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 7th June 2006, 04:00 PM   #1
Bonce is offline Bonce  United Kingdom
diyAudio Member
 
Join Date: Dec 2005
Location: Newbury/York, England
Default Grounding Issues

Hi Im sure this has been exhausted before, but I have searched and havent been able to find any topics on this.

Anbyway I'll explain my setup. I've had my chip amp sat on a piece of MDF board for a little while and decided to put it into an aluminium box. Im not using a star grounding system, as I didnt on the MDF board and never had any problems. Im using the PCB's from Chipamp.com, and am using one trafo and rectifier PCB for two amplifier boards. The trafo (0-25, 0-25 rectifies to +-36v) has two seperate windings so Im using 8 diodes and have the V+, PG+, V- and PG - connections going from the rectifier to each Amp board. Also each input and ouput ground is connected to the PCB at the correct place. The only electrical connection to my alumunium chassis is earth from the mains socket.

The problem I have is that there is a voltage from any of the grounds on the PCB to the chassis which is earthed. The strange thing is that it isnt 36v, but 12v. This is fine when im using a source which isnt referenced to earth (laptop etc) but If i try to use my PC for a source the soundcard's ground is earthed and so I get 12v running from my amp back to earth through the PCB, making the cable very hot!

I know you may just say "do a star ground" but I dont see how this would solve the problem. If someone could explain what Im doing wrong It would be much appreciated!
  Reply With Quote
Old 7th June 2006, 04:19 PM   #2
joensd is offline joensd  Germany
diyAudio Member
 
Join Date: Dec 2001
Location: Germany
Hi,
you can read up on the subject of earthing here,
http://sound.westhost.com/earthing.htm
Although you´ll find 1000x as much here in the forums,
it´s just not so nicely summed up.

Quote:
but If i try to use my PC for a source the soundcard's ground is earthed and so I get 12v running from my amp back to earth through the PCB, making the cable very hot!
But the 12V as you say are only on the chassis and earth from the main socket. So how can that cause any current flow and particularly go through your PCB?

greets
__________________
jens
  Reply With Quote
Old 7th June 2006, 04:45 PM   #3
Bonce is offline Bonce  United Kingdom
diyAudio Member
 
Join Date: Dec 2005
Location: Newbury/York, England
Well my RCA grounds are 12v DC above the earth in the mains, whereas the grounds on the output of my soundcard are at 0v with reference to earth, so there is 12v between the inputs to my amp and the ouputs of the soundcard, and when i connect them up with a phono cable there is 12v with about 0.1 ohm of resistance in the cable = bad

I just tried another amp I have, and its RCA connectors are at ground, just like my PC.

Thanks for the link though, I'll have a read!
  Reply With Quote
Old 7th June 2006, 09:00 PM   #4
Mad_K is offline Mad_K  Norway
diyAudio Member
 
Mad_K's Avatar
 
Join Date: Sep 2002
Location: Norway
Try the grounding arrangement described here:

LM3875 circuit ready to solder?
__________________
Mads K
  Reply With Quote
Old 8th June 2006, 10:25 PM   #5
Bonce is offline Bonce  United Kingdom
diyAudio Member
 
Join Date: Dec 2005
Location: Newbury/York, England
I looked at that site, but I cant see how exactly that will help me. As far as I know I dont have a ground loop problem. In fact maybe I should change the title of this thread.

Any other suggestions before I rip this amp apart and put it back on the piece of MDF?
  Reply With Quote
Old 8th June 2006, 11:11 PM   #6
poobah is offline poobah  United States
diyAudio Member
 
poobah's Avatar
 
Join Date: Nov 2005
What is the voltage from V+ to PG?

What is the voltage from V- to PG?

What is the voltage from PG to EARTH? both AC and DC?

What is the voltage from NEUTRAL to EARTH? both AC ans DC?
  Reply With Quote
Old 8th June 2006, 11:50 PM   #7
cpemma is offline cpemma  United Kingdom
diyAudio Member
 
Join Date: Jul 2003
Location: S Yorkshire OK
If you've got +12V on the amp's signal ground you have a fault in the amp circuit. The input cap should block any DC from the chip side.
  Reply With Quote
Old 8th June 2006, 11:59 PM   #8
preiter is offline preiter  United States
diyAudio Member
 
preiter's Avatar
 
Join Date: May 2006
Is the ground from the mains connected to the ground coming from the power supply and the ground from the amplifier boards?
  Reply With Quote
Old 9th June 2006, 02:27 AM   #9
poobah is offline poobah  United States
diyAudio Member
 
poobah's Avatar
 
Join Date: Nov 2005
I think the DC he is seeing, is actually alot of AC... probably due to asymmetry in the AC input and the capacitance fron pri to sec, OR the phasing (polarity) of the secondaries.

It's probably nothing... but the 12 volts DC to earth is cause for question.

  Reply With Quote
Old 9th June 2006, 10:02 AM   #10
Bonce is offline Bonce  United Kingdom
diyAudio Member
 
Join Date: Dec 2005
Location: Newbury/York, England
Hello again. I've just made a bit of a strange discovery. The box the amplifier is in is very small so I have to take it apart somewhat in an attempt to get the voltages you asked for. Well I found that when the amp was apart the voltage from earth to PG/SG/OG was gone completely, and the amp is now working fine.

After reassembling the case I was expecting the problem to return, but it didnt. Looking at how tightly everything is crammed in Im thinking that maybe the top of one of the rectifying diodes could have been touching the bare metal on the top of a capacitor. Would this have caused problems?

Anyway, I've decided that when I get time, I will probbaly redo the whole grounding as suggested in the other thread and perhaps use the whole chassis as a star ground that is also earthed. The one thing Im worried about now is the offset reappearing in use and destroying something.

Anyway, some pics:

Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.
  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
Lions and Tigers and Grounding Problems, Oh My! DoZ Grounding... EchoWars Solid State 37 3rd August 2008 08:50 AM
LM3875 kit grounding, optimal grounding for separate amps and psu? findog Chip Amps 9 16th May 2005 09:27 PM
Grounding issues miguel2 Chip Amps 5 24th May 2004 06:55 PM
Grounding Issues PaulHilgeman Parts 5 26th June 2003 09:36 AM


New To Site? Need Help?

All times are GMT. The time now is 06:52 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