Help with a LM3876 amp! (nOOb) - 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 23rd June 2005, 06:36 AM   #1
Fizx is offline Fizx  New Zealand
diyAudio Member
 
Join Date: Jun 2005
Location: Under the eyes of the gods
Default Help with a LM3876 amp! (nOOb)

Hail to all

I have put together a kitset amp from jaycar, it uses the LM3867 chip.

The problem I have right now is that there seems to be some parts in songs (mainly bass) thats not being played, I'm not too good at the whole frequancy range thing but I have found that the begining of Metallicas St. Anger and Unnamed Felling is missing completely.

I also find that my bass distorts badly if I put the volume up just on the bass. I had a 12V amp that did a better job at bass! (I reversed the polarity on that amp and blew the IC up >

I plan on building a stero amp so I have a 160VA tordial with 4700uF caps on it, my powersupply works, I have checked that all the components are in there right places! I am stumped!

Can some one please point me in the right direction? Also, where can I find amp theory? Like why you put caps and resistors on the audio input path and the theory behind inductors and resistors-cum-inductors.
  Reply With Quote
Old 23rd June 2005, 07:16 AM   #2
diyAudio Member
 
Join Date: Mar 2005
Location: Germany, lower saxonny (Bremervörde)
Send a message via Skype™ to slackman
Hi Fizx,

first have a look at Nationals datasheet.

Maybe you have the wrong input caps. Try bigger values to lower the entry frequence.

Also the Overture Design Guide may help to select matching power supply:

Be sure to add lots of elko capacity if you don't have a regulated powersupply, better for tighter bass. If you want to rebuild your supply check the LM338 regulated psu thread...
There are also some infos about snubbering the National chips.

Michael
  Reply With Quote
Old 23rd June 2005, 07:33 AM   #3
diyAudio Member
 
Greg Erskine's Avatar
 
Join Date: Jan 2002
Location: Sydney/Australia
hi Fizx,

You should post a link to the Jaycar amp in question.

Have you got it mounted on a heatsink? The Jaycar chipamp I looked at said "Heatsink Optional", which is incorrect.
__________________
Greg Erskine
  Reply With Quote
Old 24th June 2005, 07:22 PM   #4
diyAudio Member
 
Join Date: Apr 2005
Location: In the Wild, Wild West
There is lots that could be happening. The two inputs so far are very good. Depending on the schematic there could be several capacitor values that need adjustment. Your power supply may be drooping under heavy bass causing clipping at much lower power, the IC may be too hot if not heat sinked properly which will greatly increase distortion when the protection circuits come on. Do as SlackMan say, read through the datasheet (the LM4780 has the most information which applies to the LM3876 as well), and try the Design Guide.

If you can provide a schematic that will really tell all.
  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
LM3876 and 4-ohm drivers astrodog Chip Amps 15 2nd July 2008 11:22 PM
LM3876 for small sub amp? phreeky82 Chip Amps 11 5th July 2006 05:50 PM
LM3876 vs. LM3875 Wynand Chip Amps 3 12th July 2005 09:03 PM
Lm3876 bobossa Chip Amps 1 1st March 2005 04:18 PM
hi - LM3876 problems... RichardA Chip Amps 7 14th September 2004 04:32 PM


New To Site? Need Help?

All times are GMT. The time now is 11:48 PM.


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