Balanced LM3886 + UcD180 grounding - 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 1st June 2014, 03:04 PM   #1
diyAudio Member
 
Join Date: Apr 2014
Default Balanced LM3886 + UcD180 grounding

Hi,

I'm on my way building "the only amp I'll need" and would be happy for some opinions and input about grounding and other things. Basically, I'm having the DacMagic Plus as DAC/pre and since it's got balanced XLR out I felt compelled to put together a power amp with balanced inputs. For that I'm planning to use INA128 (which seems to be INA137's brother and not as good suited to audio?) and a basic non-inverting LM3886 circuit. What I also have lying around is a Hypex UcD180 and a really huge and ugly 12"+15" sub box. So what I want to do is have a Linkwitz-Riley LP filter from the inputs to the UcD180 which is just gonna be sub out.

Click the image to open in full size.

Click the image to open in full size.

Now, I've got most of the stuff planned and crammed into the case, but the actual grounding of the modules is where I'm kind of stuck. I've seen some examples and none seem to suit this thing.
* Where should I make the low current ground star?
* Where should the +-15V PSU circuit be grounded?
* At what end would I ground the shielded cables coming from the INA128 (two from each input, one to the LM and one to the UcD)?
* Is shielded cable even needed after that (probably not)?
* Is it ok to individually run a ground wire from the rectifier and each psu cap to the ground star?
* Will the small transformer interfere much with the LM3886's if they're placed between the inputs and that transformer?

Yes, I can and will experiment with this, but it takes such time to redo grounding and placement of stuff and there are a lot of variables here.

Thanks for any input!
  Reply With Quote
Old 2nd June 2014, 12:02 PM   #2
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Default Grounding

Audio Component Grounding and Interconnection - diyAudio
__________________
regards Andrew T.
  Reply With Quote
Old 2nd June 2014, 01:09 PM   #3
diyAudio Member
 
Join Date: Apr 2014
Thanks, just what I needed! I've been browsing around for weeks but did not see this article. Great!
  Reply With Quote
Old 2nd June 2014, 11:00 PM   #4
diyAudio Member
 
Speedskater's Avatar
 
Join Date: Sep 2002
Location: Lakewood, Ohio
Note that the XLR pin 1's go to the chassis not to the circuit ground (GND).
__________________
Kevin
  Reply With Quote
Old 3rd June 2014, 05:37 PM   #5
diyAudio Member
 
Join Date: Apr 2014
Ah, yes, that "pin 1 problem" appeared to me as I read this article. However, since I have planned to not connect safety earth (chassis) to the audio ground so the PC won't pollute it, I don't see how connecting the XLR shield to the chassis would help.

Also, the preamp is not connected to the safety earth at all (powered by 2-prong wall wart) and then "floating". If I leave pin 1, the shield, unconnected at the power amp end, won't the reference then also be floating? That's why I thought that the receiving end should connect that shield to the audio ground star... a bit confused here...
  Reply With Quote
Old 4th June 2014, 07:49 AM   #6
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
All exposed conductive parts should be connected to Chassis.
__________________
regards Andrew T.
  Reply With Quote
Old 4th June 2014, 08:57 PM   #7
diyAudio Member
 
Speedskater's Avatar
 
Join Date: Sep 2002
Location: Lakewood, Ohio
It's a different problem. The pin 1 problem is al about not connecting the shield to the circuit common. The cable shield is an extension of the chassis shield. It's not part of the audio circuit/power supply ground star point.
__________________
Kevin
  Reply With Quote
Old 5th June 2014, 08:40 PM   #8
diyAudio Member
 
Join Date: Apr 2014
Ok, I get the concept of letting the shield extend the chassis as only an EMI/RFI if its put that way. But now I've been reading the Rane notes (151) and it suggests to connect the signal ground to the chassis ground to "keep the signal ground potentials between units small" and show this diagram as you've probably seen before:
Click the image to open in full size.

So far so good I guess. But since my DAC does not connect to safety earth and my power amp does, will that mean any specific problems or will it just mean that I should route the cable in the power amp connecting my signal ground star to the chassis ground (protective earth) way away from any low level audio signal wires to not get affected by potentially noisy ground currents being shunted to protective earth?
  Reply With Quote
Old 6th June 2014, 09:15 AM   #9
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by AndrewT View Post
All exposed conductive parts should be connected to Chassis.
Applies to all mains powered Class1 equipment.

BTW,
I like the post8 drawing.
It's the first time I have noticed the shield drawn as an extension to the enclosing Chassis.
It clearly shows that PIN1 only connects to Chassis.
__________________
regards Andrew T.

Last edited by AndrewT; 6th June 2014 at 09:17 AM.
  Reply With Quote
Old 6th June 2014, 02:13 PM   #10
diyAudio Member
 
Join Date: Apr 2014
Yes, every touchable conductive part will be connected to protective earth, I'm well aware of that. That will of course include the XLR jack housings too as they're directly in contact with the chassis and if I'm going with this shielding/grounding scheme, it looks most convenient to connect pin 1 and pin 4 together on the XLR connectors as pin 4 has direct contact with the chassis.

Your remark about that it clearly shows that pin 1 is only connected to the chassis... care to expand? What I see is that pin 1 current will go through the chassis, to chassis ground (protective earth) and to my signal ground. If a physical layout is not given, I might tie the two pin 1's, protective earth from the IEC socket, the chassis and signal ground all together in one point and it would still be schematically equivalent. So what's the difference here, that makes you say that pin 1 does not connect to signal ground? Is it because the pin 1 connection point in the chassis is closer to the protective earth than the signal ground is?

Basically I'm just not sure what to do with my currently "floating" signal ground star. Guess that's easy enough to experiment some with though...
  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
LM3886 Grounding Question aoeuhtns Chip Amps 31 6th March 2014 02:25 PM
Hypex ucD180 balanced to unbalanced r100 Class D 4 14th November 2013 01:30 PM
Grounding in balanced passive pre? Nisbeth Analog Line Level 28 30th March 2012 12:23 AM
UCD180 balanced via soundcard mlihl Class D 5 18th December 2007 10:37 PM
Balanced Line Stage - grounding scheme Possum Pass Labs 6 18th December 2003 10:07 AM


New To Site? Need Help?

All times are GMT. The time now is 01:12 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