Smoothing capacitors for LM3875 power supply - 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 13th March 2012, 07:07 PM   #1
maurycy is offline maurycy  United States
diyAudio Member
 
Join Date: Dec 2005
Location: NJ
Default Smoothing capacitors for LM3875 power supply

I am rebuilding my LM3875 chipamp (new case, adding second transformer and ps board). Currently, the power supply board (based on CarlosFM unregulated PS schematic) has two 10uF 50V smoothing capacitors. Since I am rebuilding the amp, should I upgrade the caps to a higher value?

The setup is run by 21V-0-21V 80VA center tap trafo per channel. Speakers are 8Ohms with sensitivity of about 86db. I also have 6Ohm speakers with sensitivity of 94db but I know that LM3875 does not play well with less than 8Ohm speakers.

Thanks.
  Reply With Quote
Old 13th March 2012, 08:58 PM   #2
Puffin is offline Puffin  United Kingdom
diyAudio Member
 
Join Date: Feb 2006
Location: U.K
From memory Carlos's schematic uses 2 or 3 sets of 10,000uf caps?

EDIT - here it is.

Click the image to open in full size.

Last edited by Puffin; 13th March 2012 at 09:02 PM.
  Reply With Quote
Old 13th March 2012, 09:34 PM   #3
maurycy is offline maurycy  United States
diyAudio Member
 
Join Date: Dec 2005
Location: NJ
The power supply is from BrianGT (chipamp.com) kit. It says that it is based on unregulated CarlosFM power supply but it only has two 10uF caps. The PS has only full wave rectifier and smoothing caps. It is not snubberized.
  Reply With Quote
Old 13th March 2012, 10:17 PM   #4
Minion is offline Minion  Canada
diyAudio Member
 
Join Date: May 2006
Location: Cowican Bay , vancouver island
10uF in the whole power supply ?? I don"t see how it is possible and still sound good , You would think there would be a lot of ripple , My latest amp used 20,000uf per rail (40,000uF total) for a single lm3886 chip ......
  Reply With Quote
Old 14th March 2012, 12:11 AM   #5
maurycy is offline maurycy  United States
diyAudio Member
 
Join Date: Dec 2005
Location: NJ
This is for the older Rev. C of BrianGT's (chipamp) LM3875 kit. Yes, there are only two 10uF caps. There are 1500uF 50V caps too but they are on the amp board. I can't find the schematic, but looking at the PCB it looks like it is simple full wave rectifier with those 10uF smoothing caps. The PS just changes AC to DC.

So if I were to replace those 10uF caps with bigger ones, what value should I go for?

Thanks.
  Reply With Quote
Old 14th March 2012, 12:40 AM   #6
diyAudio Member
 
Join Date: Feb 2006
Location: On a hill, in a wooden shack, next to the woods, in Somerset.
Go for something like 10,000uF on each rail.
  Reply With Quote
Old 14th March 2012, 02:09 AM   #7
Minion is offline Minion  Canada
diyAudio Member
 
Join Date: May 2006
Location: Cowican Bay , vancouver island
Quote:
Originally Posted by maurycy View Post
The PS just changes AC to DC.

So if I were to replace those 10uF caps with bigger ones, what value should I go for?

Thanks.
The PSU does more than that , a psu has to also filter out the ripple from the AC , It also has to store enough energy to supply enough current for loud transients in the amp , and the capacitors together with the impedance of the power supply form a filter that affect the audio ..... Most poeple claim that the more capacitance in the PSU the better the low frequency responce of the amp ......

  Reply With Quote
Old 14th March 2012, 03:12 AM   #8
diyAudio Member
 
Join Date: Aug 2008
With such a small VA transformer, there wouldn't be a lot of point going for too high a value, but I would go for at least 4700uF per rail.
__________________
Tyler
  Reply With Quote
Old 14th March 2012, 07:06 AM   #9
Puffin is offline Puffin  United Kingdom
diyAudio Member
 
Join Date: Feb 2006
Location: U.K
180va tranny at least.
  Reply With Quote
Old 14th March 2012, 12:27 PM   #10
maurycy is offline maurycy  United States
diyAudio Member
 
Join Date: Dec 2005
Location: NJ
Thanks for replies.

I will try 4700uF on each rail and see how the amp performs. I think I may have those in my parts bin.

As to the trafo, I have one 80VA for each chip. It should run just fine. Before, I have used only one trafo like that for both chips and never had any problems with it. Not everybody pushes their amps to the limits. My main rig is 2x16W Marantz receiver which has plenty of power for my type of listening.
  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
Fotios need help with power supply smoothing capacitors. fotios Solid State 13 15th August 2007 02:08 AM
Problem building a power supply, no output after smoothing caps? markiemrboo Parts 11 15th January 2007 05:10 PM
LM3875 power supply questions... nycavsr2000 Chip Amps 3 11th October 2006 05:42 PM
4x Elna Silmic 22000uF 56v Smoothing Capacitors (very rare) Kevinbd Swap Meet 13 23rd March 2006 11:57 AM
HV smoothing capacitors DeXXSter Tubes / Valves 8 11th December 2001 10:10 PM


New To Site? Need Help?

All times are GMT. The time now is 04:26 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