, but necessary. I recommend you revisit the data sheet, read the whole thing through (maybe a couple of times), then come back with your questions. TomChr, a forum member here, has a nice web page dedicated to this very subject, I highly recommend you read it also. http://www.neurochrome.com/audio/?pa...#ThermalDesign

Mike
  Reply With Quote
Old 26th August 2014, 09:17 PM   #5
diyAudio Member
 
Join Date: Aug 2014
Quote:
Originally Posted by Michael Bean View Post
The power supply voltage is too high, the "optional components" in most cases are not truly optional, but necessary. I recommend you revisit the data sheet, read the whole thing through (maybe a couple of times), then come back with your questions. TomChr, a forum member here, has a nice web page dedicated to this very subject, I highly recommend you read it also. Neurochrome.com : : Audio : Taming the LM3886 Chip Amplifier

Mike
I've read the datasheet. I didn't expect the voltage to jump from 30v to 45 when making my power supply. The site I was reading said a transformer between 25-28 volts should be used, 3v isn't that much higher. The datasheet says you don't need a regulated supply and the chip can handle up to 84 volts as well.
  Reply With Quote
Old 26th August 2014, 09:31 PM   #6
diyAudio Member
 
Join Date: Feb 2008
Location: Jackson,michigan
I 30V-0-30V transformer will make 42.4264 Vdc.

30VACrms*sqr2 or 30V * 1.414 =42.4264Vdc out of the supply.

This exceeds the 84Vdc for the chip for a Bipolor Supply configuration (2x).

Even though there is some voltage drop across the rectifier diodes (typically .3 to .6 volts) it may not be enough of a drop.

Also what is the impedance that you are trying to drive as it sounds like spike is kicking in as mentioned.

When you are running them at such a high voltage it is advisable that you should use a Paralleled configuration (PA100).

FWIW

jer
  Reply With Quote
Old 26th August 2014, 09:49 PM   #7
diyAudio Member
 
Join Date: Aug 2014
Quote:
Originally Posted by geraldfryjr View Post
I 30V-0-30V transformer will make 42.4264 Vdc.

30VACrms*sqr2 or 30V * 1.414 =42.4264Vdc out of the supply.

This exceeds the 84Vdc for the chip for a Bipolor Supply configuration (2x).

Even though there is some voltage drop across the rectifier diodes (typically .3 to .6 volts) it may not be enough of a drop.

Also what is the impedance that you are trying to drive as it sounds like spike is kicking in as mentioned.

When you are running them at such a high voltage it is advisable that you should use a Paralleled configuration (PA100).

FWIW

jer
Ohh I thought it meant 84v per rail...crap. I'm getting 44.38 volts per rail exactly. I plan on using 2 chips plus a few other circuits for my entire project and didn't want to cut the voltage to close. I haven't found a suitable solution to lower the voltage to a decent level either.
  Reply With Quote
Old 26th August 2014, 10:05 PM   #8
diyAudio Member
 
Join Date: Feb 2008
Location: Jackson,michigan
There are a few options but not many and they may or may not apply to your nreeds.

1#~ You can make a regulator or get the proper voltage transformer.

2#~ You can add some diodes in series with the rails but this would take a lot of them to drop at least 3-4 volts and they would have to be high current types, Not very cost effective but it works.

3#~ You can use 2 or 4 chips per channel in a bridged amp (BA100 or BPA200) configuration and run it on your 44.38Vdc supply in as a single ended supply configuration.
This would be great providing your transformer can supply enough current, else stick with the 2 chip design such as the BA100.

4#~ You can also use a single chip in a single ended configuration on your 44.32Vdc supply providing you use a output capacitor on the amp as well.

jer
  Reply With Quote
Old 26th August 2014, 10:12 PM   #9
diyAudio Member
 
Join Date: Aug 2014
Quote:
Originally Posted by geraldfryjr View Post
There are a few options but not many and they may or may not apply to your nreeds.

1#~ You can make a regulator or get the proper voltage transformer.

2#~ You can add some diodes in series with the rails but this would take a lot of them to drop at least 3-4 volts and they would have to be high current types, Not very cost effective but it works.

3#~ You can use 2 or 4 chips per channel in a bridged amp (BA100 or BPA200) configuration and run it on your 44.38Vdc supply in as a single ended supply configuration.
This would be great providing your transformer can supply enough current, else stick with the 2 chip design such as the BA100.

4#~ You can also use a single chip in a single ended configuration on your 44.32Vdc supply providing you use a output capacitor on the amp as well.

jer
I thought about the diodes but before I go that route I wanted to explore my options. How would I go about making a regulator?
  Reply With Quote
Old 26th August 2014, 10:27 PM   #10
diyAudio Member
 
Join Date: Feb 2008
Location: Jackson,michigan
There are several discussion on regulator's.
I found one a while back but I never tried it.
They are not that hard to design.
You may find a few in circuits in the power supply threads that will work, I think that is were I found the one I was going to try.

jer
  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
problem with lm3886 parallel laki101 Chip Amps 13 9th November 2010 05:51 PM
Parallel LM3886 problem shmulik Chip Amps 30 21st December 2009 06:16 AM
LM3886 problem, HELP! Matthewong Chip Amps 36 7th February 2006 06:00 PM
LM3886 problem skyraider Chip Amps 15 20th January 2004 09:49 AM
LM3886 problem skyraider Solid State 11 20th January 2004 08:17 AM


New To Site? Need Help?

All times are GMT. The time now is 07:22 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