Lm3886 Pcb - 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 16th January 2004, 11:50 AM   #1
diyAudio Member
 
Join Date: Sep 2003
Location: Illinois
Default Lm3886 Pcb

Hi, I finished designing some pcb patterns for the LM3886. This amp will be used to power a small 8-inch subwoofer speaker.


Please tell me if there is anything wrong with it.

Thank you!

-Mike
Attached Files
File Type: zip lm3886 pcbs.zip (28.6 KB, 2107 views)
  Reply With Quote
Old 17th January 2004, 01:35 AM   #2
diyAudio Member
 
Join Date: Sep 2003
Location: Illinois
Anybody?

Please tell me how this would work.

I based it off of the schematic on the first page of the 3886 datasheet

thanks, Mike
  Reply With Quote
Old 17th January 2004, 07:23 AM   #3
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
I have just taken a very short look, but where are the deoupling caps? The trace between the LM3886 pins... not good. The trace width, consider this is a >10 A device! I think the pcb will act as fuses. Otherwise I think it's not so hard to succeed.

You can get some inspiration if you take a look at my LM3886 project. Download the pdf's for the pcb layout. Note also that I'm going to have 95 um copper (2.7 oz).
__________________
/Per-Anders (my first name) or P-A as my friends call me
Super Regulator SSR03 Group buy
  Reply With Quote
Old 17th January 2004, 12:34 PM   #4
diyAudio Member
 
Join Date: Sep 2003
Location: Illinois
The trace between the chips is the ground, so it doesn't matter, right? And the caps won't do anything, since the ps board is very close to the amp board.

I'll look at your project, though.

-Mike
  Reply With Quote
Old 17th January 2004, 12:49 PM   #5
diyAudio Member
 
Join Date: Sep 2003
Location: Illinois
Actually, I changed my mind. I think I will just put the ps on the amp board. That will eliminate the need for the decoupling caps.

If I don't put the ps on the amp board, do I really need the 100uf decoupling cap? I would use the .1, though. I didn't put it on my pcb due to size. If I could just use the .1 cap, that would be easy to add.

Also, about the gnd. gnd carries no voltage, right? So does it really have to be thick?


If you didn't notice on the pcb, the pads on the top right are for input (this amp is for a sub, so connection to the input/crossover/volume board), the bottom center is for speaker, and the top left is power in. The pad connecting to the speaker pin is a jumper over the + voltage wires


I couldn't find your pdf file, but I only looked quickly.


Also, how much do traces limit power? The original amp I designed with the 3886 used all thin traces, not much wider than the pins themself. I designed that one manually using rub-on traces from radioshack.

Will using the thicker traces improve sound quality also?

Thanks, mike
  Reply With Quote
Old 17th January 2004, 02:19 PM   #6
diyAudio Member
 
Join Date: Oct 2002
Location: pittsboro, NC
Your PCB layout is a great first effort and you are applauded for your interest and work.
however............
IMO, the design will most likely oscillate at a very high frequency, maybe not at idle, but during power peaks. This will show itself as a lot of heat when running at a 'normal' level. I would not want to use my best speaker during your testing.
Please, please take the time to read the earlier GC threads. There is a lot of time saving information there.
Ground:
Note on page 1 of the LM3886 datasheet that the 8 ohm 'load' is connected to Ground. (please note that this is Power Supply ground - not earth ground.) On page three (near the bottom) there is a symbol "I out" which is "Output Current Limit". note the value is 7 Amps. This current has to flow through your speaker and "return" to the power supply (during audio peaks). Also the LM3886 needs to sense this current, hence it needs to be between the power supply and the load. This current path will cary high peak Amps and a small trace will have a (relatively speaking) resistance causing voltage drop. (Mr Ohm at work!).
Part deaux: if this 'ground' (with its varing output load voltage) has connected to it some of the input parts, they will see a voltage change where there is no change to the actual input signal. Instant oscillation. Meltdown.
So a GC PCB layout needs to account for this.
PS, IMO, most "automatic" PCB layout programs do not make power traces wide enough.
  Reply With Quote
Old 17th January 2004, 04:31 PM   #7
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
Quote:
Originally posted by soundNERD
I couldn't find your pdf file, but I only looked quickly.
You just have to click at "downloads" in the left frame or you can click here
__________________
/Per-Anders (my first name) or P-A as my friends call me
Super Regulator SSR03 Group buy
  Reply With Quote
Old 19th January 2004, 02:30 AM   #8
diyAudio Member
 
Join Date: Sep 2003
Location: Illinois
I looked at peranders pcb. I don't need anything that fancy, all I need is a small amp to power a small 8-inch subwoofer.

So, I would like to use the PCB I designed, but just modify it to not oscillate.

Lets say that I thickened up the PCB traces somehow (or left them as is, and covered them with a layer of solder, or solder a bare wire across all of them). Would that be enough for the speaker? If I made them as wide as the + and - supply wires, would that be enough?

What would be the cause of the HF oscillation? Is it the gnd trace? Or something else. If it isn't the ground, how could I fix it?

Thank you for the help, Mike
  Reply With Quote
Old 19th January 2004, 07:42 AM   #9
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
Quote:
Originally posted by soundNERD
Actually, I changed my mind. I think I will just put the ps on the amp board. That will eliminate the need for the decoupling caps.
One of the most importantthings are good ground and good power supply decoupling.

I think you should take a look at AN-1192 and the recommended design. Change then the design if you really know what you are doing.

If you remove the "fancy stuff" from my design see what's left and where it's located. Check also Thomas Madsen's LM3886 "Das Modul".

Consider AN-1192 as "the law" at the moment.

The casue of oscilllations is often not sufficiently low impedance (at the MHz region) between supply voltage and ground sensed at the LM3886.

BTW: I will order my LM3886 monster pcb's today. EDIT: Done!
__________________
/Per-Anders (my first name) or P-A as my friends call me
Super Regulator SSR03 Group buy
  Reply With Quote
Old 19th January 2004, 04:57 PM   #10
diyAudio Member
 
Join Date: Jan 2004
Location: malaysia
quote:
'The casue of oscilllations is often not sufficiently low impedance (at the MHz region) between supply voltage and ground sensed at the LM3886.'


can you explain further?
  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
My First LM3886 GC samsagaz Chip Amps 49 29th June 2008 07:55 PM
Psu Lm3886 Mayday Chip Amps 29 29th April 2007 06:10 PM
Lm3886 Bpa Tombson Chip Amps 99 21st August 2006 12:04 PM
Are two separate lm3886 = 2*lm3886 in parallel or bridge mode rs1026 Chip Amps 11 21st October 2004 10:24 AM


New To Site? Need Help?

All times are GMT. The time now is 11:27 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