another noob grounding thread - 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 19th June 2014, 10:48 PM   #1
diyAudio Member
 
Join Date: Feb 2008
Default another noob grounding thread

so ive constructed my chipamp.com 3886 stereo kit, and tested it today.

not completely cased up but partially.

works ok but there is a noticeable mains hum. this changes in amplitude with volume pot adjustment. it also reduces when a source is connected.

i was reading a few threads about grounding but i got quite confused. the chipamp.com 3886 construction guide simply mentions connecting the ground from the amp pcbs to the case ground.. this i have done, at the same point the mains earth lead is connected.

if im following the guide this is all i need to connect to ground from the kit. (apart i guess from the points where the pcbs are bolted to the chassis? id obviously have a connection there. dunno if thats a ground connection too? only the psu board is bolted like this though, amp pcbs are floating and supported by chips on heatsink.)

however some of the posts mention grounding the speaker and input grounds too..?
at the moment i have these isolated and independent, only going to their respective connectors.

(also mentions of multiple other points being grounded, but i think they are referring to actually designing your own 3886 implementation, not when using a kit.)

i have the psu and toroid close to the amps, in the same earthed case, but they are separated from the amps and i/o connections by a 2mm aluminium wall, also earthed. input leads from in to pot and pot to amp, are tightly twisted.

any practical advice on killing my hum most appreciated.
  Reply With Quote
Old 19th June 2014, 11:08 PM   #2
diyAudio Member
 
Join Date: Jan 2011
Location: Lower Mainland
Hi,

My english skills are below average so I did not understand some of your comments. I'm sure others have better ideas but....

My bad experience with GND issues were because the amp earth GND pin was connected to a different earth GND point than my source. Both had 3 pin earth pins and were connected to different sockets.

I'm not advocating this as a pertinent solution but for a quick test you could try to use a 2 prong plug with your amp and see if the HUM goes away. This would tell you if you have this problem, but safety first. Maybe an isolation transformer would do the trick.

You setup is:
Chip amp LM3886 and PSU GND are connected at the same point on your setup? Then the Chasis and earth GND are connected together but not connected to your PSU GND? Or is your Chasis and earth GND connected to the PSU GND? The location of this connection could make a difference in noise. You mentioned a kit, I assume it is a proven design so bypass caps are nice and close to the LM chip?
  Reply With Quote
Old 19th June 2014, 11:38 PM   #3
diyAudio Member
 
Join Date: Feb 2008
thanks for the reply.. unless im missing something, there is no ground connection on the chipamp.com psu board.

only ground connection is from the amp boards. at the moment i have this bolted to the chassis at the same point as the mains earth connection (andrewT i have seen your other grounding comments, i intend to move chassis earth next to the power in socket.

i see no mention in kit instructions of connecting signal input or output ground to the chassis, this is the main thing im asking about clarification on. at the moment the signal gnds from the amp boards are joined together at the potentiometer, and then a single signal gn lead goes from the potentiometer to the rca connectors.. these have the outer collar (gnd) connectors soldered together. they are isolated from the chassis.

output gnds are independent and connect only to output posts.

thanks, Robin.
  Reply With Quote
Old 20th June 2014, 01:14 AM   #4
diyAudio Member
 
Join Date: Jan 2011
Location: Lower Mainland
Seems like the system is a dual power supply, the PGND pins are the signal and Power supply GND but sounds like you've double checked the connections. Also sounds like you've got things connected correctly.

Might want to double check the output(-) reference. I believe they should not be floating (probably should be PGND) if the chip is not in bridged mode. The kit instructions should tell you if it is bridged mode or not. This is speculation on my part as I'm not familiar with the kit schematics so please double check before doing anything.

If possible, I'd use a 2 prong power plug instead of a 3 prong, just to test hum. If the hum goes away, Source and Amp grounds are causing a problem. Try to plug them in next to each other at the same outlet. The 2 prong is not a permanent solution as it is not that safe.
  Reply With Quote
Old 20th June 2014, 07:53 AM   #5
diyAudio Member
 
Join Date: Jul 2003
Location: Dona paula, Goa
Can you shift the toroid away and check whether things improve.

Gajanan Phadte
  Reply With Quote
Old 20th June 2014, 12:50 PM   #6
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Do you have a dummy Zero ohm input plug. For stereo, you need two.

Plug the zero ohm into both inputs.
Power ON, measure the hum + noise at the output. Measure the output offset.
Post your results.
__________________
regards Andrew T.
  Reply With Quote
Old 20th June 2014, 01:28 PM   #7
diyAudio Member
 
Join Date: Feb 2008
I dont have a dummy zero ohm plug.. im assuming shorting the inputs is the same thing. I also dont have a way to measure the noise apart from with my ears. I can measure the offset however. Wirh no inputs it was 50 mv on one channel and 36 on the other. Ill try now with inputs shorted and post.
  Reply With Quote
Old 21st June 2014, 10:19 AM   #8
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Buy a cheap DMM that has a 200mVdc scale and a 200mVac scale.

Build up a dummy Zero ohms input plug.
__________________
regards Andrew T.
  Reply With Quote
Old 21st June 2014, 01:20 PM   #9
diyAudio Member
 
Join Date: Feb 2008
well i didnt get as far as shorting the inputs and testing, as i solved the hum issue first.


i had the 240v feed running under the psu board, and the ac was inducing hum in the dc side. i tightly twisted the ac cables and wrapped a grounded foil around them, before heat shrinking the lot. all hum has dissapeared and i now have a great sounding amp.

thanks for the advice!


p.s. i already have a decent dmm.. thats how i measured the offset.. do i measure noise using the ac setting?

Last edited by robinlawrie; 21st June 2014 at 01:42 PM.
  Reply With Quote
Old 21st June 2014, 08:15 PM   #10
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
yes
The bandwidth is undefined. But the results are still very good for comparasons.
__________________
regards Andrew T.
  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
The New Member Noob Newbie Questions Thread miragem3i Everything Else 4 25th June 2013 07:19 PM
Nooby-noob thread. Appreciate pointers. iamthefly Subwoofers 33 14th January 2013 10:44 PM
Should a person who starts a thread have quasi moderator status on their own thread? erin The Lounge 15 23rd October 2012 11:41 PM
Lions and Tigers and Grounding Problems, Oh My! DoZ Grounding... EchoWars Solid State 37 3rd August 2008 09:50 AM
LM3875 kit grounding, optimal grounding for separate amps and psu? findog Chip Amps 9 16th May 2005 10:27 PM


New To Site? Need Help?

All times are GMT. The time now is 06:21 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