Balanced output confusion - diyAudio
Go Back   Home > Forums > Source & Line > Analog Line Level
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

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 4th February 2011, 12:49 AM   #1
diyAudio Member
Join Date: Apr 2004
Location: Wisconsin
Default Balanced output confusion

I have a slight 60hz buzz in my new preamp. It is just loud enough to drive me nuts, but not bad really. It is a differential circuit that I am running into a single ended amp. I have been toying with the idea of going to a true balanced amp. How do I test my preamp to make sure the change to a balanced amp will remove what I hope is a common node buzz. The more I think about it the more I get confused. I have a computer based two channel oscilloscope and another balanced preamp. Any suggestions would be appreciated.

  Reply With Quote
Old 4th February 2011, 01:14 AM   #2
diyAudio Member
nigelwright7557's Avatar
Join Date: Apr 2008
Location: Carlisle, England
Could be an earth loop problem.
Try adding an earth connection to the ground line.
Or try removing the earth from the ground line.
Dont disconnect the earth from the chassis.
Murton-Pike Systems PCBCAD51 pcb design software.
  Reply With Quote
Old 4th February 2011, 10:28 PM   #3
Join Date: Oct 2005
Location: Central Florida
It really depends on the input and output circuitry and how you have them connected. Are you using one phase and ground from the preamp or tying one of the output phases to ground at the amp. You could always use a trafo at the amp input.
  Reply With Quote
Old 4th February 2011, 10:49 PM   #4
Did it Himself
diyAudio Member
richie00boy's Avatar
Join Date: Nov 2003
Location: Gloucestershire, England, UK
The easiest way is to unplug everything from the input to the amp, if the noise goes away then it's probably a ground loop and going to full balanced should cure it.
__________________ my website for UK diy audio people - designs, PCBs, modules and more.
  Reply With Quote
Old 6th February 2011, 03:46 PM   #5
DF96 is offline DF96  England
diyAudio Member
Join Date: May 2007
Can you see the buzz on the output with your 'scope? Is it common-mode or differential-mode? Does the preamp have a true balanced output, or just a rough approximation such as a phase-antiphase output pair? Can you ground the other output phase instead?
  Reply With Quote
Old 7th February 2011, 02:10 PM   #6
AndrewT is offline AndrewT  Scotland
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders
Originally Posted by DF96 View Post
Is it common-mode or differential-mode?
How do we test for this?
regards Andrew T.
Sent from my desktop computer using a keyboard
  Reply With Quote
Old 8th February 2011, 09:33 AM   #7
DF96 is offline DF96  England
diyAudio Member
Join Date: May 2007
Put the scope on both outputs simultaneously. See if buzz signal is in phase or inverted on one of them.
  Reply With Quote
Old 10th February 2011, 10:43 PM   #8
diyAudio Member
Join Date: Apr 2004
Location: Wisconsin
Well I put both channels on the scope and they were in phase. I hooked it up to my other pre amp that does not have the same noise issue and it was gone when I hooked it up balanced but there with SE. I am 90% sure that it is an issue involving poor placement of the transformers. I am going to do some shielding experiments and see if it helps. The pre is a true balanced design, assuming that an ARC ref3 is a balanced design.

Thanks all
  Reply With Quote
Old 11th February 2011, 11:20 AM   #9
DF96 is offline DF96  England
diyAudio Member
Join Date: May 2007
If it is in-phase (i.e. common mode) then probably caused by grounding. If there is an output transformer then grounding is about the only possible cause. If the balanced out comes from op-amps etc. then it could be PSRR within the circuit, or internal grounding issues.

Common-mode noise will always disappear when connected to a true balanced input.
  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

Similar Threads
Thread Thread Starter Forum Replies Last Post
How to mix few balanced output? Steinberg Analog Line Level 3 20th November 2010 03:30 PM
How can I check if its balanced output Pbassred Everything Else 9 11th December 2006 10:54 PM
RIAA with balanced output? roger-k Analogue Source 19 17th March 2006 04:42 PM
output diode bridge confusion Danko Power Supplies 4 17th August 2005 10:45 AM
balanced output wuffwaff Solid State 14 16th January 2002 06:54 AM

New To Site? Need Help?

All times are GMT. The time now is 07:38 AM.

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