Ground loop problems - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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 29th February 2016, 11:53 AM   #1
diyAudio Member
 
Join Date: Jan 2011
Location: LONDON
Default Ground loop problems

Applogise if this is a question which has been asked before but I've scoured this forum, tried all of the suggestions put forward and still have problems. I recently built my 6n6p tube DAC into a steel chassis. Prior to this I had it built in a plastic storage box as a prototype. Since boxing it up I've suffered many problems with hum caused by various ground loops. Initially I made the big mistake of using the chassis as the main signal ground but I have since lifted the signal ground from the earthed chassis via back to back diodes and a parallel resistor/capacitor. I have also decoupled the signal grounds at the RCA output sockets to chassis using 0.1uf discs. I have physically isolated the transformers from the chassis using paxolin board and earthed their metal parts to the chassis. The heaters are smoothed DC and hum remains when their power is removed.

These modifications changed the characteristics of the hum but have not eliminated it. I can however completely stop all hum by disconnecting the screen of either one of the RCA cables.

Can anyone offer any advice based on previous experience of this kind of ground loop.?

Any advice would be appreciated as I'm at that stage where I feel like throwing the damn thing in the bin!
  Reply With Quote
Old 29th February 2016, 12:09 PM   #2
Jerms is offline Jerms  United Kingdom
diyAudio Member
 
Join Date: Jun 2015
Location: High Wycombe, Bucks, UK.
Reads like you've tried lots more than I have. I ended up using a 6 ground loop isolator box from Amazon. Prior to that, my only work around was to power my source/DAC separately from my amp.

Do you lose signal from the RCA with the disconnected ground? Without lifting the screen, can you merge the grounds without causing other problems?
  Reply With Quote
Old 29th February 2016, 04:52 PM   #3
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
If disconnecting one RCA screen cures the hum then maybe the stereo pair of screens act as a ground loop? Having a steel chassis provides good scope for coupling magnetic fields from here to there.
  Reply With Quote
Old 29th February 2016, 05:16 PM   #4
Jeffs is offline Jeffs  United States
diyAudio Member
 
Join Date: Oct 2011
Location: Austin
Blog Entries: 1
I'm reading your statement as the original plastic box had no problems, then putting it in metal is when you have the issues. I originally tried wood, and didn't have noise then went to aluminum where it all went downhill.
I've been fighting similar issues, haven't tried as many solutions. When running input from a television I get a bad ground loop. It goes away if I (just to test... ok, I watched one movie) use plug adapter which removes the safety ground.
The last comment - one RCA removed cures the hum and stereo pair acting as ground loop. Had similar issues but it was grounding one channel to the chassis would cause the other channel to become quiet but not both ways. I was using an aluminum chassis originally, then removed the RCA jacks and let the lie over the edge of the chassis. Putting the input and output cables in steel tube I had laying around, about 150mm each with the steel tube resting on the edge of the aluminum chassis, the RCA jacks dangling off the ends - it was ridiculous but quieted it down. Mainly 60hz and some 120 hz hum.
I lifted the grounds from the chassis / safety ground with a thermistor and it helped some.
Maybe there is a market for a nice non-flammable plastic and wood chassis out there for those going insane.
  Reply With Quote
Old 29th February 2016, 05:21 PM   #5
rayma is offline rayma  United States
diyAudio Member
 
Join Date: Apr 2011
Location: Upper midwest
Quote:
Originally Posted by BikerBod View Post
I can however completely stop all hum by disconnecting the screen of either one of the RCA cables.
Try a 10 Ohm resistor from each input RCA socket ground lug to the circuit ground, instead of a direct connection.
It sounds like you may have those input ground lugs connected together.

Last edited by rayma; 29th February 2016 at 05:26 PM.
  Reply With Quote
Old 29th February 2016, 05:40 PM   #6
diyAudio Member
 
Join Date: Jan 2011
Location: LONDON
Quote:
Originally Posted by rayma View Post
Try a 10 Ohm resistor from each input RCA socket ground lug to the circuit ground, instead of a direct connection.
It sounds like you may have those input ground lugs connected together.
I'll give this a try next time I'm in the workshop. Thanks. It did cross my mind to try this but I figured that It's a sticking plaster type solution rather than getting to the root of the issue. But I guess the steel chassis is causing hum induction into the circuit and the only real solution is to go to a non-ferrous enclosure.
  Reply With Quote
Old 29th February 2016, 05:46 PM   #7
diyAudio Member
 
Join Date: Jan 2011
Location: LONDON
Quote:
Originally Posted by rayma View Post
It sounds like you may have those input ground lugs connected together.
I forgot to mention, the valve stage takes its inputs internally from an ak4396 DAC board. The RCAs are the outputs from the valve stage. And yes their ground tags are connected together with a single thick wire joining this to the star ground.
  Reply With Quote
Old 29th February 2016, 09:34 PM   #8
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Socket ground tags should be wired alongside the signal conductor, not separately. This is because the 'ground' is actually the signal return. By sending the signal return currents via your 'single thick wire' you have introduced a big loop in the output wiring, which may pick up hum magnetic fields.

The sockets should normally be isolated from the chassis, otherwise you get another ground loop, but I think you did this.
  Reply With Quote
Old 1st March 2016, 04:28 AM   #9
diyAudio Member
 
Join Date: Jan 2011
Location: LONDON
Thanks DF96, I had never thought of this. It never occurred to me to separate the returns from both sockets because the run from the RCA to the valve is a matter of about 10cm. I'll let you know how I get on.
  Reply With Quote
Old 1st March 2016, 06:39 PM   #10
diyAudio Member
 
Join Date: Jan 2011
Location: LONDON
Thanks for your advice guys. I didn't have any 10R resistors in the box so tried 100R Instead for now. I also ran separate ground returns to the star from each RCA socket and voila, ground loop has almost completely gone. All that remains is a very low level 60hz hum when my amplifier is turned up to unsociable levels with no music playing. I would still like to completely eliminate this background hum , maybe 10R Resistors would improve this? Thoughts?
  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
Ground loop problems with ZEN4 Skorpio Pass Labs 7 22nd September 2012 02:37 PM
hum,ground loop,earth loop problem with your answers please frank2395 Pass Labs 2 17th May 2005 07:46 PM
Chassis Ground = Circuit Ground --> Problems? rhildenbrand Pass Labs 5 23rd April 2004 02:08 AM
Ground loop problems - looking for opinions Glass_painter Tubes / Valves 4 13th July 2003 12:16 PM
does connecting mains ground with circuit ground create a ground loop? jarthel Everything Else 0 25th June 2003 01:55 PM


New To Site? Need Help?

All times are GMT. The time now is 08:43 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2016 DragonByte Technologies Ltd.
Copyright 1999-2016 diyAudio

Content Relevant URLs by vBSEO 3.3.2
Wiki