LM4835 Help Please! - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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 29th December 2005, 07:00 AM   #1
diyAudio Member
Join Date: Aug 2005
Default LM4835 Help Please!

I am working on an upgrade for my portable PS2 (see original at www.freewebs.com/segasonicfan) however, I am having an audio problem I can't seem to fix and this is the only place I know of that can help...

The PSOne LCD Screen PCB has an integrated surface mount LM4835 chip amp. This chip produces 2W total, has headphone switch and output and it also has some other digital features.

The problem I'm having is whenever bass hits the speakers the display changes horziontal sync for a moment...kind of blinks along to the music. This doesn't go away unless I lower the volume to almost nothing (below 1W).

I found a partial fix when I took out the 7805 used to drive the amp and severed a trace from the regulator output to an LM1881 sync seperator. I then used a 5v AC adapter and I though my problems were solved.

However, I've now begun powering the system from a single source and so I used a high current (3A, LT1085) voltage reg to take the 8.5v input down to 5v. Then the problem showed up again >

I tried regulating the LT1085 every way I knew...3K resistors to ground, 10k resistors to ground for the audio lines, 1000uf caps, 22uf tantalum cap (required for stability it says on the datasheet). It seems to me it might be problem in the ground line.

Can anyone give me any advice on this problem? I would *really* appreciate it. This is one of the final obstacles I'm trying to overcome and I just don't think I can do it by myself. If anyone would like to see a video of the problem I would be happy to upload one if that would help. Thanks in advance!!

  Reply With Quote
Old 29th December 2005, 12:48 PM   #2
lineup is offline lineup  Sweden
diyAudio Member
lineup's Avatar
Join Date: Dec 2005
Location: the north
Looks like you get some spikes in power supply rails.
Digital and analog ground rails/planes are best kept separate.
And only joined at one point in the supply.
  Reply With Quote
Old 30th December 2005, 12:19 AM   #3
diyAudio Member
Join Date: Aug 2005
The LCD board combines them though...so you're saying I should seperate the amps ground from everything else and just join it to one point on the supply? That would take some time but I guess I can do that...any other suggestions? Thanks for your help,

  Reply With Quote
Old 30th December 2005, 05:03 AM   #4
diyAudio Member
neutron7's Avatar
Join Date: Dec 2003
Location: Toronto Canada
maybe it would be better if you give the amp its own regulator with a fairly big capacitor as well.
  Reply With Quote
Old 30th December 2005, 10:16 AM   #5
diyAudio Member
Join Date: Aug 2005
I DID give the amp its own regulator with a big capacitor....didn't help As long as the same supply is going to the system/screen and reg->amp the problem persists. I've noticed however the composite signal doesn't get as distorted from the bass.

Separating it from all other grounds is going to be *really* hard tho...it's surrounded by a bunch of fragile traces and that would take hours. I'll probably end up doing that anyway but I'm still hoping to find another solution..

  Reply With Quote
Old 30th December 2005, 01:35 PM   #6
diyAudio Member
Join Date: Aug 2005
Well...I spent the past 4 hours cutting and drilling the ground rails on the PCB and.............

IT WORKED!!! Thank you so much lineup! I really owe you one Members on the Benheck forums and I have been trying to solve this problem for a long time...it was both a ground and supply rail problem. I separated the 5v supply but the ground connection was still there. Oddly enough Sony tried to isolate the grounding around the chip a little bit, but only in one area.

Moderator, you can close this topic. Thanks again lineup

  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

New To Site? Need Help?

All times are GMT. The time now is 06:15 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2